General anaesthesia

general anesthesia are the drug given before surgery which have reversible effect on consciousness. discussing ideal GA, stages of GA, mechanism of action of GA, classification of drugs parenteral or inhaled.

1. General Anaesthesia Yogeeta goyat M. Pharma ( ist year) Pharmacology

2. Introduction : GA’s are the drugs which causes reversible loss of all sensation and consciousness. C ombination of medications that is given before a surgery or other medical procedure.  Induce sleep like state.

3. Ideal GA should cause : Sedation and reduction of anxiety Lack of awareness and amnesia Skeletal muscle relaxation Suppression of undesirable reflexes Analgesia

4. Difference between GA and LA: DESCRIPTION GA LA Site of action CNS PNS Area of body involved Whole body Restricted area consciousness lost Unaltered Major surgery preferred Cant be used Minor surgery Cant be used Preferred Poor health patient risky safer

5. MECHANISM OF ACTION OF GENERAL ANAESTHETICS GABA –A receptor : Potentiated by Halothane, Propofol, Etomidate , Enflurane, isoflurane, Desflurane, sevoflurane NMDA receptors : Inhibited by Ketamine, nitrous oxide and xenon Glycine receptors : Potentiated by Halothane, Propofol, Enflurane, isoflurane, Desflurane, sevoflurane Also has effect on neuronal nicotinic receptors and 5-HT3 receptors

6. Stages of GA Stages in general anaesthesia Body reaction 1. Stage of analgesia Patient remain conscious but drowsy 2. Stage of delirium Patient loss consciousness, increased sympathetic activity , increased heart rate, blood pressure, dilated pupil, increased muscle tone, irregular breathing 3. Stage of anesthesia 1.Roving eyes 2.Loss of corneal and laryngeal reflexes 3.Pupil starts dilating, light reflux lost 4.Intercoastal paralysis, dilated pupil 4. Stage of medullary paralysis Depressed respiratory and vasomotor center Death occurs within few minutes.

7. Classification : inhalation Parenteral

8. Inhalation anaesthesia Nitrous oxide • Nitrous oxide is completely eliminated by the lungs. • Non toxic to liver , kidney and brain. No much adverse effects on CVS , respiratory system . • Probably the safest with 30% oxygen. • N2O is a weak, low potency anesthetic agent. Action is quick and smooth . • Recovery is rapid. Rarely exceeds 4 min

9. • It is a poor muscle Relaxant. • It has significant analgesic effects. • Nitrous oxide is used primarily as an adjunct to other inhalational or intravenous anesthetics mainly during maintenance phase. • 70% N2O +25-30% oxy + 0.2-2% potent anaesthetic Adverse effects Pneumothorax. Megaloblastic anaemia peripheral neuropathy (because of methionine synthetase inactivation

10. 2 . Halothane Induction is relatively slow. Halothane is soluble in fat and other body tissues, it will accumulate during prolonged administration. Halothane can sensitize the myocardium to the arrhythmogenic effects of Adrenaline Uses : Induction and maintenance anaesthesia in pediatric age group. Maintenance anaesthesia in adults

11. 3.Enflurane • Induction of anaesthesia and recovery from enflurane are relatively slow. • It is primarily utilized for maintenance rather than induction of anaesthesia. • Enflurane provokes seizure attacks in susceptible patients. • Enflurane produces significant skeletal muscle relaxation

12. 4.Isoflurane • Induction with isoflurane and recovery from isoflurane are faster than with halothane. • It is typically used for maintenance of anesthesia after induction with other agents because of its pungent odor. Another e.g , Desflurane. Disadvantage Slightly irritant, it is costly.

13. Parenteral anaesthesia : Thiopental : It is an ultra short acting barbiturates. Consciousness regained within 10-20 mins by redistribution to skeletal muscle. It is eliminated slowly from the body by metabolism and produce hang over. It can be used for rapid control of seizures. Main side effect are Cardiovascular and respiratory depression

14. Propofol : Most commonly used IV anaesthetic Unconsciousness achieved in 45 seconds and lasts 15 minutes Anti-emetic in action Non-irritant to airways Suited for day care surgery (residual impairment is less marked) Side effect : Cvs and respiratory depression and pain at site of injction administration (Pain during injection, Fall in BP)

15. Ketamine : Dissociative anaesthesia Produce - profound analgesia, immobility, amnesia with light sleep. Acts by blocking NMDA receptors Heart rate and BP are elevated due to sympathetic stimulation Respiration is not depressed and reflexes are not abolished .

16. Ketamine Emergence delirium, hallucinations and involuntary movements occurs during recovery (can be minimized by diazepam or midazolam). It is useful for burn dressing and trauma surgery. Dangerous for hypertensive and IHD patients. Side effect : Psychotomimetic effect following recovery, post operative nausea , vomiting, salivation

17. References: Essential of medical Pharmacology, K.D. TRIPATHI, 7 TH Edition, chapter 9, page 365-379 Lippincott illustrated reviews: Pharmacology, 6 th Edition, chapter 6, page- Medical Pharmacology by Padmaja Udaykumar , revised 4 th edition, chapter .

18. Thank you