Fig. 1. Typical changes in the end-tidal carbon dioxide (ETco²) waveform resulting from a pinhole in the sampling line, made with a 23-gauge needle. A capnography monitor (BP508, sidestream type; Nippon Colin Co., Komaki, Japan) was used, and gases were sampled by the capnometer at a rate of 200 ml/min. A pinhole made with a 23-gauge needle decreased ETco²from 35 mmHg to 24 mmHg; when we enlarged the pinhole with an 18-gauge needle, ETco²decreased from 24 mmHg to 14 mmHg.