Resp Care
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We evaluated the water-vapor output from four brands of unheated, prefilled bubble humidifiers-the Aerwey 300, the Aquapak 301, the McGaw 250, and the Travenol 500-at oxygen flowrates of 2, 4, 6, and 81/min. We recorded relative humidity (RH) and temperature in a test chamber at intervals over a minimum period of 24 h, and we calculated water-vapor content (WVC) and corresponding RH at 37 degrees C. Ambient RH was 53.4% +/- 5.25% (mean +/- 1 SD) at a test-chamber temperature of 26.2 degrees C +/- 0.79 degrees C. ⋯ A statistically significant decrease in mean WVC and RH at 37 degrees C occurred as the oxygen flowrate increased (P less than 0.001). None of the humidifiers was able to hydrate the source gas to a mean equivalent of 50% RH at 37 degrees C, at any flowrate. The design of the humidifier bubble diffuser and the source-gas flowrate appear to be the prime determinants of the humidification efficiency of unheated, prefilled bubble humidifiers.
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Degree of hearing loss in the infant is related to high-intensity or high-frequency sound (noise). We measured sound levels of 6 models of pneumatic nebulizers and 8 models of humidifiers at various flowrates, FIO2 settings, and water levels, when they were attached to incubators and oxygen hoods; we also evaluated sound levels from 2 models of ultrasonic nebulizers at various output settings. Among the pneumatic nebulizers, the recommended 58-dbA maximum sound level was exceeded by the Aquapak 621, Ohio Deluxe, and Puritan All-Purpose devices. ⋯ Among the humidifiers, all produced sound levels below the recommended 58-dbA maximum except the Travenol humidifier; the Bennett Cascade, Conchapak, Foregger, and Hudson humidifiers produced mean sound levels in the 43.0- to 43.5-dbA range. Sound levels increased under all conditions when the devices were used with oxygen hoods. The ultrasonic nebulizers produced low sound levels, but the high-frequency ultrasound they also produce may be undesirable for infants; this question requires further investigation.