Low systemic vascular resistance state in patients undergoing cardiopulmonary bypass

Objective: To determine the prevalence, hemodynamic characteristics, and risk factors for the low systemic vascular resistance (SVR) state in patients who have undergone cardiopulmonary bypass. Design: Prospective cohort study. Setting: The intensive care unit of a tertiary care hospital. Patients: Seventy-nine consecutive patients who underwent coronary artery bypass graft, mitral valve, or aortic valve procedures. Interventions: None. Measurements and Main Results: Low SVR was defined as an indexed systemic vascular resistance (SVRi) of <1800 dyne.sec/cm(5).m(2) at two consecutive times postoperatively. SVRi, cardiac index, mean arterial pressure, temperature, and central venous pressure were recorded before bypass and at 0, 1, 2, 4, 8, and 16 hrs after bypass. We recorded age, gender, urgency of operation, use of angiotensin-converting enzyme inhibitors and calcium channel blockers, ejection fraction, pump time, cross-clamp time, use of antifibrinolytics, type of oxygenator, amrinone rise, postoperative biochemical and hematologic values, medication use, fluid balance, intensive care unit admission duration, and hospital admission duration. We assessed the role of diabetes mellitus, current smoking, and systemic hypertension. The incidence of the low-SVR state was 35 of 79 patients during a 3-month period (44%). At 8 hrs postoperatively, the SVR, in low-SVR and non-low-SVR patients was 1594 +/- 50 (SEM) and 2103 +/- 56 (SEM) dyne.sec/cm(5).m(2), respectively (p < .001). In low-SVR patients, there was an initial and sustained increase in cardiac index and central venous pressure that preceded the decrease in mean arterial pressure. The decrease in mean arterial pressure was maximal at 8 hrs postoperatively. patients with low SVR were more likely to have longer cross-clamp times, to be male, and to have lower postoperative platelet counts (p < .05 for all). Low-SVR patients were less likely to require dobutamine in the first 4 hrs postoperatively. Conclusions: Low SVR, a probable manifestation of systemic inflammatory response syndrome, is common in patients after cardiopulmonary bypass. These patients may respond better to a vasopressor to restore vascular tone than to volume loading to further increase cardiac index.