Sri Venkateswara Veterinary University: College Of Veterinary Science,tirupati

SRI VENKATESWARA VETERINARY UNIVERSITY COLLEGE OF VETERINARY SCIENCE,TIRUPATI DEPT. OF VETERINARY SURGERY AND RADIOLOGY TRACKING PROGRAM : ANAESTHESIOLOGY TOPIC : INHALANT ANAESTHETICS PRESENTED BY K.VASUDHA, TV/2015-76.

PRESENTED TO Dr. VEENA, PROFFESOR.

INHALANT ANAESTHETICS

DEFINITION “The Inhalant Anaesthetics are gas or volatile liquid that produces general anaesthesia when inhaled”. These are absorbed from alveoli to blood stream and blood is carried to brain. Primarily eliminated through LUNGS.

PROPERTIES OF IDEAL ANAESTHETIC  Non irritant  Non inflammable  Non explosive  Pleasant to inhale  Minimal metabolism in the body  Minimal organ depression  Low blood gas solubility  Adequate muscle relaxant action  Rapid induction and recovery

INHALANT ANAESTHETIC MACHINE Inhalant anaesthetics are given through inhalant anaesthetic machines.

METHODS OF ADMINISTRATION There are mainly four methods of administration. 1. Open Insufflation 2. Semi Open System Without Non Breathing Valves. 3. Semi Open System With Non Breathing Valves. 4. Semi Closed And Closed Systems.

EXAMPLES OF INHALANT ANAESTHETICS Ether Halothane Isoflurane Desflurane Sevoflurane Nitrous oxide

MINIMAL ALVEOLAR CONCENTRATION •

“The alveolar concentration of anaesthetic that is needed to prevent movement in 50% of subjects in response to surgical stimulus.” • Anaesthetic dose is commonly determined in terms of multiples of MAC ie;1.5 times of MAC.

FACTORS AFFECTING MAC • • • • • • • •

Hypothermia Hyponatremia Hypotension Pregnancy Geriatric age Hyperthermia Hypernatremia CNS Stimulating drugs

Decreases MAC

Increases MAC

INHALANT

MAC in DOGS MAC in cats

Halothane

0.87%

1.19%

Isoflurane

1.3%

1.6%

Desflurane

7.2%

9.8%

Sevoflurane

2.3%

2.6%

Nitrous oxide

188%

255%

BLOOD GAS PARTITION CO EFFICIENT • Also called as OSTWALDS COEFFICIENT • It is the ratio of concentration of compound in one solvent to the concentration in another solvent at equilibrium. • It shows how the gas will partition itself between two phases at equilibrium.

• Higher partition coefficient = higher lipophilicity = higher potency =higher solubility. • Higher solubility=more anaesthetic needs to be dissolved= slower onset. • MAC and blood gas partition coefficient are inversely related.

ETHER Colourless Pungent smell Highly volatile liquid Induction and recovery is slow Good muscle relaxant Irritant Available at low cost

SIDE EFFECTS Causes excessive salivation Increase in respiratory mucous recreations Interferes with respiration Sometimes may also lead to Oliguria Post Anaesthetic Nausea Cardiac Arrhythmia

HALOTHANE Non inflammable Non irritant Non explosive Fast acting Quick recovery Less soluble than ether

SIDE EFFECTS Arrhythmia Dose dependant cardiac depression activity Depressed respiration Bradycardia Hypotension Post anaesthetic shivering

ISOFLURANE • • • • • •

Less potent than halothane Non Inflammable and Non Explosive Good Cardiovascular Stability Low blood solubility Resistance to hepatic metabolism Suitable for patients with compromised hepatic function.

SIDE EFFECTS Depression of cardiovascular system CNS Depression Affects ventilation.

DESFLURANE Popular in DOGS. Less soluble Quicker induction Rapid recovery As it boils at close to room temperature,electronically controlled vaporisers are required. Side effects are similar to that of Isoflurane.

SEVOFLURANE Less potent and less soluble in blood than Halothane and Isoflurane. Minimal analgesic property More rapid induction and rapid change in anaesthetic depth. Highly expensive Hence hinderance in veterinary patients.

NITROUS OXIDE • • • • • •

Oldest Inhalant Anaesthetic Inert Non inflammable and non explosive Non irritant High MAC value Use of nitrous oxide in veterinary anaesthesia has four main indications.

1. MAC sparing effect when used in combination with potent inhalant. 2. Supplement analgesia during surgical procedure. 3. Speed induction of inhalant anaesthesia through “SECOND GAS EFFECT”.(large volume of nitrous oxide is taken up from alveoli into pulmonary capillary blood ,conc. of gases remaining in alveoli is increased.) 4. Used as sole anaesthetic in debilitated patients.

At sub anaesthetic dose, it is a very good analgesic. Should not be used in patients with respiratory compromise. Ex. Pneumothorax,Pneumoperitoneum.

INHALANT

INDUCTION DOSE

MAINTENANCE DOSE

Halothane

1-4%

0.5-2%

Isoflurane

2-4%

1-2%

Desflurane

12-18%

8-10%

Sevoflurane

4-5%

2.5-4%

REFERENCES • INHALANT ANAESTHETICS BY ROBERT D. KEEGAN. • RUMINANT SURGERY BY R.P.S. TYAGI,JIT SINGH. • A TEXTBOOK OF VETERINARY SURGERY AND RADIOLOGY. • INTERNET SOURCE.