The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts


Author: John W. Earl RRT, BS
Director Respiratory Care Service (retired)
VA Medical Center, White River Jct. Vermont 05009
Objectives. To determine oxygen flow rate needed to provide an FiO2 greater than 90% using a non-rebreather mask (NRB), simple mask (SM), and a simple mask with side ports taped (SMT).

Flow rates of 10, 15, 30, 45, and 60 LM were tested. Each test was performed using a healthy subject wearing a firmly secured mask while performing quiet breathing at a rate of 12-18 breaths per minute at tidal volumes of 300-500 mls. Each test was performed for 5 minutes. A five-minute time frame was established by having participant perform an N2 washout (<1.5% N2) within 3 minutes. Nitrogen (N2) washout method was used to determine the partial pressure of oxygen (PO2) contained in the lungs following each test. The study was performed using Sensor Medics V-Max ® N2 washout system. Calibration was performed per manufacturers recommendations. N2 washout measurements were taken following a final deep breath exhaled into a closed system. Each test was separated by a 10-minute interval per previous established criteria.

Results: Expired PO2:
10 LM 15 LM 30 LM 45 LM 60 LM  
 SM-51% SM-51% SM-55% SM-73% SM 86%

NRB-50% NRB-56% NRB-77%, NRB-78% SM taped-93%

Discussion: 60 LM came closest to providing >90% FiO2. It is apparent that a simple mask can be almost as effective as a NRB mask using high flow, and more so with ports taped shut. Taping or providing reservoirs to the side ports of mask works well to increase FiO2 and does not incur backpressure or increased work of breathing. It must also be noted that resting minute ventilation was performed which is rarely observed of patients suffering SOB from fluid filled lungs or pneumonia.

It would seem prudent to provide a taped simple or NRB mask operating above 60 LM to ensure maximum supply of FiO2 over the short term. Flow meters will deliver 90 LM on flush setting. Current thinking that a NRB mask running at 15 Lm is an acceptable way to deliver high FIO2 is not valid and should be revised.

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