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

Abstract

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 PaCO 2 , PaO 2 , or pH between the CAT and MAT groups ( P = .341, .593, and .503, respectively). In overweight patients (body mass index ≥ 23 kg/m 2 ), MAT prevented dramatic reductions in PaO 2 and SaO 2 ( P < .05 for both). In the patients who had hypoxic brain injury due to hanging, differences in PaO 2 and SaO 2 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.

Apnea Testing for the Determination of Brain Death: A Systematic Scoping Review

“…In a Korean study comparing MAT to conventional AT, mean duration of AT was similar, without significant differences in change of PaCO 2 , PaO 2 or pH. In overweight patients, however, MAT prevented dramatic PaO 2 reductions, and in patients with hypoxic brain injury due to hanging, differences in PaO 2 and SaO 2 in the MAT group were significantly smaller than in the conventional AT group [19]. Less clear benefit was found in a multicenter Canadian study involving 14 ICUs with 77 patients comparing a group with O 2 catheters placed inside the ETT to a group with an Ambu bag with a CPAP valve attached to the ETT, without significant difference in the degree of PO 2 reduction, rate of PCO 2 rise or pH decline [12].…”

“…As with brain death protocols in general, there is significant variability in the specifications for AT both within the USA and worldwide [81]. For the target laboratory value to signify a positive apnea test, most US protocols require a PaCO 2 target of 60mmg Hg, but some require a different PaCO 2 target < 60mmHg [10]; this variability also exists worldwide; for example, Korea requires the absence of spontaneous respiration when the PaCO 2 is 50 mmHg or greater [19]. As opposed to the USA, where the common target apnea laboratory value is the PCO 2 level, some countries require a target arterial pH < 7.30 [7] and some require pH ≤ 7.28 [82] in addition to the PaCO 2 elevation > 60 mm Hg.…”

“…In Canada, one apnea test is sufficient if two clinical brain death exams are done concurrently, but if done at different times, they should each be followed by an apnea test [82]. In Korea, two apnea tests separated by six hours are needed [19]. Regarding timing of AT, it is recommended that AT is performed at the end of the BD assessment to minimize risk of harm [4,7,15,86].…”

Optimal Duration of the Apnea Test for Determining Brain Death: Benefit of the Short-Term Apnea Test

“…This may be due to complications of the apnea test, which include hypoxemia, hypotension, acidemia, hypercapnia, increased intracranial pressure, pulmonary hypertension, and arrhythmias [7][8][9][10][11][12][13][14]. Compared to the conventional apnea test, the modi ed apnea test (MAT) maintains positive end-expiratory pressure (PEEP) and can prevent lung atelectrauma and hypoxia even after mechanical ventilator removal [10]. However, MAT does not reduce other hypercapnia-and hypoxia-induced complications.…”

“…The implementation pattern of the apnea test is more closely related to the condition of the patient waiting for brain death determination. This may be due to complications of the apnea test, which include hypoxemia, hypotension, acidemia, hypercapnia, increased intracranial pressure, pulmonary hypertension, and arrhythmias [7][8][9][10][11][12][13][14]. Compared to the conventional apnea test, the modi ed apnea test (MAT) maintains positive end-expiratory pressure (PEEP) and can prevent lung atelectrauma and hypoxia even after mechanical ventilator removal [10].…”