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J Thorac Cardiovasc Surg 1995;109:597
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Myocardial rewarming during normothermic cardiopulmonary bypass

Providence, RI 02903

Reply to the Editor:

Dr. Regragui and his colleagues report no difference in myocardial rewarming among three groups of patients undergoing hypothermic, moderately hypothermic, and normothermic cardiopulmonary bypass (CPB) perfusion. We ¹ found a clinically small (mean temperature difference of 4.0° to 6.3° C) but significant enhancement of myocardial rewarming in our normothermic patients before redosing with cold blood cardioplegia. Although the surgical techniques used in both studies were similar (two-stage venous cannulation, single aortic crossclamping period), the cardioplegia composition and conduct were not identical. Both studies initiated electromechanical arrest with 1000 ml of 6° to 8° C crystalloid cardioplegic solution and achieved nearly identical (approximately 10° C) myocardial cooling in all groups. Thereafter our cardioplegia protocol included multidose cold (10° to 12° C) blood cardioplegia after construction of each distal anastomosis, which resulted in a mean temperature difference of 1.8° to 4.0° C between the hypothermic and normothermic groups after each run of cardioplegia and absolute myocardial temperatures of less than 17° C in both groups. Dr. Regragui's study redosed with colder crystalloid cardioplegic solutions at 30-minute intervals or earlier if electrical activity occurred and achieved absolute myocardial temperatures of 18° to 20° C in all groups before removal of the aortic crossclamp. At that time both studies found no significant myocardial temperature differences between hypothermic and normothermic perfusion groups. Additionally, myocardial cooling was augmented in Dr. Regragui's patients with 1000 ml of ice-cold saline solution, a significantly greater volume than contained in our topical saline slush. These differences in cooling techniques most likely resulted in the observed differences in our findings.

We note with gratification that the work described by Dr Regragui and his associates confirms our findings that clinically protective levels of myocardial hypothermia can be maintained in patients undergoing normothermic CPB. The outcome data presented in their letter also support our findings that normothermic CPB will not compromise myocardial protection and result in post-CPB ventricular dysfunction if myocardial temperatures are maintained sufficiently cold.

12/8/59357

References

1. Bert AA, Singh AK. Right ventricular function after normothermic versus hypothermic cardiopulmonary bypass.J THORAC CARDIOVASC SURG 1993;106:988-96.
   

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