Background: Using portable oxygen cylinders with integrated flow meter/regulator assemblies has become commonplace in the clinical setting for staff convenience. Single unit cylinders allow for the end-user to select a cylinder and use right away without first needing to attach a regulator. These single unit cylinders typically have both low flow and 50 psig attachments to meet most needs within the hospital. The flow meter for the regulator is a restrictor-type device which is comprised of a variable orifice which controls gas flow. Per Charles/Gay-Lusac’s law, gas volume changes with variation in temperature. Our purpose is to investigate the degree of variation in gas delivery with changes in cylinder temperature Methods: Oxygen cylinders which have been stored for a minimum of 24 h within the hospital were eligible for investigation. The following data was collected: ambient temperature, cylinder temperature, cylinder serial number, supplier, cylinder material, and flow values at 2, 4, 8, and 15 L/min settings. Flow was validated using a Liter Meter (ResOne, Bentonville, AR) for either 0 – 8 L/min or 0 – 15 L/min. Cylinder temperature was determined using an infrared thermometer (Kobalt, model 54526) with the target aimed onto the metal surface of the cylinder. Results: 415 unique portable cylinders were evaluated. Ambient temperature ranged from 68 –75.8˚F (20 – 24.3˚C) and cylinder temperature ranged from 62.8 – 76.1˚F (17.1 – 24.5˚ C), P < .01. Cylinder temperature did have a significant influence on measured flow (P < .01). Conclusions: It is unlikely to maintain a uniform temperature throughout a hospital. Cylinder temperature does have a statistically significant effect on flow output, but this variation may not be enough to be clinically significant. Ambient temperature variation within the building can influence flow meter performance. Devices connected to portable cylinders such as small volume nebulizers may not perform optimally. Flow meters are calibrated at 70˚ F and temperature variation may affect performance. Care should be taken when using portable cylinders to assure the patient is maintaining the desired SpO2 and flow adjustments may be necessary.Table 1: Measured flow by cylinder temperature groupingFigure 1: Effect on measure flow with variation in cylinder temperature
Evans et al. (Tue,) studied this question.