Equivalence of Field-Expedient Oxygen Reservoirs for Transport Ventilators Paired With Portable Oxygen Concentrators: A Bench Evaluation

Introduction Portable oxygen concentrators (POCs) are increasingly replacing compressed oxygen cylinders for mechanical ventilation in prolonged field care (PFC), en route critical care, and disaster response. Because POCs deliver a maximum continuous flow of 3-10 L/min while transport ventilators generate peak inspiratory flow rates exceeding 60 L/min, an interposed oxygen reservoir is required to buffer this flow mismatch and maintain an adequate fraction of inspired oxygen (FiO2). When proprietary reservoir kits are unavailable, clinicians improvise using bag-valve-masks (BVMs) or corrugated ventilator tubing. A persistent practice involves removing the BVM valve assembly to reduce perceived resistance. No study has comparatively evaluated these field-expedient techniques against the proprietary standard, quantified the magnitude of the reservoir effect itself, or tested performance across the physiologic extremes encountered in critical illness. Materials and Methods A controlled in vitro factorial design tested six configurations—proprietary 3L reservoir (control), intact BVM with filter, intact BVM without filter, modified BVM with valve removed, corrugated tubing, and a no-reservoir baseline reference—across nine minute ventilation (VE) settings (5.0-25.0 L/min) using a Zoll 731 ventilator and DeVilbiss 10L concentrator. Ten independent teardown/rebuild trials were performed per condition (n = 540). Non-inferiority to the proprietary standard was assessed at δ = −0.05 FiO2 units. Results Without any reservoir, the POC-ventilator system delivered inadequate oxygen enrichment, with FiO2 declining from 0.61 at VE 5.0 L/min to 0.35 at VE 25.0 L/min—approaching room air. All reservoir configurations dramatically improved oxygenation (ΔFiO2 = +0.24 to +0.56 versus no reservoir). Among the five reservoir configurations, field-expedient options performed equivalently to one another, with absolute FiO2 separation typically less than 2%. The proprietary reservoir was optimal at standard demands (VE ≤12.5 L/min); at high demands (VE ≥20 L/min), all field-expedient configurations outperformed it, with corrugated tubing achieving the highest FiO2. BVM valve removal conferred no benefit at any demand level and significantly worsened performance at high flows (intact BVM FiO2 0.746 vs. modified 0.722 at VE 17.5 L/min; P < .001). Conclusions Oxygen reservoir interposition is essential for clinically meaningful oxygen delivery from POC-ventilator systems. Field-expedient reservoirs deliver adequate enrichment and perform equivalently to one another across a broad range of demands. Clinicians can improvise with confidence using available materials. BVM valve removal is unnecessary and should be avoided to preserve the device’s dual-use capability as a manual resuscitator.