The document summarizes several physiological changes that occur during pregnancy and their implications for anesthesia. Key changes include increased blood volume, cardiac output and lung volume. Regional blocks require lower drug doses due to increased sensitivity. Opioids readily cross the placenta so their use is limited in labor. Neuraxial techniques provide effective labor analgesia with less fetal exposure than parenteral opioids. Positioning is important to prevent supine hypotension from aortocaval compression.

1. Physiological Changes in
pregnancy and anesthetic
implications
MODERATOR:- DR HARVAN
PRESENTER :- DR PRIT PAL

2. Physiological Changes in pregnancy
 Pregnancy produces profound physiological changes that become more significant as
pregnancy progresses
 These changes occur as a result of -
a) Hormonal Changes
b) Mechanical effects of Gravid uterus
c) Increased oxygen & metabolic requirement
d) Haemodynamic alteration

3. Cardiovascular changes
 A) Intravascular volumes and haematological changes :-
The total plasma volume is increased during pregnancy by 45% ,Where as Red cell
volume increases by only 30%.
 The greater increase in the plasma volume is the cause of the Physiological anaemia
in pregnancy.
 Maternal intravascular volumes start increasing in first trimester as result of
Increased activity of Renin angiotensin-aldosterone system, which promotes the
Na+ & Water retention.
 At term, maternal blood volume increases by 1000-1500 ml , allowing them to easily
tolerate blood loss in Delivery.

4.  A state of hypercoagulability exists during pregnancy , Due to increased levels of the
Fibrinogen , Factor 7,8,9,10&12 (only factor 11 decreases). There is decrease in the fibrinolytic
activity and antithrombin 3.
 This probably , a protective adaptation to lessen the risk of acute haemorrhage that occurs at
delivery.
 The platelet count remain remains unchanged throughout most of pregnancy, but it may get
reduced in third trimester <1.5L.
 The pregnant women who are associated with the high risk of thromboembolism ,
anticoagulants are used , with taking foetal risk in consideration.

5.  Standard heparin (unfractioned) preparation prophylaxis in low doses i.e.
5000 I.U. Subcutaneously can be used, as it do not cross the placenta.
 For performing the neuraxial block 4-6 hr gap should be there after the dose.
 In case of epidural anesthesia, catheter removal should be done 1 hr prior to the next dose or
3-4 hr after the dose.
 Neuraxial anesthesia should be avoided in patient on the I.V. heparin with increased Partial
thromboplastin time. If the patient is started on heparin after placement of catheter, removal
of catheter is to be done after evaluation of the coagulation profile.

6.  Low molecular weight heparin can be used , and Anti-Xa levels should be
maintained between 1.0 to 1.2 U/ml.
 Neuraxial block should be performed after the minimum gap of 12 hr from the last dose (if
receiving higher dose e.g. enoxaparin 1mg/kg neuraxial block should be performed after 24
hr gap).
 Platelet count should be obtained in the patient receiving LMWH from more than 4 days to
prevent heparin induced thrombocytopenia.
 Post-op LMWH can be started only after 12 hr from the spinal needle insertion.
 Use of oral anticoagulants is restricted as these agents can cross placenta.

7.  B) Cardiac output :-
 Cardiac output start increasing by 5th week of first trimester and continue to increase in second and
third trimester and at term approx. 40-50% above non pregnant values.
 Heart rate increases by approx. 20-30% in response to the increased oxygen demand
 Cardiac output is highest right after delivery (approx. 60-100% ) due to release of aorto-caval
compression and uterine contractions.
 Peripheral vascular resistance decreases due to vasodilatory effect of progesterone.
 Because of decrease in VR( inspite of increase in CO ), arterial BP shows a slight fall in BP in
uncomplicated pregnancy.

8. Anesthetic Implications
 Physical examination of the term pregnant woman may also be abnormal with the auscultation
commonly revealing a wide, loud 1st heart sound , an S3 sound and soft systolic ejection murmur.
 So it is necessary to differentiate abnormal cardiac changes from Normal physiological changes of
pregnancy
 Criteria to diagnose cardiac disease during pregnancy:
1) Presence of diastolic murmur
2) Systolic murmur of severe intensity (grade 3)
3) Presence of severe arrhythmias , atrial fibrillation or flutter

9. Aorto-caval Compression:-
 Enlarged uterus compresses IVC and lower Aorta when the patient lies supine, there is
decreased venous return that leads to decrease in cardiac output
 Blood from lower extremities return via the alternate pathways: via paravertebral veins and
azygos veins
 Supine Hypotension Syndrome:- Approx. 8-15% of pregnant women have Overt Caval
Compression. Patient have Hypotension, Bradycardia , Sweating , Nausea , Vomiting.
 Prevention of SHS : Displace the uterus by tilting the table left side or by placing the rigid
wedge >15 degree under the right hip.

10. Respiratory changes
 Changes in the respiratory system during pregnancy involves the upper airway, minute ventilation,
lung volume , oxygen consumption.
 Major changes occurs in the respiratory system during pregnancy, due to combination of both
hormonal and mechanical factors.
 The maternal respiratory pattern changes as the uterus enlarges :- Diaphragm rises up by 4 cm ,
causes reduction in the Functional residual capacity by 20% patient prefers thoracic breathing over
the Abdominal.
 Due to increased metabolic demands, Oxygen consumption and minute volume increases (40-
50%) progressively.

11.  Progesterone sensitizes the respiratory center to CO2 – directly stimulating the Ventilation, there is
increase in tidal volume, this cause Decrease in PACO2 to 28 to 32 mm Hg , here significant
alkalosis is prevented by the compensatory in plasma HCO3 concentration.
 Both Vital capacity and Closing capacity are minimally affected but Functional residual capacity
decreases by 20% , Due to reduction in the Expiratory reserve volume more than tidal volumes.
 Rapid Gaseous induction:- The decrease in FRC with increase in minute volume , accelerates the
uptake of inhaled anesthetics agents .

12.  Decreased FRC and Increased oxygen consumption promotes rapid oxygen desaturation during
period of apnoea , So the preoxygenation for 3-5 minutes is mandatory to avoid hypoxemia.
 Capillary engorgement of mucosa and oedema of oropharynx, larynx and trachea may result in
difficult intubation, bleeding and trauma ; so smaller ET tube should be used and repeated
attempts should be minimised .

13. CNS changes
 Pregnant patients are more sensitive to both local and inhaled anesthetics.
 The minimum alveolar progressively decreases during pregnancy and at term , by 40% for all
anesthetic agents and return to normal by 3rd day after delivery.
 There will be rapid induction with the inhalation agents due to increase in the minute
ventilation and decrease in the Functional residual capacity.
 L.A. required for subarachnoid or epidural anesthesia are reduced in pregnancy by 20 to 30%
due to increased sensitivity to drugs , caused by progesterone .

14.  Obstruction of the IVC enlarged uterus distends the epidural venous plexus and increases
epidural blood volume; this results in the
A) Decrease in the CSF volume,
B) Decrease in the potential volume of epidural space
C) Increased Pressure in the Epidural and subdural Space
These reasons are responsible for the more cephalad spread of the drug, So
result in decreased requirement of drug dose. And bearing down during labour
further accentuates the effect.
Engorgement of the epidural Veins increases the chances of placement of Epidural needle or catheter
in vein resulting in unintentional intravascular injection.

15. GIT changes
 The patient should be considered a full stomach patient during most of gestation
 Upward and anterior displacement of the stomach by the uterus , leads to decreased tone of
lower oesophageal sphincter that can lead to aspiration.
 Placental gastrin causes hypersecretion of the gastric acid.
 Gastric emptying is delayed with labour.
 Minimum recommended fasting period for the Cesarean section is 6 hr for the light meal and 8
hr for heavy meal.

16.  An H2 Blocking drug e.g. Ranitidine 50 mg i.v. and/or metoclopramide 10 mg i.v. should be
considered for the high risk patient.
 H2 blocker reduces both gastric volume and pH , Metoclopramide promotes Gastric emptying
and increases Lower oesophageal sphincter tone.
 Opioids and anticholinergic reduces the Lower oesophageal sphincter tone and delays gastric
emptying, may result in GERD.

17. Renal changes
 With increase in cardiac output, there is increase in GFR and Renal plasma flow by 50%
 As a result the serum creatinine and Blood urea nitrogen decreases as low as 0.5 mg/dL and 9
mg/ dL respectively.
 Decrease renal tubular threshold for glucose & amino acids leads to mild glycosuria (1-10
g/day) & proteinuria(< 300 mg/dl ).
 Plasma osmolality decreases by 8 to 10 mOsm/kg

18. Hepatic changes
 Hepatic function and blood flow are unchanged
 A mild decrease in the plasma albumin is due to the expanded plasma volume, thus the free
fraction of albumin bound drug increases
 All liver function markers may rises to upper limit of normal values.
 A 25-30% activity of plasma pseudo cholinesterase is decreased at term but rarely affects the
significant prolongation of muscle relaxation by succinylcholine.
 High progesterone levels inhibits the release of cholecystokinin , results in incomplete gall
bladder emptying. This increase incidence of cholesterol gall bladder stones formation.

19. Metabolic changes
 Pregnancy is Diabetogenic as insulin steadily rises during pregnancy and the human placental
lactogen (aka human chorionic Somatomamotropin) causes relative insulin resistance.
 Pregnancy is biochemically a starving like state (blood glucose and amino acids are low and
Free fatty acids , ketones and triglycerides are high) to promote the Foetal growth.
 Secretion of HCG and Elevated oestrogen levels promotes hypertrophy of the thyroid gland.
 There is increased in the production of thyroid globulin: although T3, T4 levels are elevated but
the free T3, T4 & TSH remain normal

20. Musculoskeletal Effects
 Elevated levels of relaxin hormone throughout the pregnancy results in the Softening and thinning
of various Ligaments , inhibits uterine contractions , relaxation of pubis symphysis and pelvic joints.
 Ligamentous laxity of spine contributes to the relative frequent occurrence of back pain during
pregnancy.

21. Utero-placental physiology
 At term uterine blood flow is 10% of the cardiac output(600-700ml), out of this 80% goes to
placenta and rest to myometrium.
 Pregnancy maximally dilates the uterine vasculature as autoregulation is absent but uterine
vasculature remains sensitive to Alpha adrenergic agonists
 Uterine blood flow is directly proportional to the difference between the uterine artery &
venous pressure and is inversely proportional to the uterine vascular resistance.
 Uterine vasculature has alpha adrenergic and some beta adrenergic receptors.

22.  Each uterine contraction displaces 300-500 ml of blood from uterus to central circulation ,
Cardiac output increases by 45% above the 3rd trimester value
 Maximum strain on heart occurs immediately after delivery , Uterine involution and sudden
relieve of IVC pressure increases Cardiac output by 80% above prelabour values.

23.  Three major factors decreases uterine blood flow during pregnancy
 Systemic hypotension Uterine Vasoconstriction Uterine Contractions
 Aorto-caval compression Stress induced endogenous Labour
Catecholamine's during labour
 Hypovolemia Alpha adrenergic agonists
 Previously , vasoconstrictor with predominant beta adrenergic activity (Ephedrine) is treatment of choice for
hypotension in pregnancy, Recent studies shows that alpha adrenergic drugs ( Phenylephrine) shows similar result with
less foetal acidosis.

24. Factors affecting placental transfer of drugs
 Lipid Solubility:- The placental membrane is freely permeable to lipid soluble substances,
higher the solubility higher is the drug transfer. Highly ionized substances have poor lipid
solubility.
 Protein binding:- Protein bound drugs will not diffuse easily, only free drug would cross the
placental barrier easily , reduced albumin levels will increases the unbound portion of drug in
plasma.
 Maternal drug concentration :- Directly proportional , Affected by the dose and route of
administration

25. Analgesia of labour and vaginal delivery
 Pain pathway during labour:-
a)Uterine pain is transmitted in sensory
fibres and ends in dorsal horn of T10
to L1
b) Vaginal pain is transmitted via the
S2 to S4 nerve root
 Labour analgesia can be achieved by
Systemic medication, Inhalational
technique , Neuraxial blocks.

26. Parenteral agents
 All Opioids and sedatives crosses the placenta
 Concern regarding the foetal depression, limits the use of the Opioids to the early stage of labour.
 Meperidine or Pethidine is a commonly used opioid for the labour analgesia dose 10-25 mg i.v. or
25-50 mg i.m. upto a total of 100 mg
 Maximal Maternal and Foetal respiratory depression is seen in 10-20 minutes of i.v.
administration and 1-3 hr after i.m. administration.
 Meperidine is usually administered when delivery is not expected for atleast 4 hrs.

27.  I.V. Fentanyl is an alternative analgesic option, usual dose is 25-50 mcg i.v. peak effect in 3-5
minutes and last upto 30-60 minutes.
 Agent with mixed opioid Kappa agonist and Meu antagonist (Butorphanol 1-2 mg and
nalbuphine 10-20 mg) is also effective, onset is 2-3 min i.v. 10-15 min i.m. and analgesia last
upto 6 hrs. This drug produce Sinusoidal FHR pattern so not used .
 Remifentanyl is short acting Meu receptor agonist, rapid clearance , non specific esterases
degradation, and minimum foetal exposure due to these properties make it an attractive
alternative systemic analgesia in whom the regional anaesthesia is contraindicated.
 Promethazine 25-50 mg i.m. and hydroxyzine 50-100 mg i.m. can be used alone or in
combination with opioids.

28.  A small dose of midazolam (upto 2 mg) along with small dose of fentanyl (upto 50 mcg) i.v.
can be used to facilitate analgesia effect of neuraxial blockade.
 Low dose of ketamine 10-15 mg I.V. is a powerful analgesic, good analgesia can be
obtained in 2to 5 minutes. Ketamine in dose of 25-50 mcg can be used in the incomplete
neuraxial blockade for Cesarean section.

29. Inhaled analgesia
 It includes the administration of the sub anaesthetic concentrations of inhaled anesthetics
to provide analgesia during labour.
 Entonox (50:50 : : N2O:O2) can be used to relieve the mild labour pains but do not provide
complete analgesia for many. Lack of scavenging system can put the staff at risk of
exposure.
 Desflurane(0.2%) , Enflurane and Isoflurane (0.2 to 0.25%) can provide analgesia but their
effectiveness is similar to the Entonox .

30. Regional analgesia
 Assess the patient before placement of the Regional block by obtaining the medical and
obstetric history, clinical examination and evaluating the airway.
 Informed consent must be obtained and the anaesthetist must explain the procedure and
complications of technique.
 EPIDURAL ANALGESIA :- Low doses of local anesthetic or opioids can be administered
(usually by infusion) to provide continuous T10-L1 block during first stage , further
supplementation may be required in second stage of Labour to achieve sacral block.
It has benefit of pain relief without motor blockade.

31.  Epidural for 1st stage of labour:-
 Epidural catheter is placed in the L3-L4 or L4-L5 interspace
 Test for unintentional intravascular placement of catheter using test dose of 3 ml of L.A.
with 1:2,00,000 epinephrine in between contractions
 After 5 min if no sign of intravascular placement of catheter of catheter is there, administer
10 ml of Local anesthetic –opioid mixture in 5ml increments, waiting for 2-3 min between
the doses to achieve T10 –L1 sensory blockade
 Initial bolus includes 0.1-0.2% Ropivacaine or 0.0625 to 0.125% bupivacaine combined
with either Fentanyl or sufentanyl. Monitor vitals frequently . Administer O2 via face mask.
 Repeat the above step until first stage is completed
 Alternatively a continuous epidural technique may be employed @ 10 ml/hr

32.  EPIDURAL DURING 2nd STAGE OF LABOUR:- During second stage of labour block is to be
extended to S4 dermatome level.
 Catheter is already in place, place the patient in the upright or sitting position.
 Give a 3 ml of test dose
 After 5 minute, if no sign of intravascular placement is seen administer 10-15 ml additional
opioid-anesthetic mixture at rate of 5 ml every 1-2 minute.
 Lay the patient supine with left uterine displacement and monitor vitals

33. Complications and management
1. Hypotension:- Vasopressors ( phenylephrine, Mephentermine, Ephedrine ) , supplemental O2 ,
I.V. fluids .
2. Unintentional intravascular injection:- Early recognition and use of small repeated doses can
prevent the serious local anesthetic toxicity, such as seizure and cardiovascular collapse.
Propofol 20-50 mg will terminate the seizure activity . Maintenance of the patent airway and
adequate oxygenation is critical. An immediate infusion of 20% intralipid solution is used in
reversing cardiotoxicity .
3. Unintentional intrathecal injection:- Hypotension must be treated promptly with vasopressors
and i.v. fluids . Moderate to profound hypotension requires epinephrine (50-100 mcg) or
vasopressin (0.4-2.0 units i.v.).
4. A high spinal level can also results in the diaphragm and intercostal muscle paralysis, in this
situation intubation and ventilation with 100% O2 is necessary.

34. • Management of high spinal:-
• Airway - secure airway and administer 100% oxygen
• Breathing - ventilate by facemask and intubate.
• Circulation - treat with i/v fluids and vasopressor
 e.g. ephedrine 3-6 mg or metaraminol 2mg increments or 0.5-1ml adrenaline 1:10 000 as
required
• Continue to ventilate until the block wears off (2 - 4 hours)
• As the block recedes the patient will begin recovering consciousness followed by breathing
and then movement of the arms and finally legs.

35. 5. Post Dural Puncture Headache:-
 Due to leak of CSF from Dural defect leads to traction in supporting structure especially
in dura and tentorium & vasodilatation of cerebral blood vessels .
 Usually bifrontal and or occipital, usually worse in upright , coughing , straining .
 Treatment plan include keeping patient supine, adequate hydration, NSAIDS with
without caffeine [increases production of CSF and causes vasoconstriction of intracranial
vessels], if not relieved within 12-24 hr then epidural blood patch .
 Epidural blood patch consists of giving 20 ml of autologous blood in epidural space to seal
CSF leak .

36. Spinal Analgesia
A single shot subarachnoid injection of local anesthetic of local anesthetic or opioid provides
effective and rapid onset analgesia. It is particularly useful in very early labour , where the
parturient is distressed.

37. Combined Spinal Analgesia and epidural
analgesia
This technique uses combined spinal and epidural analgesia and anesthesia.
 It benefits patients with severe pain in early labour and those who require analgesia
immediately prior to the delivery.
 A epidural catheter is inserted followed by spinal needle placement at lower space.
 Spinal injection is given with the opioids alone or in combination with L.A.
 Continuous spinal infusion of dilute L.A. plus opioids, provides sensory analgesia without
motor blockade.
 Bupivacaine 2.5 mg or Ropivacaine 3-4 mg with opioids Fentanyl 10-12.5 mcg or
sufentanyl 5 mcg, are used for analgesia in 1st stage of labour.

38. General anethesia
General anesthesia for vaginal delivery is avoided except in case of the emergency
Indications for the General Anesthesia during vaginal delivery :-
A) Foetal distress during Second stage of labour
B) Tetanic uterine contractions
C) Breech Extraction
D) Version and Extraction
E) Manual removal of retained Placenta
F) Replacement of Inverted uterus.

39. ANESTHESIA FOR CESAREAN SECTION
Spinal anesthesia:-
Spinal anesthesia is achieved by the delivery of the 10-15 mg of bupivacaine in the
L4-L5 interspace, adding fentanyl 10-25 mcg or sufentanyl 5-10 mcg enhances the intensity
of spinal blockade and prolongs the duration without adversely affecting the neonatal
outcome.
Epidural Anesthesia:-
It is performed by placing the epidural catheter which allows the drug supplementation and
provides an excellent route for postoperative opioid administration.
After negative aspiration and negative test dose , 15 to 35 ml of local anesthetic drug slowly
injected in the 5 ml increments. Opioids can be added to enhance the analgeia

40.  If pain develops as sensory levels recedes, additional local anesthetic in increment of 5 ml is
administered to maintain a T4 sensory level.
 If there is patchy anesthesia, it is treated by 10-20 mg of i.v. ketamine in combination with
the 1-2 mg of midazolam or 30% N2O.
Combined spinal and epidural anesthesia:-
For cesarean section , it provides the rapid , reliable blockade of spinal anesthesia with flexible
utility of the epidural catheter. Catheter can be used for the post-op analgesia.

41. General anesthesia:-
 All the patients should receive antacid prophylaxis with 0.3 M sodium citrate , 30 ml 30-45
minutes prior to the induction and ranitidine 50 mg i.v. or metoclopramide 10 mg (or both)
1-2 hr prior to the induction.
 Premedication with glycopyrrolate , helps reduce airway secretions
 Anticipation of difficult endotracheal intubation may helps reduce the likelihood of failed
intubation
 Examination of neck, mandible, teeths and oropharynx helps predicts the problem
 Useful predictors of difficult intubation are Mallampati classification , short neck , receding
mandible , prominent maxillary incisors
 Proper positioning of head and neck may facilitates the endotracheal intubation: elevation of
shoulders, flexion at cervical spine and extension of atlanto occipital joint.

42.  When a difficult airway is suspected, video assisted laryngoscope has greatly reduced the
chances of failed intubation.
TECHNIQUE
1. The patient should be placed in supine with wedge under the right hip (for left
displacement of the uterus )
2. Oxygenation with 100% O2 for 3 to 5 minutes.
3. When the surgeon is ready, Rapid sequence induction is initiated with the Propofol 2mg/kg,
or ketamine 1-2 mg/kg and succinylcholine 1.5 mg/kg (Ketamine is preferred in the pt. with
hypovolemia).
4. Once relaxation of muscles is achieved, Cricoid pressure is applied and the laryngoscopy is
performed and Endotracheal tube is inserted.
5. Proper placement of the tube is confirmed (with 5 point auscultation method), after proper
placement confirmed tube is fixed.

43. 6. Fifty % air in O2 with upto 1 MAC expiratory volatile agent is for maintenance of the
anesthesia until delivery of infant. Than after N2O upto 70% with reduction in Volatile
agent to 0.75% MAC. Low dose volatile agent do not cause uterine relaxation in
excess or interferes with contractions following oxytocin administration.
Cisatracurium , vecuronium or rocuronium can be used for relaxation but may exhibit
prolonged neuromuscular blockade in pt. receiving magnesium sulphate.
7. On completion of the procedure , aspiration of the gastric contents via oro-gastric
tube should be made prior to emergence from the G.A. to reduce risk of aspiration.
8. At the end , the muscle relaxant is completely reversed using the mixture of glycopyrrolate
and neostigmine . Patient is extubated when awake to reduce the risk of aspiration.

44. Thank You