329 - Limits of Airway Pressure Release Ventilation (APRV) as a Mode of Non-Invasive Ventilation Using the RAM Cannula

Publication Number: 329.5951

Andrew Mire, University of Tennessee Health Science Center College of Medicine, Memphis, TN, United States; Mohamad Elabiad, University of Tennessee Health Science Center College of Medicine, Memphis, TN, United States

Background: Evidence supports Nasal Intermittent Positive Pressure Ventilation (NIPPV) as a non-invasive ventilation (NIV) method that is associated with lower risk of extubation failure than CPAP. The RAM cannula (RC) is a popular interface device to provide NIV. Research has shown that when using a RC to deliver NIV, the delivered peak inspiratory pressure (PIP) is lower than the set PIP. The leak around the cannula-nares interface explains this theory. One suggested approach to offset this leak is to extend the inspiratory time (IT). Airway pressure release ventilation (APRV) is one such mode that incorporates a long IT.

Objective: Hypothesis: APRV, as a respiratory mode to deliver NIV, delivers pressures consistent with those set on the ventilator. In a bench design format, and by using a test lung model, our objective is to evaluate changes in delivered pressures across increasing levels of set pressures when using a RC to deliver NIV using APRV mode.

Design/Methods: A 3.0 mm outer diameter (OD) RC was used with two different nares sizes: a 3.5mm and 4.0 internal diameter (ID) nasal adaptor (figure1a). A Drager 500 ventilator was used for the APRV ventilator mode. Experiments were run at 3 different levels each of P-high and T-high for a total of 9 combination settings. P-low was set at 0 cmH2O and T-low at 0.2 sec. RC set up connection order consisted of: ventilator to RC to artificial nares to sensor, and then to test lung (figure 1b). Test lung rate was set to mimic PIP/Peep at 16/7, RR 60, for a measured Vt of 4.9 ml. The N4900 micro-preemie, the smallest, cannula was used. Set and measured ventilator readings were collected and compared using paired T-tests. Data are presented as mean (±SD) and the percent drop in pressure delivered compared to pressure set was calculated.

Results: There was a statistically significant difference between set and delivered pressures when using a 3.0 OD RC with both the 3.5 and the 4.0 mm nares sizes. The 3.0 RC to 3.5 mm nares showed a drop in set pressure by an average of 9±1 %, and the 3.0 RC to 4.0 mm connection showed a drop by 76±1 % (table 1).

Conclusion(s): This study highlights the importance of using the RAM cannula as designed while maintaining appropriate leaks around the nasal interface. A mismatch between the RC and nares sizes was associated with a clinically significant drop in delivered pressures when compared to intended or set pressures. Leveraging the long IT of APRV to compensate for large leaks due to inappropriate RC to nares size did not work, and the delivered pressure remained significantly and clinically low.

Figure 1a and Figure 1b
PAS Picture 1: demonstrating experiment setup

Table 1
Results Table

Picture 2
PAS Picture 2: Demonstrating Vent settings for one of the runs displayed in Table 1