Recovery from metabolic impairments after hypothermic cardiopulmonary bypass: postoperative changes in arterial-venous carbon dioxide tension difference.

Arterial-venous carbon dioxide tension differences (Pv-aCO2) are known to increase during the resuscitation phase following several types of shock. We hypothesized that Pv-aCO2 increases immediately following hypothermic cardiopulmonary bypass (CPB) because of the metabolic impairments that occur during CPB. Fifty-six adult patients underwent hypothermic CPB for cardiac surgery. Arterial and mixed venous blood gases were analyzed every 6 hours for the first 24 hours following cardiac surgery. Immediately after surgery, the Pv-aCO2 was elevated (8.2 +/- 2.9 mmHg), but gradually returned to a normal range within 12 hours (6.2 +/- 3.2 mmHg, p < 0.001). Factors (X) which correlated significantly with the postoperative Pv-aCO2 (Y) included the minimum rectal temperature during CPB (Y= 27.3 - 0.664X, p = 0.011) and the duration of CPB (Y= 5.6 + 0.0172X, p = 0.047). The abnormally high Pv-aCO2 during the early postoperative period may be caused by metabolic impairments during hypothermic CPB. The recovery stage following open heart surgery is therefore similar to the resuscitation phase after shock.