Higher bypass temperature correlates with increased white cell activation in the cerebral microcirculation

Abstract

Objective Cardiopulmonary bypass induces a systemic inflammatory response, which in turn promotes a cascade of leukocyte and endothelial cell activity. We investigated whether differences in bypass temperature and flow rate affect endothelial cell and leukocyte adhesion in the cerebral microcirculation. Methods Thirty-six piglets (13.0 ± 1.1 kg) had a cranial window placed over the parietal cortex to evaluate the microcirculation by means of intravital microscopy. Animals were cooled to a temperature of 15°C, 25°C, or 34°C on cardiopulmonary bypass with hematocrit levels of 20% or 30% by using pH-stat management, followed by 60 minutes of reduced flow (10, 25, or 50 mL · kg −1 · min −1). Rhodamine staining was used to observe adherent and rolling leukocytes in postcapillary venules. Results Higher bypass temperature correlated with significantly more adherent and rolling leukocytes during the full 60 minutes of low-flow bypass ( P < .05). Poisson regression revealed more adherent leukocytes at 34°C than at 15°C and at a flow rate of 10 mL · kg −1 · min −1 compared with a flow rate of 50 mL · kg −1 · min −1. There was an inverse correlation between flow rate and the number of adherent and rolling leukocytes at 30, 45, and 60 minutes of low-flow bypass ( P < .05). Temperature was a multivariable predictor of histologic score, with greater neurologic damage found after bypass at 34°C ( P < .01). Conclusions Leukocyte activation in cerebral microcirculation is increased with higher temperature and lower flow rate, suggesting that these variables influence the inflammatory response during cardiopulmonary bypass.