Halothane is a volatile anesthetic used for both induction and maintenance of general anesthesia in various surgical procedures across patients of all age groups.

When inhaled, Halothane is absorbed through the alveoli into the bloodstream and distributed throughout the body, primarily targeting the brain. It produces a progressive and reversible depression of the central nervous system, starting from the higher brain centers (cerebral cortex) and extending to vital centers in the medulla. The exact mechanism of action remains unknown. Halothane has low blood solubility, allowing rapid equilibration between alveolar and blood concentrations. After discontinuation, its concentration declines in a triexponential manner, reflecting distribution into three compartments: vessel-rich organs (brain, heart, liver), muscle tissue, and adipose tissue.

Approximately 80% of inhaled Halothane is excreted unchanged via the lungs, while the remaining 20% undergoes hepatic metabolism through oxidative and reductive pathways. The primary metabolites include trifluoroacetic acid, bromide, chloride, and fluoride salts. These metabolites reach peak levels about 24 hours after surgery and are gradually eliminated through the kidneys over the following week.

A number of anaesthetic vaporisers specially designed for use with Halothane are available. Open, semi-open, semi-closed and closed circuit systems have all been used with good results.

For induction of anaesthesia:

• Adult: A concentration of 2–4% Halothane in Oxygen or Nitrous Oxide may be used.
• Children: A concentration of 1.5–2% Halothane in Oxygen or Nitrous Oxide is used.

For maintenance of anaesthesia:

• Adults and children: A concentration of 0.5–2% is usually required for maintenance of anaesthesia. The lower concentration is usually most suitable for elderly patients.

There is an increased risk of ventricular arrhythmias when Halothane is used with epinephrine. The risk of malignant hyperthermia may increase when combined with suxamethonium. Concurrent use with ketamine may prolong recovery from anesthesia. Halothane may enhance the effects of non-depolarizing muscle relaxants and hypotensive agents such as hexamethonium bromide and trimetaphan camsilate.

Halothane has the potential to cause liver injury, including severe hepatic damage such as jaundice and hepatic failure, although the exact incidence is unknown. The risk of liver toxicity may increase with repeated exposure. Even long intervals between exposures do not completely eliminate this risk.

Precautions before use include:

• A thorough anesthetic history should be taken to identify prior exposure and any adverse reactions to Halothane.
• Repeated administration within at least 3 months should be avoided unless absolutely necessary.
• Patients with a history of unexplained jaundice or fever following Halothane use should not receive it again unless essential.
• Patients should be informed about previous adverse reactions and may be advised to carry a medical alert card.

Common side effects include postoperative nausea, vomiting, shivering, respiratory depression, hypotension, muscle relaxation, and bradycardia.

Although animal data cannot be directly applied to humans, it is recommended to avoid inhalational general anesthetics during early pregnancy unless necessary. There are no well-controlled studies in breastfeeding women. Halothane has been detected in breast milk, but its effects on infants are not clearly established

Caution is required when administering adrenaline to patients under Halothane anesthesia, as it may trigger cardiac arrhythmias. Therefore, the dose of adrenaline should be limited, and beta-blockers may be used if needed. Proper ventilation of the operating area must be ensured, and the concentration of Halothane in the air should be kept as low as possible.

Effect on ability to drive or operate machinery: Patients should be advised that their ability to perform skilled activities, such as driving or operating machinery, may be impaired for a period following general anesthesia.

Accidental ingestion: If accidentally ingested, treatment should be symptomatic and supportive. Since Halothane causes relaxation of uterine muscles, it is recommended to maintain the lightest possible level of anesthesia during obstetric procedures. In neurosurgical procedures, moderate hyperventilation is advised to help reduce increases in cerebrospinal fluid pressure that may occur with Halothane. Malignant hyperthermia has been reported in some patients receiving Halothane; this condition may respond to intravenous dantrolene sodium.

During induction of anesthesia with Halothane, a moderate decrease in blood pressure is commonly observed. Blood pressure may rise when the concentration is reduced to maintenance levels but generally remains below preoperative values. This hypotensive effect can be beneficial by reducing bleeding and providing a clearer surgical field. However, if necessary, intravenous methoxamine (usually 5 mg) may be administered to correct hypotension.

Cardiac arrhythmias may occur during anesthesia. Halothane enhances the effects of non-depolarizing muscle relaxants. Caution must again be exercised when using adrenaline due to the risk of arrhythmias. Adequate ventilation should always be maintained, and environmental exposure minimized.

General inhalational anesthetic

Halothane should be stored in tightly closed containers in a cool, dry place away from light. It should remain in its original container until use. In liquid form, it should not be diluted or contaminated, but in vapor form, it may be administered with oxygen or nitrous oxide mixtures.