Upper airway reflex sensitivity following general anaesthesia for day-case surgery

We have studied changes in upper airway reflex sensitivity following general anaesthesia using dilute ammonia vapour as a chemical stimulant in 16 patients undergoing elective laparoscopic gynaecological surgery. We measured the threshold concentration of ammonia vapour required to elicit a transient reduction of inspiratory flow caused by glottic closure, defined as a glottic stop. Measurements of upper airway reflex sensitivity and auditory reaction time were obtained before surgery, and at 60 and 120 min after recovery. Auditory reaction time was depressed significantly at 60 min but was similar to baseline values 120 min after recovery. Upper airway reflex sensitivity remained significantly reduced at 60 and 120 min despite the return of auditory reaction time to normal. The lack of correlation between upper airway reflex sensitivity and auditory reaction time suggests that central nervous system depression alone does not explain the delayed recovery in airway reactivity.