Strategic analysis of apnea testing to determine brain death with PaCO2 and pH targets in China: A multi-center retrospective study.

BACKGROUND

Brain death (BD) means the irreversible loss of whole brain function. Apnea testing (AT) is crucial when determining BD. AT criteria has been updated to combine PaCO2 and pH rather than an individual PaCO2 target. In this study, we aimed to explore the influencing factors of AT under the new standard to reduce non-diagnostic results and complications.

METHOD: Data were retrieved from five hospitals from 2018 to 2023 in China. Samples were grouped based on AT duration, temperature, pre-PaCO2, oxygenation index (OI, PaO2/FiO2) respectively to compare. Multivariate linear regression analysis analysis was used to identify related clinical indicators.

RESULTS

We included 620 BD patients that underwent AT. Diagnostic rate for dual AT targets was 92.4 %, which is 3.4 % lower than that under conventional criteria. Diagnostic rate no longer improved for AT duration (time disconnected from the ventilator) that lasted longer than 9 min (χ2 = 0.049, p = 0.826), but the incidence of severe hypercapnia (PaCO2 > 80 mmHg) and severe acidosis (pH < 7.10) increased. The pre-PaCO2 ≥ 40 mmHg group had shorter required durations (p = 0.029), and higher diagnostic rate (p = 0.041) than pre-PaCO2 < 40 mmHg group. The duration could last significantly longer in OI ≥200 than OI < 200 group (8.675 ± 0.077 min vs. 8.063 ± 0.165 min; p < 0.001). Weight, heart rate baseline, pre-pH, pre-PaCO2 and duration were related to the final PaCO2 and pH.

CONCLUSION

For most patients, 7-9 min of AT duration is appropriate to reach dual diagnostic targets. Modulating the baseline level of PaCO2 (≥40 mmHg), pH and OI (≥200) can help reduce non-diagnostic results and improve the safety of AT implementation.