Maximizing oxygen delivery during mechanical ventilation with a portable oxygen concentrator.

BACKGROUND: Transportation of the critically ill or injured war fighter requires the coordinated care and judicious use of resources. Availability of oxygen (O2) supplies for the mechanically ventilated patient is crucial. Size and weight of cylinders makes transport difficult and presents an increased risk of fire. A proposed solution is to use a portable oxygen concentrator (POC) for mechanical ventilation. We tested the SeQual Eclipse II POC paired with the Impact 754 and Pulmonetics LTV-1200 ventilators in the laboratory and evaluated the fraction of inspired oxygen (FIO2) across a range of minute volumes.

METHODS: Each ventilator was attached to a test lung and pressure, volume, flow, and inspired oxygen (FIO2) was measured by a gas or flow analyzer. Ventilators were tested at a tidal volume (VT) of 500 mL; an inspiratory time of 1.0 second; respiratory rates of 10, 20, and 30 breaths per minute; and positive end-expiratory pressure of 0 and 10 cm H2O. The LTV 1200 was tested with and without the expiratory bias flow. The Eclipse II was modified to provide pulse dosing on inspiration at 3 volumes (64, 128, and 192 mL) and continuous flow at 1 L/min to 3 L/min. Six combinations of ventilator settings were used with each POC setting for evaluation. O2 was injected at the ventilator gas outlet and patient y-piece for pulse dose and continuous flow. Additionally, continuous flow O2 was injected into the oxygen inlet port of the LTV 1200, and a reservoir bag, on the inlet port of the Impact 754. All tests were done with both ventilators using continuous flow, wall source O2 as a control. We also measured the FIO2 with the concentrator on the highest pulse dose setting while decreasing ventilator VT to compensate for the added volume.

RESULTS: The delivered FIO2 was highest when oxygen was injected into the ventilator circuit at the patient y-piece using pulse dosing, with the VT corrected. The next highest FIO2 was with continuous flow at the inlet (LTV), and reservoir (Impact). Electrical power consumption was less during pulse dose operation.

SUMMARY: Oxygen is a finite resource, which is cumbersome to transport and may present a fire hazard. The relatively high FIO2 delivered by the POC makes this method of O2 delivery a viable alternative to O2 cylinders. However, patients requiring an FIO2 of 1.0 would require additional compressed oxygen. This system allows O2 delivery up to 76% solely using electricity. An integrated ventilator or POC capable of automatically compensating VT for POC output is desirable. Further patient testing needs to be done to validate these laboratory findings.