methods of induction

1. {
INDUCTION OF
ANAESTHESIA
Presenter – Dr. Parul Gupta
Moderator – Dr. Rohan

2.  1540 - ethyl ether was first created by a German scientist Valerius
Cordus, he termed it as laughing gas.
 1773 - Joseph Priestly discovered nitrous oxide.
 1846 – William Morton did first public demonstration of ether
administration on October 16.
 1853 – Dr. John Snow administered chloroform to Queen Victoria
and anesthesia for childbirth in UK.
HISTORY

3.  1929 - Cyclopropane was discovered accidentally and
was very popular for almost 30 yrs.
 1951 - Halothane was synthesized by Charles Suckling
and introduced into clinical practice in 1956.
 1990 - Sevoflurane was introduced into clinical practice.
 1993 – Desflurane was introduced.

4.  The word was coined by Oliver Wendell
Holmes in 1846 from a Greek word:
meaning without sensation
ANAESTHESIA

5.  It is reversible CNS depression, to render
patient unaware and unresponsive to painful
stimuli, using inhalational and intravenous
routes.
GENERAL ANAESTHESIA

6. COMPONENTS –
 Analgesia
 Amnesia
 Unconsciousness
 Akinesia
 Abolition of autonomic reflexes

7. STAGES OF ANAESTHESIA
(GUEDEL’S STAGES)
Stage 1
 Stage of analgesia or disorientation
 (From beginning of induction of to loss of
consciousness)

8.  Stage of excitement or delirium
 Loss of consciousness to onset of automatic breathing
 Eye lash reflex disappear but other reflexes intact
 Cough, vomiting, struggling may occur
 Respiration may be irregular with breath holding

9.  Stage of surgical anaesthesia
 Onset of automatic respiration to respiratory paralysis
 4 planes-
 1 . Onset of respiration to cessation of eyeball movement
 Swallowing reflex disappear
 Marked eye ball movement may occur
 Conjunctival plane is lost at bottom of plane
 2. cessation of eyeball movement to beginning of intercostal muscle
paralysis
 Laryngeal reflex lost
 corneal reflex disappears
 Respiration is automatic and regular
 Response to skin stimulation disappears
 3. from beginning to completion of intercostal muscle paralysis
 Diaphragmatic respiration persist
 Pupil dilate
 Light reflex abolish
 4. complete intercostal muscle paralysis to diaphragmatic paralysis

10.  Stage of impending respiratory and circulatory failure
 From stoppage of respiration to death of patient
 Medullary paralysis with respiratory arrest and vasomotor
collapse
 Pupils widely dilated and unreactive
 Muscles relax

12.  It refers to transition from an awake to an
anaesthetized state
INDUCTION OF
ANAESTHESIA

13.  Induction of anaesthesia can be done by drugs given via
1. Inhalational route
 Gaseous – N2O
 Volatile liquid –
o Ether
o Halothane
o Sevoflurane
2. Intravenous route
o Propofol
o Thiopentone
o Etomidate
o Ketamine
o Midazolam
o Opoid agonist (fentanyl)
3. Intramuscular route
4. Rectal route

14. INHALATIONAL
INDUCING AGENT

15.  It should have a pleasant odour, non-irritant to the respiratory tract
and allow pleasant and rapid induction of anaesthesia.
 It should possess a low blood/gas solubility, which permits rapid
induction of and rapid recovery from anaesthesia.
 It should be chemically stable in storage and should not interact with
the material of anaesthetic circuits or with soda lime.
 It should be neither flammable nor explosive.
 It should be capable of producing unconscious-ness with analgesia and
preferably some degree of muscle relaxation.
Characteristics of inhalational anesthetic agents
used for induction of anaesthesia

16.  It should not be metabolized in the body
 It should be sufficiently potent to allow the use of high inspired oxygen
concentrations when necessary.
 it should be nontoxic and not provoke allergic reactions.
 It should produce minimal depression of the cardiovascular and
respiratory systems and should not interact with other drugs used
commonly during anaesthesia, e.g. pressor agents or catecholamines.
 It should be completely inert and eliminated completely and rapidly in
an unchanged form via the lungs.
 It should be easy to administer using standard vaporizers
 It should not be epileptogenic or raise intracranial pressure.

17. INDICATIONS FOR INHALATIONAL INDUCTION
 Young children
 Upper airway obstruction, e.g. epiglottitis
 Lower airway obstruction with foreign body
 Bronchopleural fistula or empyema
 No accessible veins

18.  As it is usually done in young children, mask or hand is introduced
gradually to the face from the side
 The use of a transparent perfumed mask can render the procedure less
unpleasant.
 While talking to the patient and encouraging normal breathing, adjust
the mixture of the fresh gas flow and observes the patient’s reactions.
 Initially, nitrous oxide 70% in oxygen is used and anaesthesia is
deepened by the gradual introduction of increments of a volatile agent,
e.g. sevoflurane which can can be increased up to an inspired
concentration of 6%.
 Maintenance concentrations of isoflurane (1–2%) or sevoflurane (2–3%)
are used when anaesthesia has been established.
Induction procedure -

19.  A single-breath technique of inhalational induction has been
advocated for patients who are able to cooperate.
 One vital capacity breath from a prefilled 4 L reservoir bag
containing a high concentration of volatile agent (e.g.
sevoflurane 8%) in oxygen (or nitrous oxide 50% in oxygen)
results in smooth induction of anaesthesia within 20–30 s.
 Observation of the colour of the patient’s skin and pattern of
ventilation, palpation of the peripheral pulse, ECG and
SpO2 monitoring, and measurement of arterial pressure are
important.

20. Complication and difficulties-
 Slower induction of anaesthesia
 Problems particularly during Stage 2 of anaesthesia
 Airway obstruction, bronchospasm
 Laryngeal spasm, hiccups
 Environmental pollution

21.  first used by William T.G. Morton in the USA in 1846
 After learning that ether dropped on the skin provided analgesia,
he began experiments with inhaled ether, an agent that proved to be
much more versatile than nitrous oxide.
 Bottles of liquid ether were easily transported
 volatility of the drug permitted effective inhalation.
 concentrations required for surgical anesthesia were so low that
patients did not become hypoxic when breathing ether vaporized in air.
Diethyl Ether

22.  It also possessed what would later be recognized as a unique property
among all inhaled anesthetics: The quality of providing surgical
anesthesia without causing respiratory depression.
 slow rate of induction
 But because of its flammability, the use of ether has been abandoned
 Induction and recovery are both slow with ether.

23.  received attention, by James Simpson in 1847
 apart from its pleasant odour and nonflammability, it had
major problems,
 severe cardiovascular depression (sudden death ? VF)
 dose dependent hepatotoxicity
CHLOROFORM

24.  Sweet smelling, non irritant, colorless gas
 Good analgesic
 Weak anaesthetic
 MAC is 105%
 N2O alone is insufficient to produce an adequate depth of anaesthesia
Nitrous Oxide

25.  Inhibitory effect on N-methyl D-aspartate (NMDA)
glutamate receptors
 Stimulatory effect on dopamine α1 and α2 adrenergic
receptors
 Analgesic action is via activation of opoid receptors in
periaquaductal area of midbrain.
 Used in combi. With volatile agent and reduces its
required dose.

26.  2 bromo 2 chloro 1,1,1, trifluroethane
 Smooth induction
 Minimal stimulation of salivary and bronchial secretions.
 Bronchodilation
 Colorless, pleasant smell liquid
 Decomposed by light( add 0.01% thymol in amber color bottles)
 Corrodes metals in vapourizers and and breathing system.
Halothane

27.  Highest blood gas solubility coefficient of all modern agents.
 Non irritant and pleasant to breathe during induction of anaesthesia
 Rapid loss of pharyngeal and laryngeal reflexes and inhibition of salivary
and bronchial secretions.
 Potent depressant of myocardial contractility and myocardial metabolic
activitydue to inhibition of glucose uptake by myocardial cells.
 Good anaesthetic
 Poor analgesic
 CBF and ICP increases

28.  Currently most commonly used volatile anesthetic liquid
 Non pungent
 Low blood gas solubility allowing smooth induction of anesthesia
 Deep levels of anaesthesia are required to achieve satisfactory intubating
conditions when using sevo as sole agent, increasing risk of adverse
effects as hypotension.
Sevoflurane

29.  2 principal techniques-
 Tidal volume induction – patients are instructed to breathe
normally through facemask
 Starts with low conc. And then gradually it increases.
 Vital capacity induction – patients are instructed to exhale to
residual volume and then take a vital capacity breath from
face mask.
High conc. Of sevo (8% ) is used for vital capacity induction
N2O can be used with any method to speed induction via
second gas effect

30. INHALATIONAL
AGENT
BLOOD / GAS
COEFFICIENT
MAC%
N2O 0.47 105
SEVOFLURANE 0.65 1.8
HALOTHANE 2.4 0.75

31. INTRAVENOUS
INDUCING AGENTS

32.  Rapid onset – this is achieved by an agent which is mainly unionized at
blood pH and which is highly soluble in lipid; these properties permit
penetration of the blood–brain barrier
 Rapid recovery – early recovery of consciousness is usually produced
by rapid redistribution of the drug from the brain into other well
perfused tissues, particularly muscle. The plasma concentration of the
drug decreases, and the drug diffuses out of the brain along a
concentration gradient.
 The drugs with slow metabolism are associated with a more prolonged
‘hangover’ effect and accumulate if used in repeated doses or by
infusion for maintenance of anaesthesia
Characteristics of intravenous anesthetic agents
used for induction of anaesthesia

33.  Analgesia at subanaesthetic concentrations
 Minimal cardiovascular and respiratory depression
 No emetic effects
 No excitatory phenomena (e.g. coughing, hiccup, involuntary movement)
on induction
 No emergence phenomena (e.g. nightmares)
 No interaction with neuromuscular blocking drugs No pain on injection
 No venous sequelae

34.  Safe if injected inadvertently into an artery
 No toxic effects on other organs
 No release of histamine
 No hypersensitivity reactions
 Water-soluble formulation
 Long shelf-life
 No stimulation of porphyria.

35. Induction of anaesthesia with an i.v. agent is suitable for most routine
purposes and avoids many of the complications associated with the
inhalational technique
Patient monitors should be attached before induction of anaesthesia.
Preoxygenation of the lungs may begin, using a close fitting face mask
and 100% oxygen delivered by a suitable breathing system for 3 min.
Alternatively, three to four large (vital capacity) breaths may be used.
Preoxygenation before routine elective induction of anaesthesia avoids
transient hypoxaemia before establishment of effective lung ventilation.

36.  Induction dose varies with the patient’s weight, age, state of nutrition,
circulatory status, premedication and any concurrent medication.
 Slow injection is recommended in the aged and in those with a slow
circulation time of the drug on the cardiovascular and respiratory
systems are assessed.
 After i.v. induction, a rapid transition to stage 3 anaesthesia is
achieved; this is maintained by the introduction of an inhalational
agent or by repeated bolus injections or a continuous infusion of an i.v.
anaesthetic agent.

37.  Regurgitation and vomiting
 Intra arterial injection of thiopental - Pain and blanching in the
hand and fingers occurs as a result of crystal formation in the
capillaries. The cannula should be left in the artery and 40mg
papaverine should be injected with local anaesthetic (e.g.
lidocaine 1% 5mL). Further treatment includes stellate ganglion
block, brachial plexus block or sympathetic block with i.v.
guanethidine.
 Perivenous injection - this causes blanching and pain and may
result in a small degree of tissue necrosis.
Complications

38.  Cardiovascular depression - this is likely to occur
particularly in the elderly, the hypovolaemic or the
untreated hypertensive patient. Reducing the dose and
speed of injection is essential in these patients.
 Respiratory depression
 Histamine release - Thiopental in particular may cause
release of histamine with subsequent formation of typical
wheals

39.  porphyria. An acute porphyric episode may be precipitated
by barbiturates in susceptible individuals.
 Other complications. Pain on injection (especially with
etomidate or propofol), hiccup or dystonic muscular
movements may occur. The use of lidocaine 10–40mg per
20mL propofol 1% reduces the incidence of pain on
injection.

40. PROPOFOL THIPENTON
E
KETAMINE ETOMIDATE MIDAZOLA
M
FENTANYL
Di iso propyl
phenol
Thiopental
sodium
Phencyclidin
e structural
analogue
Contain
carboxylated
imidazole
ring
Short acting
benzodiazipi
nes
Opoid
agonist

41. AGENT INDUCTION DOSE
(mg/kg)
Onset time (sec)
THIOPENTAL 3 -5 15 - 30
ETOMIDATE 0.2 – 0.6 <60
PROPOFOL
For >60yrs
age
1 – 2.5
1(premedicated)
1.75 (unpremedicated)
30
KETAMINE 2 30 - 60
Methohexital 1 - 2
Midazolam 0.1 – 0.2 (premedicated)
0.3 (unpremedicated)
30 - 60

42.  Excellent drug for induction of anaesthesia
 Prompt onset (15 – 30 sec) of action, smooth induction
 Rapid emergence particularly after single use for
induction
 Produces minimal to no direct effect on skeletal, cardiac
or smooth muscles.
Thiopentone

43.  Onset after 0.03 mg/kg is rapid(one arm brain circulation)
 Appropriate for cardiac dis, reactive airway dis,
intracranial hypertension.
 Hemodynamic stability is unique among rapid onset
agents used to induce anaesthesia.
 Used in angioplasty, aneurysm repair, thoracic surgery,
cardio version, neurosurgical procedure as giant
aneurysmal clipping.
ETOMIDATE

44.  Can be used for induction where it is req. to reduce ICP
when maintenance of cerebral or coronary perfusion pressure
is imp.
 Trauma pts. With questionable intravascular volume status
 But induction with etomidate is an independent risk factor in
development of emergence delirium.
 Involuntary myoclonic movements are common due to
alteration in balance of inhibitory and excitatory influences
on thalamocortical tract.
 Frequency of myoclonic like activity can be attenuated by
prior administration of an opoid

45.  It has become drug of choice for induction in many forms of
anaesthesia especially when rapid and complete awakening is
considered desirable.
 Induction dose must be reduced in elderly
 Awakening typically occors at plasma propofol concentration of
1 – 1.5mcg/ml.
 Complete awakening without residual CNS effects is the
principal reason this drug has replaced thiopentone for
induction of anaesthesia
PROPOFOL

46.  Cardiovascular stimulatory effects make it desirable for induction of
anesthesia in unstable cardiovascular pts.
 Bronchodilation and profound analgesia allowing use of high oxygen
concentrations make it an excellent choice for pts with reactive airway
disease.
 Pts with trauma with extensive blood loss are typical pts for RSI with
ketamine.
 Other diseases that may benefit are cardiac tamponade, restrictive
pericarditis
 Its property to preserve HR and right atrial pressure by its sympathetic
stimulating effects make it excellent inducing agent.
KETAMINE

47.  Only IV barbiturate for induction that can compete with
thiopental
 Rapid induction and emergence
 More rapid clearence than thiopentone
 Drug of choice for providing anesthesia during
electroconvulsive therapy.
 Lowers the seizure threshold
Methohexital

48.  It is the benzodiazipine of choice for induction
 When combined with other anaesthetic drug (coinduction)
often synergistic interaction occurs(usuallly with opoids or
hypnotic agents)
 Emergence depends on dose of midazolam and adjuvant drug
 Lacks analgesic effect
 Plasma level of more than 50 to 100ng/ml occurs when used
with adjuvant opoids or inhaled anaesthetic drugs with bolus
initial dose of 0.05 to 0.15mg/kg and continuous infusion of
0.25mg/kg to 1 mcg/kg/min. This level is sufficient to keep pt.
asleep but arousable at end of surgery.
Midazolam

49. Intramuscular Induction
 The intramuscular route is infrequently used for induction of anesthesia
in children
 it is painful
 induction is slow
 there is a risk of sterile abscess formation
 The only anesthetic currently used for intramuscular injections in
children is ketamine. This approach is usually reserved for adolescents
who are cognitively impaired, extremely uncooperative.

50. Rectal Induction
 Rectal induction of anesthesia has been popular in young
children (<5 years of age) in the past
 Several regimens have been used for rectal induction:
Methohexital 15 to 25 mg/kg, midazolam 1 mg/kg, ketamine 5
mg/kg, or thiopental 30 to 40 mg/kg.
 poor bioavailability of the induction agent
 Laryngospasm
 delayed recovery from anesthesia.
 In immune-compromised patients, rectal administration of
drugs may lead to sepsis.