Inhalational agents

These are volatile liquids which readily vaporise, permitting administration by inhalation in oxygen-enriched air or an O2/N2O mix.They help maintain anaesthesia and decrease awareness (by an unclear mechanism).

Halothane

A colourless, pleasant-smelling gas (which, unlike the other agents, is not an ether). First used as an anaesthetic in the 1950s. It has little analgesic effect, but decreases cardiac output (vagal tone increased, leading to bradycardia, vasodilation, hypotension. It sensitises the myocardium to catecholamines (beware in patients with arrhythmias and in surgical infiltration with local anaesthetic and adrenaline). Halothane has now been replaced by safer inhalational agents due to the rare but serious complication of post-op hepatitis (uo to 1 in 4,000 for multiple exposures).

Isoflurane

A halogenated ether. Theoretically induction should be quick, but isoflurane is irritant, so coughing, laryngospasm, or breath-holding may complicate the onset of anaesthesia.

Sevoflurane

Well-tolerated halogenated ether. Agent of choice for inhalation induction of general anaesthesia with low blood:gas solubility.

Desflurane

Another halogenated ether with a pungent smell, rapid onset of anaesthesia and quick recovery.

All can cause malignant hyperthermia.