Upper airway collapsibility in anesthetized children.

We sought to establish the feasibility of measuring upper airway narrowing in spontaneously breathing, anesthetized children using dynamic application of negative airway pressure. A secondary aim was to compare differences in upper airway collapsibility after the administration of sevoflurane or halothane. Subjects were randomized to either drug for inhaled anesthetic induction. Each was adjusted to their 1 MAC value (0.9% for halothane and 2.5% for sevoflurane) and a blinded anesthesia provider held the facemask without performing manual airway opening maneuvers but with inclusion of an oral airway device. Inspiratory flows were measured during partial upper airway obstruction created by an adjustable negative pressure-generating vacuum motor inserted into the anesthesia circuit. Critical closing pressure of the pharynx (Pcrit) was obtained by plotting the peak inspiratory flow of the obstructed breaths against the corresponding negative pressure in the facemask and extrapolating to zero airflow using linear correlation. Fourteen children were enrolled, seven in each anesthetic group. Two children in the halothane group did not develop flow-limited airway obstruction despite negative pressures as low as -9 cm H2O. Pcrit for sevoflurane ranged from -6.7 to -11.6 (mean +/- sd, -9.8 +/- 1.9) cm H2O. Pcrit for halothane ranged from -8.1 to -33 (mean +/- sd, -19.4 +/- 9.3) cm H2O (sevoflurane versus halothane, P = 0.048). We conclude that when using dynamic application of negative airway pressure, halothane appears to cause less upper airway obstruction than sevoflurane at equipotent concentrations.