Distinct Alterations in Sublingual Microcirculatory Blood Flow and Hemoglobin Oxygenation in On-Pump and Off-Pump Coronary Artery Bypass Graft Surgery

Objective: The authors hypothesized that cardiopulmonary bypass (CPB) (on-pump) is associated with more severe changes in the microcirculatory blood flow and tissue oxygenation as compared with off-pump coronary artery bypass surgery. Design: An observational study. Setting: A university hospital and teaching hospital. Participants: Patients undergoing on-pump (n = 24) or off-pump (n = 24) cardiac surgery. Interventions: Microcirculatory measurements were performed before CPB and 10 minutes after the switch to CPB or before and during cardiac luxation in off-pump patients. Measurements and Main Results: Sublingual microcirculatory perfusion was investigated using side-stream dark field imaging, and sublingual microcirculatory oxygenation was measured using reflectance spectrophotometry. Conversion to CPB resulted in an increase in cardiac output from 4.0 +/- 0.2 to 4.8 +/- 0.3 L/min (p < 0.01) and a 40% reduction in arterial hemoglobin concentration. Cardiopulmonary bypass was associated with an increase in venular blood velocity from 349 +/- 201 mu m/s to 563 +/- 227 mu m/s (p < 0.05), a reduction in functional capillary density of 43%, and an increase in hemoglobin oxygenation of the red blood cells in the remaining filled capillaries from 47.2% +/- 6.1% to 59.7% +/- 5.2% (p < 0.001). The decrease in cardiac output during cardiac luxation from 4.5 +/- 1.7 to 1.8 +/- 0.8 L/min (p < 0.01) without hemoglobin changes was associated with a complete halt of capillary blood flow and a reduction in maximum capillary blood velocity from 895 +/- 209 to 396 +/- 178 mu m/s (p < 0.01). The functional capillary density remained unchanged, whereas the hemoglobin oxygenation declined from 64.2% +/- 9.1% to 48.6% +/- 8.7% (p < 0.01). Conclusions: On-pump and off-pump cardiac surgery are associated with distinct alterations in sublingual microcirculatory perfusion and hemoglobin oxygenation. Although on-pump surgery results in a fall out of capillaries resulting in decreased oxygen extraction, off-pump surgery results in a cessation of flow during luxation resulting in decreased convection of oxygen transport. (C) 2011 Elsevier Inc. All rights reserved.