Changes of P50 during Hypothermia for Cardiopulmonary Bypass Surgery

Kim, Kyung Han; Chang, Tae Ho; Kim, Se Hwan; Kang, Sung Hee; Kim, Joon Sun

Abstract

Hemodilution and hypothermia during extracorporeal circulation for open heart surgery affect the oxygen-carrying capacity to the tissue and hemog)obin affinity for oxygen. P50, as an indicator of alteration of hemoglobin affinity, is dependent on the temperature, pH, PCO2 concentration of 2, 3-DPG and type of hemoglobin, and thus it changes with the shift of the oxyhemoglobin dissociation curve to the right or left. We took the blood samples during 3-different stages of cardiopulmonary bypass in 23 patients who underwent open heart surgery; stage I(before chest incision), stage II(during hypothermia), stage III(after chest closure) and measured the level of arterial blood gas and the value of P50 The results were as follows: 1) At the uncorrected temperature, the value of the P50 in stage II(24.80+/-2.06 mmHg) showed a significant decrease compared to the stage I(28.23+/-2.56 mmHg) (P<0.05), but this value was almostly in the normal range. 2) At the corrected temperature, the value of the P50 in stage II(18.59+/-1.88mmHg) showed also a significant decrease compared to the stage I(26.71+/-2.92mmHg) (P<0.01), and increased to the normal range after rewarming. 3) At the uncorrected temperature, arterial PO2 in stage II(380.18+/-48.86mmHg) showed a significant increase compared to stage I(237.62+/-29.20mmHg), which suggested that the increase of the PO was resulted from the effect of the increased FiO2 despite lowered body temperature, while PCO was decreased due to lowered body temperature.