Intrapulmonary and extrapulmonary shunt in ducks

We measured shunt in seven anesthetized, mechanically ventilated Pekin ducks by the multiple inert gas elimination technique (MIGET) and by the oxygen method during 100% O2 breathing (O2 shunt). MIGET shunt measures only intrapulmonary shunt but O2 shunt measures intra- and extrapulmonary shunt (e.g. bronchial drainage). O2 shunt was calculated from oxygen contents of blood estimated from measured PO2 and standard O2 equilibrium curves at appropriate pH and hematocrit measured in 4 other ducks. In normal lungs MIGET shunt was 1.3 +/- 0.4 (mean +/- SEM) percent of cardiac output and O2 shunt was 6.3 +/- 1.3%. O2 shunt exceeded MIGET shunt by 5.4 +/- 1.4% which we attribute to extrapulmonary shunts. These include part of the bronchial circulation, thebesian veins and vertebral venous-pulmonary circulation connections. Both MIGET and O2 shunts increased when water was introduced into lungs. Overall, the relationship between % MIGET shunt and % O2 shunt was described by the equation: O2 shunt = 0.86 X MIGET + 5.67 (r = 0.96, n = 24).