Static compliance of the respiratory system (Crs) was measured by the interrupter technique in 18 anesthetized children to compare the effects of
ketamine on Crs with those of
halothane. Crs was the slope of the pressure-volume (P-V) curve obtained by repeated brief airway occlusions throughout relaxed expiration, and the intercept of the P-V curve on the pressure axis was the intrinsic positive end-expiratory airway pressure (PEEPi). Expiratory time (Te) was measured during a period of quiet breathing, and the passive expiratory time constant (tau) was measured during the relaxed expiration after an end-inspiratory occlusion. Nine children were anesthetized with a continuous infusion of
ketamine and a matching group of nine children inhaled
halothane in
oxygen. Crs was significantly greater in the
ketamine group (22.8 +/- 6.2 ml/cm H2O) than in the
halothane group (15.7 +/- 5.5 ml/cm H2O). The tau value was also significantly greater in the
ketamine group. Mean PEEPi in the
ketamine group was 2.3 +/- 1.8 cm H2O and in the
halothane group was 0.4 +/- 0.8 cm H2O. PEEPi correlated inversely with Te/tau according to a logarithmic function. It was concluded that, in children anesthetized with
ketamine, Crs is significantly greater than that in children anesthetized with
halothane, and the resultant prolongation of tau and decreased Te/tau with
ketamine anesthesia lead to increased PEEPi.