The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

EFFECTS OF LUNG MECHANICS ON OXYGEN DELIVERY USING SIMPLE OXYGEN MASKS

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

INTRODUCTION: Chronic obstructive pulmonary disease (COPD) is often treated with supplemental oxygen through an oxygen mask. The fraction of inspired oxygen (FiO2) is estimated with a mathematical model that includes oxygen contribution from the device plus the patient’s anatomic reservoir. The model assumes the reservoir is flushed with oxygen during the last portion of normal expiration when expiratory flow is zero – a potentially incorrect assumption for patients with COPD as expiratory flow may never be zero. The purpose of this study was to compare FiO2 llevels in simulated normal and COPD adult patients using two different mask types, a simple and diffusing mask. Diffusing masks differ from simple masks in that they direct oxygen flow towards the nose and mouth by causing a vortex to form. We hypothesized that COPD lung mechanics would decrease FiO2 levels and that the diffusing mask would result in lower FiO2 levels than the simple mask due to its lack of a reservoir. METHODS: A lung simulator (ASL 5000 Ingmar Medical, Inc.) and a simulated head with nares was used to test one simple mask (SM, Cardinal Health Airlife, adult size) and one diffusing mask (DM, Southmedic OxyMask, Adult Size). Each mask was sealed around the face to represent optimal oxygenation conditions. A tube (100 mL dead space) connected the head to the simulator. Lung simulator settings: sinusoidal patient effort, 33% inspiration, closed loop control of tidal volume = 500 mL. For normal lung: frequency (F) = 12 breaths/min. compliance (C) = 100 mL/cmH2O, resistance (R) = 3 cmH2O/L/sec. For COPD lung: F = 15/min, C = 85 mL/cmH2O, R = 12 cm H2O/L/sec. Oxygen flows were 5-9 L/min. Data were collected every 10 seconds for each experimental setup. Mean values (of 10 measurements) were compared with 2 way ANOVA. RESULTS:Mean values are shown in the Figure. All standard deviations were < 1%. FiO2 for normal lung was higher at all flows than COPD (P < 0.001). FiO2 was higher for the simple mask at all flows. CONCLUSIONS: These findings suggest that COPD lung mechanics decrease the amount of oxygen delivered with simple and diffuser oxygen masks. Despite the fact that both devices we evaluated are classified as simple oxygen masks, the newer design of the diffuser mask seems to result in less oxygen delivery than the conventional design. This study reinforces the idea that low flow oxygen therapy must be titrated to individual patient needs (eg using pulse oximetry). Sponsored Research - None

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