Isoflurane waste gas exposure during general anaesthesia: the laryngeal mask compared with tracheal intubation

We have compared exposure to isoflurane while using the laryngeal maskairway (LMA) during anaesthesia under positive pressure ventilation withexposure while using tracheal intubation. Trace concentrations ofisoflurane were measured directly using a highly sensitive photoacousticinfrared spectrometer (Bruel and Kjaer 1302, Denmark) during generalanaesthesia in 20 eye surgery procedures. Measurements were made at sixlocations (three personnel-related, three leakage- related) in theoperating theatre. Despite some high isoflurane values (greater than 2000ppm at one leakage-related measurement point) all measured values at thepersonnel-related points were low (the majority were less than isoflurane 2ppm). In the LMA group, mean trace concentrations were slightly higher thanin the tracheal tube (ET) group. Mean exposure to isoflurane, expressed asmedian (range) related to anaesthetic administration, was highest for theauxiliary nurse (0.64 (0.22-26.89) ppm for the LMA compared with 0.31(0.02-1.07) ppm for the tracheal tube), followed by the anaesthetist (0.50(0.28-2.28) ppm for the LMA compared with 0.35 (0.02-0.73) ppm for thetracheal tube) and the surgeon (0.36 (0.20-3.93) ppm for the LMA comparedwith 0.29 (0.01-0.50) ppm for the tracheal tube). We conclude that the useof the LMA in patients undergoing ventilation is not associated necessarilywith high concentrations of isoflurane in a modern working environment.