Hemodynamic status susceptible to slowing of heart rate during thermodilution cardiac output determination in anesthetized patients

To identify hemodynamic variables that might indicate susceptibility to slowing of heart rate (HR) and to mean arterial pressure (MAP) decrease caused by cold injectate during thermodilution (TD) cardiac output determination, we measured hemodynamic variables in 32 anesthetized patients undergoing major surgery. A total of 608 cardiac output determinations were evaluated for any relationship between the magnitude of HR decreases and basal hemodynamic variables. The magnitude of HR decrease was pronounced in low cardiac index (CI), low mean pulmonary artery pressure (MPAP), and high systemic vascular resistance index (SVRI). Although there was some decrease in MAP associated with cold injectate, neither changes in SVRI nor those in the other hemodynamic variables correlated with the decreases in MAP. These results suggest that decreased CI and MPAP associated with elevated SVRI may be more susceptible to slowing of HR during cardiac output determination by TD in anesthetized patients.