Anaesthetic gas analysers: potential for confusion and errors if you live and work at moderate altitude

Abstract

In this issue of the SAJAA, Smith et al report on the effects of various end-tidal concentrations of nitrous oxide on the processed electroencephalogram (EEG) in the presence of approximately 1 MAC of sevoflurane. At low concentrations (10–60%), nitrous oxide had minor effects on ‘state entropy’ as measured by the M-entropy S/5 Module (GE Healthcare). However, at 70% there were statistically significant and clinically important decreases in entropy. Whereas previous studies have shown that nitrous oxide when given alone has few if any effects on EEG entropy, when administered with 1 MAC volatile anaesthetic agent, there is a threshold at which the effects of the volatile agent are potentiated by nitrous oxide. These findings are in accordance with other reports concerning studies of the clinical effects of combinations of nitrous oxide and oxygen.