Halothane

HALOTHANE

PHYSICAL & CHEMICAL PROPERTIES:

• Potent general anaesthetic used via inhalation.
• Volatile heavy liquid.
• Non-explosive & non-inflammable.
• Induction & maintenance anaesthetic agent.
• Least pungent.
• Not an analgesia.
• 0.01% thymol used as preservative.
• Decomposes when exposed to light.
• Maintained in amber coloured bottles.
• Stabilized by addition of thymol.
• Dissolve rubber & corrodes metals.
• Brand Name – Fluothane.

ACTIONS:

• Sensitizes myocardium to catecholamines.
• Potentiates competitive neuromuscular blockers.

CLINICAL USES AND ADMINISTRATION:

• Induction & maintenance of anaesthesia without assistance from other CNS depressants.
• Best uterine relaxation.
• Used in closed rebreathing system with precision thermo-stable/thermo-compensated, calibrated vaporisers.

At high levels:

• Cardiac depression.
• Cardiac sensitisation to norepinephrine.
• Potent bronchial relaxation.

DOSE:

Induction (Halothane alone)

• All species: 2.0 – 4.0% of inspired air.

Maintenance (Halothane alone)

• Small animals : 0.5 – 1.5%
• Large animals : 1.0 – 2.0%

Minimum alveolar concentration/MAC:

• Humans – 0.76

PHARMACOKINETICS:

• Rapidly absorbed & excreted through lungs.
• 20% : Biotransformation in liver & excreted through lungs
• 60 %: Excreted unchanged through lungs
• 20 %: Excreted via other routes, either unchanged/metabolised.
• Stored in body for many hours to days.
• Portal flow is maximally reduced.
• Presence of trifluoroacetic acid (TFA) in urine indicates that volatile anaesthetic agent used was Halothane.

ADVERSE EFFECTS:

• Vasodilatation.
• Hypotension.
• Shivering tremors on recovery.
• Malignant hyperthermia.
• Cardiac Arrhythmias.
• Postoperative hepatitis (Methoxyflurane avoided in future).
• Centrilobular necrosis in the liver 
• Post-operative jaundice
• Cardiopulmonary depression.
• Cardiac arrest

CONTRAINDICATIONS AND PRECAUTIONS:

• Increased CSF & Head injury.
• Previous history of adverse halothane exposure
• Cardiac arrhythmia