The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

MECHANICAL EFFECTS OF HIGH FLOW NASAL CANNULA IN NORMAL AND OBSTRUCTIVE ADULT LUNG MODELS

Sherry Babic, Shannon Cook, Robert L. Chatburn; Respiratory Institue, Cleveland Clinic, Cleveland, OH

BACKGROUND: Studies demonstrate that high flow (>2 L/min) nasal cannulas in neonates produce continuous positive airway pressure (CPAP) similar to conventional nasal CPAP. The purpose of this study was to measure the mechanical effects generated by high flow nasal cannula (HFNC) adult normal and obstructive lung models. Specifically, we tested the hypothesis that both cannula flow and lung mechanics affect tidal volume and end expiratory pressure. METHODS: One adult HFNC (Hudson RCI) was used. Nares were simulated by holes drilled through an aluminum block. Breathing was simulated with an ASL 5000 lung simulator (Ingmar Medical, Inc.). Simulator settings for the COPD patient were: compliance = 85 mL/cm H2O, resistance = 12 cm H2O/L/sec, frequency = 24 breaths/min, muscle pressure (Pmus) = sinusoidal, 15 cm H2O, 33% rise, 0% hold, 33% release, to generate a volume of 500 mL. Settings for the normal patient were: compliance = 90 mL/cm H2O, resistance = 3 cm H2O/L/sec, frequency = 12 breaths/min, 33% rise, 0% hold, 33% release, Pmus = sinusoidal, 5.2 cm H2O to generate volume = 500 mL. Cannula flows 0, 10, 20, 40 and 60 L/min. For each experimental setting averages of 10 breaths were compared by t-tests for both PEEP and volume. Differences between lung modes were tested with Mann Whitney Rank Sum test. Differences with P < 0.05 were considered significant. RESULTS: The added resistance of the cannula in the nose, without flow, caused a decrease in tidal volume (498 and 467 mL, normal and COPD respectively, P < 0.001). For both the normal and COPD lung, a perfect, negative, polynomial (degree = 3) correlation (R2 = 1) between volume and flow and a positive polynomial (degree = 3) correlation between PEEP and flow (R2 = 1) were observed (Figure). For COPD. tidal volume was 44 mL lower than normal across flows and PEEP was higher 1.0 cm H2O (P < 0.029). CONCLUSION: HFNC generates a small PEEP effect which is larger in COPD. However, with an increased airway resistance (i.e., COPD patients), it can be assumed that significant air trapping occurred, evident by a decrease in expiratory volume. Caution should be used when using HFNC in adult COPD patients. Sponsored Research - None

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 2009 Abstracts » MECHANICAL EFFECTS OF HIGH FLOW NASAL CANNULA IN NORMAL AND OBSTRUCTIVE ADULT LUNG MODELS