Apnea testing using the oxygen insufflation method for diagnosis of brain death may compromise pulmonary function

Investigation of Apnea Testing During Brain Death Determination in China

Apnea testing (AT) is one of the key steps for brain death (BD) diagnosis and confirmation. However, the completion rate of AT is not well in China. The aim of this study was to investigate the completion rates of the AT during BD determination in China and analyze the determinant factors. We reviewed and analyzed potential BD patients registered in our database from 2013 to 2019. The patients were divided into those with completed and aborted AT. Preconditions and organ function status were compared between the two groups. A total of 1,531 (1,301 adults and 230 pediatrics) cases of potential BD were extracted, and BD determination was performed 2,185 and 377 times in adults and pediatrics respectively. The nonperformance and aborted rates of AT were 12.2% and 34.5% in adults, and 11.7% and 44.4% in pediatrics respectively. Compared with the completed group, the aborted group had a lower PaO2, systolic blood pressure, PaO2/FiO2 ratios, and higher alveolar-arterial (A-a) gradient both in adults and pediatrics, and higher PaCO2 and higher heart rates in adults. PaO2 and A-a gradient had higher predictive efficacy for AT completion in both adults and pediatrics. The implementation and completion rates of AT are not ideal in China. PaO2 and A-a gradient are important factors for the successful completion of AT and should be optimized before AT.

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

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% FiO₂ and CPAP value of 10 cm H₂O 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 (PaO₂/FiO₂ index ≥ 200 mmHg) and hypoxemic (H) with poor lung function (PaO₂/FiO₂ index < 200 mmHg). PaO₂ and PaCO₂ 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 PaO₂/FiO₂ was observed throughout the AT but not in the CPAP-AT NH subgroup. The PaO₂/FiO₂ 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 CO₂ 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 CO₂ increase rate was 5 mmHg/min, which, in most patients, would allow the test to be completed after just 5 min.