Recovery after single‐breath halothane induction of anaesthesia in daycase patients

Abstract

Inhalational induction of anaesthesia in adults, which employs a single-breath technique' with halothane and oxygen. is faster than conventional techniques of inhalational induction, because it produces a more rapid rise in alveolar halothane concentration.z The addition of nitrous oxide to the mixture further reduces induction time, by decreasing the alveolar concentration of halothane required to induce anae~thesia.~ and by means of the second gas This technique is a safe and practicable alternative to intravenous induction in cooperative a d u k 6Thiopentone is almost completely metabolised by the liver: it has a long terminal half-lift' and is associatcd with a prolonged hangover effect. The avoidance of thiopentone may incrcase the speed of recovery from anaesthesia, which would be of particular benefit to daycase patients.8 We have used tests of psychomotor function to assess recovery from anaesthesia in unpremedicated daycase patients, and to compare single-breath halothane induction with thiopcntonc. MethodsForty patients who underwent check cystoscopy as day cases gave informed consent, and were admitted to the study, which was approved by the hospital ethics committee. All wcrc agcd between 18 65 years, and ASA grade 1 3. N o paticnts were included who had taken any psychotropic medication within 72 hours, or had had a ha1o:hane anaesthetic within the previous 3 months, or in whom an anaesthetic longer than 20 minutes was anticipated. All patients were unpremedicated, and werc allocatcd randomly to receive either single-breath halothane induction or thiopentone. Anaesthetics were conducted by two of us (J.G.L.S. and E.P.McK.). and psychomotor tests by one of us (J.J.N.), who was unaware of the anacsthctic tcchniquc employed.Each patient undertook four tests on admission to the ward. The critical flicker frequency (CFF) is an index of the effect of centrally acting depressants.g Choice reaction time (CRT)'O was recorded as the mean of 20 times. using a serial five-choice test. Digit span and letter deletion tests were also performed. Practice runs were performed with all tests to minimise learning effects. These tests were undertaken before and repeated 1. 2 and 4 hours after, operation.Monitoring was started in the anaesthetic room with : z continuously displayed electrocardiograph, and automatic oscillometric measurement of blood prcssurc (Dinamap) rccorded every 60 seconds. A 23-gauge cannula was inserted into a vein. Anaesthesia was induced either by single-breath