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Metabolic Acidosis and Its Correction in Patients Undergoing Open-Heart Operation

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Abstract

THE occurrence of metabolic acidosis in patients undergoing open-heart operation has been recognized by Lillehei and his associates.1 According to our observations, the most significant changes in blood pH occur not during, or immediately after operation, but about three hours postoperatively. As long-as the patient is under anesthesia and his respiration is “helped” by the anesthetist, an excess of CO2 is blown off and the pH does not fall significantly. While the patient’s circulation is being maintained by the heart-lung machine, the removal of CO2 via the oxygenator also helps to keep the pH within normal limits. However, three or more hours after completion of the operation the blood pH occasionally falls to a level that is incompatible with life. Whatever the underlying cause, the mechanism of death in some cases seems to be an acidosis leading to respiratory failure followed by cardiac arrest.

It has been suggested that these unfavorable acid-base imbalances are caused by damage to the blood itself by the pump-oxygenator during the period of bypass. This hypothesis, however, is not supported by the data in this paper. Our experimental results demonstrate that the blood pH and the CO2 content can be lowered simply by reducing the cardiac output. Our clinical results show that the occurrence of reduced blood pH and CO2 content in patients treated with a heart-lung machine is correlated with corresponding periods of hypotension before, during, or after the period of bypass. Furthermore, unfavorable changes in blood pH and CO2 content are known to . . .


 

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