Oropharyngeal Oxygen Concentration Is Dependent on the Oxygen Mask System and Sampling Location

Abstract

Background: Numerous oxygen delivery systems are used to treat hypoxemia. It is unknown if F_IO2 at the lips predicts oropharyngeal F_IO2 for various oxygen mask systems. We tested whether F_IO2 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_IO2 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_IO2 levels differed significantly for the 4 delivery mask systems (P < .001) and by sampling catheter location (P < .001). Differences in mean F_IO2 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_IO2 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_IO2 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_IO2 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_IO2 measures at the oropharynx and the lips were only consistent for the closed mask system. (ClinicalTrials.gov registration NCT02523586.).

Keywords: critical care; equipment design; hypoxemia prevention and control; oxygen inhalation; perioperative; respiratory insufficiency; respiratory therapy; therapy.