Does correction of acidosis influence microcirculatory blood flow during cardiopulmonary bypass?

We studied 15 patients undergoing cardiopulmonary bypass (CPB) to examine the effect of response to correction of acidosis on microcirculatory blood flow. Acidosis was defined when base excess was less than -10.0 mmol litre-1 while carbon dioxide partial pressure was within the normal range. CPB was carried out at almost normothermic temperature (smallest rectal temperature 35.2 (SD) 0.4 degrees C). Sodium bicarbonate (NaHCO3) was given to correct acidosis during steady state CPB. Skin microcirculatory blood flow was assessed using a double-channel laser Doppler flow (LDF) monitor. LDF was measured on the patient's forehead and forearm before infusion of NaHCO3 (baseline) and 30 s, 1, 3, 5, 7, 10 and 15 min later. Skin, blood, rectal and nasopharyngeal temperatures did not change during the investigation. Plasma viscosity, haemoglobin and carbon dioxide partial pressure also remained unchanged. Mean arterial pressure (MAP) and systemic vascular resistance (SVR) decreased slightly after infusion of NaHCO3 (MAP -29%; SVR -32%). A total of NaHCO3 99.4 (4.4) mmol litre-1 was given for correction of acidosis. pH and HCO3- were within the normal range shortly after the infusion of NaHCO3. LDF measured on both the forehead (+49%) and the forearm (+29%) increased significantly after infusion of NaHCO3. Changes in pH correlated positively with changes in LDF (analyses of co-variance, P < 0.02), but haemodynamic and other laboratory values did not correlate with LDF. We conclude that the microcirculatory response to correction of acidosis with NaHCO3 during CPB can be monitored using skin laser Doppler flowmetry. Infusion of NaHCO3 resulted in a significant improvement in skin microcirculatory perfusion.