Acid-Base Management During Hypothermic Cardiopulmonary Bypass Does Not Affect Cerebral Metabolism but Does Affect Blood Flow and Neurological Outcome

Abstract

In order to compare the effects of blood-gas management on cerebral blood flow, metabolism and neurological outcome after hypothermic cardiopulmonary bypass (CPB) we have studied 65 patients undergoing aorto-coronary bypass surgery allocated randomly to either a pH-stat (temperature-corrected blood-gas management) or an alpha-stat (temperature-uncorrected blood-gas management) group. All patients were examined neurologically on the day before and the 7th day after operation. In 20 patients of the pH-stat group and in 15 patients of the alpha-stat group we measured cerebral blood flow (CBF), using the argon washin technique, and also cerebral oxygen (CMRO2) and glucose (CMRg) uptake. Measurements were performed in awake patients, after induction of anaesthesia with fentanyl, midazolam and pancuronium under normothermic conditions, during CPB at a venous blood temperature of 26 degrees C and at the end of surgery. Compared with postinduction values, hypothermia was associated with an 18% reduction in CBF and decreases in CMRO2 and CMRg of 61% and 60%, respectively, in the alpha-stat group. In the pH-stat group, CMRO2 and CMRg decreased also, by 58% and 74%, respectively, whereas CBF increased by 191%, indicating uncoupling of flow and metabolism. As there were no statistically significant differences between the metabolic variables in both groups, we conclude that acid-base management did not affect cerebral metabolism, despite its influence on blood flow. After rewarming, CBF and cerebral metabolism normalized independently of acid-base management during hypothermia. Nevertheless, neurological dysfunction occurred more often in the pH-stat group (P = 0.036).

Arterial blood gas management during cardiopulmonary bypass

“…They found that an increase in arterial PaCO 2 is associated with a decrease in SVR and a concomitant (12,13,21,22). The results of our study are quite comparable with that of AJston and colleagues (13) wherein no significant changes in SVR could be observed when the two groups of patients undergoing either a stat' or 'pH stat' management were compared; however, in both groups of patients SVR increased with duration of CPB.…”

“…Despite numerous studies on the effects of acid base management on organ blood flow, little information is available on the effects of cr stat' versus 'pH stat' management on systemic haemodynamics (5,12). This study demonstrates that there is no difference in systemic vascular resistance in patients undergoing hypothermic CPB under either ct stat' or 'pH stat' conditions.…”

Effects of Hypothermia on Energy Metabolism in Mammalian Central Nervous System

“…Newborns, young animals, and adults exhibit similar variations. Interestingly, the strategy of acid-base management has no significant effect on the hypothermic decrease in CMRO 2 [piglet (Aoki et al, 1993;Cheng et al, 1995), rabbit (Hindman et al, 1993), and man (Murkin et al, 1987;Stephan et al, 1992)]. An exception is the study by Skaryak et al (1995) in piglets that found a somewhat lower metabolic rate for oxygen with pH-stat as compared with ␣-stat management.…”

Mild and Moderate Hypothermia (α-Stat) Do Not Impair the Coupling Between Local Cerebral Blood Flow and Metabolism in Rats

“…A majority have reported a hypothermia-induced decrease in CBF, 11,12 whereas others observed unchanged or even increased CBF, 2,13 especially during pH-stat management. 14 Furthermore, whether anesthesia and hypothermia interfere with the CBF-CGU coupling remains to be determined. In clinical studies of patients undergoing cardiopulmonary bypass, an unchanged or increased mean CBF associated with a markedly decreased mean CGU ("hyperperfusion") has been interpreted as uncoupling of CBF from metabolism.…”