Hyperperfusion and cerebral dysfunction. Effect of differing acid-base management during cardiopulmonary bypass

Area of Science:

• Neurosurgery
• Cardiovascular Surgery
• Physiology

Background:

• Cardiopulmonary bypass (CPB) can alter cerebral blood flow (CBF), potentially increasing patient morbidity.
• Acid-base management during CPB, specifically arterial carbon dioxide levels, is implicated in these CBF changes.

Purpose of the Study:

• To compare the effects of two CPB acid-base management protocols, pH-stat and alpha-stat, on cerebral blood flow and cognitive function in patients undergoing coronary artery bypass surgery (CABS).

Main Methods:

• Randomized controlled trial involving 70 patients undergoing elective CABS.
• Cerebral blood flow (CBF) measured using xenon-133 isotope clearance.
• Cerebral oxygen metabolism assessed via cerebral metabolic rate for oxygen (CMRO2) and cerebral extraction ratio for oxygen (CERO2).
• Neuropsychological tests administered pre-surgery and at 6 weeks post-surgery.

Main Results:

• During hypothermic CPB (28°C), CBF was significantly higher in the pH-stat group (41 ml/100 g/min) compared to the alpha-stat group (24 ml/100 g/min) (P < 0.001).
• Cerebral extraction ratio for oxygen (CERO2) indicated a more pronounced mismatch between cerebral perfusion and demand in the pH-stat group (0.12) versus the alpha-stat group (0.25).
• This suggests greater disruption of cerebral autoregulation with pH-stat management.

Conclusions:

• Alpha-stat acid-base management during CPB appears to maintain better cerebral blood flow and autoregulation compared to pH-stat.
• The findings suggest that alpha-stat may be a preferred strategy to mitigate neurological complications associated with CPB in CABS patients.