Pulmonary arteriovenous shunts during halothane anesthesia in dogs

The fraction of cardiac output flowing through pulmonary arteriovenous anastomoses (Qav/Qt) was measured in dogs during halothane anesthesia and compared with results obtained in normal awake dogs. Flow through arteriovenous anastomoses was measured using 99mTc-labelled polystyrene microspheres (50 microns diameter). The fraction of cardiac output perfusing pulmonary arteriovenous anastomoses during halothane anaesthesia was 4.1% (+/- SD 1.75) compared with 4.6% (+/- SD 0.73) in air-breathing awake control dogs. In spite of variations in arteriovenous shunt fraction, no significant relationship between the Qav/Qt and Qs/Qt was detected. These results suggest that pulmonary arteriovenous anastomases do not contribute significantly to the physiological shunt observed during halothane anaesthesia.