© 2006 American Thoracic Society
The Low-Flow or High-Flow Oxygen Delivery System and a Low-Flow or High-Flow Nonrebreather MaskTo the Editor:I read with interest the recent article by Baillard and colleagues, wherein the authors have suggested that preoxygenation using noninvasive ventilation (NIV) is more effective at reducing arterial oxyhemoglobin desaturation than the usual method (1). However, the conclusions are limited by the fact that, in the control group, we are unable to determine the FIO2, which may well have been suboptimal. The authors have used nonrebreather masks, which are low-flow oxygen delivery systems that generally provide oxygen at flow rates lower than the patient's inspiratory demands. In other low-flow systems, if the total minute ventilation exceeds the flow capacity of the oxygen reservoir, room air is entrained (2). However, in the nonrebreather masks, there are two sets of one-way valves: one set located between mask and reservoir allows oxygen from the reservoir into the face mask but not in the other direction; the other set of valves at the exhalation port prevents room air from entering the mask, while allowing gas to escape during exhalation (3). In the study, the authors have used oxygen flow rates of 15 L/min, which is far lower than the usual flow demand of a patient in acute respiratory failure (more than 25–30 L/min) (4). In fact, the reservoir bag should not collapse during inspiration as this suggests flow rates that are insufficient to meet the patient's ventilatory demand. This can increase the patient's work of breathing as the patient struggles against the one-way valve to entrain room air. Thus, to compare the two groups adequately, in a similar study, a higher oxygen flow rate (close to 25–30 L/min) in the control arm or a high-flow nonrebreather mask (5) needs to be used to avoid discrepancy in oxygen delivery between the study and the control arm.
Postgraduate Institute of Medical Education and Research, Chandigarh, India FOOTNOTES Conflict of Interest Statement: R.A. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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