Neonatal Intensive Care Population

According to the World Health Organization, during 2017 in the United States, 517,400 newborns were born prematurely or “preterm” — that is delivered before the 37th week of gestation [N1].  Globally, approximately 15 million babies are born prematurely each year.  Most of these newborns will require care in neonatal intensive care units (NICUs). 

Due to the opioid crisis in the U.S., in 2016, an additional 31,700 babies were born substance-dependent, often requiring prolonged NICU admissions for management of Neonatal Abstinence Syndrome (NAS) related to opioid substance withdrawal [N2].  NAS babies are a rapidly increasing proportion of NICU patients in the U.S.

Noise Exposure during NICU Care

NICU babies have significantly higher risks of sensory and neurodevelopmental delays (e.g. hearing loss, speech impediment, delayed cognitive development) when compared to normal full term infants [N3]. Increasingly, evidence suggests that post-natal exposure to noise, particularly high frequency sounds, produce stress, and may play a significant role in these problems [N4].

Despite the best efforts of NICU caregivers, NICU’s tend to be intermittently quite noisy — often far exceeding AAP guidelines [N5-6]. Vulnerable and fragile NICU patients are frequently exposed to noxious levels of noise generated by life-sustaining respiratory equipment required to keep these babies alive, and monitor alarms specifically designed to alert NICU caregivers to important changes in patient status.

Excess noise has been associated with physiological instabilities in infant heart rate, respiratory rate, blood pressure, and blood oxygenation, as well as disrupted sleep [N5, N7-10], behaviors that mimic acute pain stress responses [N11-13] and is a suspected contributing factor in neurodevelopmental delays in NICU graduates [N14].

Noise Exposure during Transport

Annually in the U.S, about 70,000-80,000 neonatal patients are emergency-transported to hospital NICUs by helicopter, ambulance, and fixed wing aircraft [T1].

Sound levels experienced by ill newborns during fixed wing, helicopter, and ground transportation can average over 80 dBA, with peak levels as high as 85-95 dBA [T2-5], greatly exceeding the recommended guideline of maximum sound level of 60 dBA inside transport incubators [T6, T7]. 

High sound levels during air and ground ambulance transport have been associated with increased heart rate in neonatal patients during ambulance transport, a potentially adverse change that may reflect increased stress [T5]. Because of the association between loud noises and physiological instability [T5], it is important to reduce patient noise exposure during ambulance transport.  

Noise Exposure during MRI Examinations

Magnetic resonance imaging (MRI) has become an important tool to augment brain ultrasound in the evaluation of neonates, especially in preterm and very low birth weight infants, due to its better sensitivity detection of for white matter lesions and brain abnormalities than cranial ultrasound [M1]. 

The sound levels during high-field-strength MR scanning are high. MR brain imaging pulse sequences average approximately 98 dBA for a conventional MRI scanner, and approximately 88 dBA for a specially designed NICU scanner [M2].

Loud noise generated by the MR scanner is an important clinical issue in neonatal MRI examinations, because such noise can elicit autonomic instability, as reflected in cardiac rhythm changes, in neonates [M3, M4].

Also, due to the occurrence of motion artifacts associated with noise-related patient agitation, sedation — while undesirable — sometimes is necessary used during MRI studies [M5]. Reduced exposure to noise increases the probability that the MR examination can be completed without sedation and with fewer motion artifacts [M5].

For these reasons, passive hearing protectors (e.g., foam earplugs and/or ear muffs) capable of abating noise by 10 to 30 dB [M6] are used on patients, including infants and neonates [M2] to reduce noise exposure during MRI examinations. 

Prior Strategies for Reducing NICU Noise Exposure

Most previous attempts at limiting noxious noise exposure of preterm infants are based on elimination of sources of noise away from the infant. These approaches include work practice and behavior modification, sound monitoring coupled with alarms, and facility architectural re-design with sound-absorbing materials. To-date, none of these approaches individually or in combination, have met the AAP guidelines, can be implemented in an easy, safe and cost-effective manner, and permit appropriate auditory stimulation.

Work practice behavior modifications to reduce sound levels are often insufficient or ineffective, because despite the best intentions, busy care staff in the high-stress intensive care environment tend to revert back to more comfortable work practices that generate loud sounds. Noise alarms are easily and frequently ignored or bypassed as they interfere with urgent care practices.

Complete architectural renovation from the traditional open ward style NICU to isolated single-patient private rooms equipped with sound-absorbing materials has complications associated with design, work flow implications, and comes with high cost of over $200,000 per infant station [N17] that is prohibitively expensive for many hospitals.

Comparison of a private room and open room NICU configuration demonstrated that while the private room is quieter (55 dBA for private room vs. 58 dBA for open room) and has less noise events, transient and loud acoustic events (average level 64 dBA, average peak 90 dBA) still frequently occur [N18].   Therefore, even in a well-engineered quiet private room, certain respiratory equipment, alarms, and behaviors will increase the sound level well above AAP recommended levels.  Moreover, recent data has raised concerns over delays in speech and language acquisition among patients treated in nearly silent private room environments [N16].

Clinical Studies and Use of Ear Muffs and Ear Plugs

A more viable solution to mitigating neonatal noise exposure would seem to be individual patient hearing protection – ear muffs or ear plugs. 

Using a research ear muff device made from thick acoustic foam attached to the inside of a knit cap, D’Agati found a small group of NICU patients experienced reduced respiration rate, increased oxygen saturation level, and increased percent of total sleep time spent in quiet sleep [E1].  In a number of studies, infants wearing adhesively-bonded earmuffs were shown to have lower heart rates and lower blood pressure [E2], lower respiratory rate [E2, E3], higher oxygen saturation levels [E4, E5], more time spent in the quiet sleep state [E4, E5], reduced tremor, twitch, and startle motor responses [E3, E6], and increased weight gain [E6].  Even more significantly, very low birth weight NICU infants who wore silicone insert earplugs had increased weight gain (by 225 g), head circumferences (by 2.6 cm), and higher Bayley Mental Development Index scores (by 15 points) after 18-22 months, compared to a control group [E7].  

Unfortunately, the adoption of adhesively-bonded ear muffs and ear canal inserted ear plugs has been limited by concerns about trauma to the extremely sensitive skin of NICU patients, due to the frequent cycle of application-to-removal-to-reapplication of these devices (repeated every 3-4 hours) required to comply with NICU best-practice care protocols.

Thus, many hospitals have limited use of these adhesively-bonded ear muffs and insert ear plugs to short-duration, very high-noise situations such as MRI examination and emergency transport. Even in those particular situations, concerns about damage to the skin and ear canal remain and special care must be taken during device application and removal.