INHALANT_ANAESTHETICS_USED_IN_VETRINARY_PRACTICE.pptx

DESCRIBES INHALANT ANAESTHESIA USED FOR ANIMALS IN A NORMAL HOSPITAL SETUP

1. INHALANT ANAESTHETICS USED IN VETERINARY PRACTICE ASHISH KUMAR BVN20008

2. DEFINITION The Inhalant Anaesthetics are gas or volatile liquids that produce general anaesthesia when inhaled. These are absorbed from alveoli to blood stream and blood is carried to the brain. Primarily eliminated through LUNGS. Example:- Nitrous Oxide, Cyclopropane, Isoflurane

3. CLASSIFICATION Gaseous agents Nitrous Oxide, Cyclopropane, Carbon Dioxide Volatile liquids Ethyl ether, Methoxyflurane, Isoflurane, Sevoflurane

4. PROPERTIES OF IDEAL ANAESTHETIC Non irritant Non inflammable Non explosive Minimal metabolism in the body Low blood gas solubility Adequate muscle relaxant action Rapid induction and recovery

5. INHALANT ANAESTHETIC MACHINE Ventilator consistent supply of oxygen and anesthetic gases Flow meter measure and regulates the flow rate of gases Soda lime absorb and neutralize exhaled CO2 APL valve allow excess gas to escape Vaporizer convert liquid anaesthetic in to gas and mixes it with O 2

6. MINIMAL ALVEOLAR CONCENTRATION ( MAC ) The alveolar concentration of anaesthetic that is needed to prevent movement in 50% of subjects in response to surgical stimulus It is the measure of potency of inhalation anaesthetics The anaesthetic potency of inhaled anaesthetic is inversely related to MAC Potency =1/MAC i.e. an agent having low anaesthetic potency will have high MAC value and vice versa

7. FACTORS AFFECTING MAC Hypothermia Hyponatremia Hypotension Pregnancy Geriatric age Hyperthermia Hypernatremia CNS stimulating drugs Decrease MAC Increase MAC

8. INHALANT MAC in DOGS MAC in CATS Nitrous oxide 188% 255% Cyclopropane 17.5% 19.7% Isoflurane 1.28% 1.63% Sevoflurane 2.4% 2.6% Methoxyflurane 0.24% 0.23%

9. BLOOD-GAS PARTITION COEFFICIENT Also called as OSTWALDS COFFICIENT It is the ratio of concentration of compound in one solvent to the concentration in solvent at equilibrium Higher partition coefficient = Higher lipophilicity= higher solubility Higher solubility = slower onset MAC and blood gas partition coefficient are inversely related

10. OIL-GAS PARTITION COEFFICIENT A measure of fat solubility, determines the potency of an anesthetic and also influence the kinetics of its distribution in the body High lipid solubility delays recovery from anaesthesia

11. METHODS OF ADMINISTRATION There are mainly four methods of administration. Open insufflation Semi open system without Nonrebreathing valves Semi open system with Nonrebreathing valves Semi closed and Closed system

12. Open Insufflation The anesthetic gas or vapor, together with air and/or oxygen is delivered to the mouth or trachea by a mask or catheter

13. 2. Semi-Open System without Non-Rebreathing Valves Ayers T- tube This simple non-rebreathing system has no valve and very little resistance which make it useful for very small patients. It also has very little dead space.

14. 3 . SEMI-OPEN SYSTEM WITH NONREBREATHING VALVE Stephen Slater Valve Inspired and expired gases are separated by a valve as close to the animal as possible Rebreathing is minimal and the animal breathes only the anesthetic mixture delivered

15. 4. Semi-Closed and Closed System Gases are partly exhaled to the atmosphere and partly rebreathed. So relatively high fresh gas flow thus required

16. NITROUS OXIDE Rapid onset and recovery due to its low blood-gas solubility coefficient Minimal cardiovascular depression Non-irritating to respiratory tract suitable for paediatric and small animal cases It enchases the uptake of other anaesthetic gases ( second gas effect ) leading to quicker induction when used with agent like isoflurane Nitrous oxide must be administrated with oxygen (usually at least 30% oxygen)

17. Adverse Effect Chronic exposure to nitrous oxide can interfere with vitamin B12 metabolism, leading to megaloblastic anemia Contraindicated in pneumothorax, bowel obstruction Risk of hypoxia when discontinuing

18. CYCLOPROPANE Potent anesthetic effective at low concentration Rapid induction and recovery Increases heart rate and cardiac output Minimal respiratory depression, less impact on respiration compared to other agents For induction 20-30% in oxygen and for maintenance 5-15% in oxygen

19. Adverse Effect Risk of excitement during induction or recovery Explosiveness Cardiac arrhythmias Can exacerbate ischemia in patients with heart disease

20. ISOFLURANE Minimal cardiac depression, safer for patients with heart condition Low metabolic rate Compatible with wide range of species Minimal accumulation so suitable for prolonged anaesthesia 3-5% isoflurane in oxygen for mask induction

21. Adverse Effect Respiratory depression Hypotension Malignant hyperthermia Pungent odor can cause coughing and breath-holding during induction

22. SEVOFLURANE Rapid induction and recovery (low blood-gas coefficient) Non-Irritating: Non pungent, making it suitable for mask induction, especially in small animal For induction in dog and cat 4-6% sevoflurane in oxygen and for horses 5-7% sevoflurane in oxygen Good muscle relaxation without significant additional agents

23. Adverse Effect Dose-Dependent Hypotension Postoperative agitation Nephrotoxicity risk Malignant hyperthermia

24. METHOXYFLURANE Potent analgesic Used as an emergency analgesic Vapour is pleasant and of fruity aroma Mild cardiovascular effect

25. Adverse Effect Very slow onset and offset Nephrotoxicity Concurrent use of oxytetracycline and methoxyflurane results in fatal renal toxicity

26. DESFLURANE I deal for short procedure due to it’s low blood-gas partition coefficient Effective at low concentration Minimal hepatic metabolism, reducing the risk of liver toxicity Cardiovascular stability Concentration of desflurane maintained between 3-6% for induction and 1.5-3% for maintenance

27. Adverse effect Respiratory irritation, can cause coughing airway irritation and increased secretions especially during induction and emergence Tachycardia and hypertension Environmental impact

28. REFERENCE VETERINARY ANESTHESIA BY WILLIAM V. LUMB, E. WYNN JONES VETERINARY ANAESTHESIA 8 th EDITION BY L. W. HALL, K. W. CLARKE ESSENTIAL OF VETERINARY PHARMACOLOGY AND THERAPEUTICS 2 nd EDITION BY HARPAL SINGH SANDHU

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