The acid-base vector of open-heart surgery.

THE outstanding acid-base change associated with extracorporeal circulation in cardiac surgery has been demonstrated to be metabolic acidosis, which has been variously reported to occur during perfusion or in the postoperative period.1 4 Since thoracic operations other than cardiac are known to produce marked changes in acid-base balance,5-7 intensive serial study of patients during openheart surgery might help to unravel some of the events influencing a patient 's acid-base status during these very complicated operative procedures. The present report presents the data derived from 14 patients studied iil an attempt to relate acid-base changes to operative events. The technic of plotting serial acid-base changes on the nomogramn of Hastings and Steinhaus8 had long been used in our laboratory for following the course of patients with other acid-base disturbances, such as those produced by diarrhea or salicylate intoxication. This nomogram, shown in figure 1, is useful because a single point describes the relation of the three variables of the Henderson-Hasselbach equation; thus simultaneous values of pH, pCO2, and (HCO3)can be plotted serially over an extended period. The changes that occur in these values can be identified as respiratory or metabolic in origin by the direction of the graphic pathway on the nomogram. Changes in relative concentrations of fixed cations and anionis are displayed along, or in a direction parallel to, the metabolic axis; those representing primarily