Effect of the anatomic reservoir on low-flow oxygen delivery via nasal cannula: constant flow versus pulse flow with portable oxygen concentrator.

Abstract

The F(IO(2)) for a nasal cannula with constant flow (CF) depends on the anatomic reservoir (AR), which is affected by changes in frequency and end-expiratory flow. Conversely, pulse flow (PF) devices do not require the AR. The purpose of this study was to compare the F(IO(2)) delivered by a nasal cannula supplied by CF via oxygen tank with that delivered by PF delivered via portable oxygen concentrator. Hypotheses were (1) a lung model of COPD with non-zero end-expiratory flow decreases F(IO(2)) for CF more than for PF, and (2) CF and PF perform differently in terms of F(IO(2)) delivery, despite having equivalent settings. Normal and COPD lung models were simulated (IngMar Medical ASL 5000) using published human data: normal: breathing frequency = 15 breaths/min, R(in) = 4 cm H2O · s · L(-1), R(out) = 4 cm H2O · s · L(-1), C = 60 mL · cm H2O(-1), tidal volume (VT) = 685 mL, P(max) = 11.95 cm H2O, increase = 33%, and release = 28; COPD: breathing frequency = 20 breaths/min, R(in) = 12 cm H2O · s · L(-1), R(out) = 25 cm H2O · s · L(-1), C = 66 mL · cm H2O(-1), VT = 685 mL, Pmax = 24.52 cm H2O, increase = 35%, and release = 23%. CF was 1-5 L/min. Portable oxygen concentrators used were Solo2 (Invacare), XPO2 (Invacare), FreeStyle (AirSep), Focus (AirSep), One G3 (Inogen), and LifeChoice ActivOx (Inova Labs). CF produced significantly higher F(IO(2)) at all settings for normal lungs but lower for COPD lungs compared with Solo2. COPD reduced the F(IO(2)) for CF but had a smaller variable effect for PF. Data show there is no equivalency between PF setting and CF rates for the portable oxygen concentrators tested. CF oxygen delivery via a nasal cannula is significantly reduced by elimination of the AR in a model of COPD, yielding clinically important decreases in F(IO(2)). PF (delivered with a portable oxygen concentrator) is relatively unaffected. This study supports the recommendation that clinicians and caretakers should titrate the PF setting to each patient's unique oxygen requirements.