Sympathetic response during cardiopulmonary bypass: Mild versus moderate hypothermia

Objective: To determine the sympathetic response during cardiopulmonary bypass at mild (34°C) and moderate (28°C) hypothermia. Design: A randomized study. Setting: Tertiary university hospital. Patients: Adults undergoing elective coronary artery bypass grab surgery. Interventions: None. Measurements and Main Results: Plasma norepinephrine, epinephrine, and neuropeptide Y concentrations were measured. Moderate, but not mild, hypothermic cardiopulmonary bypass evoked a significant sympathetic response with increases in plasma norepinephrine and neuropeptide Y concentrations. A significantly higher incidence of postoperative atrial fibrillation was also observed in the moderate hypothermic compared with the mild hypothermic group. Conclusions: Our results indicate that the degree of hypothermia significantly influences the sympathetic response during cardiopulmonary bypass. The higher incidence of postoperative atrial fibrillation in the moderate hypothermic group suggests that the enhanced sympathetic response might be one contributing factor in the development of atrial fibrillation.