ANAESTHETICS

1. ANAESTHETICS

2. What are Anaesthetics? • Anaesthetics are drugs that causes reversible loss of sensation with or without reversible loss of consciousness

3. Classification a) General Anaesthetics These are drugs that causes reversible loss of sensation, along with reversible loss of consciousness, affecting the whole body b) Local Anaesthetics These are drugs that causes reversible loss of sensation, without loss of consciousness, affecting a localized area

4. Classification of General Anaesthetics I) Inhalational General Anaesthetics • Volatile Liquids: Chloroform, Diethyl ether, Ethyl chloride, Trichloroethylene, halothane, Enflurane, Isoflurane • Gases: Cyclopropane, Nitrous oxide

5. Classification of General Anaesthetics II) Intravenous anaesthetics • Barbiturates Thiopentone sodium, Methohexital • Non – barbiturates Midazolam Ketamine Etomidate Propofol

6. Classification of Local Anaesthetics • Injectable • Low potency, short duration Procaine, Chloroprocaine • Intermediate potency and duration Lignocaine, Prilocaine • High Potency, Long duration Tetracaine , Bupivacaine, Ropivacaine, Dibucaine

7. II) Surface Anaesthetic a) Soluble Cocaine Lignocaine Tetracaine Benoxinate b) Insoluble Benzocaine Butylaminobenzoate (Butamben) Oxethazine Classification of Local Anaesthetics III) Other Drugs Propranolol, Chlorpromazine, Quinine

8. General AnaestheticsLocal Anaesthetics

9. Stages of general Anaesthesia • Stage of Analgesia • Loss of pain sensation • Stage of Delirium • ↑ BP & ↑ respiratory rates • Stage of surgical anaesthesia • Regular respiration • Skeletal muscle relaxation • Progressive loss of eye reflexes • Cessation of eye movements • Fixed Pupil • Medullary Paralysis • Severe depression • DEATH Respiratory centre Vasomotor centre

10. Properties of an Ideal Anaesthetic • Pleasant • Non – irritating • Non – inflammable • Good anaesthetic, analgesic, skeletal muscle relaxant • No action on heart, BP, respiration • Smooth induction • No post anaesthetic nausea and vomiting • Cheap

11. Nitrous Oxide • Colorless , Non-irritating gas • Odourless, Non – inflammable • Low potency anaesthetic • Good analgesic • Poor skeletal muscle relaxant • Low blood solubility, Quick onset • Rapid recovery • No effect on other organs • Shows second gas effect & Diffusion hypoxia • Used as an adjuvant/carrier • ALONE in dental and Obstetric analgesia • Cheap , very commonly used

12. Second Gas Effect • When certain anaesthetics like N2O are administered in high concentrations,the other anaesthetic which is given along with N2O ,is also pullen & its alveolar tension rises more rapidly than when it (second anaesthetic) is given alone.This is known as second gas effect • ↓ concentration of second anaesthetic • ↓ adverse effects

13. Diffusion hypoxia • When anaesthetics like N2O is discontinued after prolonged use- N2O having low blood solubility ,rapidly back diffuses into alveoli & dilutes alveolar air (↓ oxygen content) hypoxia

14. Ether • Colorless , volatile liquid • Pungent odour • Highly irritant & Inflammable • Potent anaesthetic • Good analgesic & skeletal muscle relaxant action • ↑ respiratory rate • BP & heart rate are well maintained • No interference with uterine contractility • Cheap • Shouldn’t be given in Alcoholics

15. Halothane • Fluorinated volatile liquid • Structurally similar to chloroform • Sweet fruity odour • Non – irritant & Non – inflammable • Potent anaesthetic • Poor analgesic & muscle relaxant • ↓ solubility in blood • Smooth induction • Rapid recovery

16. Halothane • Depresses myocardial contractility • ↓ BP & heart rate • Arrhythmia • Respiratory depression • ↓ urine formation • HEPATITIS • Malignant hyperthermia • Most popular anaesthetic

17. Nitrous Oxide and Diethyl ether

18. Diethyl Ether Nitrous Oxide

19. Nitrous Oxide & Halothane

20. Nitrous Oxide Halothane

21. Ether & Halothane

23. Nitrous Oxide & Halothane

24. Nitrous Oxide Halothane

25. Ether & Halothane

27. Thiopentone Sodium • Quick and pleasant induction • hypnosis deep sleep anesthesia • Consciousness lost first  reflex activity muscle tone  medullary centres depressed • Pupils contracted to light • Cerebral blood flow and cerebral metabolic rate ↓↓ intra cranial tension↓

28. Absence of eye lid reflex sign of adequate induction Absorption,fate,excretion • Very short duration of action high lipid solubility • With successive doses of drug ,body fat depots get saturated with drug • Slow release back into plasma drowsiness after cessation • Cross placental barrier

29. Therapeutic uses • For Induction • As anesthetic agent, for operations of short duration • As ananesthetic, in patients with malignant hyperthermia • As an Anticonvulsant

30. Advantages • Quiet respiration ,non-explosive Disadvantages • Pharyngeal, laryngeal reflexes persist coughing ,laryngospasm • Depression of respiratory centre

31. KETAMINE Pharmacologically related to hallucinogen phencyclidine Anesthesia induced by im(5-10mg/kg) or iv (1-2mg/kg) Site of action: cerebral cortex, limbic system Analgesic in sub narcotic doses, immobility, amnesia with light sleep

32. Given iv quick acting ,following single dose dissociative anesthesia  complete analgesia & amnesia • Analgesia 40 minutes; anesthesia 15 minutes • No CVS & respiratory depression • Bronchodilator • BP ,HR,CO  noradrenaline • Used in shock

33. Disadvantages of Ketamine • Involuntary movements ,hypertonus • Delirium ,hallucinations during induction and recovery ; avoided by diazepam • Poor muscle relaxation ,intra ocular pressures & intra cranial pressures

34. PROPOFOL Rapid induction & recovery, small hangover effect Used for induction & maintenance of GA Dose dependent cortical depression, anticonvulsant Metabolized by liver 88% Adv: antiemetic action, daycare surgery, safe during pregnancy

35. NEUROLEPTANALGESIA Method of IV anesthesia combining neuroleptics & opioids. Conscious & cooperative during anesthesia Droperidol + Fentanyl

36. Fentanyl • Opioid supplementary analgesic in inducing GA • 100 times more potent than morphine • Droperidol 2.5mg & fentanyl citrate 50mcg in 1 ml Advantage • Smooth onset and rapid post operative recovery

37. Less danger of hypotension ,suppression of coughing ,vomiting • Continued analgesia in post operative period • Patient’s co-operation • Useful in old people

38. Adverse reactions • Extra pyramidal disturbances ,respiratory depression • Fentanyl has shorter duration of analgesic action; supplementary doses of fentanyl has to be given

39. PREANAESTHETIC MEDICATION Defined as “preanaesthetic medication", drugs with specific pharmacological actions administered preoperatively with specific goals to achieve.

40. GOALS OR OBJECTIVES OF PREMEDICATION • RELIEF OF APPREHENSION OR ANXIETY • SEDATION • ANALGESIA • ANTISIALOGOGUE EFFECT • REDUCTION OF GASTRIC ACIDITY & VOLUME • PREVENTION OF NAUSEA & VOMITING • FACILITATION OF ANESTHETIC INDUCTION

41. OPIOIDS– morphine (10mg),or pethidine(50mg-100mg),fentanyl ANTIANXIETY DRUGS– BZDs,diazepam(5-10mg) Diazepam is anxiolytic ,amnesic &sedative SEDATIVE-HYPNOTIC– pentobarbitone(100mg). night before and in morning to calm the patient. ANTICHOLINERGICS– atropine or hyoscine(0.6mg i.m or i.v.) TO PREVENT VAGAL BRADYCARDIA& HYPOTENSION. Decrease salivary & bronchial secretion. H2 BLOCKERS – ranitidine(150mg) or famotidine(20mg) Raises gastric pH, reduce gastric volume gastroesophageal reflux. ANTIEMETICS– metoclopramide(10-20mg) i.m preoperatively, is effective in reducing post operative vomiting