Comparison of pH-stat versus Alpha-stat during hypothermic cardiopulmonary bypass in the prevention and control of acidosis in cardiac surgery.

OBJECTIVES: To compare the effects of blood-gas management using either alpha-stat (temperature-uncorrected blood-gas management) or pH-stat (temperature-corrected blood-gas management) strategies, 30 patients undergoing coronary artery bypass surgery allocated randomly to either one of the approaches were studied. Acid-base balance, tissue oxygenation, and biochemical parameters were measured at distinct times: before bypass, after 15 min of hypothermia at 32 degrees C, after 45 min of hypothermia at 32 degrees C, after 15 min of rewarming at 37 degrees C, and 45 min after the end of bypass in normothermic conditions. RESULTS: The groups were similar with regard to physical characteristics, physiological parameters, and bypass time. In the pH-stat group, CO2 administered with the aim of correcting pH for the patients hypothermic temperature caused a significant increase in temperature-uncorrected PaCO2 and a decrease in arterial temperature-uncorrected pH at 45 min. During the rewarming period and following bypass, the pH was lower and PaCO2 higher in the pH-stat group (P < 0.001). CONCLUSION: It was found that during the rewarming period and following bypass, the resulting acidosis caused by the procedure was less in the alpha-stat group. It was found that there were no difference between the two groups, with regard to tissue perfusion, as is seen by the tissue oxygenation parameters and lactic acid concentration.

Decreased 2,3-diphosphoglycerate concentration in low cardiac output patients and its influence on the determination of in vivo p50.

We investigated whether 2,3-diphosphoglycerate (2,3-DPG) is altered in patients with low cardiac output and the influence of its concentration on the calculation of in vivo P(50). Biochemical and blood gas analysis were performed along with the measurement of cardiac output and body temperature in 13 patients submitted to cardiopulmonary bypass surgeries without the use of donor blood. In vivo P(50) was calculated using the measured (P(50m)) and the estimated 2,3-DPG (P(50e)). 2,3-DPG concentration was lower in these patients when compared to the values obtained in normal volunteers (6.9 +/- 2.2 vs. 11.9 +/- 2.4 microm/gHb). P(50m) was lower than P(50e) (21.6 +/- 1.1 vs. 30.1 +/- 1.2 mm Hg) at all time points. Our data show that in patients with low cardiac output, 2,3-DPG concentration is reduced. Therefore, in these patients, the use of standard values for this variable may introduce an error in the calculation of in vivo P(50).