Changes in arterial blood PO2, PCO2, and pH during deep hypothermic circulatory arrest in adults

Safe limits of time and temperature during sleep hypothermic circulatory arrest (DHCA) still remain controversial. Furthermore, continuous changes of PaO2, PaCO2, and pH have never been measured during DHCA in humans. Continuous intraarterial blood gas (CIABG) monitoring is a new technology allowing us to study chronological changes occurring due to metabolism during DHCA. When the patients' temperature reached 18 approximately 20 degrees C following establishment of cardiopulmonary bypass (CPB), circulatory arrest was initiated. After a 20-minute period of DHCA, reperfusion commenced with 18 degree C blood. We continuously monitored PaO2, PaCO2, and pH immediately before, during and following DHCA. Data was analyzed by Student's t-test. PaO2, PaCO2, and pH of pre- and 5 minutes post DHCA were not significantly different from each other. However, during DHCA, the PaO2 was significantly decreased from 229 +/- 34 to 30 +/- 23 mmHg at 20-minute intervals. But the PaCO2 increased significantly after 20 minutes of circulatory arrest from 34 +/- 5 to 42 +/- 6 mmHg. However, the pH did not change significantly over the 20-minute period. The PaO2 level after 20 minutes is much lower than before DHCA, it would be well tolerated in normothermic adults. The PO2 level in the brain may be even lower given its high metabolic rate. So measuring arterial PO2 continuously during DHCA may provide a surrogate method for determining maximum safe time under DHCA for adults.