The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

EFFECTS OF LUNG MECHANICS ON OXYGEN DELIVERYWITH NASAL CANNULAE

Steven Zhou, Shannon E. Cook, Megan McKenney, Robert L. Chatburn; Respiratory Institute, Cleveland Clinic, Cleveland, OH

The standard model for prescribing oxygen for chronic obstructive pulmonary disease (COPD) patients assumes the fraction of inspired oxygen (FiO2) increases by 4% per L/min of oxygen delivered by nasal cannula (Respiratory Care Equipment 2nd ed, Lippincott, 1999:66). The model also assumes that a nasal “anatomic reservoir” (AR) is flushed with oxygen during the last portion of expiration when expiratory flow is zero. However, with COPD, expiratory flow may not be zero, thus reducing the FiO2. The purpose of this study was to evaluate the effects of breathing patterns on FiO2 and the sensitivity of oxygen delivery to the presence of an AR. We hypothesized that simulated FiO2 would decrease with the COPD breathing pattern at lower flows and that FiO2 would be the same at higher flows for both lung models. METHODS: A high flow cannula (Fisher & Paykel) and a low flow cannula (Airlife) were tested on an ASL 5000 lung simulator (Ingmar Medical, Inc) along with simulated nares. Cannula flow was 1-60 L/min. The lung simulator was set at sinusoidal patient effort, 33% inspiration with closed loop control of tidal volume = 500 mL. Simulator settings were normal lungs: compliance (C) = 100 mL/cm H2O, resistance (R) = 3 cm H2O/L/sec, frequency (F) = 12 breaths/min; COPD settings were: C = 85 mL/cm H2O, R = 12 cm H2O/L/sec, F = 15 breaths/min. Data were collected approximately every 10 seconds for each experimental setup. Mean values (of 10 measurements) for FiO2 were compared with two-way ANOVA; P values <0.05 considered significant. RESULTS: Data are shown in figure. FiO2 was less with COPD pattern for flows less than 40 L/min (P< 0.001). For normal lung, FiO2 (%) = 4.5 + 24. For COPD, FiO2 (%) = 4.1 + 21. CONCLUSIONS: Differences from normal breathing patterns caused by obstructive lung disease can make clinically important decreases in FiO2 by nasal cannula. There may be approximately a 1 L/min increase in flow necessary to obtain the same FiO2 for patients suffering from COPD compared to normal patients. Very high flows (40 or 60 L/min for either the normal or COPD lung model) can generate about 100% FiO2. Sponsored Research - None

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