Hemodynamic and cardiometabolic effects of infrarenal aortic and common iliac artery declamping in man--an approach to optimal volume loading.

Nineteen patients undergoing abdominal aortic aneurysm surgery were randomly assigned to two groups and investigated to elucidate the mechanisms of declamping hypotension. The control group of nine patients was kept at an average mean pulmonary artery occlusion pressure (MPAOP) of 11 mmHg (1.46 kPa) before declamping. The other group was volume loaded to a MPAOP of 16 mmHg (2.13 kPa) shortly before declamping. Following declamping there was a significantly greater decrease in mean arterial pressure in the control group, with the same reduction of MPAOP in both groups. In parallel, cardiac and stroke volume indices decreased in the control patients, but remained unchanged in the volume-loaded patients. In the control group there was a reduction in myocardial substrate utilization which was not seen in the volume-loaded patients. No signs of myocardial ischemia could be demonstrated in any of the groups. The results indicate that mismatching between intravascular volume and blood volume is the main cause of infrarenal aortic or common iliac artery declamping hypotension. Volume loading before declamping to a slightly elevated MPAOP can effectively prevent hypotension, while a normal MPAOP does not guarantee a stable hemodynamic situation after declamping.