The Efficacy of a Novel Method to Provide Apneic CPAP for the Apnea Test: A Benchtop Study

Background:

The apnea test is routinely performed for brain death assessment. During mechanical ventilation cessation, provision of oxygen is required to attenuate oxygen desaturation. Apneic CPAP is associated with the lowest PaO₂ rate of decrease and a similar PaCO₂ rate of increase compared to oxygen delivered via intratracheal insufflation and T-piece and reduces the frequency of complications leading to test termination. Weingart introduced a novel method using a bag valve mask (BVM) for CPAP delivery in the emergency department. This study aims to evaluate the efficacy of this method in simulated apneic conditions during apnea testing.

Methods:

The proposed method converts a BVM to a CPAP system using a PEEP valve and continuous gas bias flow. A digital manometer (HT-1890, China) was connected to the manometer port and an O₂ catheter was connected to the M-port of a disposable resuscitator (Ambu SPUR II, Denmark). A fixed-value PEEP valve (Intersurgical, UK) was attached to the BVM expiratory port. Oxygen flow was measured using a flow analyzer (5310-2, TSI). Experiments were conducted with different oxygen flows (1, 4, 8, 12, and 15 L/min^-1) and PEEP valve pressures (10 and 20 cm H₂O). Each configuration was measured three times, observing the sustained positive pressure over time. The BVM was connected to a 1-L adult test lung (Maquet, Germany), and data were recorded and analyzed using Microsoft Excel 360 v 2304.

Results:

Thirty experiments were performed. Table 1 presents the CPAP levels measured using several flows and PEEP valves. Figure 1 depicts the mean duration required to establish the CPAP pressures from a completely deflated test lung.

Conclusions:

This novel method achieves consistent CPAP levels even at low flows of 1 L/min^-1. The time required to reach a certain pressure level depends on the PEEP valve level and flow. This method offers several advantages as an apneic oxygenation technique. It increases oxygenation thus extending safe apnea time and is noninvasive thus reducing the risk of infection and barotrauma compared to intratracheal O₂ insufflation. It uses simple, small, inexpensive, and readily available equipment (BVM and PEEP valves), avoids false triggers, and allows for prolonged periods of apnea. Further studies are needed to explore its efficacy in various patterns of spontaneous ventilation with and without gas leak.

OPEN IN VIEWER

Figure 1. The mean time (sec) taken to establish a PEEP valve level of 10 cm H₂O, left panel (A), and 20 cm H₂O, right panel (B), from a complete test lung deflation.

OPEN IN VIEWER

Table 1. The CPAP levels measured while using different flow rates and PEEP valves.