[Effect of changes in cardiac output on oxygenation and intrapulmonary short circuit (Qs/Qt) under inhalation anesthesia].

OBJECTIVES

To assess the relation between changes in pulmonary shunt and minute volume induced by blood loss, using an animal model with anesthetic maintenance by isoflurane CAM 1.

MATERIAL AND

METHODS

Eight dogs were given balanced anesthesia with pancuronium and isoflurane. Variables monitored were systemic and pulmonary arterial pressures, central venous and pulmonary capillary pressures and minute volume. Arterial and mixed venous blood gas measurements were taken from the pulmonary artery catheter, and blood samples were analyzed for hemoglobin in order to calculate pulmonary shunt (Qs/Qt). Two levels or stages of hypovolemia were studied: a) level I = loss of 20% blood volume and b) level II = loss of 30%.

RESULTS

A significant decrease of 35% (139 +/- 43 to 90 +/- 24 ml/min-1/kg-1; p < 0.001) in minute volume was observed at the first level of hypovolemia; a 52% (139 +/- 43 to 69 +/- 23 ml/min-1/kg-1; p < 0.001) decrease was found at the second. This decrease was accompanied by similar drops in Qs/Qt of 34% (18.2 +/- 5% to 12.1 +/- 5%; p < 0.01) and 47% (18.2 +/- 5% to 9.2 +/- 5%; p < 0.01) at the first and second levels, respectively. Linear regression analysis showed a direct relation between changes in Qs/Qt with changes in minute volume.

CONCLUSIONS

The data reported in this study indicate that changes in Qs/Qt are directly related to those of minute volume in the presence of isoflurane.