The effect of cardiopulmonary bypass on brain and heart metabolism: A ³¹P NMR study

Abstract

The development of a large animal preparation using 31P nuclear magnetic resonance (NMR) spectroscopy for the study of cerebral and myocardial metabolism during cardiopulmonary bypass (CPB) is reported. The effect of normothermic CPB on myocardial and cerebral metabolism was evaluated. Adolescent sheep were used which have low levels of 2,3-diphosphoglycerate, a compound which can interfere with the calculation of intracellular pH and inorganic phosphate content. CPB was performed using standard procedures modified for the presence of a high magnetic field and limited access to the animal. High quality 31P NMR data were obtained from the brains and hearts of these animals before and during normothermic CPB. These results demonstrate that the initiation of normothermic CPB does not change high energy phosphate levels or intracellular pH. In particular, the decreased myocardial oxygen demand associated with CPB is not associated with improvement in the levels of adenosine triphosphate or phosphocreatine. The measurements of energy metabolism and intracellular pH of the brain and heart during CPB were possible within the constraints of the NMR experiment without compromising the CPB procedure. Combining NMR and CPB techniques permits future studies of cerebral and myocardial metabolism, especially those relating to ischemia.

Monitoring the Conjunctiva for Carbon Dioxide and Oxygen Tensions and pH During Cardiopulmonary Bypass

“…The changes caused by the various interventions during the surgical procedure tended to be rapid and short lived. Studies of the effect on brain and tissue metabolism of normothermic cardiopulmonary bypass (as used in our study) did not change high energy phosphate levels or intracellular pH (16). The earliest report of conjunctival pH noted that the conjunctival pH was generally .2 pH units lower than the arterial value (17).…”

“…A prior investigation which measured muscle gastric mucosal oxygen levels during JECT. 2011;43: [13][14][15][16][17][18] CPB showed that tissue oxygenation fell sharply during the initiation of cardiopulmonary bypass and remained significantly below baseline for 3 to 5 hours following the procedure (19). These investigators did not find any relationship between arterial blood gas levels and the tissue pH or oxygen tension.…”

Mechanisms of injury and methods of protection of the brain during cardiac surgery in neonates and infants

“…8 " 10 Experimentally, Watanabe et al" have demonstrated intracellular cerebral hypoxia and acidosis during and after deep hypothermic bypass, most pronounced in animals subjected to circulatory arrest. In a study using magnetic resonance imaging in lambs, Swain et al 12 have demonstrated the lack of recovery of energy stores in the brain after bypass. Most importantly, they demonstrated the association of these findings with poor neurologic outcome.…”

“…Data from both humans and animals suggest that these estimates represent a reasonable approximation of acceptable minimal rates of flow during hypothermic bypass. Swain et al 12 have demonstrated that rates of flow of 10 ml«kg~1«min" 1 at 15 °C for periods of up to two hours in eight-week old sheep maintain normal levels of adenosine triphosphate and phosphocreatine, together with normal pH of the brain. When flow is reduced to 5 ml'kg~1»min" 1 at 15 °C, organic phosphates become depleted and the pH of the brain begins to fall.…”

Cerebral blood flow and metabolism during infant cardiac surgery

“…CBF and CMR02 are reduced below baseline measurements and oxygen extraction does not increase. Animal data suggest that after DHCA the brain is acidotic and hypoxic (Watanabe et al 1991a;Swain et al 1990). With reperfusion, the rate at which the brain recovers ATP, pH and Po2 is markedly delayed when compared with continuous flow CPB.…”