The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

EFFECTS OF IMPOSED RESISTANCE ON TIDAL VOLUME WITH FIVE NEONATAL NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE SYSTEMS

Robert Chatburn1, Shannon Cook1



Background: Nasal continuous positive airway pressure (NCPAP) has been traditionally used to improve outcomes in neonates with respiratory distress syndrome. NCPAP can be generated using different methods: (1) electronic feedback control valve (e.g., ventilator or Cardinal Health AirLife nCPAP System), (2) underwater seal (bubble CPAP), (3) flow opposition (FO), (4) flow opposition with fluidic flow reversal on expiration (FOF). Few studies have compared the NCPAP methods and what data exists seems contradictory regarding the effect of resistive load on breathing patterns. The purpose of this study was to compare the effect of resistive load on spontaneous tidal volume using four methods of generating NCPAP.

Methods:
Five CPAP systems were evaluated at CPAP = 5 cm H2O: (1) Fisher and Paykel Nasal CPAP tubing with Maquet Servo-i ventilator in NIV CPAP mode (2) Fisher and Paykel Nasal CPAP tubing with water seal pressure generator (3) AirLife Infant nCPAP Generator Kit (4) Hamilton Medical Arabella fluidic NCPAP generator, (5) Cardinal Health AirLife nCPAP System (CHAS). Spontaneous breathing was simulated with an Ingmar ASL 5000 lung simulator (Ingmar Medical Inc.). Simulator settings were: compliance = 0.5 mL/cmH2O, resistance = 125 cmH2O/L/s, muscle pressure (Pmus) = sinusoidal, 25% rise, 0% hold, 25% release, frequency = 65/min. Pmus was varied from 6.5 to 26 cm H2O to generate tidal volumes of 3 -12 mL. Volumes from 5 breaths were compared with Kruskal-Wallace ANOVA, mean Pmus values were compared with t-test. Differences with P < 0.05 were considered significant.

Results:
Mean tidal volume data are summarized in the table. Tidal volumes were statistically different at all Pmus settings. All pairwise comparisons were significant at tidal volume = 9 mL so devices could be ranked from low to high effect on tidal volume: ventilator, simulator only (unloaded), FO, FOF, bubble, CHAS. The ventilator overcompensated a small amount (0.7 cm H2O cm H2O) thus increasing volume slightly (0.46 mL) compared to unloaded breathing. For bubble or CHAS, patient effort (Pmus) would have to increase from 2% to 11% to maintain tidal volume delivery. This was significantly different (P < 0.001) from an increase of 0% to 3% for FO or FOF systems.

Conclusions:
The large variability in NCPAP design may effect breathing pattern and patient effort enough to have clinical importance. In this simulation, the ventilator imposed the least load and the AirLife nCPAP System imposed the most.