Do neonates hear what we measure? Assessing neonatal ward soundscapes at the neonates ears

TL;DR

These findings support the adoption of binaural measurements along with the integration of additional (psycho)acoustic metrics, such as tonality and transient event occurrence rates, to reliably characterise the neonatal auditory experience.

Abstract

Acoustic guidelines for neonatal intensive care units (NICUs) aim to protect vulnerable neonates from noise-induced physiological harm. However, the lack of recognised international standards for measuring neonatal soundscapes has led to inconsistencies in instrumentation and microphone placement in existing literature, raising concerns about the relevance and effectiveness of these guidelines. This study addresses these gaps through long-term acoustic measurements in an operational NICU and a high-dependency ward. We investigate the influence of microphone positioning, bed placement, and ward layout on the assessment of NICU soundscapes. Beyond traditional A-weighted decibel metrics, this study evaluates C-weighted metrics for low-frequency noise, the occurrence of tonal sounds (e.g., alarms), and transient loud events known to disrupt neonates' sleep. Using linear mixed-effects models with aligned ranks transformation ANOVA (LME-ART-ANOVA), our results reveal significant differences in measured noise levels based on microphone placement, highlighting the importance of capturing sound as perceived directly at the neonate's ears. Additionally, bed position and ward layout significantly impact noise exposure, with a NICU bed position consistently exhibiting the highest sound levels across all (psycho)acoustic metrics. These findings support the adoption of binaural measurements along with the integration of additional (psycho)acoustic metrics, such as tonality and transient event occurrence rates, to reliably characterise the neonatal auditory experience.

Figures (4)

• Figure 1: Floor plan depicting the layout of the neonatal intensive care unit (NICU) and high dependency (HD) ward. Measurement positions within the NICU are highlighted in violet, while the measurement point in the HD ward is marked in green. In both the NICU and HD wards, a SoundSign device was strategically positioned high on the wall.
• Figure 2: (a) Photo and (b) diagram of the in-situ measurement setup of the incubator in the NICU, and (c) a photo and (d) diagram of bassinet setup in the high-dependency ward.
• Figure 3: A- and C-weighted decibel metrics averaged by hour of the day across the entire measurement duration at NICU-A, NICU-B and HD-A measurement points.
• Figure 4: Occurrence rate of $\textit{OR}^h_\text{SNR}(5)$ and $\textit{OR}_{T}^h(0.4)$ averaged over the same daily 1-h period throughout the entire measurement campaign. A-weighted decibel metrics and tonality metrics averaged by hour of the day across the entire measurement duration at NICU-A, NICU-B and HD-A measurement points.