Effects of aortic occlusion in heparinized and non-heparinized pigs.

The aorta and common iliac arteries were clamped for 2 hours in 27 pigs under general anaesthesia. Ten pigs were heparinized and the other 17 did not receive heparin. A further 5 pigs were used as sham-operated non-heparinized controls. Blood gases and also mean arterial, pulmonary arterial, pulmonary capillary wedge and left atrial pressures were recorded before, during, and after clamping. In the non-heparinized pigs there was a significant increase in pulmonary capillary wedge pressure during and after clamping of the aorta, slight variations in the left atrial pressure (measured in 5 non-heparinized pigs) and a decrease in PaO2, which was especially pronounced after declamping of the aorta. No such changes occurred in heparinized or control animals. The discrepant results in heparinized and non-heparinized animals indicate a mechanism influenced by heparin. Clamping and declamping of the aorta obviously accelerated the changes in the non-heparinized animals. It is suggested that these changes are caused by pulmonary embolism induced by the clamping and declamping of the aorta. Alterations in the pulmonary circulation indicated that the mean pulmonary capillary wedge pressure is not a reliable indicator of left ventricular filling pressure during aortic surgery.