A halothane surge phenomenon during paediatric mask induction using the Tec 4 vaporizer in the Ohmeda Modulus II Plus Anaesthesia System

A prospective study of 30 paediatric patients who received a halothane inhalational induction revealed that in all 30 a brief halothane surge, i.e. an anaesthetic gas concentration greater than dialled on the vaporizer, occurred with the opening of the Tec 4 vaporizer (Ohmeda Tec 4 continuous flow vaporizer, Fluothane) dial setting to 0.25%. The surges were of brief (< 30 s) duration but ranged up to peak concentrations of 3% with a mean of 1.7% (± 0.8 SD). Measurements were made on the Ohmeda RGM 5250 respiratory gas monitor. While two of the children were crying throughout the induction and were not included in the totals, 11 (39%) of the remaining children were noted to withdraw from the mask when halothane was begun despite the use of sweet-flavoured (e.g. strawberry) scent application. Although no physiologic parameters were changed as a result, the effect on parents present during induction and the alteration of a calm, pleasant induction into one with a crying, uncooperative child make this factor pertinent to the paediatric anaesthetist.