Acoustic environment at a neonatal intensive care unit

Introduction:

Newborns who are sick, premature or of low body weight require special care provided in neonatal units where they spend their earliest moments of life. The fetus of 16 – 19 weeks gestational age is able to respond to auditory stimuli, the first reactions are to 500 Hz or lower frequencies and then reaching higher frequency range when maturing to term. Little attention has been paid to the auditory surrounding of premature babies, although environmental noise has been identified as a potential risk factor for worse neurological development. Extrapolation of adult data led to the recommendation of the American Association of Pediatrics to define a sound pressure level (SPL) below 45dB to be accurate for a neonatal intensive care units (NICU). This project aims at the characterization of the typical acoustic environment of a preterm baby.

Methods:

Within an empty incubator (GE Giraffe, Omnibed), currently not in use but turned on, sound was recorded in multiple settings at a minimum sampling rate of 48 kHz and linear depth of 16 bit. Using this approach, we were able to characterize the frequency response of the incubator which is used at our Neonatology department (GE Giraffe, Omnibed) and to additionally assess for the acoustic surrounding in the Neonatal intensive care unit (NICU).

Results:

There was a noise floor of 44 dB SPL within a frequency range of 1300 – 1500 Hz originating from the fan inside the incubator. The average sound pressure level during acoustic evaluation within the NICU was 53 dBA and it was 54% of the time above 45 dB. Due to the incubator“s acoustic properties, there was only little dampening at a frequency of 250 Hz (closed doors). At higher input frequencies SPL was reduced by 20dB on average. During a recording time of 6 hours (from 10 to 16 o' clock), we detected 194 peak events at beyond 65dBA, most of them were short (< 0.4 s). ECG alarms from different stations could be detected inside the incubator with no information on the eventual position of the sound source. However, most of the peaks were attributable to opening and closing of the doors at the cabinets or the entrance of the NICU.

Discussion:

Opening and closing of cabinet doors or drawers are an important source of mechanical, loud (> 65dB SPL) and short (< 0.4 seconds) noise. They are the main source of transient noises recorded. However, preterms are exposed to considerable high [VK1] and diffuse basal acoustic stimuli. Since higher frequencies were more strongly attenuated by the investigated incubator than lower ones, monitor manufacturers could use alarms at higher frequencies to reduce acoustic impact on the baby. The definition of a „good acoustic environment“ based simply on a threshold sound pressure level should be replaced by one that includes at least the frequency spectrum. The ultimate goal will be to balance sounds and shape the preterm acoustic environment according to the baby“s needs.