The effect of humidification and smoking habit on the incidence of adverse airway events during deepening of anaesthesia with desflurane

The effect of two levels of humidification on the incidence of adverse airway events was studied in 58 adult female patients during deepening of anaesthesia using up to 12% desflurane. Humidification was provided by a breathing system filter with either low moisture-conserving performance (17.2 mg x l(-1) at 0.5 1 tidal volume, Group L) or high moisture-conserving performance (33.5 mg x l(-1) at 0.5 1 tidal volume, Group H). Forty-eight per cent of patients smoked and there were more smokers in Group L than in Group H. Adverse airway events consisted of coughing and laryngospasm. For coughing, the dominant explanator was smoking. When both humidity and age were included in the analysis, there was a significant smoking-humidity interaction (p < 0.05), such that high humidity decreased the incidence of coughing in nonsmokers but not in smokers. The incidence of laryngospasm was significantly lower in Group H than in Group L (p < 0.05). We conclude that when patients inspire high concentrations of desflurane during induction of anaesthesia, increasing humidification to the levels achieved in this study decreases the incidence of coughing among nonsmokers and of laryngospasm in both smokers and nonsmokers.