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1. 1

2. Contents
Introduction
Urgency classification of CS
Pain Pathways
General Principles
 Indications for Anesthesiology
Consultation
 ASA Classification
 Placental Transfer
Summary of Anesthetic Drugs
Categories of Anesthesia
 General Anesthesia
 Local Anesthesia
 Neuraxial (Regional) Analgesia
 Sedation(Monitored Anesthesia Care)
Postoperative Pain Care
Do analgesia and anesthesia affect
breastfeeding?
Components of WHO surgical
safety checklist
2

3. Introduction
• In the absence of a medical contraindication, maternal request is a sufficient medical
indication for pain relief during labor (ACOG, 2019: Level C)
• Frequency of various forms of analgesia - during labor
– Spinal or epidural block: ~ 77%
– Narcotics, Barbiturates Tranquilizers: ~ 34%
– Paracervical block: ~ 2%
• The choice of anesthetic technique is determined by
– Diagnostic, therapeutic, surgical intervention
– patient condition ,cost and adverse effects
• Case fatality rates and rate ratios of anesthesia-related death
 GA (6.5%) > Regional (3.8%)
 GA: ~ 2/3rd  intubation failure or induction problems (W 25th)
 Regional Analgesia: high spinal or epidural blocks (26%); respiratory failure (19%); drug
reaction (19%) (W 25th )
3

4. Urgency Classification of CS
ACOG , NICE, RCOG
• decision-to-delivery interval (DDI)
– < 30 min for Category 1 CS
– 30 - 75 min for Category 2 CS
• delay for > 75 min → poor outcome
Decision to delivery interval and associated
factors for emergency cesarean section: a
cross-sectional study
• conducted at Bahir Dar City Public
Hospitals from February to May 2020
• Decision-to-delivery interval below 30 min
was observed only in 20.3%
• factors significantly associated
– Referral status
– Time of cesarean section
– Status of surgeons
– Type of anesthesia
– Transfer time
4
A classification relating the degree of urgency to the presence
or absence of maternal or fetal compromise
Four defined categories remains useful – RCOG

5. • For emergent cesarean delivery
– Options
• Spinal anesthesia, CSE, or general anesthesia are suitable for emergent cesarean
delivery when no epidural is in place (ACOG, 2019: Level B)
• If general and neuraxial anesthesia are not available, infiltration of local
anesthetics
– Lidocaine is the most commonly used
– Intravenous sedation may be needed as an adjunct to infiltration of local anesthetic
– Adequate spinal anesthesia
• has been reported to take only 8 minutes from the time the patient is positioned to
the time a satisfactory block is achieved
• the median time to achieve a T4 dermatome level using lidocaine is 10 minutes
– bupivacaine takes a few minutes longer (ACOG, 2019)
5

6. Pain Pathways
Pain during
• First stage of labor
Causes
– Uterine contractions
• result in myometrial ischemia, causing the release of potassium, bradykinin, histamine, and serotonin
– stretching and distention of the LUS & cervix stimulate mechanoreceptors
– Pain travel from uterus through visceral afferent (sympathetic) nerves
• posterior segments of T10-12
• SSOL
– Perineal stretching - as fetal head distends the pelvic floor, vagina, and perineum
• painful stimuli through the pudendal nerve and sacral nerves S2 through S4
• Cortical responses to pain and anxiety during labor
– Complex
– May be influenced by maternal expectations for childbirth, her age, preparation through education,
emotional support, and other factors
• Pain perception is heightened by fear and the need to move into various positions
• A woman may be motivated to have a certain type of birthing experience, and these opinions
will influence her judgment regarding pain management
6

7. • Dorsal root: Sensory axon & cell body
• Ventral root: Axon of motor neuron
7
Pain pathways of labor and delivery and nerves
blocked by various anesthetic techniques

8. 8
Sources of pain during labor and maternal physiological responses
There is a lack of an
objective, universally
applicable measure for
intensity of pain (ACOG,
2019)

9. • During cesarean delivery,
– incision is usually around thoracic spinal nerve 12 (T-12)
dermatome
– anesthesia is required to the level of thoracic spinal nerve 4 (T-4)
to completely block peritoneal discomfort, especially during
uterine exteriorization
– Pain after cesarean delivery is due to both incisional pain and
uterine involution
9

10. Effects of Pain & Stress
10
• intensity and quality of pain
– Nulliparous > Parous
• Mental stress, anxiety, fear of labor pain, the unknown space of the labor room and
lack of trust in its staff can contribute to increased labor length and the proliferation
of pain through secretion of catecholamines, cortisol, and epinephrine to overcome
these tensions
– both epinephrine and norepinephrine can decrease uterine blood flow in the absence of
maternal heart rate and blood pressure changes, which contributes to occult fetal asphyxia
– In pregnant sheep, catecholamines increase and uterine blood flow decreases after painful
stimuli and after nonpainful stimuli such as loud noises induce fear and anxiety, as
evidenced by struggling
• hyperventilation may induce hypocarbia
• most substantial predictors of pain intensity
– ultimately low socioeconomic status and prior menstrual difficulties
• distraction techniques can reduce the pain and stress of labor

11. 11
• ACTH, adrenocorticotropic
hormone
• ADH, antidiuretic hormone
• FFA, free fatty acid;
• FSH, follicle-stimulating hormone
• TSH, thyroid-stimulating hormone
The stress response

12. • Epidural analgesia
– prevents increases in both cortisol and 11-hydroxycorticosteroid
levels during labor, but systemically administered opioids do not
– attenuates elevations of epinephrine and norepinephrine and β-
Endorphin levels
• β-Endorphin, is an endogenous opioid neuropeptide and peptide
hormone
– ↓es risk of postpartum depression
12

13. • Concerning walking during the first stage
of labor, which of the following is true?
– A.Ambulation affects labor duration.
– B.Ambulation does not affect the need for
analgesia.
– C.Ambulation is harmful to the
fetus-neonate.
– D. None of the above.
• Q: Which of the following are considered
plausible causes of uterine contraction
pain?
– A. Myometrial hypoxia
– B. Uterine peritoneum stretching
– C. Compression of nerve ganglia in the
cervix
– D. All of the above
13
• In this figure, which sensory block level would
provide the best analgesia during early labor?
– A.A B. B C. C D. D

14. General Principles
14
• Anesthesia is a state of controlled, temporary loss of
sensation or awareness that is induced for medical purposes
– analgesia (pain control)
– Amnesia: absence of anxiety
– adequate muscle relaxation
• Techniques
– Pharmacologic
– Non pharmacologic

15. Nonpharmacologic
• ± parenteral or neuraxial techniques
1. Acupuncture
• alleviates labor pain and reduces use of both
epidural analgesia and parenteral opioids
• may be helpful for patients who feel strongly
about avoiding epidural analgesia
• but few data are available
2. Immersion in water during SSOL
• safety and efficacy: not established
• No maternal or fetal benefit
3. Intradermal sterile water injections at
four sites in the lower back
4. Transcutaneous electrical nerve
stimulation (TENS)
• efficacy techniques (3 & 4) is largely
unproven because of a lack of RCTs,
– But, no serious safety concerns
Psychoprophylaxis
• is any nonpharmacologic method that
minimizes
– Perception of painful uterine contractions
• Include
– Relaxation
– concentration on breathing
– gentle massage, and
– partner or doula participation
15

16. Indications for Anesthesiology Consultation
Cardiac Disease
 Congenital and acquired disorders such as repaired tetralogy
of Fallot and transposition of the great vessels
Cardiomyopathy
 Valvular disease such as aortic and mitral stenosis, tricuspid
regurgitation, and pulmonary stenosis
 Pulmonary hypertension and Eisenmenger syndrome
 Rhythm abnormalities such as supraventricular tachycardia
and Wolff–Parkinson–White syndrome
 Presence of an implanted pacemaker or defibrillator
Hematologic Abnormalities or Risk Factors
 Immune and gestational thrombocytopenia
 Coagulation abnormalities such as von Willebrand disease
 Current use of anticoagulant medications
 Jehovah’s Witness
Spinal, Muscular, and Neurologic Disease
 Structural vertebral abnormalities and prior surgeries such as
vertebral fusion and rod placement
 Prior spinal cord injury
 Central nervous system problems such as known arterial–
venous malformation, aneurysm, Chiari malformation, or
ventriculoperitoneal shunt
Major Hepatic or Renal Disease
 Chronic renal insufficiency
 Hepatitis or cirrhosis with significantly abnormal liver
function tests or coagulopathy
History of or Risk Factors for Anesthetic Complications
 Anticipated difficult airway
 Obstructive sleep apnea
 Previous difficult or failed neuraxial block
 Malignant hyperthermia
 Allergy to local anesthetics
Obstetric Complications That May Affect Anesthesia
Management
 Placenta accreta
 Nonobstetric surgery during pregnancy
 Planned cesarean delivery with concurrent major abdominal
procedure
Miscellaneous
 Body mass index >30 kg/m2
 History of solid organ transplantation
 Myasthenia gravis
 Dwarfism
 Sickle cell anemia
 Neurofibromatosis
16

17. 17
American Society of Anesthesiologists (ASA) Physical Status Classification System
ASA PS classification Definition Examples, including, but not limited to:
ASA I A normal healthy patient. Healthy, non-smoking, no or minimal alcohol use.
ASA II A patient with mild systemic disease.
Mild diseases only without substantive functional limitations. Current smoker, social
alcohol drinker, pregnancy, obesity (30<BMI<40), well-controlled DM/HTN, mild lung
disease.
ASA III
A patient with severe systemic
disease.
Substantive functional limitations; one or more moderate to severe diseases. Poorly
controlled DM or HTN, COPD, morbid obesity (BMI ≥40), active hepatitis, alcohol
dependence or abuse, implanted pacemaker, moderate reduction of ejection fraction,
ESRD undergoing regularly scheduled dialysis, premature infant PCA<60 weeks, history
(>3 months) of MI, CVA, TIA, or CAD/stents.
ASA IV
A patient with severe systemic
disease that is a constant threat to
life.
Recent (<3 months) MI, CVA, TIA, or CAD/stents, ongoing cardiac ischemia or severe
valve dysfunction, severe reduction of ejection fraction, sepsis, DIC, ARDS, or ESRD not
undergoing regularly scheduled dialysis.
ASA V
A moribund patient who is not
expected to survive without the
operation.
Ruptured abdominal/thoracic aneurysm, massive trauma, intracranial bleed with mass
effect, ischemic bowel in the face of significant cardiac pathology or multiple
organ/system dysfunction.
ASA VI
A declared brain-dead patient whose
organs are being removed for donor
purposes
The addition of "E" to the numerical status (eg, IE, IIE, etc.) denotes Emergency surgery (an emergency is defined as existing when delay in treatment
of the patient would lead to a significant increase in the threat to life or body part).

18. Placental Transfer
• Essentially, all analgesic and anesthetic agents except highly
ionized muscle relaxants cross the placenta freely
18

19. Summary of Anesthetic Drugs
19

20. Categories of Anesthesia
• Four main categories of anesthesia
General Anesthesia
Local (Regional) Anesthesia
• Peripheral nerve blocks
Neuraxial (Regional) Analgesia
• refers to local anesthetics placed around the nerves of CNS, such as spinal
anesthesia, caudal anesthesia, and epidural anesthesia
Sedation: aka Monitored anesthesia care (MAC)
Conscious Sedation without anesthesia personnel
20

21. General Anesthesia
Introduction
Depth of GA
Agents for GA
Balanced GA
Induction-Intubation-Maintenance-Reversal-Extubation
Complications of GA
Preventive method
– Patient Preparation
General Anesthetics in Pregnancy
21

22. Introduction
• General anesthesia establishes a reversible state that includes:
– Hypnosis (reduced peripheral awareness), Amnesia (memory loss), Analgesia, Akinesia
– Autonomic and sensory block
• General anesthesia
– is used for < 5% of elective and roughly 25% of emergent cesarean deliveries
– Although safe for the newborn, general anesthesia can be associated with failed intubation
and aspiration, causes of anesthesia-related maternal mortality
• General anesthesia is uncommon for vaginal or cesarean delivery in contemporary
obstetrics
• Its use usually is limited to emergency cesarean deliveries or scenarios in which neuraxial
anesthesia cannot be performed or has already failed
• Feared complication
– Aspiration of gastric contents
22

23. Contraindications to general anesthesia
• No absolute contraindications
• Relative contraindications
– patients with medical conditions that are not optimized prior to
elective surgery,
– patients with a difficult airway, or
– other significant comorbidities (severe aortic stenosis, significant
pulmonary disease, CHF, etc.),
23

24. Depth of GA
• General anesthesia is a drug-induced state that is characterized by an
absence of perception to all sensations
– global and reversible depression of central nervous system (CNS)
– Components: Analgesia, Amnesia, Unconsciousness, Immobility (Akinesia),
Reduction of autonomic responses to stimulation
Guedel's classification, introduced by Arthur Ernest Guedel in
1937
• 4 stages: each of which reflects greater depression of brain function
1. Stage I - stage of Analgesia
2. Stage II - stage of delirium/excitement
3. Stage III - Surgical stage
4. Stage IV - Medullary paralysis anesthesia
24

25. 1. Stage I- stage of Analgesia: Analgesia and Amnesia – aka induction
– period between the administration of induction agents and loss of consciousness
– Patient is conscious and rational, with decreased perception of pain
2. Stage II- stage of delirium/excitement: ↑HR, RR
– Patient is unconscious; body responds reflexively; irregular breathing pattern with
breath holding
3. Stage III-Surgical stage: ↓HR, RR, Apnea
– Increasing degrees of muscle relaxation; unable to protect airway
– eyes roll, then become fixed; Corneal and laryngeal reflexes are lost; pupils dilate
and light reflex is lost
– Intercostal paralysis and shallow abdominal respiration occur.
4. Stage IV- medullary paralysis anesthesia - overdose
– There is depression of cardiovascular center (medulla oblongata) and respiratory
center (medulla oblongata & pons) ➔ cardiorespiratory arrest & death
• The so-called anesthetic stages are too unpredictable and inconsistent to be
attributed to modern-day general anesthetics
25

26. 26

27. Agents for GA
Ideal anesthetics
 Nonflammable
 Potent
 Fast onset
 Wide therapeutic index
 Good vapor pressure, and
 Few or no significant adverse effects
 Low cost
• Inhaled Anesthetics
• Intravenous Anesthetics
– Systemic Opioid (Narcotic) Analgesia
• Patient-Controlled Analgesia (PCA)
– Sedatives
27

28. Inhaled Anesthetics
• Used for both induction and maintenance phase
• Can be controlled by anesthesiologist continuously
• Volatile anesthetics
– Low vapor pressure and high boiling point
– They are liquid at room temperature
– Halothane , enflurane, isoflurane, desflurane, sevoflurane
• Gaseous anesthetics
– High vapor pressure and low boiling point
– They are in gaseous state at room temperature
– Nitrous oxide, xenon
– Nitrous oxide (N2O; laughing gas) is the only inorganic anesthetic gas in clinical use
• Produce dose-dependent systemic effects
• Associated with Malignant Hyperthermia
28

29. • With the endotracheal tube secured, anesthesia is maintained with a
halogenated agent, typically mixed with air or nitrous oxide
• The most commonly used inhalational anesthetics in the United States
include desflurane and sevoflurane.
– Both have low solubility in blood and fat
– As a result, they offer faster onset and clearance than more traditional gases such
as isoflurane
– In addition to providing amnesia, they produce profound uterine relaxation when
given in high concentrations
• This is advantageous when relaxation is a requisite, such as for
– internal podalic version of the second twin,
– breech decomposition, or
– replacement of the acutely inverted uterus
• That said, unless the woman is already under general anesthesia, intravenous nitroglycerine
is preferred by many in such situations
29

30. 30
Inhalation anesthetic agents
Generic name Nitrous oxide Halothane Isoflurane Sevoflurane Desflurane
Chemical formula N2O C2HBrClF3 C3H2ClF5O C4H3F7O C3H2F6O
Odor Slightly sweet Sweet Sweet Sweet Sweet
Color Colorless Colorless Colorless Colorless Colorless
Pungency None Moderate High Low Very high
Blood pressure effect Negligible
Dose-dependent
hypotension
Dose-dependent
hypotension
Dose-dependent
hypotension
Dose-dependent
hypotension
Vascular effect Negligible Negligible Vasodilation Vasodilation
Initial
vasoconstriction,
later vasodilation
Inotropic effect Negligible Negative Slightly negative Slightly negative
Initial positive, later
negative
Chronotropic effect Negligible Bradycardia Tachycardia Tachycardia >1 MAC Tachycardia
How supplied
Pressurized bottled
gas
Bottled liquid Bottled liquid Bottled liquid Bottled liquid
How delivered Flowmeter Vaporizer Vaporizer Vaporizer
Electric heated
vaporizer
Fire risk Supports combustion Non-flammable Non-flammable Non-flammable Non-flammable
Notes Nausea/emesis
Nausea/emesis;
bradycardia/asystole;
inhalational
induction; no longer
used in US
Nausea/emesis;
potentially significant
tachycardia
Nausea/emesis;
inhalational induction
Nausea/emesis;
airway irritation;
initial
sympathomimetic

31. Nitrous Oxide
• has a rapid onset and offset that provides analgesia during episodic contractions
• It can be self-administered as a mixture of 50-percent nitrous oxide and 50-percent oxygen
– premixed in a single cylinder (Entonox) or
– using a blender that mixes the two gases from separate tanks (Nitronox)
• Use
– for labor pain: safe for the mother and newborn
– but pain control is less effective than epidural analgesia (which is more definitive)
• MOA:
– General CNS depressant action
– may act similarly as inhalant general anesthetics by stabilizing axonal membranes to partially inhibit action potentials
leading to sedation
– may partially act on opiate receptor systems to cause mild analgesia
– central sympathetic stimulating action supports blood pressure, systemic vascular resistance, and cardiac output;
– it does not depress carbon dioxide drive to breath
– Nitrous oxide increases cerebral blood flow and intracranial pressure while decreasing hepatic and renal blood flow; has
analgesic action similar to morphine
31

32. Inhaled Nitrous Oxide (N2O)
• colorless, odorless to sweet-smelling, and nonirritating to the tissues
• commonly used during general anesthesia
– Also used for labor and postpartum laceration repair analgesia
• is self-administered using a mouthpiece or facemask, with a 50% mix of nitrous oxide in 50%
oxygen
• has a rapid onset and offset that provides analgesia during episodic contractions
• use of intermittent nitrous oxide for labor pain is generally regarded as safe for the mother
and newborn, but pain control is less effective than epidural analgesia
• In many cases, nitrous oxide simply serves to delay more definitive neuraxial analgesia
• For maximal efficacy, nitrous oxide is inhaled 30 seconds prior to the start of a contraction,
although this prevents adequate rest for the mother
• Nitrous oxide is also associated with nausea and vomiting
• The environmental and health risk of its use without proper scavenging remains to be
carefully evaluated
32

33. 33
Fate of inhalational General Anesthetic agents

34. Factors that control uptake & distribution
• Inspired concentration
• Ventilation
• Solubility
– Blood: gas partition coefficient
– The higher the coefficient the higher uptake to the blood from alveolar space → takes
longer time for induction
– Lower soluble agent e.g N2O,Desflurane, Sevoflurane
– Higher soluble agent : Halothane, Isoflurane
• Cardiac output
– Increase blood flow to lungs→ increase uptake →distribution to all tissues→ decrease to
rate of induction
• Alveolar- venous pressure difference
– The higher the difference the faster anesthetic uptake
34

35. Elimination
• Elimination is mainly through the lung
• Factors that affects elimination
– Similar factor with induction
– Metabolism
• Less important for elimination but crucial for toxicity
• Different for different anesthetics
• Halothane > enflurane > sevoflurane >isoflurane >
desflurane > N2O
35

36. Pharmacodynamics
• Hepatic effect
– ↓portal vein flow but compensated by hepatic aa flow→ no change overall
– Transient increase in liver enzymes. E.g halothane
• Renal
– Decreased GFR but compensated by increase in filtration fraction→ no change overall
• Muscle
– High enough concentrations will relax skeletal muscle
– Correlation : Manual removal of placenta, PPH
• Respiration
– Depressed respiration and response to PaCO2 → hypoventilation
– Bronchodilation but may be irritant(desflurane, Isoflurane)
– ↓tidal volume +↑RR → ↓alveolar ventilation.
– Exception Nitrous oxide
– ↓ Mucociliary function of the tract
– Correlation : respiratory depression, asthma, shallow and fast resp. pattern, respiratory infection
36

37. • Cardiovascular System
– Generalized reduction in arterial pressure and peripheral vascular resistance. Isoflurane maintains CO
and coronary function better than other agents
– Preserve cardiac blood flow
• ↑coronary blood flow
• ↓oxygen demand
– Increase catecholamine sensitivity of myocardium →HR→ Risk of aryhthemia
• Central Nervous System
– ↓ metabolic rate and vasodilation →affects cerebral blood flow depending on concentration
• at 0.5 MAC ↓CMR + Vasodilation→ ↓blood flow
• At 1MAC ↓CMR + Vasodilation→ no change blood flow
• At 1.5 MAC ↓CMR + Vasodilation→ ↑blood flow
– N2O has always increased blood flow effect to brain
• Clinical importance:
• ↑ICP vs high concentration of agents
• Role of hyperventilation→ ↓PaCO2→vasoconstriction→ ↓Blood flow to the brain
37

38. Complications of Inhalational. A
Acute complication
1. Hepatotoxicity : Halothane
2. Malignant hyperthermia: Halothane
– Susceptibility is genetic and autosomal
dominant
– Mutation in endoplasmic reticulum Ca++
channel
– Excessive efflux of Ca++
– Treated with dantrolene
3. Renal toxicity: Enflurane, sevoflurane
4. Hematologic toxicity
– N2O ↓methionine synthase activity →
megaloblastic anemia
– All other agents + dry base absorbent in
machine -→CO → Toxicity
• E.g desflurane
Chronic complication
1. Mutagenicity
2. Carcinogenicity
3. Teratogenicity
– There is evidence of teratogenicity in
animal but no strong evidence on
human
4. Reproduction
. There is evidence of high rate of
abortion in health professionals in but
difficult to interprate
– High rate of abortion in first TM
surgery but is due to agents
38

39. Intravenous Anesthetics
• Mainly used for induction because of fast onset
• Difficult to control throughout the surgery, thus caution is important before administration
• Unlike inhalational anesthetics
– Usually used for induction agents except propofol
– Anesthesiologist has less control
– Have almost similar duration of action when administered as single dose but differ in
metabolism
– Have lipid solubility that is responsible for fast onset of action
• Barbiturates: Thiopental
• Propofol - better used for maintenance than other IV agents
• Imidazole group: Etomidate
• Ketamine
39

40. Context- sensitive half time
• Describes the drug’s elimination half-time after discontinuation
of a continuous infusion as a function of the duration of the
infusion
• It is measure of suitability of the drug for maintenance phase
• E.g propofol is better used for maintenance than other IV
agents
40
Context sensitive Half time of different IV GA

41. Thiopental
• It is an ultra-short acting barbiturate
• It is potent anesthetic but weak analgesic
• Induces anesthesia with in seconds but will accumulate for a long time and has a residual effect
• Only 15% of the drug will be metabolized
Propofol
• It has intralipid formulation
• Fast acting and metabolism
• Used for both induction and maintenance phase of G.A
• Currently anesthetic choice for induction replacing thiopental b/c of no nausea and vomiting effect
• Causes decreased BP with out increasing heart rate
• Decreases ICP
• It causes sever pain at injection site.
– Fospropofol can be used as proactive drug but it is more prolonged onset
41

42. Etomidate
• It an imidazole used for induction of anesthesia
• Less cardiorespiratory depression because of lack of sympathetic activity
• Can suppress 11β hydroxylase enzyme which is used for cortisol synthesis
• Can cause pain at injection site
• Clinical correlation:
– heart disease patients, shock patients, prolonged infusion (>8hrs) vs low cortisol blood level
Ketamine
• Highly lipid soluble phencyclidine derivative
• Is dissociative anesthetics (the pt seems awake but analgesic & amnesic state)
• Seems to act through inhibition of NMDA rec.
• Increase cardiac output (unique feature)
• Causes unpleasant hallucination
• Has low protein binding capacity and is fast acting IV anesthetic
• Metabolized in the liver to be excreted via urine
• It causes vasodilation of cerebral vessel and increase blood flow to the brain
42

43. Adjuvant Drugs
• They are drugs that provide additional effects that are desirable
during surgery but are not necessarily provided by the general
anesthetics.
• Benzodiazepine: anxiolytic and sedative effect
– Midazolam
– Lorazepam
– Diazepam
• Opoids : analgesic effect
– Fentynel
– morphine
• Muscle relaxants: muscle relaxation
43

44. Systemic Opioid (Narcotic) Analgesia
• The term “opioids” includes compounds that are extracted from the poppy seed as well as
semisynthetic and synthetic compounds with similar properties that can interact with opioid
receptors in the brain
• ACOG, 2019
– Parenteral opioids continue to have a role in peripartum analgesia
– inexpensive and their use requires no specialized expertise
– But, parenteral opioids have little effect on maternal pain scores, provide unreliable analgesia, and
commonly have adverse effects such as nausea and vomiting
• Opioids are associated with adverse effects for the woman and the fetus or newborn, most
significantly respiratory depression, so attention should be paid to respiratory status (ACOG,
2019: Level A)
• Parenteral opioids for labor analgesia work primarily by sedation and, except at high doses,
result in minimal reduction of maternal pain
– Side effects: maternal nausea and respiratory depression in both the mother and newborn
– The routine use of promethazine in conjunction with opioids should be avoided
• Promethazine can potentiate the sedating effect of opioids, increasing the risk for apnea and respiratory depression
44

45. Commonly Used Parenteral or Systemic
Opioids for Labor Analgesia (ACOG, 2019)
45

46. • Opioids have analgesic and sedative effects
• If neuraxial analgesia is contraindicated or unavailable or is declined,
– One narcotic + one tranquilizer-antiemetic drugs such as promethazine
(Phenergan)
• Meperidine and Promethazine: every 2 to 4 hours
• Opioids in common use today: Meperidine, nalbuphine, fentanyl, and remifentanil
– Morphine fell out of favor – since it results in increased respiratory depression in the
newborn compared with meperidine
• Meperidine readily crosses the placenta and can have a prolonged half-life
in the newborn
• Nalbuphine
– mixed opioid receptor agonist–antagonist analgesic
– Small doses may also be used to treat pruritus associated with neuraxial opioids
46

47. • may cause addiction
• All opioids provide sedation and a sense of euphoria,
– but their analgesic effect in labor is limited, and
– their primary mechanism of action is sedation
• Opioids can also produce nausea and respiratory depression in the mother,
the degree of which is usually comparable for equipotent analgesic doses.
• Also, all opioids freely cross the placenta to the newborn and decrease
beat-to-beat variability in FHR
• They can increase the likelihood of significant respiratory depression in the
newborn at birth and can increase the subsequent need for treatment
• Disadvantage
– Maternal Prolonged gastric emptying
• if general anesthesia becomes necessary, the risk of aspiration is increased
47

48. 48
Class of opioids Strong Agonists
Mild to Moderate
Agonists
Opioids with Mixed
Receptor Actions
Phenanthrenes
• Morphine
• Hydromorphone
• Oxymorphone
• Codeine
• Oxycodone
• Hydrocodone
• Nalbuphine
• Buprenophrine
Phenylheptylamines • Methadone • Propoxyphene
Phenylpiperidines
• Fentanyl
• Meperidine (pethidine)
• Diphenoxylate
• Loperamide
Opioid Classification
Opioids can be categorized as
1. Endogenous (endorphins, enkephalins, dynorphins),
2. Opium alkaloids (morphine, codeine),
3. Semisynthetic (oxycodone), or
4. Synthetic (methadone, fentanyl)
Naturally occurring Semi-synthetic
compounds
Synthetic compounds
Morphine
Codeine
Thebaine
Papaverine
Heroin
Dihydromorphine
Buprenorphine
Oxycodone
Pethidine
Fentanyl
Methadone
Alfentanil
Remifentanil
Tapentadol

49. Some Parenteral Analgesic Agents for
Labor Pain
49

50. Opioid overdose (WHO)
• Opioid use can lead to death due to the effects of opioids on the part of the brain
which regulates breathing
• three signs and symptoms:
– pinpoint pupils
– unconsciousness; and
– difficulties with breathing
• Death following opioid overdose is preventable if the person receives basic life
support and the timely administration of the drug naloxone
• Naloxone is an antidote to opioids that will completely reverse the effects of an
opioid overdose if administered in time
• Naloxone has virtually no effect in people who have not taken opioids
50

51. • Q:A multiparous woman has had painful uterine contractions every 2 to 4 min for the last 17 h.The
cervix is dilated to 2 to 3 cm and effaced 50%; it has not changed since admission
• Meperidine (Demerol) 100 mg intramuscularly
– The multiparous patient is in prolonged latent phase, characterized by painful uterine contractions without
significant progression in cervical dilation.
– Prolongation of the latent phase is defined as 20 h in nulliparas and 14 h in multiparas.
– The diagnosis of this category of uterine dysfunction is difficult and is made in many cases only in retrospect.
– Only rarely is there need to resort to oxytocic agents or to cesarean section.
– The recommended management is meperidine (Demerol) 100 mg intramuscularly; this will allow most
patients to rest and wake up in active labor.About 10% of patients will wake up without contractions and the
diagnosis of false labor will be made. Only about 5% of patients will wake up after meperidine in the same
state of contractions without progression.
– Epidural block may lead to abnormal labor patterns and to delay of descent of the presenting part
• Naloxone may not be administered to which of the following patients?
– A. Mothers with severe preeclampsia
– B. Mothers with respiratory depression
– C. Newborns of narcotic-addicted mothers
– D. Mothers who have just received IV morphine
• Naloxone:Antidote; Opioid Antagonist
– Pure opioid antagonist that competes and displaces opioids at opioid receptor sites
– commonly used to counter decreased breathing in opioid overdose
51

52. Patient-Controlled Analgesia (PCA)
• Indication
– for women who have a contraindication to neuraxial analgesia
(severe thrombocytopenia)
• Route: IV [Fentanyl, remifentanil & meperidine]
• The infusion pump is programmed to give a predetermined
dose of drug upon patient demand
• Advantages of this method include
– Sense of autonomy, which patients appreciate, and
– Elimination of delays in treatment while the patient’s nurse obtains
and administers the dose
52

53. Meperidine (Demerol)
• synthetic opioid
• 100 mg is roughly equianalgesic to morphine 10 mg but has been
reported to have a somewhat less depressive effect on respiration
Fentanyl
• is a fast-onset, short-acting synthetic opioid with no active
metabolites
• 50 to 100 µg every hour provided equivalent analgesia with fewer
neonatal effects and less maternal sedation and nausea
• Main drawback: short duration of action, which requires frequent
redosing or the use of a patient-controlled IV infusion pump
53

54. 54
Some Parenteral Analgesic Agents for Labor Pain

55. Sedatives
• Sedatives
• Barbiturates: Phenobarbital, Pentobarbital, Thiopental
• Phenothiazines:
• Benzodiazepines: Diazepam, Lorazepam, Midazolam
– Two major disadvantages of benzodiazepines
✓ cause undesirable maternal amnesia
✓ may disrupt thermoregulation in newborns, which renders them less able to maintain an
appropriate body temperature
 Flumazenil, a specific benzodiazepine antagonist, can reliably reverse benzodiazepine induced
sedation and ventilatory depression
– do not possess analgesic qualities
• All sedatives and hypnotics cross the placenta freely, and except for
the benzodiazepines, they have no known antagonists
• Sedation is rarely desirable during the childbirth experience
55

56. Balanced GA
• The term balanced general anesthesia
– refers to a combination of various agents—including
• hypnotic agents to induce sleep, inhalation agents, opioids, and muscle relaxants
– The opposite of high concentrations of potent inhalation agents alone
– It is preferred for obstetric applications
• Decrease toxicity of each agent as dose will be decreased
• Better for anesthesiologist to control single drug for side effects that may happen
• E.g
– N2O(rapid induction & recovery) Plus Isoflurane
– Thiopental (induction) + halothane (maintenance)
• Thiopental passes stage II of anesthesia fast
– Opioids (morphine) + inhalational agent in cardiac patient
• Opioids prolongs the effect of anesthesia
56

57. • Benzodiazepine: Relieve anxiety
• Barbiturate: Sedation
• Antihistamine: Prevent allergic reaction
• Muscle relaxant: Muscle relaxation
• Antiemetic: Prevent aspiration
• Opioids: Analgesic
• Anticholinergic drugs: Prevent secretion and bradycardia
57

58. 58
Amnesia/Hypnosis
(Unconsciousness)
Muscle relaxation
Analgesia
Triads of balanced anesthesia

59. Induction-Intubation-Maintenance-Reversal-
Extubation
• Equipment: laryngoscopes, fiberoptic
intubation
• Usually important phases
– Preoxygenation
– Induction
• Intubation
– Maintenance
– Reversal (Recovery)
• Extubation
59

60. Induction
• rapid sequence induction and intubation
• is a period from the onset of administration of the
anesthetic to the development of effective surgical
anesthesia
• Induction aims at achieving the triad of Anesthesia
– Loss of Consciousness: IV or Inhalational
– Muscle relaxation: using muscle relaxants
– Analgesia
60

61. • Agents for induction
– The ideal induction agent has a rapid onset of action, minimal cardiopulmonary or other
side effects, and is cleared from the bloodstream quickly so that recovery is rapid
1. Inhalational
– Gaseous: Nitrous oxide gas (N2O)
– Volatile liquid (halothane, isoflurane, sevoflurane, desflurane, ether)
– Indication: Young children, Upper airway obstruction (epiglottitis), Lower airway
obstruction (Foreign body), Bronchopulmonary fistula, Inaccessible veins
2. Intravenous – commonest (Faster: 5 to 10 minutes)
– Opioids: Remifentanil, Fentanyl, Sufentanil, Alfentanil, Hydromorphone, Morphine
• Remifentanil is most suitable for continuous infusion during a TIVA technique, particularly when the
intensity of surgical stimulation will vary during the procedure. For bolus dosing, we typically employ
a short-acting opioid such as fentanyl.
– Propofol, Thiopentone, Etomidate, Ketamine, Midazolam
61

62. • Positioning for induction of
general anesthesia
– obtained by lifting the patients chin
upward (when supine)
– Since the patient is no longer able to
protect their airway or provide an
effective respiratory effort
– goal
• to provide adequate ventilation and
oxygenation during GA
• Head up
– reverse Trendelenburg or
– semi-sitting / semi-Fowler position
• Preoxygenation is accomplished
using 100 percent oxygen (O2)
62

63. • Rapid sequence induction (RSI)
– For patients who are at risk of aspiration of gastric contents into the lungs
• patients who are inadequately starved, have impaired gastric emptying or are known to have a history of
gastric reflux
• NB: almost all parturients are considered to have a full stomach
– It involves loss of consciousness during cricoid pressure followed by intubation without
face mask ventilation
• IV anesthetic and rapid-onset muscle relaxant are simultaneously administered while cricoid pressure is
applied by an assistant
– Positive mask ventilation during rapid sequence induction is typically avoided to lower the
risk of increased intragastric pressure, which raises the risk of vomiting
Anesthetic premedication: New horizons of an old practice
• several reasons to explain why we do not give medication to every patient before
sending them to the operating theater
– the induction time of general anesthesia in current practice is much shorter than that of
ether anesthesia
• Since we use intravenous anesthetics as induction agents; for most intravenous agents, onset of action
occurs within 60 seconds
– sedative or opioid agents cross placenta and can depress the newborn
• Sedation should be unnecessary if the procedure is explained well and the patient is
reassured
63

64. • With short-acting induction agent to render the patient unconscious
– appropriate dose of any of these agents has little effect on the fetus
– Agents: propofol, etomidate, and ketamine, all of which are rapidly redistributed in both
mother and fetus
– Women who receive ketamine for induction require less analgesic medications in the first
24 hours after their cesarean delivery compared with those who received thiopental
– Ketamine antagonism of N-methyl-D-aspartate (NMDA) receptors may prevent central
hypersensitization and provide preemptive analgesia
• obstetricians are often concerned about
1. Induction-to-delivery interval (I-D) during GA
• prolonged I-D interval → fetal uptake of inhaled anesthetic and depressed Apgar scores, but fetal acid-
base status is normal, and effective ventilation is all that is needed
2. Uterine incision-to-delivery interval (U-D) is more predictive of neonatal status
• prolonged U-D interval > 3 minutes leads to depressed Apgar scores with neuraxial or GA & is
associated with elevated fetal umbilical artery norepinephrine concentrations and associated fetal
acidosis
64

65. Common drugs for induction
Class Drug Description
Benzodiazep
ine
Diazepam
Lorazepam
Midazolam
Imidazole Etomidate • often selected in patients with hemodynamic instability due to any cause, because it does
not change blood pressure (BP), cardiac output (CO), or heart rate (HR)
• Advantages: hemodynamic stability, anticonvulsant properties, and ability to decrease ICP
• Potential adverse effects of etomidate include transient acute adrenal insufficiency, higher
incidence of nausea and vomiting than other induction agents, pain on injection, absence of
analgesic effect, involuntary myoclonic movements, and mild increases in airway resistance
Alkylphenol Propofol • quick onset and recovery → so lower incidence of nausea and vomiting
• Since thiopental is no longer available, propofol is used as the primary agent (agent of
choice ) for induction due to its rapid onset and offset, beneficial properties, and relatively
benign side effects
Arylcyclohex
ylamines
Ketamine • selected to induce anesthesia in patients with actual or potential severe hypotension because
administration typically increases BP, HR, and CO
• Advantages: bronchodilation, profound analgesic properties, maintenance of airway reflexes and
respiratory drive
• adverse cardiovascular effects: increased HR, BP, CO & pulmonary arterial pressure (PAP)
• can be used but is avoided in hypertensive women
65

66. Intravenous anesthetic induction
agents
Drug Uses
Suggested induction
dose
Advantages Potential adverse effects
Propofol
Induction agent of
choice for most
patients
 1 to 2.5 mg/kg
 Older age: 1 to 1.5
mg/kg
 Hypovolemia or
hemodynamic
compromise: ≤1
mg/kg
o Rapid onset and offset
o Antiemetic properties
o Antipruritic properties
o Bronchodilation
o Anticonvulsant properties
o Decreases CMRO2, CBF, and
ICP
• Dose-dependent hypotension
• Dose-dependent respiratory depression
• Pain during injection
• Microbial contamination risk
• Rare anaphylaxis in patients with allergy to its soybean oil emulsion
with egg phosphatide
Etomidate
May be selected in
patients with
hemodynamic
instability due to
any cause
 0.15 to 0.3 mg/kg
 Presence of
profound
hypotension: 0.1 to
0.15 mg/kg
o Rapid onset and offset
o Hemodynamic stability with
no changes in BP, HR, or CO
o Anticonvulsant properties
o Decreases CMRO2, CBF & ICP
• High incidence of PONV
• Pain during injection
• Involuntary myoclonic movements
• Absence of analgesic effects
• Transient acute adrenocortical suppression
Ketamine
May be selected in
hypotensive
patients or those
likely to develop
hypotension (eg,
hypovolemia,
hemorrhage,
sepsis, severe
cardiovascular
compromise)
 1 to 2 mg/kg
 Chronic use of
tricyclic
antidepressants: 1
mg/kg
 Presence of
profound
hypotension: 0.5 to
1 mg/kg
 Intramuscular
dose: 4 to 6 mg/kg
o Rapid onset
o Increases BP, HR, and CO in
most patients
o Profound analgesic
properties
o Bronchodilation
o Maintains airway reflexes and
respiratory drive
o Intramuscular route available
if IV access lost
Cardiovascular effects
• Increases myocardial oxygen demand due to increases in HR, BP & CO
• Increases pulmonary arterial pressure (PAP)
• Potentiates cardiovascular toxicity of cocaine or tricyclic
antidepressants
• Exacerbates hypertension, tachycardia, and arrhythmias in
pheochromocytoma
• Direct mild myocardial depressant effects
Neurologic effects
• Psychotomimetic effects (hallucinations, nightmares, vivid dreams)
• Increases CBF and ICP; may increase CMRO2
• Unique EEG effects may result in misinterpretation of BIS and other
processed EEG values
Other effects
• Increases salivation
66

67. 67
Muscle Relaxants: Properties of neuromuscular blocking agents
Agent Vecuronium Rocuronium Pancuronium Mivacurium Atracurium Cisatracurium Succinylcholine
Type (structure)
Non-
depolarizing
Non-
depolarizing
Non-
depolarizing
Non-
depolarizing
Non-
depolarizing
Non-
depolarizing
Depolarizing
Type (duration) Intermediate Intermediate Long Short Intermediate Intermediate Ultrashort
Onset time
(min)
3 to 4 1 to 2 2 to 3 3 to 4 3 to 5 4 to 6 1
Time to 25%
recovery (min)
20 to 35
30 to 50 (60 to
80 with RSII
dose)
60 to 120 15 to 20 20 to 35 30 to 60 5 to 10
Comments
Not for
prolonged ICU
administration
(myopathy);
reversible by
sugammadex;
elimination half-
life halved in
late pregnancy;
3-desacetyl
metabolite has
60% of the
parent
compound
potency
Pain on
injection; easily
reversible by
sugammadex;
elimination half-
life prolonged in
ICU patient; 17-
desacetyl
metabolite has
20% activity
Significant
accumulation,
prone to
residual block
(3-OH
metabolite has
50% activity of
pancuronium)
Reversal by
cholinesterase
inhibitors;
mixture of 3
isomers (cis-cis
minimal);
edrophonium
for antagonism
more effective
during deep
block
Organ-
independent
elimination
Trivial histamine
release; minimal
plasma
laudanosine and
acrylate levels
Fastest onset,
most reliable
NMBA for rapid
tracheal
intubation

68. Common muscle relaxants
Drug Description
Succinylcholine
• For muscle relaxation
• a rapid-onset, short-acting depolarizing muscle relaxant
• It offers intense muscle relaxation to aid endotracheal intubation but also allows for the rapid return of
spontaneous respiration in the case of failed intubation
• remains the agent of choice in most patients
• CI: muscular dystrophy; children; receptor up-regulation settings; pseudocholinesterase deficiency
• Reversal – with Sugammadex
Rocuronium
• is an alternative muscle relaxant if succinylcholine is contraindicated or unavailable
• Its duration is much longer than succinylcholine unless its effect is reversed by sugammadex, a specific
binding agent recently approved by the FDA
Reversal Muscle Relaxants
• necessary for most patients who received a nondepolarizing neuromuscular blocking agent (NMBA)
– anticholinesterase agent
• Neostigmine (administered along with glycopyrrolate), edrophonium (coadministered with atropine),
– Sugammadex, a gamma-cyclodextrin agent that encapsulates and subsequently inactivates steroidal NMBAs
(eg, rocuronium, vecuronium)
68
o To decrease the incidence of fetal respiratory depression, an intermediate or long-acting opioid is usually
avoided upon induction of general anesthesia
o The intense stimulation from direct laryngoscopy may worsen hypertension and tachycardia in certain women

69. Intubation
• Immediately after the induction agent → gives a
muscle relaxant ➔ intubation
Sellick maneuver
• now commonly referred to as cricoid pressure
• cricoid cartilage is a hard, ring-like structure inferior to
the cricothyroid cartilage at level C6
• Cricoid pressure
– applied by a trained assistant
• To prevent
– Aspiration pneumonitis and pneumonia
• Surgery should begin only after
– an airway is secured or,
– depending on the status of the mother and fetus,
effective ventilation has been established
69

70. Endotracheal tube (ETT)
• Preferred for
– Those with high risk of aspiration
– those that require high inspiratory
pressures
– for longer cases requiring muscle
relaxation.
Supraglottic airway (SGA)
• Preferred for
– shorter procedures (<3 hours)
– Those with low risk of aspiration
– procedures which will not require a
prolonged period of muscle relaxation
70
Endotracheal tube (ETT) Vs Supraglottic airway (SGA)

71. Awake intubation
• should be considered if there is anticipated difficulty with
tracheal intubation AND one of the following
– Both mask and supraglottic airway (eg, laryngeal mask airway
[LMA]) ventilation are likely to be difficult
– The stomach is not empty (the patient is at risk for aspiration of
gastric contents)
– The patient will not tolerate an apneic period (eg, severe obesity,
pregnancy, pulmonary disease)
71

72. Failed Intubation
• common cause of death
• occurs in approximately 1 of every 400 general anesthetics administered to pregnant women
– Pregnant > Non pregnant: This is due to the anatomic and physiologic changes that occur during
pregnancy and labor
• Options of mgt
– Ventilate by mask → cricoid pressure is applied to reduce the aspiration risk
– In elective cases
• awake intubation or videolaryngoscopy
• regional analgesia
– Urgent condition: Surgery may proceed with mask ventilation
• Rx of life-threatening emergency
– percutaneous or open cricothyrotomy and begun ventilation
– Failed intubation drills
72

73. 73
An algorithm for the management of failed intubation in the obstetric
patient. LMA, laryngeal mask airway

74. 74

75. Preanesthetic evaluation
• The anesthesiologist will
assess four factors:
1. The ability to visualize
oropharyngeal structures
(Mallampati classification);
2. range of motion of the
neck;
3. presence of a receding
mandible, which indicates
the depth of the
submandibular space; and
4. whether protruding
maxillary incisors are
present
75
Modified Mallampati classification for difficult
laryngoscopy and intubation
• Class I - soft palate, uvula, and pillars are
visible;
• Class II - soft palate and base of the uvula are
visible
• Class III - only the soft palate is visible
• Class IV - only the hard palate is visible

76. 76
Cormack-Lehane grading scheme for laryngoscopy
• Difficulty of direct laryngoscopy correlates with the best view of the glottis, as defined
by the Cormack-Lehane Grading
• With this scale,
• a grade I view connotes a full view of the entire glottic aperture,
• grade II represents a partial glottic view,
• grade III represents visualization of the epiglottis only, and
• grade IV represents inability to visualize even the epiglottis

77. Maintenance
• For the duration of the procedure, a plane of anesthesia is maintained
using either continuous inhalation or intravenous agents, either alone
or in combination
• Agents
– Inhalational: mixture of oxygen, nitrous oxide, and a volatile anesthetic
(sevoflurane, isoflurane, or desflurane)
• Inhaled agents are frequently supplemented by IV anesthetics, such as opioids
( Fentanyl) and sedative-hypnotics (usually propofol or Midazolam)
– IV: propofol
• for a propofol-based anesthetic, supplementation by inhalation agents is not required
• provides a sustained surgical anesthesia
– to prolong anesthesia for the required duration of surgery
77

78. Reversal (Recovery)
• discontinuation to regaining consciousness
• At the end of surgery, the volatile or intravenous
anesthetic is discontinued.
• Recovery of consciousness occurs when the concentration
of anesthetic in the brain drops below a certain level
(usually within 1 to 30 minutes, depending upon the
duration of surgery)
78

79. Extubation
• endotracheal tube may be safely removed only if
– woman is conscious to a degree that enables her to follow commands (GCS
> 8)
• To prevent aspiration
• NB: Coughing and bucking do not necessarily indicate that the patient is awake,
merely that she is in the second stage—the excitement stage—of anesthesia
– She is capable of maintaining oxygen saturation with spontaneous
respiration
• Empty stomach with nasogastric tube before extubation
• Of 15 anesthesia-related deaths of pregnant women from 1985 to
2003 in Michigan, none occurred during induction
– Five resulted from hypoventilation or airway obstruction during
emergence, extubation, or recovery
79

80. Airway complications that may occur
during or after extubation include
• Upper airway obstruction  relaxation of airway muscles
• Laryngospasm, bronchospasm
– Presence of airway device or airway secretions can lead to airway irritation, especially at light
levels of anesthesia as occur on emergence.
• Hypoventilation – Can be due to residual anesthesia and narcotic medication.
• Hemodynamic changes – Hypertension and tachycardia
• Aspiration – Secretions or stomach contents may be aspirated while the patient is unable
to protect the airway.
• Negative pressure pulmonary edema – Can occur when the patient attempts to breathe
against upper airway obstruction, as with laryngospasm, or when the patient occludes the
airway device by biting it with inadequate bite block in place.
• Coughing or straining – Can disrupt surgical wound with straining, as after hernia repair,
or with venous congestion and bleeding, as might occur after facial plastic surgical
procedures
80

81. Complications of GA
• Intra operative
– Laryngoscope: trauma to lip, teeth, tongue, epiglottis, vocal cords
– Endotracheal tube: Injury to trachea, Blockage of tube (secretions, blood clot, foreign body),
Bronchospasm
– Anesthetic drugs
• Hypoxia, hypotension/hypertension, hypercarbia/hypocarbia, hypothermia/hyperthermia,
Hypoglycemia/hyperglycemia, Less or over fluid infusion
– Air embolism , fat embolism
• Post operative:
– Inadequate reversal, Laryngospasm, Bronchospasm, Meiosis, Bradycardia, Urine retention
• Awareness with recall (AWR)following general anesthesia
– Incidence: 1 to 2 cases/1000 in North America and Europe
– Anesthetic underdosing is the major risk factor
– 1/3 – 2/3 of patients with AWR develop psychological sequelae
– potential psychological complications can be devastating, passing through acute stress disorder
and leading to subsyndromal pictures until post-traumatic stress syndromes
81

82. Aspiration
• Massive gastric acidic inhalation may cause pulmonary insufficiency from aspiration
pneumonitis
Pathophysiology
• Right mainstem bronchus usually offers the simplest pathway for aspirated material to reach
the lung parenchyma, and therefore, the right lower lobe is most often involved
• In severe cases, there is bilateral widespread involvement
• Aspiration → airway obstruction → decreased oxygen saturation along with tachypnea,
bronchospasm, rhonchi, rales, atelectasis, cyanosis, tachycardia, and hypotension are likely to
develop
• To minimize this risk,
– Fasting: 6 to 8 hours for solid food prior to elective cesarean delivery or puerperal tubal ligation
– Antacids
– Intubate accompanied by cricoid pressure
– Regional analgesia is employed when possible
82

83. Treatment
• close monitoring: RR & SO2
• Inhaled fluid should be immediately and thoroughly wiped from the mouth and
removed from the pharynx and trachea by suction
• Saline lavage may further disseminate the acid throughout the lung and is not
recommended
• If large particulate matter is inspired,
– bronchoscopy may be indicated to relieve airway obstruction
• No convincing evidence supports that corticosteroid therapy or prophylactic
antimicrobial administration is beneficial
– If infection develops, however, then vigorous treatment is given
• If acute respiratory failure develops, mechanical ventilation with positive end-
expiratory pressure may be lifesaving
83

84. Patient Preparation
• Aspiration Prophylaxis
1) NPO (Nil Per Os)
• preoperative fasting
– Solid food: 8 hrs before induction
– Liquid: 4 hrs before induction
– Clear water: 2 hrs before induction
• Pediatrics: stop breast milk feeding 4 hrs
before induction
2) Antacid administration
• shortly before anesthesia induction (< 1
hour
• nonparticulate antacid, an H2-receptor
antagonist, or metoclopramide
• As soon as it is known that the patient
requires cesarean delivery, be it with
neuraxial or general anesthesia,
• 30 mL of a clear, nonparticulate antacid—
such as
– 0.3 M sodium citrate,
– Bicitra (citric acid and sodium citrate), or
• Alka Seltzer, 2 tablets in 30 mL water
– is administered to
• decrease gastric acidity and
• ameliorate the consequences of aspiration,
– chalky white particulate antacids are
avoided because they can produce lung
damage if aspirated
84

85. American Society of Anesthesiology Preoperative NPO
Guidelines
Food NPO requirement Example
Clear Liquids 2 hours Apple juice, water (NO orange juice)
Breast Milk 4 hours Unfortified
Infant Formula 6 hours Unfortified
Non-Human Milk 6 hours Almond milk, soy milk, unfortified
Light Meal 6 hours
Tea and toast (no added fats, like
butter)
Full Meal 8 hours Fatty meal
85

86. Pharmacologic aspiration prophylaxis
• Options include
– 40 to 60 minutes prior to induction
• sodium citrate: 30 mL by mouth immediately prior to anesthesia
• OR H2 receptor antagonist: ranitidine 50 mg IV
– 15 minutes prior to induction
• + Metoclopramide
– 10 mg IV slowly
86

87. 3) Lateral uterine displacement
• To prevent inferior vena cava (IVC) compression & Supine Hypotension
• IVC compression leads
– reduced venous return to the heart,
– reduced cardiac output, and
– reduced uteroplacental perfusion
• Aortocaval compression is detrimental to both mother and fetus
• duration of anesthesia has little effect on neonatal acid-base status when
left uterine displacement is practiced
– however, when patients remain supine, Apgar scores decrease as time of
anesthesia increases
87

88. 4) Preoxygenation
• To minimize hypoxia between the time of muscle relaxant injection
and intubation, oxygen is introduced into the lungs in place of
nitrogen
• Administer 100-percent oxygen via face mask for 2 to 3 minutes
before anesthesia induction
• In an emergency, four vital capacity breaths of 100-percent oxygen
via a tight breathing circuit will provide similar benefit
• Preoxygenation is especially important in pregnant patients, who
have decreased functional residual capacity and are more likely than
nonpregnant patients to rapidly become hypoxemic if difficult
intubation accompanied by apnea occurs
88

89. • There is no strong evidence of congenital anomalies in
single exposure of G.A drugs
• But there are reports that shows:
– N2O is associated with aplastic anemia to the baby, abortion
and congenital anomaly
– Benzodiazepines are associated with cleft palate
• Diazepam is associated with hypotonia and difficult
thermoregulation in the new born if used during labor
89
General Anesthetics in Pregnancy

90. 90
General anesthetic/Adjunct Pregnancy risk category
Desflurane B
Enflurane B
Sevofluarne B
Isoflurane C
Halothane C
Nitrous oxide C
Propofol B
Etomidate C
Ketamine Not classified yet
Thiopental C
Fentanyl C
Midazolam D
Diazepam D
Pregnancy risk category of G.A and Adjuvant drugs

91. • Which parenteral anesthetic agent has the shortest neonatal half-life?
– A. Morphine B. Nalbuphine
– C. Meperidine D. Butorphanol
• Of the following steps taken prior to the induction of general anesthesia,
which has been the key factor in decreasing maternal mortality rates from
general anesthesia?
– A.Antacids B. Preoxygenation
– C. Uterine displacement D.Aggressive IV hydration
• Intravenous administration of ergot alkaloids should be avoided because it
can initiate which of the following?
– A.Anaphylaxis B.Transient bronchoconstriction
– C. Bleeding D.Transient hypertension
91

92. Local Anesthesia
• Introduction
• Local Anesthetics
– Commonly Used Local Anesthetic Agents in Obstetrics
– Toxicity of Local Anesthetic
• Pudendal Block
• Paracervical Block
• Local Infiltration for Cesarean Delivery
• Intravenous Regional Anesthesia
92

93. Introduction
•  disruption of afferent neural traffic via inhibition of impulse generation or
propagation
• Local infiltration, paracervical block, pudendal block
• Infiltration anesthesia
– blocks sensory nerve endings
– Motor function is not affected
• Nerve block anesthesia (Conduction block)
– injected around nerve trunks so that the area distal to injection is an anesthetized and
paralyzed
– Choice mainly dictated by the required duration of action;
• For intermediate duration of action – up to 2hrs -- most commonly used is lidocaine
• For longer duration - bupivaciane
– The latency depends on the drug and the area to be covered by diffusion
– lidocaine anaesthetizes intercostal nerves within 3 min, but brachial plexus block may take
15 min
– Paracervical and pudendal block
93

94. Epinephrine added to local anesthetic solutions
Adding of adrenaline
• to delay absorption and increase duration of
blockade by inducing vasoconstriction of the
blood vessels in the area
– Enhances duration by decreasing removal
• it also serves as a marker for intravascular
injection
– ↑ in HR or BP suggests that the mixture has
entered the maternal circulation
• Enhances intensity of blockage
• Decreases systemic toxicity
• Injection is more painful
• Provides bloodless field at surgery
• Increases local tissue edema subsequently -
hypoxia
• Delays wound healing
Avoid adrenaline
• cardiac disorders - that necessitate the
avoidance of maternal tachycardia
• HTN, CAD, hyperthyroidism,
pheochromocytoma
• Digital anesthesia in patient with PAD
• Periorbital infiltration in narrow angle
glaucoma
• Patients receiving b-blockers, MAOI,TCAs
• In case of catecholamine sensitivity
94

95. Local Anesthetics
• are weak bases
• usually made available clinically as salts to increase solubility and stability
• Local Anesthetics
– Esters: Cocaine, Procaine, Tetracaine, Benzocaine
– Amides: Lidocaine, Mepivacaine, Bupivacaine, Prilocaine, Ropivacaine
• Primary MOA: blockade of voltage - gated sodium channels
95
Pharmacokinetic Properties
Agent Half-Time of
Distribution (min)
t1/2 (h) Vdss (L) CL
(L/min)
Bupivacaine 28 3.5 72 0.47
Lidocaine 10 1.6 91 0.95
Mepivacaine 7 1.9 84 0.78
Prilocaine 5 1.5 261 2.84
Ropivacaine 23 4.2 47 0.44
CL, clearance; Vdss, volume of distribution at steady state.
• Density, specific gravity, and baricity of
different substances and local anesthetics
 Hypobaric
– Lidocaine - 0.5% in water
 Isobaric
– Lidocaine - 2% in water
– Bupivacaine - 0.5% in water
 Hyperbaric
– Lidocaine - 5% in 7.5% dextrose
– Bupivacaine - 0.5% in 8% dextrose
– Bupivacaine - 0.75% in 8% dextrose

96. Commonly Used Local Anesthetic Agents in Obstetrics
96

97. Lidocaine
• Class Ib antiarrhythmic
• intermediate duration anesthetic
• Lidocaine (60 to 100 mg) is rarely used for spinal
anesthesia for cesarean delivery because of the relatively
high risk of transient neurologic symptoms (TNS) in the
nonobstetric population
• Although there is some evidence that pregnancy and the
postpartum period protect against lidocaine-induced TNS,
lidocaine is usually avoided for spinal anesthesia
97

98. Bupivacaine
• MOA: prevents depolarization by bindng to the intracellular portion of sodium channels and
blocking sodium ion influx into neurons
• Agent of choice for cesarean delivery
– hyperbaric 0.75% in 8.25% dextrose
– usual dose 11 to 12 mg when combined with an opioid (eg, fentanyl and morphine
– onset time of bupivacaine is 5 – 8 minutes
• agent of choice for epidural infusions in postoperative pain control & labor analgesia
• Baricity
– hyperbaric bupivacaine is preferred due to - its rapid onset, and the option to modify the spinal level
by changing the position of the operating table
– Plain bupivacaine (ie, slightly hypobaric, prepared in saline) may also be used for spinal anesthesia for
cesarean delivery
– The literature comparing safety and efficacy of hyperbaric with isobaric bupivacaine for cesarean
delivery is inconclusive
• Duration of action
– By 1.5 hours, the midthoracic sensory level will have receded, although total duration of action
extends beyond 2.5 hours
• More prone to cardiac toxicity
–  decrease in cardiac contractility ➔ prolonged QTc, VT, VF
• Newer preparation & less cardiotoxic with similar potency: levobupivacaine and ropivacaine
98

99. Toxicity of Local Anesthetic
• Anaphylaxis
– may occur with use of chloroprocaine and tetracaine
– but is unlikely with bupivacaine, lidocaine, and ropivacaine
• Central Nervous System Toxicity
– Early: those of stimulation
– As serum levels rise: depression follows
• light-headedness, dizziness, tinnitus, metallic taste, and numbness of the tongue and
mouth
• Patients may show bizarre behavior, slurred speech, muscle fasciculation and excitation,
and ultimately, generalized convulsions, followed by loss of consciousness
• Cardiovascular Toxicity
– hypertension and tachycardia are soon followed by hypotension, cardiac
arrhythmias, and impaired uteroplacental perfusion
99

100. Transient neurological symptoms (TNS)
• characterized by low back pain that radiates to the buttocks or
legs after recovering from spinal anesthesia
• can be distressing to patients and providers
• Risk of TNS after spinal anesthesia with
– [lidocaine] >> [bupivacaine, levobupivacaine, prilocaine,
chloroprocaine or procaine]
• In addition, hyperbaric and isobaric lidocaine showed higher
TNS rates than other lidocaine.
100

101. Pudendal Block
 pudendal nerve (Sensory: ventral branches of S2-4)
– sensory innervation: perineum, anus, vulva & clitoris
– passes beneath sacrospinous ligament just as the
ligament attaches to the ischial spine
 Usually, 5 to 15 mL of 1% lidocaine suffices
– Within 3 to 4 minutes - successful block
 Two ways of approach
– Transperineal: to the ischial spine
– Transvaginal: Mostly preferred
 Purpose
– SSOL : Bilateral
– Episiotomy (perineal lacerations): Unilateral
 Pain control for
– Labor pain after Cx > 7 cm: spinal anesthesia >>
pudendal block
– episiotomy repair: spinal anesthesia = pudendal block
101
Transvaginal technique showing the needle
extended beyond the needle guard and
passing through the sacrospinous ligament to
reach the pudendal nerve

102. Paracervical Block
• provides satisfactory pain relief during first-stage labor
• anatomic basis
– upper vagina, cervix, and lower uterus are innervated by uterovaginal (or Frankenhäuser)
plexus, which contains fibers derived from the inferior hypogastric (pelvic) plexus (T10-L1)
and sacral nerve roots (S1-S4)
• does not: affect the motor pathways or doesn’t provide pain relief to the perineum
• Laboring (obstetric procedures
– inject into the cervix laterally at 3 and 9 o’clock (W 25th, Gabbe 7th)
– 1% lidocaine or 1% or 2% 2-chloroprocaine without epinephrine
– fallen out of favor owing to its association with the fetal bradycardia that follows in 2%
to 70% of applications
• Non laboring (gynecologic procedures) – local anesthetics with epinephrine
– 2 mL at the 12 o’clock position of the anterior lip of the cervix prior to tenaculum placement
• followed by a four-site injection at - 2, 4, 8 & 10 o’clock positions of the cervicovaginal junction
– Spare 3 & 9 o'clock – because uterine artery is at risk
102

103. Local Infiltration for Cesarean Delivery
• A local block is occasionally useful to augment an inadequate or “patchy” regional block
that was given emergently
• Rarely, local infiltration may be needed to perform an emergent cesarean delivery to
save the life of a fetus in the absence of anesthesia support
• Two Injection sites
1. Field block of major branches supplying abdominal wall
• Halfway between the costal margin and iliac crest in the midaxillary line to
block the 10th, 11th, and 12th intercostal nerves
– 5 to 8 mL of 0.5-percent lidocaine is injected.
– The procedure is repeated at a 45-degree angle cephalad and caudad to this line
• At the external inguinal ring blocks branches of the genitofemoral and
ilioinguinal nerves
– injection is started at a site 2 to 3 cm lateral from the pubic tubercle at a 45-degree angle
• These need infiltration bilaterally
• Finally, the skin overlying the planned incision is injected
2. Along the line of proposed skin incision
• subcutaneous, muscle, and rectus sheath layers are injected
• Up to a total of 70 mL of 0.5-percent lidocaine with 1:200,000 epinephrine
• Injection of large volumes into the fatty layers, which are relatively devoid of
nerve supply, is avoided to limit the total dose of local anesthetic needed
103

104. Intravenous regional anesthesia
• also called Bier block
• is an alternative to a peripheral nerve block for short
• For procedures on the hand and forearm such as carpal tunnel
release, Dupuytren's contracture release, or reduction of wrist
fracture
• No role on OBGYN
104

105. Neuraxial (Regional) Analgesia
 Introduction
 CI for Neuraxial Anesthesia
– Thrombocytopenia; Anticoagulation; Preeclampsia-Eclampsia;
 General versus neuraxial anesthesia
 Spinal Vs Epidural Anesthesia
 Sensory Block Level (SBL)
 Spinal Anesthesia
– Saddle block
– Continuous spinal analgesia (CSA)
– Complications of Spinal Analgesia
– Strategies to prevent and treat neuraxial anesthesia shivering
 Epidural Analgesia
 Combined Spinal–Epidural Analgesia
 Ineffective Neuraxial Anesthesia
105

106. Introduction
• Neuraxial anesthesia refers to local anesthetics placed around the nerves of CNS, such
as spinal anesthesia, caudal anesthesia, and epidural anesthesia or CSE procedures
• If fetal status permits and no maternal contraindications exist,
– neuraxial anesthesia is preferred for cesarean delivery
• Level of blockade
1. Vaginal delivery (T10 to S5)
– 1st SOL needs a sensory block to the level of the umbilicus (T10)
– SSOL needs a sensory block of S2 through S4
2. Cesarean delivery T4 to the S1)
– A level of sensory blockade extending to the T4 dermatome (
• Neuraxial analgesia does not appear to increase the cesarean delivery rate and, therefore,
should not be withheld for that concern (ACOG, 2019: Level A)
106

107. CI for Neuraxial Anesthesia
• Absolute CI to neuraxial anesthesia
– Patient refusal
– Uncorrected hypovolemia
– Maternal coagulopathy
• Due to concerns for development of a spinal or
epidural hematoma
– Low-molecular-weight heparin within 12 hours
– Thrombocytopenia (variously defined)
– Untreated maternal bacteremia
• Skin infection over site of needle placement
– Increased intracranial pressure caused by a mass
lesion
• Relative CI to neuraxial anesthesia
– Coagulopathy
– Sepsis
– Fixed cardiac output states
– Indeterminate neurological disease
• Significant ongoing hemorrhage is a firm
contraindication to neuraxial anesthesia
because
– Sympathetic blockade overrides compensatory
vasoconstriction and
• potentially precipitates cardiovascular
decompensation
• In healthy patients, the choice between
epidural, spinal, and CSE anesthesia
primarily rests with the anesthesiologist
107

108. Thrombocytopenia
• Thrombocytopenia is a relative contraindication to neuraxial blockade, but
a safe lower limit for platelet count has not been established (ACOG, 2019:
Level B)
• ACOG (2016b): women with platelet counts of 80,000 to 100,000/μL may
be candidates for regional analgesia – IF
– stable platelet count
– no acquired or congenital coagulopathy,
– normal platelet function,
– no antiplatelet-specific drugs, and
– anticoagulation parameters – NORMAL
• between 50,000 and 80,000: individualize decision on risks and benefits
– Single-shot spinal anesthesia with a 25-gauge needle is less traumatic than epidural
or combined spinal-epidural anesthesia
108

109. Anticoagulation
• Consider the following prior to Interruption of anticoagulation
1. Estimate thromboembolic risk
– If higher risk ➔ minimizing the interval without anticoagulation or bridge or delay surgery until the risk
returns to baseline, if possible
– atrial fibrillation, prosthetic heart valve, Recent thromboembolism (Venous /arterial),
– DVT or pulmonary embolism (PE)
2. Estimate bleeding risk
– If high → longer period of anticoagulant interruption or ? Vit K
3. Determine the timing of anticoagulant interruption
– depends on the specific agent the patient is receiving
4. Determine whether to use bridging anticoagulation
– With short-acting parenteral agent
• bridging with LMWH, with last dose on the morning of day minus 1
– to reduce the interval without anticoagulation, because it increases bleeding risk without reducing the rate
of thromboembolism
109

110. • Patients using medications that affect hemostasis are at increased risk for spinal epidural
hematoma (SEH) after neuraxial anesthesia. The risk is estimated to be
– 1 in 18,000 for epidurals, and
– 1 in 158,000 for spinal anesthetics
• risk factors for SEH after neuraxial anesthesia include
– bleeding diathesis, timing of antithrombotic drugs in relation to neuraxial needle placement or
catheter removal, difficult or traumatic (bloody) placement, spinal abnormalities, female gender,
and possibly older age
– Patients with multiple risk factors for
– Use of more than one antithrombotic medication
• NB: Use of aspirin or another NSAID as a single agent does not increase the risk of SEH
after a neuraxial technique
• Patients using herbal medications that affect platelet function (eg, garlic, ginkgo, and
ginseng) may be considered for neuraxial anesthesia since there is no evidence of increased
risk of SHE
• Patients with significant symptoms leading to suspicion of SEH should have emergent
MRI and/or neurosurgical evaluation
– Long-term neurologic outcome of SEH is better if decompressive surgery is performed less
than eight hours after symptom onset
110

111. Indications for preoperative bridging anticoagulation
• Embolic stroke or systemic embolic event within the previous three months
• Mechanical mitral valve
• Mechanical aortic valve and additional stroke risk factors
• Atrial fibrillation and very high risk of stroke
– CHADS2 score of 5 or 6, stroke or
– systemic embolism within the previous 12 weeks
• Venous thromboembolism (VTE) within the previous three months
– preoperative and postoperative bridging
• Recent coronary stenting (eg, within the previous 12 weeks)
• Previous thromboembolism during interruption of chronic anticoagulation
111

112. 112
Category Specific drug t1/2
Stop prior
to surgery
Re
initiate
Remarks
Vitamin K
Antagonist
Warfarin
36 to 42
hours
4 to 5 days
12 to 24
hours
 INR <1.5; INR >1.5 → low dose vitamin K (1 to 2 mg)
 Use of bridging preoperatively
 After warfarin is restarted in the perioperative setting, it
takes 5 to 10 days to attain a full anticoagulant effect as
measured by an INR above 2.0
Heparin
Unfract
ionated
Therapeuti
c
2 to 4 hours 1 hour  normal aPTT
 aPTT (30-40 seconds); PTT (60-70 seconds)
 If taken for > 4 days → r/o HIT
Prophylaxi
s
LMW
H
Therapeuti
c
4-7 hrs >24 hr 6 to 8 hr
 delay 24 hours after traumatic placement
Prophylaxi
s
10 - 12 hr 6 to 8 hr
Factor Xa
inhibitors
Fondaparinux
18 to 21
hours
2 – 3 days
12 hrs
Rivaroxaban 7 - 11 hr 2 – 3 days 6 hrs
 coagulation tests - not validated for ensuring that its
effect has resolved
 Rather anti-factor Xa activity
Apixaban 6-12 hrs 2 – 3 days 6 hrs
 PTT & aPTT are used to test for the same functions;
 But, for aPTT, an activator is added that speeds up the clotting time and results in a narrower reference range. So aPTT is considered a more sensitive
version of the PTT and is used to monitor the patient’s response to heparin therapy
 PTT - evaluate a person's ability to appropriately form blood clots. It measures the number of seconds it takes for a clot to form

113. 113
Category Specific drug t1/2
Stop prior to
surgery
Re
initiate
Remarks
Thrombin
inhibitors
Dabigatran 8-17 hrs
5 days (7 days if
renal failure)
2 – 3 days
 coagulation tests - not validated for ensuring
that its effect has resolved
Argatroban
40-50
mins
Antiplatelet
medication
P2Y12 receptor
antagonists
Clopidogrel 7-10 days 2 hrs
 blocks the P2Y12 component of ADP receptors
on the platelet surface, which prevents
activation of the GPIIb/IIIa receptor complex,
thereby reducing platelet aggregation
NSAIDs
Aspirin No restrictions
No
restriction
s
 Effect on platelet function normalizes within 3
days
Others No restrictions
No
restriction
s
GP IIb/IIIa
inhibitors
Tirofiban
Eptifibatide
Abciximab

114. Low molecular weight heparin (LMWH) dosing
• Therapeutic
– enoxaparin 1 mg/kg every 12
hours;
– enoxaparin 1.5 mg/kg daily;
– dalteparin 100 to 120 U/kg every
12 hours;
– dalteparin 200 U/kg daily;
– nadroparin 86 U/kg every 12
hours;
– nadroparin 171 U/kg daily;
– tinzaparin 175 U/kg daily)
• Prophylactic
– enoxaparin 30 mg every 12 hours;
– enoxaparin 40 mg daily;
– dalteparin 2500 to 5000 U daily;
– nadroparin 2850 U daily;
– nadroparin 38 U/kg daily;
– tinzaparin 50 to 75 U/kg daily;
– tinzaparin 3500 U daily)
114

115. Severe Preeclampsia-Eclampsia
Which one is better to receive
1) General anesthesia
• GA is the choice in unconscious, obtunded patients with evidence of increased ICP
Disadvantages of general anesthesia
– Difficult tracheal intubation due to upper airway edema
– can lead to severe, sudden hypertension that can cause pulmonary or cerebral edema or
intracranial hemorrhage
• Agents used to induce and maintain general anesthesia do not worsen hypertension,
– the process of securing the airway - laryngoscopy and endotracheal intubation - are potent
stimulators of the hypertensive response, which may increase risk of stroke and heart failure
• If GA is needed, the spike in blood pressure may be attenuated with opioids and b-blockers
• An additional concern is the increased risk of a difficult airway in women with
preeclampsia because edema of the soft tissues or the larynx itself can make
visualization and manipulation considerably more difficult
115

116. 2) Neuraxial anesthesia and analgesia
• generally are safe and well tolerated in preeclampsia
• Regional anesthesia in caesarean section has several advantages
– Hypertensive response to laryngoscopy (which is pronounced in preeclamptic women) can be
avoided
Potential concerns with regional anesthesia in women with SPE
o Hypotension: In a recent review, severe preeclampsia had a protective effect against developing
hypotension after spinal anesthesia; when hypotension was present, it was less frequent and less
severe
o Hypertension due to pressor agents given to correct hypotension
o Pulmonary edema  large volumes of crystalloid Why??
• diminished intravascular volumes compared with unaffected gravidas + Increased extravascular volume due to
capillary leak ➔ manifested as pathological peripheral edema, proteinuria, ascites, and total lung water
• So limit crystalloid preload to 500 – 1000 mL
• This allows maintenance of BP while simultaneously avoiding infusion of large crystalloid volume
• Thrombocytopenia due to HELLP syndrome
– epidural or spinal anesthesia is considered acceptable for platelet counts ≥ 70,000
– Neuraxial techniques are contraindicated in the presence of coagulopathy because of concerns for spinal or
epidural hematoma
– Any progression of thrombocytopenia or anticoagulated state must be factored into the timing of epidural
catheter placement and removal
116

117. General versus neuraxial anesthesia
• Advantages to neuraxial anesthesia
– Minimizes maternal morbidity
– Allows the parturient to be awake for the birth
– Minimizes intraoperative systemic medication and transfer to the fetus
– Avoids airway instrumentation
– Facilitates provision of postoperative analgesia, with the use of neuraxial opioids
– Facilitates multimodal postoperative analgesia with low-dose neuraxial opioids and
minimizes the need for the systemic administration of opioids
• General anesthesia may be preferable for cesarean delivery in the following scenarios
– insufficient time to perform neuraxial anesthetic
– Maternal refusal of, or inability to cooperate with, neuraxial anesthesia.
– Contraindications to neuraxial anesthesia
– Failed neuraxial technique
– Severe hemorrhage
117

118. Disadvantages of Neuraxial analgesia
• Patients may prefer not to be awake during major surgery
• A block that provides inadequate anesthesia may result
• Hypotension, perhaps the most common complication of neuraxial
anesthesia, occurs during 25% to 85% of spinal or epidural
anesthetics.
• Total spinal anesthesia may occur, which necessitates airway
management.
• Local anesthetic toxicity may occur.
• Although extremely rare, permanent neurologic sequelae may occur.
• Several contraindications exist
118

119. Subarachnoid (spinal) block
• Can’t be performed at any level of the
vertebral column
• Should always performed below L1 in
an adult and L3 in a child to avoid
needle trauma to the spinal cord
Epidural Anesthesia
• can be performed at any level of the
vertebral column
• NB: epidural space – bn dura mater &
vertebral wall, containing fat and
small blood vessels
119
Site: acts on dorsal horns → direct spread in CSF to the
brainstem
Spinal Vs Epidural Anesthesia

120. Sensory Block Level (SBL)
• Level of sensory block after spinal
anesthesia as a predictor of hypotension in
parturient
– When the sensory block level (SBL) is ≥ T5
/ T4, a high incidence of hypotension occurs
after spinal anesthesia
• Nerve fibers affecting the vasomotor tone of the
arterial and venous vessels arise from T5–L1
• cardioaccelerator fibers arise from T1–T4
– A rapidly ascending SBL is another risk
factor for spinal anesthesia-induced
hypotension
– However, the relationship between the
ascension rate of the SBL and spinal
anesthesia-induced hypotension remains
unclear
120

121. 121
Dermatomes
o C8: fifth finger
o T4. Nipple
o T7: Xiphoid process
o T10: Umbilicus
o T12, L1: inguinal
ligament , crest of
ileum
o S2-S4: perineum

122. • The spinal cord usually ends at
the level of L1 in adults and L3
in children
• Dural puncture above these levels
is associated with a slight risk of
damaging the spinal cord and is
best avoided.
• An important landmark to
remember is that a line joining
the top of the iliac crests is at L4
to L4/5
• MOA
– Decreases the entry of sodium
ions during upstroke of action
potential
– Local depolarization fails to reach
the threshold potential
– autonomic and sensory fibers are
blocked before motor fibers
122

123. Spinal Anesthesia
• LA is injected in the subarachnoid space
– between L2–3 or L3–4
• Site of action is the nerve root in the cauda -equina rather than the spinal cord
• Subarachnoid space during pregnancy is smaller
– Due to internal vertebral venous plexus engorgement
– So same amount of anesthetic agent in the same volume of solution produces a much higher blockade than in
nonpregnant women
• Differential sensory/motor blockade
– Cephalad level of sympathetic blockade is 2-3 segments higher than the level of sensory blockade
• Small B fibers in preganglionic sympathetic nerves possess short internodal distances and are most susceptible to conduction block
• Primary role of B fibers is to transmit autonomic information
– Sensory blockade is also higher than the level of motor blockade
• larger A-delta nociceptor fibers have longer internodal distances and require a higher LA concentration for blockade
• A-delta fibers are small, myelinated, and moderate sensory conductivity speed
– Motor paralysis about 2 segments lower than the level of cutaneous analgesia
• The larger Alpha (α) motor neurons have the greatest internodal distances and are blocked only when the LA concentration is
sufficient to inhibit three successive nodes
• Adjuvants
– Adrenaline: has direct analgesic effect-alph2
– Opioids: opioid receptor at dorsal horn
123

124. 124
Lateral Decubitus Position
Patient in sitting position with
the L4–L5 interspace marked
o hips and knees flexed, neck and shoulder flexed towards
knees
o nose to knees

125. Vaginal Delivery
• FSOL
– requires a sensory block to the level of
the umbilicus (T10)
• SSOL
– for operative vaginal delivery, a sensory
block of S2-S4 is usually adequate to
cover pain from perineal stretching
and/or instrumentation
– Analgesic options
• continuous lumbar epidural analgesia,
• combined spinal-epidural
• continuous spinal analgesia
• pudendal and paracervical blocks
CS
• Anesthesia for CS in USA
– 10%: general anesthesia
– 90%: spinal, epidural, or CSE
anesthetics
– Rarely: Local anesthesia
• A level of sensory blockade
extending to the T4
dermatome is desired for
cesarean delivery
125

126. Saddle block
• A kind of low spinal block that manifests anesthesia over the saddle area, i.e., perineum,
perianal area, medial aspect of legs and thigh [that would touch a saddle at the time of riding
a horse]
– Traditionally, it is performed with low dose of lumbar spinal anesthesia to block selectively the last
four sacral spinal segments
• routinely employed for various obstetrical, urological, anorectal procedures, and
perioperative analgesia
– Obstetric: Normal labor, Outlet/low forceps delivery, Repair of episiotomy after childbirth
• provides complete relief from the pains of parturition without narcotizing the baby
– Urological: TURP, Fournier's gangrene
– Anorectal: Hemorrhoids, Pilonidal sinus
• rapid onset, dense block, early patient mobilization, and a short hospital stay
• It was hypothesized that administering saddle block through dorsal foramen of sacrum would
avoid inadvertent block of lower limbs while providing selective segmental block and
acceptable hemodynamic stability
• Left uterine displacement should be maintained after the local anesthetic has been injected to
maintain venous return and prevent excess hypotension
126

127. 127

128. Continuous spinal analgesia (CSA)
• produces and maintains spinal analgesia by intermittent or continuous
injection of a small dose of local anesthetic using a subarachnoid catheter
• Advantages
– micro-administration, rapid-onset and satisfactory analgesia, mild motor block,
and potential to convert to surgical anesthesia for operative vaginal or cesarean
deliveries
– Compared to continuous epidural analgesia (CEA)
• CSA prevents the risk of total spinal anesthesia and local anesthetic drug block and toxicity
of local anesthetics
• Ideal analgesia can be achieved by CSA
– NB: CEA will hinder the maternal force in the second stage of labor
• is seldom used for labor because of concerns about postdural puncture
headache (ACOG, 2019)
128

129. Complications of Spinal Analgesia
Hypotension
• Definition
– not one accepted definition of hypotension in the scientific literature
– a drop of Systolic arterial pressure (SAP) to
• ≤ 100 mmHg or lower, or
• ≤ 80% baseline from baseline prior to anesthesia
•  vasodilatation from sympathetic blockade
– a decrease in systemic vascular resistance (SVR) and/or cardiac output (CO)
• compounded by obstructed venous return due to uterine compression of the great vessels
• Prophylaxis
– Isotonic crystalloid boluses should not contain dextrose because of the association with subsequent
neonatal hypoglycemia
– administration of pressors
• Ephedrine: 5- to 10-mg doses
• Phenylephrine: 50- to 100 µg increments
– left uterine displacement to prevent aortocaval compression
129

130. • Ephedrine
– binds to α- and β-receptors but also indirectly enhances
norepinephrine release
• mixed α- and β-agonist
– raises blood pressure by
• raising heart rate and cardiac output
• variably elevating peripheral vascular resistance
– less likely to compromise uteroplacental perfusion than the pure α-
agonists, but ephedrine has been associated with fetal tachycardia
• The parturient has decreased sensitivity to all vasopressors,
and that may also protect the fetus from excessive
vasoconstriction
130

131. Ephedrine Vs Phenylephrine
Ephedrine
• associated with higher degrees of fetal acidosis
• β-agonist action of ephedrine may increase fetal oxygen requirements and can lead to
hypoxia in cases of uteroplacental insufficiency
• Ephedrine may be preferable if the patient’s heart rate is below 70 at baseline
Phenylephrine
• Corrects maternal hypotension, apparently without causing clinically significant uterine artery
vasoconstriction or decreased placental perfusion even in extremely high doses
• Rather than causing abnormal increases in systemic vascular resistance, these doses may simply
return vascular tone to normal after spinal anesthesia. It is also possible that constricting
peripheral arteries may preferentially shunt blood to the uterine arteries
• The α-adrenergic agents, such as methoxamine and phenylephrine, cause reflex bradycardia
that may be useful when a parturient is excessively tachycardic in association with
hypotension, or if tachycardia associated with ephedrine would be detrimental.
• administration of phenylephrine, rather than ephedrine,
– to prevent and treat neuraxial block induced hypotension in the absence of maternal bradycardia
– For healthy patients, we administer a prophylactic, low dose,
• titrated infusion of phenylephrine with phenylephrine rescue boluses, along with intravenous volume expansion
(co-loading) with glucose free crystalloid solution, aiming for a baseline maternal BP and asymptomatic for nausea
and vomiting
131

132. High or Total Spinal Blockade
• Etiology
– excessive dose of local anesthetic or
– inadvertent injection into subdural or subarachnoid space
• Subdural injection manifests as a high but patchy block even with a small dose of local
anesthetic agent
• subarachnoid injection typically leads to complete spinal blockade with hypotension and
apnea
– paralysis of the respiratory muscles, including the diaphragm (C3-C5)
• incidence of total spinal anesthesia: 1 in 4336 (Gabbe 7th)
• Needs immediate treatment to prevent cardiac arrest
– In undelivered woman:
• (1) Displace uterus laterally & minimize aortocaval compression
• (2) Intubate - effective ventilation
• (3) Intravenous fluids and vasopressors - correct hypotension
– If chest compressions are to be performed, the woman is placed in the left-lateral
position to allow left uterine displacement
132

133. Assessment of the true level of anesthesia
 sensory level of anesthesia Vs innervation of other organs or systems
– T4 sensory level may represent total sympathetic nervous system blockade
– Numbness and weakness of the fingers and hands indicates that the anesthesia has
reached the cervical level (C6-C8), which is dangerously close to the innervation of
the diaphragm
 If the patient remains anxious or if the level of anesthesia seems to involve
the diaphragm,
– assisted ventilation is indicated, and
– endotracheal intubation will be necessary to protect the airway
 If the diaphragm is not paralyzed, the patient is breathing adequately, and
cardiovascular stability is maintained,
– administration of oxygen and reassurance may suffice
 In addition, cardiovascular support is provided as necessary
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134. Postdural Puncture Headache (spinal headache)
•  Leakage of CSF from the dura mater puncture site
• Proposed Mechanisms
1. Punctured dura with a large-bore needle (“wet tap”)
2. when the woman sits or stands, the diminished CSF volume creates traction on pain-
sensitive CNS structures
3. Compensatory cerebral vasodilation in response to the loss of CSF: The Monro-Kellie
doctrine
• Monro-Kellie hypothesis: sum of volumes of brain, CSF & intracerebral blood is constant
4. loss of CSF, which causes the brain to settle and thus causes the meninges and vessels to
stretch
• Incidence: 1% - 3% (Gabbe 7th)
• Preventive Mechanisms
– using a small-gauge spinal needle
– avoiding multiple punctures
• No good evidence that placing a woman absolutely flat on her back for several
hours is effective in preventing this headache
– spinal headache is more severe in the upright position & is relieved by the supine position
134

135. • DDx
– Migraine
– Pneumocephalus from the loss of resistance to air technique,
– Infection,
– Cortical vein thrombosis,
– Preeclampsia, and
– Intracerebral or subarachnoid hemorrhage
135

136. • Once headache develops
– It needs aggressive treatment
• If not effectively treated, postdural puncture headache can persist as a chronic headache
Expectant management
– increases hospital-stay lengths and subsequent emergency-room visits
Conservative management
– fluid administration and bed rest -- largely ineffective
– Hydration, bed rest, abdominal binders, and the prone position -- little value
Epidural blood patch (gold standard)
– 10 to 20 mL of autologous blood obtained aseptically by venipuncture is injected into the epidural
space
• provide a tamponade effect that may result in immediate relief
• Further CSF leakage is halted by either mass effect or coagulation
– Relief is almost always immediate, and complications are uncommon.
– success rate: 61 to 73 percent
– “prophylactic” blood patch - debatable and is thought not to be as effective as if performed after the
headache develops
• If no improvement despite treatment with a blood patch, other diagnoses are considered
– Pneumocephalus (air in cranial cavity)
• caused immediate cephalgia
– Intracranial and intraspinal subarachnoid hematomas have developed after spinal analgesia
136

137. Nerve Injury
 most common cause of liability in obstetric
anesthesia
 Incidence of 1 in 35,923
 Causes
– anesthetic technique
– incorrectly positioned stirrups, difficult forceps
applications, or abnormal fetal presentations
– During abdominal procedures, overzealous or
prolonged application of pressure with retractors
on sensitive nerve tissues may also result in injury
 Common injuries
– spinal cord, conus medullaris
– nerve roots
 Presentation
– pain, paraesthesia, anaesthesia and weakness in the
distribution of the affected nerve root
 Rare but devastating complications
– vertebral canal haematoma and abscess formation
137
Classification of the severity of nerve injuries

138. 138
Red flags requiring consideration of urgent further investigation

139. Other Complications
• overall risk of hematomas
– < 1 in 150,000 – with epidural analgesia
– < 1 in 220,000 - with spinal analgesia
• Breakthrough pain
• Backpain
• Convulsion
• Bladder dysfunction
• Arachnoiditis and Meningitis
• Allergy to anesthetic drug
139

140. Neonatal Effects
• Literature on the differences in neonatal outcome associated with choice of
anesthetic technique for cesarean delivery is inconclusive
– but the overall difference between general anesthesia and neuraxial anesthesia is
likely small
– Apgar scores and umbilical acid base status may be affected by variables unrelated
to the choice of anesthetic, including
• indication for the cesarean delivery,
• vasopressors administered during anesthesia (ie, phenylephrine versus ephedrine), surgical
technical issues, and others
• Neonatal exposure to anesthetic drugs during induction and maintenance
of general anesthesia can cause early neonatal depression
– The neonatal resuscitation team should be notified of all medications administered
to the mother during induction of general anesthesia, and prior to delivery.
140

141. Strategies to prevent and treat neuraxial anesthesia
shivering
• Prevention
– Prewarm with forced air warmer for 15 minutes
– Avoid cold epidural or intravenous fluids
– Intrathecal fentanyl 20 μg
– Intrathecal meperidine 0.2 mg/kg or 10 mg
– Intravenous ondansetron 8 mg
– Epidural fentanyl
– Epidural meperidine
• Treatment
– Intravenous meperidine 50 mg
– Intravenous tramadol 0.25 mg/kg or 0.5 mg/kg or 1 mg/kg
– Intravenous clonidine 30, 60, 90, or 150 μg
141

142. Epidural Analgesia
• Depending on location can be classified as
o Thoracic: injected in to midthoracic region
• narrow space, smaller dose needed
• used for thoracic & upper abdominal surgery
o Lumbar
• lower abdomen, pelvis and hind limbs
• wider space, needs larger dose
o Caudal
• Injection in to sacral canal via the sacral hiatus
• produces anaesthesia - pelvic and perineal region
• used mostly for SVD, anorectal and genitourinary operations
• Traditional epidural analgesia: 0.25% bupivacaine
– often used for CS for patients who have a labor epidural catheter in place
• Epinephrine may be added to the local anesthetic solution in very dilute doses (5 micro- grams/mL,
or 1 in 200,000) to prolong duration or increase reliability and intensity of epidural block
• Sodium bicarbonate may be added just before administration because alkalinization has been
observed to speed up onset of epidural blockade, intensify the effect, or both, especially in sacral
dermatomes
142

143. Epidural analgesia …
• Does not increase the rate of cesarean delivery but may
increase oxytocin use and the rate of instrument-assisted
vaginal deliveries
• The duration of the second stage is increased by 15 to 30
minutes
• Maternal-fetal factors and obstetric management are the most
important determinants of the cesarean delivery rate
• is associated with an increased rate of maternal fever during
labor, although the mechanism is unknown
– This does not alter the rate of documented neonatal sepsis
143

144. Timing of Epidural Placement
• Randomized trials, showed that
– timing of epidural placement has no effect on the risk of cesarean birth,
forceps delivery, or fetal malposition
• Thus, withholding epidural placement until some arbitrary cervical
dilation
– is unsupportable and
– serves only to deny women maximal labor pain relief
Safety
• No anesthesia-related maternal deaths
• Calculated risks of
– deep epidural infection: 1:145,000
– epidural hematoma: 1:168,000
– persistent neurological injury: 1:240,000
144