690 - Changes in Pressure Across the Nasal Interface: Effects of Flow Rate and Interface Type

Publication Number: 4674.690

Lakshmi Menon, The Children's Hospital at Montefiore, Bronx, NY, United States; Bianca Chakravorty, The Children's Hospital at Montefiore, Flushing, NY, United States; Edymel L. Bondal, Montefiore Medical Center (Weiler), YONKERS, NY, United States; Shantanu Rastogi, The Children's Hospital at Montefiore, Bronx, NY, United States

Background: Positive end-expiratory pressure (PEEP) delivered by continuous positive airway pressure (CPAP) often differs from the set value due to variations in interface type, flow rate, and air leak. No clinical trial has established the optimal interface to ensure precise PEEP delivery.

Objective: To compare differences between set and measured PEEP using various nasal interfaces and to assess the effect of flow rate and air leak in an in vitro neonatal model.

Design/Methods: This in vitro experiment measured airway pressure below the glottis in Baby LIV (Lung Inflation Visualizer), a 3D-printed model of a 28-week, 750-gram preterm neonate in which air leak can be controlled by opening the mouth (Fig. 1). The model includes a mechanical analog of the preterm respiratory system and a programmable breath generator simulating spontaneous breathing.
We tested the Fisher & Paykel (FP) nasal mask, FP nasal prongs, Hudson nasal prongs, and RAM cannula at set PEEP levels of 4-10 cm H₂O and flow rates of 5-10, 12, and 15 L/min (liter per minute), with and without air leak . Closed- and open-mouth conditions were used to evaluate the effect of air leak.

Results: Increasing flow significantly increased PEEP delivered below the glottis for all four interfaces, with pressures closest to the set PEEP observed at 6-8 L/min. Although pressure increased with higher flow rates in the RAM cannula, this change was not clinically significant. With an air leak from the mouth, measured PEEP dropped substantially, and even at 15 L/min, the set PEEP could not be achieved (Fig. 2).
Hudson nasal prongs delivered pressures closest to the set PEEP, followed by the FP nasal mask, while RAM cannula showed the greatest discrepancy (Fig. 3). The difference between set and measured PEEP for Hudson prongs versus RAM cannula was 2.7 ± 2.9 vs. 5.8 ± 2.0 cm H₂O (p = 0.04) at 8 L/min, 2.5 ± 3.1 vs. 5.7 ± 2.0 cm H₂O (p = 0.03) at 9 L/min, and 2.3 ± 3.2 vs. 5.7 ± 2.0 cm H₂O (p = 0.02) (Table 1).

Conclusion(s): Interface type significantly affects delivered airway pressure. Hudson nasal prongs and FP nasal masks most accurately deliver the set PEEP, while RAM cannula shows the greatest drop in set pressure. Flow rates of 6-8 L/min optimize pressure delivery, whereas higher flow rates further increase measured PEEP. Air leaks markedly reduce effective PEEP, and increasing flow alone cannot compensate for the drop in the delivered PEEP.

Table 1: Average difference between set and measured pressures in cm H2O for PEEP settings of 4 to 8 cm H₂O at different flow rates. FP= Fisher Paykel * p value <0.05 between Hudson and RAM cannula


Figure 1: Baby LIV model Figure 2 - shows 4 panels with 2a FP nasal mask, 2b FP nasal prongs, 2c Hudson nasal prongs and 2d RAM cannula. The orange fitted graph on the top is the measured PEEP with increasing flow rates for each given PEEP. The lower red fitted graph shows the increase in measured PEEP with increase in flow rates for each given PEEP.


Figure 3: Set PEEP versus Measured PEEP for different PEEP levels at a constant airflow of 8 Lpm