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

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 15degreesC, 25degreesC, or 34degreesC on cardiopulmonary bypass with hernatocrit 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 34degreesC than at 15degreesC 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 34degreesC (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.