The production of laryngospasm in the cat by volatile anaesthetic agents.

Laryngospasm and apnoea or alterations in the rhythm of respiration have been produced in decerebrate preparations of cats and in cats anaesthetized with chloralose during the start of inhalation of volatile anaesthetic agents. Ether, halothane and methoxyflurane all produced these effects when they were placed in contact with the larynx. The responses to ether occurred more rapidly than those to halothane, which in turn had a faster effect than methoxyflurane. In the concentrations used, ether vapour (10-20 per cent) and halothane vapour (6-8 per cent) stimulated laryngospasm and apnoea when administered through either the nasopharynx and larynx, the mid-cervical trachea or the distal trachea and lungs. Methoxyflurane (2.9 per cent) did not have these actions in the trachea and lungs. The responses obtained were detected in the absence of the continuity of the olfactory pathway, due to decerebration in which no loss of trigeminal afferents was occasioned. The importance of nasal, laryngeal, pharyngeal, tracheal and pulmonary stimulation in the production of laryngospasm and apnoea caused by inhaling; anaesthetic vapours has been demonstrated.