GA - General Anaesthesia for MBBS students

Basics of General anaesthesia to mbbs students

1. INDUCTION AGENTS Dr. D.A.V. Sandeep kumar Consultant Dept. Anaesthesiology & Critical Care

2. Basic Principles of Anesthesia Anesthesia defined as the abolition of sensation Analgesia defined as the abolition of pain “ Triad of General Anesthesia” need for unconsciousness need for analgesia need for muscle relaxation

3. Inhalational Agents Intravenous Agents INDUCTION AGENTS

4. Inhalational Anesthetic Agents Inhalational anesthesia refers to the delivery of gases or vapors from the respiratory system to produce anesthesia Pharmacokinetics--uptake, distribution, and elimination from the body Pharmacodynamics -- MAC value

5. The main target of inhalation anesthetics is the brain.

6. Uptake and distribution of inhalational agents

7. MAC Minimum Alveolar Concentration = MAC. 1 MAC is the Minimum Alveolar Concentration at which 50 % of humans have no response (movement) to surgical stimulus (skin incision). MAC awake is the alveolar concentration when 50 % of persons will awake to vocal stimulus. Anesthetic potency is measured in MAC MAC is consistent within a species and between species. MAC is different for each inhaled agent.

8. AGENT MAC POTENCY Methoxy-flurane 0.16% Most potent Halothane 0.74% Isoflurane 1.17% Enflurane 1.7% sevoflurane 2.05% desflurane 6.0% Nitrous oxide 104% Least potent

9. Classification of inhalational anaesthetics Outdated Gases Volatile agents Ether trilene Methoxyflurane Cyclopropane chloroform Nitrous oxide Xenon Halothane Enflurane Isoflurane Sevoflurane Desflurane

10. Halothane

11. Amber colored bottled – red colour coding Thymol preservative. Pleasant smell , non-irritant, bronco-dilatation, potent to induce in single puff make it best for paediatric induction . Agent of choice for asthmatics . Not a good analgesic

12. Most potent inhalational anesthetic MAC of 0.75% Efficacious in depressing consciousness Very soluble in blood and adipose B:G p co- ef .- 2.4 Prolonged emergence Halothane

13. Inhibits sympathetic response to painful stimuli Inhibits sympathetic driven baroreflex response ( hypovolemia ) Depresses myocardium-- lowers BP and slows conduction Sensitizes myocardium to effects of exogenous catecholamines -- ventricular arrhythmias Halothane Systemic Effects

14. Halothane Systemic Effects Decreases respiratory drive-- central response to CO 2 and peripheral to O 2 Respirations shallow-- atelectasis Depresses protective airway reflexes Potent Bronchodilator Marked increase in ICT

15. Uterus :- - Atony of uterus- disadv -postpartum hemorrhage. adv- manual removal retained placenta. Halothane shakes - post op shivering. Malignant hyperthermia :- - massater spasm- rabdomyolysis - ARF- death. calcium- rhynodyne receptors. Rx dantrolene sodium. Halothane Systemic Effects

16. Normal liver Halothane hepatitis Avoid halothane repeat exposure with in 3 months. Halothane Side Effects “Halothane Hepatitis” Pathological lesion is Centrilobar necrosis

17. Halothane Side Effects Malignant Hyperthermia- Classic-- rapid rise in body temperature, muscle rigidity, tachycardia, rhabdomyolysis , acidosis, hyperkalemia , DIC most common masseter rigidity Treatment - IV dantrolene

18. Contraindications/Precautions Malignant hyperthermia. susceptibility unexplained liver dysfunction after previous halothane exposure intracranial mass lesion aortic stenosis pheochromocytoma with aminophylline has been associated with severe ventricular dysrhythmias

19. Enflurane First to Isoflurane Stable, nonflammable liquid Pungent odor MAC 1.68%

20. Enflurane Systemic Effects Potent inotropic and chronotropic depressant and decreases systemic vascular resistance-- lowers blood pressure and conduction dramatically Inhibits sympathetic baroreflex response Sensitizes myocardium to effects of exogenous catecholamines -- arrhythmias

21. Enflurane Systemic Effects Respiratory drive is greatly depressed-- central and peripheral responses Increases ICT

22. Enflurane Side Effects Metabolism releases fluoride ion-- renal toxicity Epileptiform EEG patterns

23. Isoflurane Isomer of Enflurane Not carcinogenic Nonflammable Pungent MAC of 1.30 % B:G p co- ef is 1.17

24. Only agent that preserves baroreceptor reflex – isof . So that reflex tachycardia occurs in response to decrease B.P mantaining cardiac output. Agent of choice for controlled hypotension is isof . Excellent muscle relaxant-- potentiates effects of neuromuscular blockers Isoflurane Systemic Effects

25. Agent that cause coronary steal – isof . Agent of choice for cardiac anaesthesia as it doesn’t sensitize myocardium to adrenaline except MI Agent that causes minimal increase in intracranial tension & decreases Brain’s oxygenation demand is isof . Agent of choice for neuroanaesthesia . Isoflurane Systemic Effects

26. Isoflurane Side Effects Little metabolism (0.2%) -- low potential of organotoxic metabolites No EEG activity like enflurane Bronchoirritating , laryngospasm

27. Sevoflurane

28. Low solubility in blood-- produces rapid induction and emergence Pleasant smell , non irritant and bronchodilatation makes it agent of choice for Paediatric anaesthesia . 2 nd agent of choice for Neuro anaesthesia . Cardiac anaesthesia . asthmatics

29. Sevoflurane Minimal systemic effects-- mild respiratory and cardiac suppression Decreases portal blood flow but increases hepatic artery blood flow, so Hepatic blood flow is maintained Expensive

30. Sevoflurane and Compound A Sevoflurane reacts with soda lime used in anesthetic circuit to form “compound A” Mostly with Barylime compound A is renal toxin. Agents that should not be given with sodalime . 1) trielene .( trichlor ethylene) 2) sevoflurane . 3) desflurane

31. Desflurane

32. Pungent odour Agent that boils at room temperature(22.8*c)-DF. Agent of choice for day care (fastest induction )- DF. Does not cause coronary steal Stimulates Sympathetic system, so can be given to pt’s in SHOCK Agent of choice for geriatric (old) patients – DF. Agent of choice for hepatic failure Agent of choice for renal failure

33. Anesthetic B:G PC MAC Features Notes Halothane 2.3 0.74% PLEASANT Arrhythmia Hepatitis Hyperthermia Enflurane 1.9 1.69% PUNGENT Seizures Hyperthermia Isoflurane 1.4 1.17% PUNGENT Widely used Sevoflurane 0.62 1.92% PLEASANT Ideal Desflurane 0.42 6.1% IRRITANT Cough Nitrous 0.47 104% PLEASANT Anemia Review

34. Intravenous Anesthetic Agents

35. CLASSIFICATION Barbiturates Thiopentone Methohexitone Non Barbiturates Ketamine Propofol Etomidate Opiods Benzodiazepines Phenothiazines

36. Thiopentone Barbiturate Water soluble Alkaline Dose-dependent suppression of CNS activity--decreased cerebral metabolic rate (EEG flat)

37. Yellow Amorphous powder On dilution as 2.5 % , pH is 10.8 Should not be diluted with RL Sulphur makes it Lipid soluble Sodium salt makes Water soluble Ultra short duration due to Methyl group Prepared in atmosphere of Nitrogen

38. Unconsciousness in one arm brain circulation time (15 s) Regains consciousness due to Redistribution Metabolised in Liver , excreted in Kidney MOA – inhibitory neurotransmitters like GABA is enhanced , GABA mimetic action

39. Thiopental Systemic Effects Varied effects on cardiovascular system in people-- mild direct cardiac depression-- lowers blood pressure-- compensatory tachycardia ( baroreflex ) Dose-dependent depression of respiration, depth affected more than rate

40. Cerebral oxygen consumption, cerebral metabolic rate & ICT are decreased, so agent of choice for Cerebral protection Anticonvulsant action due to phenyl group, controls convulsions resistant to other anticonvulsants Anti - analgesic action Decreases IOP Has Anti-thyroid activity

41. Dose – 4-6 mg/kg b.w Due to redistribution, drug is eliminated after 10-12 hrs, so should be under observation for 24 hrs

42. Thiopental Side Effects High Alkalinity causes Tissue necrosis—gangrene due to perivenous or intramuscular inj. Rx – 10 ml 1% lignocaine , 100 u hyaluronidase locally

43. Intra arterial inj is dreadful complication - Precipitation & crystallization due to acidic pH of blood -Thrombus – blocked microcirculation,vasospasm – ischemia & Gangrene - Rx – leave needle at site - inj. Heparin 500 u, - inj. papaverine 40mg - inj. Xylocaine 1% 10ml - brachial plexus or stellate ganglion block

44. Contra Indications Porphyrias – mostly in Acute Intermittent Porphyria and Variegate Porphyria Shock and Hypotension Asthmatics

45. Methohexitone More potent than Thiopentone Used as1% solution with pH - 11.1 Dose – 1.5 mg/kg Given IM or perrectal in children Induces Seizures, so agent of choice for ECT.

46. Consists of phenol ring with isopropyl group Oil based preparation consisting soyabean oil, egg lecithin and glycerol. Hence milky white in colour Painful injection, preceded by Lignocaine Rapid onset and short duration of action Propofol

47. Induced in one arm brain circulation time Duration of action 5 – 10 min’s Dose 2 mg/kg b.w Metabolised by liver and excreted by kidney

48. Propofol Hypotension produced is significant Respiratory depression is more severe Produces muscle twitchings & myoclonic activity Antiemetic Antipruritic Reduces IOP

49. Uses Agent of choice for Day care surgery Agent of choice for Total Intravenous anaesthesia (TIVA) Infusion used for ICU sedation Agent of choice in susceptible pt’s of Malignant Hyperthermia

50. Disadvantages Apnea is more profound Hypotension is more severe Injection is painful Myoclonic activity Allergic reactions due to egg lecithin

51. Ketamine Phencyclidine derivative with Imidazole ring Contains Benzethonium chloride as preservative Acidic in nature – pH 3.5 Highly lipid soluble Dose – 2 mg/kg bw IV, 5 mg/kg bw IM

52. Onset of action 30 – 60 s Duration of action 15 to 20 min’s , because of redistribution Strong Analgesic Metabolised by liver, eliminated by kidney

53. Primary site of action – thalamo -neocortical projection It inhibits Cortex (unconscious) , thalamus (analgesia) and stimulates limbic system (emergence reaction and hallucinations) Hence called as Dissociative anaesthesia Action on NMDA receptors

54. Ketamine Systemic and Side Effects ICT is raised Hallucinations most common , minimised by Midazolam Characteristic of sympathetic nervous system stimulation-- increase HR, BP, CO , so IV agent of choice in Shock

55. Maintains laryngeal reflexes and skeletal muscle tone Potent Bronchodilator , so IV agent of choice in Asthmatics Tracheobronchial and salivary secretions are increased Increases Intraocular tension Increases Intragastric tension

56. USES Induction agent of choice in asthmatics, shock and children Sole agent in minor procedures Used in remote places Preferred in full stomach as reflexes are preserved

57. Contra Indications Head injury Eye injury Ischemic heart disease Hypertensives Psychiatric pts

58. Etomidate Structure similar to ketoconozole Cardiovascular stable agent , so Anaesthetic of choice for Aneurysm surgery Dose 0.3 mg/kg b.w

59. Etomidate Systemic Effects Little change in cardiac function in healthy and cardiac patients Mild dose-related respiratory depression Decreased cerebral metabolism

60. Etomidate Side Effects Pain on injection (propylene glycol) Myoclonic activity Nausea and vomiting (50%) Adreno Cortical suppression Vitamin C deficiency

61. MCQ’s

62. ------------------------------------- Thiopentone Ketamine Propofol Etomidate

63. ` Thank you