Halothane is a time-tested Inhalational Anaesthetic and is the gold standard for cost-effective induction and maintenance of Anaesthesia.
Active ingredient Halothane BP 100% v/v.
Pharmaceutical form Halothane is a clear liquid for use in a vaporiser to produce an inhalation gas.
Contents by weight, volume or dosage unit
Halothane is supplied in 250 ml amber glass bottles.
Pharmacotherapeutic group General anaesthetic.
Halothane is a general anaesthetic used in inhalation anaesthesia. Use of halothane in paediatric anaesthesia should be restricted to hospitals only.
Children under 18 years undergoing dental procedures outside hospital.
History of unexplained jaundice or pyrexia after a previous exposure to halothane is an absolute contraindication to its future use in that patient.
Halothane is contraindicated in patients with known, or suspected, genetic predisposition to malignant hyperpyrexia.
Halothane can induce liver damage. Minor changes in serum amino-transferase activity have been reported to occur in up to 30% of patients.
The incidence of severe liver damage (jaundice which may lead to hepatic failure as a consequence of massive hepatic cell necrosis) is much rarer but cases requiring liver transplants and fatalities have been reported.
The risk of developing hepatic failure appears to be greatly increased by repeated exposure to halothane. Although short intervals of time between exposures are likely to increase the risk of hepatotoxicity, even long intervals between exposures may not reduce the risks, since some patients have developed severe reactions to halothane given many years after the previous exposure. Other risk factors for hepatotoxicity include female gender, obesity, middle age and a history of drug allergy. On the information presently available, the following precautions should be taken.
Use in children: Arrhythmias are very common in children anaesthetised with halothane.
Children anaesthetised with halothane should have ECG, blood pressure, O2 saturation and end tidal CO2 monitoring in a setting where full resuscitation equipment is available and with staff fully trained in the resuscitation of children. The presence of additional arrhythmogenic factors especially hypoxia and CO2 retention, use of sympathomimetics, and other factors which may stimulate the sympathetic nervous system should also be taken into account.
An increase in CSF and/or intracranial pressure might occur during neurosurgery, the effects of which may be mitigated by the use of moderate hyperventilation.
Halothane reduces uterine muscle tone during pregnancy and generally its use is not recommended in obstetrics because of the increased risk of postpartum haemorrhage. Halothane should be used with caution in patients with:
Use of inhaled anaesthetic agents has been associated with very rare increases in serum potassium levels that have resulted in cardiac arrhythmias and death in children during the postoperative period.
The condition has been described in patients with latent as well as overt neuromuscular disease, particularly Duchenne muscular dystrophy. Use of suxamethonium has been associated with most, but not all of these cases. These patients showed evidence of muscle damage with increased serum creatinine kinase concentration and myoglobinuria.
These patients did NOT have classical signs of malignant hyperthermia such as muscle rigidity, rapid increase in body temperature, or increased oxygen uptake and carbon dioxide production.
Prompt and vigorous treatment for hyperkalemia and arrhythmias is recommended. Subsequent evaluation for latent neuromuscular disease is indicated.
The incidence of cardiac arrhythmias may be increased when adrenaline (epinephrine) is used concurrently with halothane. The use of beta-adrenoceptor antagonists during halothane anaesthesia is at the discretion of the anaesthetist.
Muscle relaxants: All commonly used muscle relaxants may be used in conjunction with halothane, but, as halothane potentiates the actions of gallamine and d-tubocurarine, the doses of these muscle relaxants must be reduced. The association of d-tubocurarine with halothane may lead to a marked fall in blood pressure.
Ganglion blocking agents: Potentiation occurs between halothane and hypotensive agents such as pentolinium and trimetaphan. These drugs must be used in reduced dosage when administered in conjunction with halothane.
Halothane, along with all other general anaesthetics, may interact with aminoglyco-side antibiotics resulting in respiratory depression. This effect may be potentiated by the concurrent use of a neuromuscular blocker.
The concurrent use of suxamethonium with halothane is not advisable due to increased possibility of hyperpyrexia.
Pregnancy and lactation: Halothane reduces uterine muscle tone during pregnancy and generally its use is not recommended in obstetrics because of the increased risk of postpartum haemorrhage. There is no clear evidence in animals that halothane is safe in early pregnancy. Avoid, unless it is essential. Traces of halothane have been detected inbreast milk. Breast-feeding should be withheld for 24 hours after halothane anaesthesia.
Effects on ability to drive and use machinery: Patients should not drive or operate machinery until fully recovered, i.e. for at least 24 hours after receiving Halothane Liquid.
Pre-medication: A small dose of pethidine with or without the addition of promethazine will produce satisfactory sedation in most patients and will reduce the tendency to tachypnoea. Atropine in an appropriate dose should be administered to all patients.
Induction:This is most conveniently carried out with a sleep dose of thiopentone sodium, to allow the application of a face mask. A gas flow of 8 litres/minute should be administered, of which at least 30% should be oxygen, and then halothane should slowly be introduced. Administration should start at 0.5% and can be increased by a further 0.5% every few breaths until the expired gases contain 3% halothane. Intubation can be carried out after five minutes inhalation of 3% halothane in a carrier gas flow of 8 litres/minute or before exposure to halothane if an intubating dose of suxamethonium is given. If intubation is performed before exposing the patient to halothane, the introduction of halothane must still be stepwise.
Maintenance: At a gas flow of 8 litres/ minute, halothane concentrations of between 0.5% and 1.5% are usually adequate. At a 2litres/minute gas flow with the vaporiser out of circuit (VOC) a concentration of 2.0 to 2.5% fed into the absorber circuit will suffice. A low resistance vaporiser may be placed within the circuit (VIC), but in this case controlled or assisted ventilation must not be used. A vaporiser for VIC use must not be capable of delivering a concentration greater than 3%.
Recovery: Recovery from anaesthesia is usually rapid and uneventful. If halothane is withdrawn as skin closure starts, reflexes will have returned by the time the dressings are in place. Shivering is occasionally seen during the recovery if there is a marked temperature difference between the theatre and the ward. This is readily controlled by the administration of a small dose of chlorpromazine, but supplementary oxygen may be required for a few minutes. Infants and children tend to require 30-50% higher concentrations than adults. Elderly patients tend to require less halothane than adults but the actual dose is dependent on the patient’s physical state.
Halothane is a potent anaesthetic and should, wherever possible, be administered via a specially calibrated and temperature-compensated vaporiser. A number of such vaporisers are now available. Halothane can also be administered from the ordinary bottle vaporiser of a Boyle’s machine, but the scale should be extended to allow fine adjustment in the concentration of halothane delivered. Open-drop anaesthesia with halothane is not generally recommended; however, a few drops carefully applied to the mask may smooth the subsequent administration of ether. Draw-over machines and inhalers can be satisfactorily used with halothane, but if air is the carrier gas, supplementary oxygen or assisted respira-tion may be necessary to maintain full oxygenation.
As with all inhalation agents, the area of use should have an effective fume extraction system. The vaporiser should be drained at regular intervals; any discoloured halothane should be discarded.
Overdosage is unlikely under normal circumstances. However, should it occur, halothane administration should cease immediately and the patient ventilated mechanically until blood gases return to an acceptable level. Cases of accidental ingestion should be treated symptomatically.
The following undesirable effects have been reported following the use of halothane. Cardiac arrhythmias are very common during halothane anaesthesia. Ventricular arrhythmias occur more frequently than with other volatile anaesthetics.
Hepatic necrosis, also known as “Halothane hepatitis” (see earlier section “Precautions for use”) occurs rarely but fatalities have been reported. Severe hepatotoxicity occurs more frequently after repeated exposure to halothane.
Eosinophilia has been reported in conjunction with halothane induced hepatotoxicity. Malignant hyperpyrexia has occasionally been reported with halothane, as with other halogenated anaesthetics.
As with other halogenated anaesthetics, halothane has a depressant effect on the respiratory and cardiovascular systems and the following undesirable effects have been reported:
If a patient has been given halothane in an emergency without a medical history being taken, this should be attended to post-operatively. The patient should be warned that if they have previously had general anaesthetics and particularly if they suffered a reaction, they might be more likely to become jaundiced after this emergency surgery. If jaundice develops in the near future, it might be due to the halothane anaesthetic and should be reported to a doctor immediately.
Do not use after the expiry date shown on the label of the bottle.
Special storage precautions
Store in a dark place below 25°C. Keep well closed.
Hasani A - Med Sci Monit - 01-JUN-2009; 15(6): CR302-6