Comparison of Two Apnea Test Methods, Oxygen Insufflation and Continuous Positive Airway Pressure During Diagnosis of Brain Death: Final Report

Abstract

Introduction: Deterioration of the pulmonary function after the apnea test (AT) conducted with the classic oxygen insufflation AT (I-AT) is often observed during the brain death (BD) diagnosis procedure. In the present study, two AT methods were compared before a method is recommended for the currently revised Polish BD criteria. Methods: Classic I-AT and continuous positive airway pressure AT (CPAP-AT) were performed in 60 intensive care unit patients. I-AT was performed at the end of two series of clinical tests, and approximately 1–1.5 h later, after BD was confirmed, a different method, CPAP-AT with 100% FiO 2 and CPAP value of 10 cm H 2 O provided by a ventilator in CPAP mode was performed. The patients in I-AT and CPAP-AT groups were further divided into two subgroups: non-hypoxemic (NH) with good lung function before AT (PaO 2 /FiO 2 index ≥ 200 mmHg) and hypoxemic (H) with poor lung function (PaO 2 /FiO 2 index < 200 mmHg). PaO 2 and PaCO 2 were recorded prior to I-AT and CPAP-AT at time-point one (T1), 5 min after each test at time-point two (T2), and after 10 min prior to the end of tests at time-point three (T3). The I-AT NH subgroup consisted of 50 patients, and CPAP-AT NH subgroup 43 patients. The I-AT H subgroup consisted of 10 patients, and the CPAP-AT H subgroup 17 patients. Results: In the I-AT NH subgroup, a gradual decrease in PaO 2 /FiO 2 was observed throughout the AT but not in the CPAP-AT NH subgroup. The PaO 2 /FiO 2 ratio during the AT in the CPAP-AT H group was stable with a slight tendency to increase but not in the I-AT H group. During the first 5 min of the AT, the mean increase in CO 2 was approximately 5 mmHg/min. Most patients in all groups met the AT criteria after 5 min of the test. Conclusions: The results from the study show that I-AT may compromise pulmonary function in some cases and is one of the reasons for the recommendation of a safer option, CPAP-AT, in the currently revised Polish BD criteria. During AT, the mean CO 2 increase rate was 5 mmHg/min, which, in most patients, would allow the test to be completed after just 5 min.