Canadian Journal of Anesthesia, Vol 15, 564-578, Copyright © 1968 by Canadian Anesthesiologists' Society

Predictable Oxygen Concentrations with the Bird Respirator

¹ Department of Anaesthesia, University of Western Ontario, London, Canada

Experimentation with the Bird Mark 7 respirator using the Bird Parallel Inspiratory Fow Mixing Cartridge (999 1289) to provide varying concentrations of oxygen in the inspired gas mixture was carried out. It was found that changes in the absolute pressure did not interfere significantly with the predictability of the oxygen concentrations obtained. However, the oxygen level did vary with changes in flow, being influenced more specifically by the ratio between the flow through the cartridge and the flow through the respirator; i.e., the oxygen concentration was directly proportional to the flow through the cartridge and inversely proportional to the flow through the respirator.

Though there is probably variation from one respirator to another, there appeared to be no reason why this mixing cartridge, when calibrated to one particular respirator, would not produce satisfactorily predictable oxygen concentrations within the framework of clinical usefulness.

Some recommendations might be made to the manufacturer, namely that (1) a graduated scale be provided for the oxygen metering valve, (2) the nebulizer air metering valve be fixed in one position, probably at one full turn, to prevent accidental closure and inadequate humidification, and (3) the respirator be operated on air without the venturi to obtain the best control of oxygen mixtures.

Note:

Presented at the Annual Meeting, Canadian Anaesthetists' Society, May 13-16, 1968.