The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

THE MAGNITUDE OF VOLUME OSCILLATIONS DURING BUBBLE NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE ARE AFFECTED BY THE CPAP LEVEL AND BIAS FLOW SETTING

Jay Zignego1, Robert M. DiBlasi1, Dennis M. Tang1, Risa K. Vanantwerp2, Peter C. Richardson1; 1Center for Developmental Therapeutics, Seattle Children’s, Seattle, WA; 2Bioengineering, University of Washington, Seattle, WA

BACKGROUND. Bubble continuous positive airway pressure (B-CPAP) is a form of non-invasive respiratory support that is commonly applied to spontaneously breathing infants with lung disease. Small amplitude, high-frequency airway pressure (PAW) oscillations are created by bubbles forming when gas exits through the water-seal column. Experimental data suggests that these pressure oscillations may enhance lung recruitment and gas mixing, similar to high-frequency ventilation in intubated subjects. However, the ventilation effects of B-CPAP have not been evaluated using a “leaky” nasal prongs interface. We designed a series of experiments to test the impact of different CPAP levels and bias flow settings on the delivered volume oscillations to an infant test lung model affixed with leaky nasal prongs during simulated B-CPAP. METHODS. In the first study, we placed an infant head model affixed with #2 Hudson nasal prongs within a plethysmograph and measured the leak at flows of 4,6,8, and 10 L/min at CPAP of 2,5,7,10, and 12 cmH2O. In the second study, we attached the head model and prongs to an infant mechanical lung model (C: 0.53 mL/cm H2O and R: 185 cmH2O/L/s) sealed within a plethysmograph. We measured pressure changes within the plethysmograph resulting from the test lung expanding during bubbling. We used the pressure changes and prelythsmograph calibration factor to calculate the volume oscillations delivered to the lung model during B-CPAP at flows of 4,6,8 and 10 L/min at CPAP of 4,6,8 and 10 cmH2O. RESULTS. The leak remained constant at each pressure, regardless of flow, yielding flow leaks of 1.54, 2.70, 3.22, 3.81, 4.21 L/min at CPAP of 2, 5, 7, 10 and 12 cmH2O respectively. The delivered volumes to the test lung can be seen in the figure below. The lower CPAP (4 and 6) settings resulting in greater pressure and volumes transmitted to the lung model at all flows, and at a bias flow of 4 L/min, CPAP of 10 cmH2O was unachievable due to 100% leak through prongs. CONCLUSIONS. Our findings suggest that volume oscillations created by bubbling increases when increasing the bubbler flow, and the prongs in the infant head model behave as a pressure dependent leak. This means the leak percentage is greatest at high CPAP settings and low bias flows, which is consistent with the finding that the delivered volume to the test lung is 50% greater at a CPAP of 4 than at 10 cmH2O when bias flow is set to 10 L/min. Sponsored Research - None

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 2009 Abstracts » THE MAGNITUDE OF VOLUME OSCILLATIONS DURING BUBBLE NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE ARE AFFECTED BY THE CPAP LEVEL AND BIAS FLOW SETTING