WHO Model Prescribing Information: Drugs Used in Anaesthesia
(1989; 60 pages) [French] View the PDF document
Table of Contents
View the documentPreface
View the documentIntroduction
Open this folder and view contentsPremedication
Close this folderGeneral anaesthetics and oxygen
View the documentKetamine
View the documentThiopental
View the documentEther
View the documentHalothane
View the documentTrichloroethylene
View the documentNitrous oxide
View the documentOxygen
Open this folder and view contentsLocal anaesthetics
Open this folder and view contentsNon-opioid analgesics
Open this folder and view contentsOpioid analgesics and antagonists
Open this folder and view contentsMuscle relaxants and cholinesterase inhibitors
Open this folder and view contentsBlood substitutes
Open this folder and view contentsSolutions for correcting water and electrolyte imbalance
Open this folder and view contentsAntacid for use in obstetric practice
View the documentAnaesthesia at the District Hospital
View the documentSelected WHO publications of related interest
View the documentBack cover
 

Halothane

Group: volatile inhalational anaesthetic agent

General information

Halothane is a colourless, volatile, non-irritant liquid with a sweet odour. It is neither flammable nor explosive. In anaesthetic dosage it depresses both cerebral function and sympathetic activity and produces little, if any, preliminary excitement.

Advantages

Halothane is a potent non-flammable inhalational anaesthetic. Induction is smooth and rapid and surgical anaesthesia can be produced in 2-5 minutes. It does not augment salivary or bronchial secretions and coughing is less readily provoked than with ether. The recovery time is rapid and the incidence of postoperative nausea and vomiting is low. It does not react with soda lime and can be used in a closed-circuit system.

Disadvantages

Severe hepatitis, which may be fatal, is a recognized complication of halothane anaesthesia with an incidence of 1:50 000. It is more likely to occur in patients who are repeatedly anaesthetized with halothane within a short period.

Little margin exists between the doses needed to produce respiratory and vasomotor depression. Because of its cardio-depressant effect halothane is usually combined with another inhalational agent, such as nitrous oxide or trichloroethylene, to produce surgical anaesthesia. Muscle relaxants are additionally required to prepare the patient for abdominal surgery.

Although it suppresses endogenous sympathetic activity halothane sensitizes the heart to the dysrhythmic effects of catecholamines.

Clinical information

Uses

Induction and maintenance of anaesthesia for all types of surgery.

Dosage and administration

Method of administration

Halothane should always be administered using a specially calibrated vaporizer. Vaporizers should be drained at regular intervals and any discoloured halothane discarded.

If draw-over machines or inhalers are used, supplementary oxygen or assisted ventilation may be necessary to maintain full oxygenation, even when air is used as the carrier gas.

Halothane is not suitable for “open drop” anaesthesia, although a few drops applied to a face mask may smooth the subsequent administration of ether.

Induction

A flow of gas containing at least 30% oxygen should be maintained. Halothane should be introduced gradually and the concentration increased every few breaths until the inspired gases contain 2-3% halothane (for adults) or 1.5-2% (for children).

Maintenance

Concentrations of 0.5-1.5% are usually adequate for adults and children.

Recovery

Recovery time is relatively fast but it varies with the concentrations used and the period of administration. Shivering is common during recovery but it is readily controlled by covering the patient with a warm blanket and, if this is insufficient, by administering chlorpromazine (10 mg i.m.). When it is available, oxygen should be given.

Contraindications

• A history of unexplained jaundice following previous exposure to halothane.
• A family history of malignant hyperthermia.
• Raised cerebrospinal fluid pressure.

Precautions

The patient’s anaesthetic history should be carefully taken to determine previous exposure and previous reactions to halothane.

At least 3 months should be allowed to elapse between each re-exposure to halothane. Repeated and frequent administration increases the risk of liver damage.

Premedication with atropine reduces the risk of hypotension and bradycardia. Nevertheless, the pulse and blood pressure must be monitored throughout anaesthesia and the inspired concentration of halothane reduced should hypotension develop. Halothane should be withdrawn if the patient’s condition gives rise to concern.

Use of epinephrine increases the risk of ventricular dysrhythmias. It should be used only by a specialist anaesthetist and if the following precautions are taken:

• The total dose should not exceed 20 ml of a 5 micrograms/ml (1:200 000) solution in 10 minutes or 30 ml in 1 hour. Higher concentrations should not be employed.

• Ventilation should be adjusted to avoid any risk of hypoxia or hypercapnia.

Use in pregnancy

Halothane should be used during pregnancy only when the need outweighs any possible risk to the fetus.

Low concentrations (no more than 0.5%) should be employed in operative delivery to avoid loss of uterine tone and excessive postpartum haemorrhage.

Adverse effects

Cardiac dysrhythmias maybe induced, in particular atrioventricular dissociation, nodal rhythm and ventricular extra-systoles.

Hepatic damage occurs in a small proportion of exposed patients. Typically fever develops 2 or 3 days after anaesthesia accompanied by anorexia, nausea and vomiting. In more severe cases this is followed by transient jaundice or, very rarely, fatal hepatic necrosis.

Drug interactions

Halothane potentiates the response to:

• hypotensive agents, including hexamethonium bromide and trimetaphan camsilate
• non-depolarizing muscle relaxants.

Recovery from anaesthesia may be prolonged when ketamine is used for induction.

Concurrent use of suxamethonium may increase the risk of malignant hyperthermia.

Overdosage

Death due to overdosage results from cardiovascular depression. No specific antidote exists.

Storage

Halothane should be stored in tightly closed amber-glass containers protected from light, below 25°C. Thymol is added as a stabilizing agent to commercially produced supplies at a concentration of 100 micrograms/ml.

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