Researchers in Vienna say while incubators might save the lives of many babies, their data suggest that the ambient noise associated with the incubator experience could pose potential risk to babies’ hearing and language development skills.
Previous studies have shown that the neonatal intensive care unit (NICU) is a noisy environment, but specific data on levels of sound inside and outside incubators are limited, wrote Christoph Reuter, MA, a musicology professor at the University of Vienna, Austria, and colleagues, in Frontiers in Paediatrics.
By the age of three years, deficits in language acquisition are detectable in nearly 50% of very preterm infants, and high levels of NICU noise have been cited as possible contributors to this increased risk, the researchers said.
Their findings showed that most of the noise situations described in the manuscript “far exceed not only the recommendation of the AAP (American Academy of Paediatrics) but also international guidelines provided by the World Health Organisation and the US Environmental Protection Agency”, which recommend, respectively, maximum dBA levels of 35 dBA and 45 dBA for daytime and 30 dBA and 35 dBA for night.
Potential long-term implications are that babies who spend time in the NICU are at risk for hearing impairment, which could lead to delays in language acquisition, they say.
Medscape reports that the findings were limited by several factors, including the variance among the incubators, which prevents generalisability.
Other limitations include the use of a simulation room rather than everyday conditions, in which the environmental sounds would probably be even louder.
However, the results provide insights into the specifics of incubator and NICU noise and suggest that sound be a consideration in the development and promotion of incubators to help protect the hearing of the infants inside them, the researchers concluded.
A generalist’s take
“This is an interesting study looking at the level and character of the sound experienced by preterm infants inside an incubator and how it may compare to sounds experienced within the mother’s womb,” said Dr Tim Joos, a Seattle-based clinician with a combination internal medicine/paediatrics practice.
“Although in general the incubators work to dampen external sounds, low-frequency sounds may actually resonate more inside the incubators, and taps on the outside or inside of the incubator itself are amplified within the incubator,” he noted. “It is sad but not surprising that the decibel levels experienced by these babies in the incubators exceed the recommended levels recommended by AAP.”
Joos told Medscape it would be interesting “to see the results of trials looking at various short- or long-term outcomes experienced by infants exposed to a lower-level noise compared to the current levels”.
A neonatologist’s perspective
“As the field of neonatology advances, we are caring for an ever-growing number of extremely preterm infants,” said Dr Caitlin Drumm of Walter Reed National Military Medical Centre, Bethesda.
“These infants spend the first few months of their lives within an incubator … so it is important to understand the potential long-term implications of environmental effects on them.
“As in prior studies, it was not surprising that essentially every environmental, handling, or respiratory intervention led to noise levels higher than the limit recommended by the American Academy of Paediatrics.
“What was surprising was just how high above the 45-dB recommended noise limit many environmental stimuli are. For example, the authors cite respiratory flow rates of 8 L/min or higher as risky for hearing health at 84.72 dBSPL,” she said.
Looking ahead, future research should focus on providing more information correlating neonatal environmental sound exposure to long-term hearing and neurodevelopmental outcomes, she added.
Study details
Living in a box: Understanding acoustic parameters in the NICU environment
Christoph Reuter, Lisa Bartha-Doering, Isabella Czedik-Eysenberg, Marcus Maeder4, Matthias Bertsch, Katharina Bib, Philipp Deind, Angelika Berger and Vito Giordano.
Published in Frontiers in Paediatrics on 27 March 2023
Background
In the last years, a significant body of scientific literature was dedicated to the noisy environment preterm-born infants experience during their admission to Neonatal Intensive Care Units (NICUs). Nonetheless, specific data on sound characteristics within and outside the incubator are missing. Therefore, this study aimed to shed light on noise level and sound characteristics within the incubator, considering the following domain: environmental noise, incubator handling, and respiratory support.
Methods
The study was performed at the Pediatric Simulation Center at the Medical University of Vienna. Evaluation of noise levels inside and outside the incubator was performed using current signal analysis libraries and toolboxes, and differences between dBA and dBSPL values for the same acoustic noises were investigated. Noise level results were furthermore classed within previously reported sound levels derived from a literature survey. In addition, sound characteristics were evaluated by means of more than 70 temporal, spectral, and modulatory timbre features.
Results
Our results show high noise levels related to various real-life situations within the NICU environment. Differences have been observed between A weighted (dBA) and unweighted (dBSPL) values for the same acoustic stimulus. Sonically, the incubator showed a dampening effect on sounds (less high frequency components, less brightness/sharpness, less roughness, and noisiness). However, a strong tonal booming component was noticeable, caused by the resonance inside the incubator cavity. Measurements and a numerical model identified a resonance of the incubator at 97 Hz and a reinforcement of the sound components in this range of up to 28 dB.
Conclusion
Sound characteristics, the strong low-frequency incubator resonance, and levels in dBSPL should be at the forefront of both the development and promotion of incubators when helping to preserve the hearing of premature infants.
Medscape article – Noisy Incubators Could Stunt Infant Hearing (Open access)
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