Newborn Incubators Do Not Protect from High Noise Levels in the Neonatal Intensive Care Unit and Are Relevant Noise Sources by Themselves

Abstract

Background: While meaningful sound exposure has been shown to be important for newborn development, an excess of noise can delay the proper development of the auditory cortex.

Aim: The aim of this study was to assess the acoustic environment of a preterm baby in an incubator on a newborn intensive care unit (NICU).

Methods: An empty but running incubator (Giraffe Omnibed, GE Healthcare) was used to evaluate the incubator frequency response with 60 measurements. In addition, a full day and night period outside and inside the incubator at the NICU of the University Hospital Zurich was acoustically analyzed.

Results: The fan construction inside the incubator generates noise in the frequency range of 1.3-1.5 kHz with a weighted sound pressure level (SPL) of 40.5 dB(A). The construction of the incubator narrows the transmitted frequency spectrum of sound entering the incubator to lower frequencies, but it does not attenuate transient noises such as alarms or opening and closing of cabinet doors substantially. Alarms, as generated by the monitors, the incubator, and additional devices, still pass to the newborn.

Conclusions: The incubator does protect only insufficiently from noise coming from the NICUThe transmitted frequency spectrum is changed, limiting the impact of NICU noise on the neonate, but also limiting the neonate's perception of voices. The incubator, in particular its fan, as well as alarms from patient monitors are major sources of noise. Further optimizations with regard to the sound exposure in the NICU, as well as studies on the role of the incubator as a source and modulator, are needed to meet the preterm infants' multi-sensory needs.

Keywords: neonatal intensive care unit; newborn incubators; noise; sound.

Figure A1

Literature review about “noise AND NICU” according to the PRISMA guideline.

Figure 1

(a) Incubator in an NICU. In the picture, half of the top of the incubator is covered by a blanket to decrease the brightness inside the incubator. Image source: University Hospital Zurich; with permission. (b) Close-up of the incubator used in the study. The paths of two main sources of noise for the incubator are indicated by red arrows: sound coming from outside and inside. The orange circle indicates the position of the measurement microphone.

Figure 2

(a) Spectrogram of the noise produced by the incubator during the start-up phase. (b,c) Spectrograms of the warning and danger sounds produced by the IntelliVue MX550, Philips monitor next to the incubator.

Figure 3

(a) Noise spectra recorded inside and outside an incubator located in an NICU. Peak frequencies are indicated at the specific peaks. The recording was done in an NICU with several incubators working and under normal clinical working conditions. (b) Time-series of SPL variations over about 2 h, measuring inside and outside an incubator. (c) Distribution of SPL values shown in (b).