CARDIOPULMONARY BYPASS AND FOREARM BLOOD-FLOW

Study objective: To assess the effect of cardiopulmonary bypass (CPB) on muscle blood now (MBF) when measured in the forearm by venous occlusion plethysmography. Design: This was a prospective study. Setting: Operating room area of a tertiary care university medical center. Participants: Twenty-seven patients (25 men and 2 women), aged 62 +/- 1.5 years, undergoing elective coronary bypass grafting. Interventions: Measurements were made during the surgical procedure: before, during cold and warm, and after discontinuation of CPB. Measurements and results: Changes in forearm blood now (FBF), derived forearm vascular resistance (FVR), mean arterial pressure (MAP), and cardiac output (CO) were evaluated by repeated measures analysis of variance. The control FBF (measured before CPB) was found to be approximately 50 percent lower than that previously reported for awake volunteers and patients. The FVR was similarly higher. From these low values, the FBF increased significantly (p<0.001) during normothermic bypass and after CPB. Forearm vascular resistance decreased significantly (p<0.001) throughout the cold, warm, and postbypass periods. Only during the warm and the postbypass periods did FBF and FVR reach normal values. Mean arterial pressure decreased significantly (p<0.01) throughout. There was no statistically significant association between any of the variables and FBF or FVR. After correcting for patient and surgical phase variability, only MAP had a statistically significant effect (p=0.042) on FVR; blood temperature, skin temperature, hematocrit level, PaCO2, serum potassium, and systemic vascular resistance (SVR) had no effect on either FBF or FVR when tested singly or in combination. When correction for multiple comparisons was applied, the lowest probability value became greater than 0.25. There was no correlation between combinations of covariates and FBF or FVR after adjustments for the surgical phase of the study either. Conclusion: These findings indicate that the increase in MBF seen during warm and the post-CPB periods is only a recovery toward normal blood flow. The role of this change in the low SVR that usually accompanies CPB is equivocal.