The effect of a right-to-left intracardiac shunt on the rate of rise of arterial and end-tidal halothane in children.

Abstract

In this prospective study, we evaluated the effect of a right-to-left intracardiac shunt on the rate of rise of end-tidal and arterial halothane concentration in children. Six children aged 23-43 mo undergoing surgical closure of atrial fenestration after Fontan procedure were given 0.8% inspired halothane. End-tidal halothane was recorded at 1-min intervals after the introduction of halothane. Arterial halothane concentrations were determined 0, 1, 3, 5, 10, and 15 min after the introduction of halothane. The sampling was performed before and after closure of the atrial fenestration. The ratio of pulmonary to systemic blood flow (Qp/Qs) increased in this patient population, from 0.58 +/- 0.04 to 0.88 +/- 0.12 (P = 0.01). The rate of rise of end-tidal halothane did not change significantly with a decrease in the magnitude of the right-to-left intracardiac shunt after closure of the atrial fenestration. The ratio of arterial to inspired halothane concentrations at 1, 3, 5, 10, and 15 min were lower before closure of the atrial fenestration compared with after closure (P < 0.05). We conclude that the presence of a right-to-left intracardiac shunt significantly slows the rate of rise of arterial halothane in the face of a constant inspired concentration. The rate of rise of end-tidal halothane is not significantly affected in the presence of a right-to-left intracardiac shunt. In this prospective study, we found a slower rate of rise of halothane in arterial blood in children with right-to-left intracardiac shunting. Induction of anesthesia by inhalation of volatile anesthetics may therefore be slower in these children.