Continuous monitoring of mixed venous oxygen saturation during aortic operations

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Abstract
Objective To systematically analyze the changes in mixed venous oxygen saturation (ASvo2) during aortic operations with tube, aortobi-iliac, and aortobifemoral grafts. Design Survey of consecutive patients. Setting Teaching community hospital. Patients Thirty-one patients (22 male, 9 female, mean age 67 ± 10 yrs), undergoing elective operations for aortic aneurysms (n = 25) and aortoiliac occlusive disease (n = 6). Interventions Svo2 was recorded throughout the operation. Cardiac output, mean pulmonary arterial pressure, arterial oxygen saturation (Sao2), and arterial pH were measured before and immediately after the unclamping of the aortic graft. Results In all patients, unclamping the aorta resulted in a marked reduction of mean Svo2, with no change in the cardiac output or Sao2. The unclamping of tube grafts was associated with a significant reduction in arterial pH (p <.01) and in Svo2 (p <.001), when compared with unclamping of bifurcation grafts. A significant (p <.05) increase in mean pulmonary arterial pressure was observed after unclamping the aorta in patients with tube grafts. Despite a longer clamp time, unclamping the second limb of a bifurcation graft resulted in a smaller ASvo2, when compared with that observed after unclamping the first limb (12% vs. 6%;p <.01). The DLSvo2 after unclamping limb II was only 2% in aortobifemoral grafts and 9% in aortobi-iliac grafts. Conclusions Reperfusion via extensive pelvic and lumbar collaterals in patients with aortoiliac occlusive disease reduces the DLSvo2 after aortic unclamping. Monitoring the changes in Svo2 during different types of aortic reconstruction helps to define precisely the physiologic alterations that occur in the course of these operations.

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