Transcutaneous Carbon Dioxide Measurement During Apnea Testing in Pediatric Patients

Abstract

Several variables affect the rate at which PaCO2 increases during apnea testing in the determination of brain death. In many cases, arterial blood gases (ABGs) are obtained at predetermined times in an attempt to demonstrate a PaCO2 value greater than 60 mmHg. This practice may result in the need to obtain multiple ABGs, terminating the apnea test before the PaCO2 is 60 mmHg, or waiting too long with a resultant compromise of hemodynamic status or arterial desaturation. We have found that transcutaneous CO2 (TC-CO2) monitoring can be used to guide the time to obtain ABGs during apnea testing. TC-CO2 monitoring was used during apnea testing in eight patients ranging in age from 1 to 16 years. In patients 1 and 2, when an ABG was obtained when the TC-CO2 value equaled 60 mmHg, the PaCO2 was less than 60 mmHg in all four cases (one ABG drawn for each apnea test in the two patients). When an ABG was obtained with the TC-CO2 value equal to 70 mmHg (n = 16), the TC-CO2 to PaCO2 difference was 2–11 mmHg (5.8 ± 2.7 mmHg) and the PaCO2 ranged from 59 to 72 mmHg (64.4 ± 3.2 mmHg). When an ABG was obtained with the TC-CO2 value equal to 80 mmHg (n = 14), the TC-CO2 to PaCO2 difference was 2–8 mmHg (5.4 ±1.9 mmHg) and the PaCO2 ranged from 72 to 83 mmHg (75.4 ± 32 mmHg). TC-CO2 monitoring can be used to help judge the timing of ABG analysis during apnea testing in children. When the TC-CO2 value reached 70 mmHg, we noted that the PaCO2 was greater than 60 mmHg in 15 of 16 cases.