Metabolic Changes after Hypothermic Cardiopulmonary Bypass Surgery

Sung, Jang Ho; Kim, Inn Se; Lee, Sang Young

Abstract

Temperature changes after cardiopulmonary bypass surgery(CPB) markedly affect postoperative ventilation. Despite core rewarming after CPB, on admission to the intensive care unit the rectal temperature is about 34~35 degrees C over the next 12 hours, the temperature rises to 38~39 degrees C. Unless minute ventilation is increased hypercarbia occurs presumably because dead space and/or CO2 production are increased. This prospective review was designed to confirm these clinical impressions and to provide direction for future studies. Temperature changes, PaCO2, pH, sodium and potassium values of 42 patients who had undergone cardiac valvular replacement surgery with hypothemic cardiopulmonary bypass were observed during surgery and during the first 12 postoperative hours in the intensive care unit. The results are as follows: 1.The mean nasopharyngeal temperature was 26.3 degrees C, 34.4 degrees C, 34.9 degrees C, and 36.4 degrees C during bypass, rewarming, admission to the intensive care unit, and after 4 hours, respectively. The temperature curve was sigmoid rather than linear. 2. During rewarming, the most common abnormality of PaCO2 on anesthetic mechanical ventilation was acute respiratory acidosis(PaCO2 45mmHg, pH 7.35) which occurred in 48% of the patients. After bypass and in the intensive care unit, respiratory alkalosis occurred in 36% and 45% of the patients, respectively. 3. The serum sodium values decreased in 19% of the patients during bypass but not significantly. 4. The serum potassium value increased in 21% of the patients during bypass surgery, but not significantly, and after surgery it returned to normal limits. This suggests that ventilatory management in the early postoperative period after hypothermic cardiopulmonary bypass surgery should be carefully monitered and adjusted as necessary to the increased metabolic rate during rapid rewarming.