A subtle break, a cause for variable end-tidal gas analysis.

The patient was having a minor procedure undertaken under general anaesthetic and was self-ventilating via a laryngeal mask. Constant gas flows and volatile agent concentration were used and the patient’s minute ventilation remained constant. However, ETCO2 values, as measured by Hewlett Packard M1026A gas analyser (Hewlett Packard, Berkshire, UK), varied between 22 and 43 mmHg. Initially no cause for these discrepancies could be found but when the patient was manually ventilated with high flows an audible leak was heard. The location of this leak was initially difficult to find but on close inspection of the capnography tubing at the patient end a complete break was noted (Fig. 1).