Anaesthetic agents

Anaesthetic agents induce controlled and reversible loss of consciousness characterized by analgesia (lack of pain), amnesia (lack of memory), muscle relaxation and immobilisation (relatively depressed reflex responses).

Anaesthetic agents can be classified in injectables and Inhalent type.

Injectable anaesthesia used to be given intravenously, intramuscularly, or subcutaneously in animals, but inhalant anaesthesia used to be given by the inhalant route with oxygen and other gaseous mixtures. Inhalent anaesthesia is safer, but it requires more equipment.

Injectable Anaesthetics

Examples of Injectable Anaesthetics are Thiopental sodium, Thiamylal, Methohexital, Pentobarbital, Phenobarbital (Barbiturates) and Ketamine (Dissociative Anaesthetic agent).

Inhalant Anaesthetics

Examples of Inhalant Anaesthetics are Nitrous oxide: (N₂O), Halothane (C₂HBrF₃), Methoxy flurane (C₃H₄Cl₂F₄O), Isoflurane (C₃H₂ClF₅O) and Sevoflurane (C₄H₃F₇O).

Halothane

Halothane is a halogenated hydrocarbon (not an ether). Only inhalant anaesthetic that having Bromine in its structure.

IUPAC name of Halothane is 2–bromo–2–chloro-1,1,1-trifluroethane. It is a Colourless and pleasant smelling gas.

It is unstable and decomposes when exposed to UV light (contains 0.01% thymol as a stabilizing agent).

Halothane is stored in dark coloured bottle since it is sensitive to light exposure. Halothane increases the cardiac sensitization to catecholamines. Catecholamines causes cardiac depression at high levels (bradycardia) and Halothane causes bronchial relaxation.

Methoxy flurane

Methoxy flurane is a halogenated hydrocarbon/halogenated ether. Vapour is pleasant and of fruity aroma.

It is a potent analgesic, Used as an emergency analgesic.

Isoflurane

Isoflurane is a halogenated ether. Vapour is pungent and irritate respiratory passage.

It has analgesia and possess muscle relaxing property. Binds to GABA, Glutamate and Glycine receptors.

Sevoflurane

Sevoflurane is a highly fluorinated methyl isopropyl ethers (used for induction and maintenance). Sweat smelling and preferred for mask induction.

It block NMDA receptors, binds to GABA  receptors.

To degradation products are produced when sevoflurane comes in contact with sodalime, compoung A and B compound A is nephrotoxic.

Calculation of Anaesthetics dosage in Dogs

Atropine

• Dose: 0.02 to 0.04 mg/kg body weight
• Availability: 0.6 mg/ml (TROPINE® inj)
• 1 ml for 15 – 30 kg body weight S/C, I/M, I/V

Glycopyrolate

• Dose: 0.01 mg/kg body weight
• Availability: 0.2 mg/ml (Pyrolate® inj)
• 1 ml for 20 kg body weight S/C, I/M, I/V

Xylazine

• Dose : 1 mg/kg body weight
• Availability : 20 mg/ml (Zine® inj)
• 1 ml for 20 kg body weight  I/M

Diazepam

• Dose : 0.1 to 0.5 mg/kg body weight
• Availability : 5 mg/ml (Calmpose® inj)
• 1 ml for 10 – 50 kg body weight  I/V

Buprenorphine

• Dose : 6 to 10 mcg/kg body weight
• Availability : 0.6 mcg/ml (Buprigesic® inj)
• 1 ml for 30 – 50 kg body weight  I/M, I/V.

Butorphanol

• Dose : 0.2 mg/kg body weight
• Availability : 2 mg/ml (Butrum® inj)
• 1 ml for 10 kg body weight  I/V

Tramadol

• Dose : 2 mg/kg body weight
• Availability : 50 mg/ml (TRAMOL® inj)
• 1 ml for 25 kg body weight  I/M, I/V

Ketamine

• Dose : 5 – 10 mg/kg body weight
• Availability : 50 mg/ml (also 10 mg/ml)
• 1 ml for 5 – 10 kg body weight  I/M, I/V

Acepromazine

• Dose :  0.04 mg/kg body weight
• Availability : 10 mg/ml (Acepril® inj)
• 1 ml for 250 kg body weight  I/V

Calculation of Anaesthetics dosage in Horses

Xylazine

• Dose : 1.1 mg/kg body weight
• Availability : 20 mg/ml (Xylazin® inj)
• 1 ml for 18 kg b.wt  I/M, I/V

Acepromazine

• Dose :  0.04 mg/kg body weight
• Availability : 10 mg/ml (Acepril® inj)
• 1 ml for 250 kg b.wt  I/V

Ketamine

• Dose : 2.2 mg/kg body weight
• Availability : 50 mg/ml (also 10 mg/ml) & 100 mg/ml
• 1 ml for 23 kg b.wt  I/V