Induction of anaesthesia

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 G reek 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 a naesthesia 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

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

12. Induction of anaesthesia can be done by drugs given via Inhalational route Gaseous – N2O Volatile liquid – Ether Halothane Sevoflurane Intravenous route Propofol Thiopentone Etomidate Ketamine Midazolam Opoid agonist (fentanyl) Intramuscular route Rectal route

13. INHALATIONAL INDUCING AGENT

14. 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

15. 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.

16. 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

17. As it is usually done in young children, mask or hand is introduced gradually to the face from the side T he 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 -

18. 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.

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

20. 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

21. 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.

22. 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

23. 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

24. 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.

25. 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. H alothane

26. 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

27. 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

28. 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

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

30. INTRAVENOUS INDUCING AGENTS

31. 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 wel l 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

32. 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

33. 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.

34. 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.

35. I nduction 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.

36. 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

37. 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

38. 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.

39. PROPOFOL THIPENTONE KETAMINE ETOMIDATE MIDAZOLAM FENTANYL Di iso propyl phenol Thiopental sodium Phencyclidine structural analogue Contain carboxylated imidazole ring Short acting benzodiazipines Opoid agonist

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. It is the b enzodiazipine 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

48. 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.

49. 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.