A Bench Study comparison of Demand Oxygen Delivery Systems and Continuous Flow Oxygen

Abstract

Background

Currently available methods for conserving oxygen include transtracheal cath-eters, reservoir cannulae, and demand oxygen delivery systems (DODS). DODS do not deliver oxygen during exhalation, and most models do not deliver oxygen during portions of the inspiratory cycle. To determine selected performance differences between DODS models and continuous flow oxygen (CFO), we conducted a bench model evaluation of 7 DODS models and CFO.

Methods

A bench model was constructed to simulate a nose, airway, and alveolar chamber. A linked ven-tilator drove the alveolar chamber to generate 3 respiratory patterns, at frequencies of 15, 20, and 26 per minute. DODS and CFO were tested at settings of 1, 2, 4, and 6 L/min. The fraction of inspired oxygen (FIO2) in the alveolar chamber was measured for each condition. Oxygen use efficiency (OUE) was calculated for each device by determining oxygen in the alveolar chamber/oxygen used by the device.

Results

The DODS models differed with regard to flow delivery profile. Supplemental oxygen (FIO2, increase over 21%) for CFO declined markedly (43%) with increasing frequency, and was better maintained for the DODS models (average of 10% decrease). DODS that deliver an early inspiratory pulse tended to maintain FIO2 with increases in frequency and to be more efficient with oxygen use. OUE was 21% for CFO, and ranged from 42% to 100% for DODS models.

Conclusions

DODS models were not equivalent to CFO or to each other in FIO2 or OUE. DODS conserve oxygen and may maintain FIO2 better than CFO when respiratory frequency increases. DODS models differ and may require setting adjustments to achieve equiva-lent FIO2 to CFO or to other models. To optimally customize oxygen therapy to the patient, the DODS model or CFO should be set to meet adequate saturation goals (ie, > 90%) under conditions of usual use, including rest and exercise.