| Sumario: | BACKGROUND: Numerous oxygen delivery systems are used to treat hypoxemia. It is unknown if F... at the lips predicts oropharyngeal F... for various oxygen mask systems. We tested whether F... measurements differed between the lips and oropharynx, and whether this difference depends on the mask system. METHODS: Ten healthy volunteers had one sampling catheter positioned at the lips and another catheter in the oropharynx. F... was sampled at each location while the subjects breathed normal tidal volumes with oxygen at 15 L/min via 4 delivery devices: a simple mask, a non-rebreather mask, a face mask with a diffuser that concentrates and directs O2 toward the mouth and nose (mask with diffuser), and a closed mask with a Jackson-Rees circuit. Data were analyzed by using a linear mixed model to account for subject crossover in the repeated measures design. RESULTS: F... levels differed significantly for the 4 delivery mask systems (P < .001) and by sampling catheter location (P < .001). Differences in mean F... between the lips and the oropharynx were observed for the mask with diffuser (difference 0.30, 95% CI 0.25-0.36; P < .001), and non-rebreather mask (difference 0.09, 95% CI 0.04-0.15; P = .001). The mean F... at the oropharynx was highest for the closed mask (0.97, 95% CI 0.92-1.00), followed by the non-rebreather mask (0.76, 95% CI 0.72-0.81), simple mask (0.62, 95% CI 0.58-0.67), and the mask with diffuser (0.51, 95% CI 0.46-0.56). At the lips, the mean F... was highest for the closed mask (0.97, 95% CI 0.92-1.00), followed by the non-rebreather mask (0.86, 95% CI 0.81- 0.90), OxyMask (0.81, 95% CI 0.76-0.86), and simple mask (0.67, 95% CI 0.62-0.71). CONCLUSIONS: With high oxygen flows and normal tidal volume breathing, F... measurements obtained at the oropharynx or at the lips depended on the device used, with the mask with diffuser showing the most significant discrepancies. F... measures at the oropharynx and the lips were only consistent for the closed mask system.
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