The Acid-Base Vector of Open-Heart Surgery

Fourteen patients submitted to open-heart surgery were studied by serial acid-base and electrolyte determinations in order to demonstrate the sequence and magnitude of disturbances associated with the procedure. Under conditions of the study, including the use of 100 per cent oxygen as the perfusing gas for the oxygenator, respiratory alkalosis develops as the initial change during perfusion but is followed by a “metabolic shift” characterized by falling pH and CO2 content, while a stable, moderately low pCO2 is maintained by the oxygenator. The resulting state of mixed respiratory alkalosis and metabolic acidosis changes into a state of relatively pure metabolic acidosis as pCO2 and bicarbonate content rise while pH falls after perfusion. The factors involved in the “metabolic shift” responsible for development of metabolic acidosis are not identified by this study although length of perfusion, perfusion pressure, and rate of flow are considered as possible factors. Acidosis persists through the early phases of the recovery period but ordinarily resolves without administration of alkali. Serial sampling technics as used in this study may aid in the interpretation of postoperative acidosis, distinguishing between patients who are deteriorating and those who are passing through a transient phase in the process of recovery.