A heated humidifier does not reduce laryngopharyngeal complaints after brief laryngeal mask anesthesia

Warming and humidification of inspired gases is standard care for intubated patients whose lungs are ventilated mechanically for prolonged periods. We examined whether active humidification of inspired gases might reduce laryngopharyngeal discomfort in patients undergoing brief laryngeal mask airway (LMA) anesthesia. In a prospective trial, 200 adult patients undergoing elective surgery under general anesthesia were randomly assigned to receive ventilation without airway warming and exogenous humidification (Group C - control), or active warming and humidification of inspired gases (Group HUM - humidified), using a humidifier with a heated wire circuit. Inhalational anesthesia was maintained via a circle system. The temperatures and relative humidities of inspired gases were monitored continuously throughout surgery. Postoperative sore throat, dysphonia, and dysphagia were assessed one and 24 hr after anesthesia. Whenever symptoms were present, their severities were graded using a 101-point numerical rating scale. The mean temperature and relative humidity of the inspired gases in Group HUM were greater compared to Group C (36.1 ± 0.4°C and 99.5 ± 0.5%vs 26.9 ± 0.8°C and 76.4 ±10.9%, respectively). Postoperatively, the overall frequencies of laryngeal and pharyngeal discomfort were similar in the two groups (53.8% and 54.9% in Group Cvs 51.6% and 41.9% in Group HUM at one and 24 hr respectively,P > 0.05). The groups were also similar with respect to the severity scores of laryngo-pharyngeal discomfort. Active warming and humidification of inspired gases has no clinically appreciable effect in reducing the incidence and severity of laryngo-pharyngeal complaints after brief (< two hours) LMA anesthesia.[PUBLICATION ABSTRACT]