Abstract
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 < 15 L/min during hyperpnea.
Conclusions:
SM O2 flows of 12-20 L/min produced consistent FIO2 > 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/m
12 L/m
15 L/m
20 L/m
SM
6 L/m
0.59
0.60
0.60
0.61
8 L/m
0.56
0.58
0.58
0.70
14 L/m
0.51
0.54
0.57
0.60
NRM
6 L/m
0.71
0.74
0.76
0.82
8 L/m
0.65
0.70
0.76
0.82
14 L/m
0.48
0.53
0.59
0.64
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