Background: O2 flow guidelines for simple masks (SM) are restricted (≤10 L/min), but open-ended for non-rebreather masks (NRM) (≥ 10 L/min),1,2 despite having uniform mask dimensions (5 x 3.3). Estimated maximum FIO2 with these flows are 0.50 and 0.60-0.80, respectively. However, these guidelines conspicuously lack supportive data. Therefore, constraining SM to 10 L/min is unreasonable and unnecessarily restricts the flexibility for O2 delivery, particularly in resource-deprived countries. We explored FIO2 delivery by SM and NRM at 4 flow settings (10, 12, 15, and 20 L/min) under 3 breathing patterns with increasing minute ventilation (VE) demand: normal-rest (6 L/min), unassisted breathing in ARDS (8 L/min) and hyperpnea (14 L/min). Methods: A custom-designed adult manikin face was attached to an ASL-5000 lung simulator (Ing Mar Medical, Pittsburgh, PA) with an O2 analyzer placed between the face piece and simulator. Masks were tightly fitted to the face-piece. A 2-point O2 calibration was done prior to study, and 1-point calibration was repeated prior to each test run. Breathing patterns for each VE were: 6 L/min (VT 350 mL x 17), 8 L/min (VT 350 mL x 24), and 14 L/min (VT 550 mL x 26). All settings and conditions were repeated. FIO2 variability with each paired-run was ≤ 0.005. Results: At all O2 flows and breathing patterns SM was able to deliver an FIO2 ≥ 0.50; often reaching an FIO2 ≥ 0.60. The FIO2 generated with NRM met guideline estimations except for O2 flows 0.50.1. AARC Clinical Practice Guidelines 2002:718. 2. Egan’s Fundamentals, 12th edition 2021:912.Table 1.Mask↓Vmin/O2 Flowrate →10 L/m12 L/m15 L/m20 L/mSM6 L/m0.590.600.600.61 8 L/m0.560.580.580.70 14 L/m0.510.540.570.60NRM6 L/m0.710.740.760.82 8 L/m0.650.700.760.82 14 L/m0.480.530.590.64
Kallet et al. (Sun,) studied this question.