Incubators save the lives of many babies, but new data suggest that the ambient noise associated with the incubator experience could put babies’ hearing and language development skills at risk.
Previous studies have shown that the neonatal intensive care unit 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, and colleagues.
“By the age of 3 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 say.
In a study published in Frontiers in Pediatrics, the researchers aimed to compare real-life NICU noise with previously reported levels to describe the sound characteristics and to identify resonance characteristics inside an incubator.
The study was conducted at the Pediatric Simulation Center at the Medical University of Vienna. The researchers placed a simulation mannequin with an ear microphone inside an incubator. They also placed microphones outside the incubator to collect measures of outside noise and activity involved in NICU care.
Data regarding sound were collected for 11 environmental noises and 12 incubator handlings using weighted and unweighted decibel levels. Specific environmental noises included starting the incubator engine; environmental noise with incubator off; environmental noise with incubator on; normal conversation; light conversation; laughter; telephone sounds; the infusion pump alarm; the monitor alarm (anomaly); the monitor alarm (emergency); and blood pressure measurement.
The 12 incubator handling noises included those associated with water flap, water pouring into the incubator, incubator doors opening properly, incubators doors closing properly, incubator doors closing improperly, hatch closing, hatch opening, incubator drawer, neighbor incubator doors closing (1.82 m distance), taking a stethoscope from the incubator wall, putting a stethoscope on the incubator, and suctioning tube. Noise from six levels of respiratory support was also measured.
The researchers reported that the incubator tended to dampen most sounds but also that some sounds resonated inside the incubator, which raised the interior noise level by as much as 28 decibels.
Most of the measures using both A-weighted decibels (dBA) and sound pressure level decibels (dBSPL) were above the 45-decibel level for neonatal sound exposure recommended by the American Academy of Pediatrics. The measurements (dBA) versus unweighted (dBSPL) are limited in that they are designed to measure low levels of sound and therefore might underestimate proportions of high and low frequencies at stronger levels, the researchers acknowledge.
Overall, most measures were clustered in the 55-75 decibel range, although some sound levels for incubator handling, while below levels previously reported in the literature, reached approximately 100 decibels.
The noise involved inside the incubator was not perceived as loud by those working with the incubator, the researchers note.
As for resonance inside the incubator, the researchers measured a low-frequency main resonance of 97 Hz, but they write that this resonance can be hard to capture in weighted measurements. However, the resonance means that “noises from the outside sound more tonal inside the incubator, booming and muffled as well as less rough or noisy,” and sounds inside the incubator are similarly affected, the researchers say.
“Most of the noise situations described in this manuscript far exceed not only the recommendation of the AAP but also international guidelines provided by the World Health Organization and the U.S. 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, the researchers indicate.
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.
The findings were limited by several factors, including the variance among the incubators, which prevents generalizability, the researchers note. Other limitations include the use of a simulation room rather than everyday conditions, in which the environmental sounds would likely 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 conclude.