Proposed safe apnea test using positive end-expiratory pressure valve and short-term blood gas analysis Observational study

The apnea test is an essential examination for the determination of brain death; however, hypotension, hypoxemia, and other complications during the apnea test can affect the stability of brain-dead patients, as well as organ function for recipients. Therefore, it is necessary to establish standard guidelines for apnea testing. The modified apnea test (MAT) comprises delivery of 100% oxygen through the endotracheal tube connected to manual resuscitator (Ambu bag) with the positive end-expiratory pressure (PEEP) valve after disconnection of the mechanical ventilator for maintenance of PEEP. Forty-nine instances of the conventional apnea test (CAT) were performed in 25 brain-dead patients; 77 instances of the MAT were performed in 39 brain-dead patients. The mean duration of the apnea test was 3.5 ± 1.4 minutes in the CAT group and 3.0 ± 1.2 minutes in the MAT group. There were no significant changes in PaCO₂, PaO₂, or pH between the CAT and MAT groups (P = .341, .593, and .503, respectively). In overweight patients (body mass index ≥ 23 kg/m²), MAT prevented dramatic reductions in PaO₂ and SaO₂ (P < .05 for both). In the patients who had hypoxic brain injury due to hanging, differences in PaO₂ and SaO₂ in the MAT group were significantly smaller than in the CAT group (P < .05). Although MAT, which was invented to maintain PEEP, was not efficient for all brain-dead patients, it could be helpful in selected patient groups, such as overweight patients or those who had hypoxic injury due to hanging. And clinicians should consider short-term apnea test to avoid unnecessarily prolonged hypoxemia. Abbreviations: ABGA = arterial blood gas analysis, APACHE = Acute Physiologic Assessment and Chronic Health Evaluation, BMI = body mass index, CAT = conventional apnea test, EEG = electroencephalogram, IRB = institutional review board, MAT = modified apnea test, PaCO₂ = arterial carbon dioxide partial pressure, PaO₂ = arterial partial pressure of oxygen, PEEP = positive end-expiratory pressure, SaO₂ = oxygen saturation, SPECT = single-photon emission computerized tomography.