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J Thorac Cardiovasc Surg 1999;118:71-81
© 1999 Mosby, Inc.

SURGERY FOR ACQUIRED CARDIOVASCULAR DISEASE

MYOCARDIAL SUBSTRATE UPTAKE AND OXIDATION DURING AND AFTER ROUTINE CARDIAC SURGERY

From the Departments of Surgery,^a Anesthesiology,^band Cardio-Thoracic Surgery,^c University Hospital Maastricht, and the Departments of Statistics and Informatics,^d Human Biology, ^f and Physiology^e of the Cardiovascular Research Institute, University of Maastricht, Maastricht, The Netherlands.

Address for reprints: H. G. Pietersen, Department of Surgery, University Hospital Maastricht, PO Box 5800 AZ, Maastricht, The Netherlands.

Objective: This study was designed to clarify whether myocardial substrate uptake and oxidation change after a period of hypothermic cardioplegic arrest during coronary artery bypass grafting procedures.
Methods: In 30 patients arterial and coronary sinus blood was sampled and coronary sinus flow measurements were performed before and after sternotomy and 10 minutes, 20 minutes, 50 minutes, and 6 hours after release of the aortic crossclamp. Measurement of free fatty acids, lactate, glucose, oxygen content, and carbon dioxide content in arterial and coronary sinus blood allowed calculations of myocardial substrate use, respiratory quotients, and myocardial oxidation rates of carbohydrates and fat.
Results: Uptake of free fatty acids and lactate was significant throughout the study and did not change in association with release of the crossclamp. Free fatty acid and lactate uptake measured 6 ± 4 µmol/min and 23 ± 26 µmol/min, respectively, before crossclamping compared with 8 ± 7 µmol/min and 19 ± 21 µmol/min, respectively, after release of the clamp. Glucose uptake was significant only during the first hour after crossclamp release and increased from 7 ± 50 to 28 ± 34 µmol/L after crossclamp release. Myocardial oxygen consumption did not change significantly (0.5 ± 0.2 mmol/L compared with 0.35 ± 0.2 mmol/L) after release of the crossclamp. Myocardial oxygen extraction ratio decreased from 58% ± 8% to 41% ± 13% after crossclamp release. Respiratory quotient increased after crossclamp release (0.85 ± 0.2 compared with 1.00 ± 0.2), which implies that carbohydrate oxidation increased at the expense of free fatty acid oxidation.
Conclusion: We conclude that hypothermic cardioplegic arrest during coronary artery bypass graft operations is associated with a transiently increased uptake and oxidation of carbohydrates during the immediate reperfusion phase.