Halothane anaesthesia with spontaneous respiration for tonsillectomy in children.

Bains's anaesthetic circuit was used in 22 children undergoing tonsillectomy under halothane anaesthesia with spontaneous respiration. End-tidal CO2 was monitored by capnography. The median maximum end-tidal CO2 was 7%, and during surgery nine patients had an end-tidal CO2 higher than 7%, corresponding to a Paco2 close to 8 kPa when the arterial to end-tidal CO2 difference is taken into consideration. Increase in fresh gas flow or change to a non-rebreathing system had virtually no effect on end-tidal CO2. However, following discontinuation of halothane or during controlled respiration, acceptable values of end-tidal CO2 were reached, leading to the conclusion that respiratory depression was responsible for the high values of end-tidal CO2 rather than properties of Bain's circuit or too low gas flow rates.