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

Ln this prospective study, we evaluated the effect of a right-to-left intra cardiac shunt on the rate of rise of end-tidal and arterial halothane conce ntration in children. Six children aged 23-43 mo undergoing surgical closur e of atrial fenestration after Fontan procedure were given 0.8% inspired ha lothane. End-tidal halothane was recorded at 1-min intervals after the intr oduction 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 rati o of pulmonary to systemic blood flow (Qp/Qs) increased in this patient pop ulation, from 0.58 +/- 0.04 to 0.88 +/- 0.12 (P = 0.01). The rate of rise o f end-tidal halothane did not change significantly with a decrease in the m agnitude of the right-to-left intracardiac shunt after closure of the atria l fenestration. The ratio of arterial to inspired halothane concentrations at 1, 3, 5, 10, and 15 min were lower before closure of the atrial fenestra tion 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 p resence of a right-to-left intracardiac shunt. Implications: In this prospe ctive study, we found a slower rate of rise of halothane in arterial blood in children with Fight-to-left intracardiac shunting. Induction of anesthes ia by inhalation of volatile anesthetics may therefore be slower in these c hildren.