Octave waveband analysis to determine sound frequencies and intensities produced by nebulizers and humidifiers used with hoods.

BACKGROUND: health-care practitioners should be aware of how their equipment and practices can increase the patient's risk for noise-induced hearing loss. PURPOSE: We conducted this study to determine the type of noise produced by humidifiers and nebulizers used with hoods in the neonatal intensive care unit (NICU). We performed octave waveband analysis to determine sound intensities and frequencies because degree of hearing loss from noise exposure is related to the intensity of sound, frequency of sound and duration of exposure. METHODS: We studies 4 simple humidifiers, 3 heated humidifiers, and 4 nebulizers. Sound levels were measured at various frequencies, flows, and water levels using Peace and Shiley oxygen hoods. RESULTS: The findings show that sound levels were significantly louder (p.0.001) for nebulizers compared to humidifiers. Aquapak nebulizers pose the greatest risk for hearing loss because they produce sound at the highest frequencies and volumes. The peak sound levels of humidifiers not only were significantly lower but also occurred at the lowest sound frequencies, which are the least damaging to hearing. Sound levels were generally higher across sound frequencies at higher flows and with the Peace Hood. CONCLUSION: We conclude that heated humidifiers produce lowest sound intensities at the lowest sound frequencies and, consequently, are most appropriate for use in the NICU.

Analysis of resistance to gas flow in nine adult ventilator circuits.

We measured the resistance in nine complete ventilator circuits, partial circuits and 7, 8, and 9 mm ID endotracheal tubes at flow rates of 20 to 120 liters per minute. We found a statistically significant (p less than 0.01) increase in resistive pressure with increases in flow rate, as the diameter of the ETT decreased, and as each component of the ventilator circuit was added to the ETT. There was a curvilinear increase in resistive pressure to increase in flow rate. However, when resistances were computed, the Bennett cascade "circuit" created higher resistance at 20 lpm than at flow rates up to 120 lpm. The Bennett cascade humidifier added the greatest resistive pressure, 3.5 to 8.5 cm H2O, the Engstrom Edith, 0.5 to 6.5 cm H2O, and the Conchapak added the least, 0.0 to 2.5 cm H2O at flow rates of 20 to 120 lpm. After all the components of the ventilator circuit were attached to the ETTs, there was approximately a 97 to 450 percent increase in resistive pressure compared to the resistive pressure created by the ETTs alone.