PULMONARY ARTERIOVENOUS SHUNTS DURING HALOTHANE ANAESTHESIA IN DOGS*

The fraction of cardiac output flowing through pulmonary arteriovenousanastomoses (Q_av/Q_t) was measured in dogs during halothane anaesthesiaand compared with results obtained in normal awake dogs. Flowthrough arteriovenous anastomoses was measured using ^$$mTc-labelledpolystyrene microspheres (50 µm diameter). The fractionof cardiac output perfusing pulmonary arteriovenous anastomosesduring halothane anaesthesia was 4.1% (±SD 1.75) comparedwith 4.6% (±SD 0.73) in air-breathing awake control dogs.In spite of variations in arteriovenous shunt fraction, no significantrelationship between the Q_av/Q_t and Q_a/Q_t was detected. Theseresults suggest that pulmonary arteriovenous anastomoses donot contribute significantly to the physiological shunt observedduring halothane anaesthesia. ^*Presented at the American Society of Anesthesiologists AnnualMeeting, Chicago, Illinois, 1975.