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 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.