What are the benefits and harms of noise or sound management in the neonatal intensive care unit for preterm or very low birth weight infants?

Key messages

• The noise in neonatal intensive care units (NICUs) is louder than in our homes or most work environments. Such noise might be very harmful to immature babies, disturbing their development and leading to hearing impairment. Reducing noise in the NICU to below 45 decibels (dB) is recommended but very difficult to achieve.

• We found only one study that evaluated the use of earplugs in the NICU, and its results were very uncertain. No studies evaluated interventions to reduce sound levels below 45 dB across the whole neonatal unit or in a room within it.

• We need studies assessing the effect of sound reduction in NICUs on the development, long-term health, and hearing of babies born too soon.

What is sound reduction management in the neonatal intensive care unit?

Infants in the NICU are exposed to stress, including very intense sounds. The environment in the NICU is louder than most home or office environments and contains disturbing noises of short duration at irregular periods. Many sound signals frequently affect the preterm infants, staff, and parents. Forty-five decibels (dB) is the maximum acceptable noise level in the ICU recommended by the American Academy of Pediatrics, yet sound levels in NICUs are often above this recommended level, ranging from 7 to 120 dB. Between 2% and 10% of infants born before their due date are diagnosed as hard of hearing, compared to only 0.1% of the general child population.

What did we want to find out?

We wanted to find out the benefits and harms of sound reduction on the long-term brain development of newborns.

What did we do?

We searched for studies that looked at sound management in the NICU, summarised the results, and rated our confidence in the evidence.

What did we find?

We found only one study, which included 34 newborn infants, and evaluated the use of earplugs as a sound reduction intervention in the NICU. Each very low birth weight (less than 1500 g) newborn was randomly allocated to one of two groups. One group did not wear earplugs and the other group wore silicone earplugs all the time until the infants were 35 weeks' postmenstrual age (i.e. 35 weeks since their mother's last menstrual period) or until they had been discharged from hospital.

The main results of this review showed that the evidence is very uncertain about whether there is any difference between infants using earplugs and infants not using earplugs, in terms of cerebral palsy, brain development, hearing function, weight, or height at 18 to 22 months of age, or in term of days of respiratory support, days of hospital stay, or risk of death during hospital stay. Side effects and harms were not reported.

What are the limitations of the evidence?

We are not confident in the evidence because there are not enough studies to be certain about the results. The one included study involved a very small number of infants (34), and did not provide information about everything that we were interested in. The study tested individual use of earplugs; there were no studies that tested sound management interventions applied to the whole NICU or a section (room) of the NICU.

How up-to-date is this evidence?

This review is an update of one originally published in 2015 and first updated in 2020. The evidence is current to August 2023.

Authors' conclusions: 

No studies evaluated interventions to reduce sound levels below 45 dB across the whole neonatal unit or in a room within it. We found only one study that evaluated the benefits of sound reduction in the neonatal intensive care unit for hearing protection in preterm infants. The study compared the use of silicone earplugs versus no earplugs in newborns of very low birth weight (less than 1500 g). Considering the very small sample size, imprecise results, and high risk of attrition bias, the evidence based on this research is very uncertain and no conclusions can be drawn.

As there is a lack of evidence to inform healthcare or policy decisions, large, well designed, well conducted, and fully reported RCTs that analyse different aspects of noise reduction in NICUs are needed. They should report both short- and long-term outcomes.

Read the full abstract...
Background: 

Infants in the neonatal intensive care unit (NICU) are subjected to different types of stress, including sounds of high intensity. The sound levels in NICUs often exceed the maximum acceptable level recommended by the American Academy of Pediatrics, which is 45 decibels (dB). Hearing impairment is diagnosed in 2% to 10% of preterm infants compared to only 0.1% of the general paediatric population. Bringing sound levels under 45 dB can be achieved by lowering the sound levels in an entire unit; by treating the infant in a section of a NICU, in a 'private' room, or in incubators in which the sound levels are controlled; or by reducing sound levels at the individual level using earmuffs or earplugs. By lowering sound levels, the resulting stress can be diminished, thereby promoting growth and reducing adverse neonatal outcomes.

This review is an update of one originally published in 2015 and first updated in 2020.

Objectives: 

To determine the benefits and harms of sound reduction on the growth and long-term neurodevelopmental outcomes of neonates.

Search strategy: 

We used standard, extensive Cochrane search methods. On 21 and 22 August 2023, a Cochrane Information Specialist searched CENTRAL, PubMed, Embase, two other databases, two trials registers, and grey literature via Google Scholar and conference abstracts from Pediatric Academic Societies.

Selection criteria: 

We included randomised controlled trials (RCTs) or quasi-RCTs in preterm infants (less than 32 weeks' postmenstrual age (PMA) or less than 1500 g birth weight) cared for in the resuscitation area, during transport, or once admitted to a NICU or stepdown unit. We specified three types of intervention: 1) intervention at the unit level (i.e. the entire neonatal department), 2) at the section or room level, or 3) at the individual level (e.g. hearing protection).

Data collection and analysis: 

We used the standardised review methods of Cochrane Neonatal to assess the risk of bias in the studies. We used the risk ratio (RR) and risk difference (RD), with their 95% confidence intervals (CIs), for dichotomous data. We used the mean difference (MD) for continuous data. Our primary outcome was major neurodevelopmental disability. We used GRADE to assess the certainty of the evidence.

Main results: 

We included one RCT, which enroled 34 newborn infants randomised to the use of silicone earplugs versus no earplugs for hearing protection. It was a single-centre study conducted at the University of Texas Medical School in Houston, Texas, USA. Earplugs were positioned at the time of randomisation and worn continuously until the infants were 35 weeks' postmenstrual age (PMA) or discharged (whichever came first). Newborns in the control group received standard care.

The evidence is very uncertain about the effects of silicone earplugs on the following outcomes.

• Cerebral palsy (RR 3.00, 95% CI 0.15 to 61.74)and Mental Developmental Index (MDI) (Bayley II) at 18 to 22 months' corrected age (MD 14.00, 95% CI 3.13 to 24.87); no other indicators of major neurodevelopmental disability were reported.

• Normal auditory functioning at discharge (RR 1.65, 95% CI 0.93 to 2.94)

• All-cause mortality during hospital stay (RR 2.07, 95% CI 0.64 to 6.70; RD 0.20, 95% CI -0.09 to 0.50)

• Weight (kg) at 18 to 22 months' corrected age (MD 0.31, 95% CI -1.53 to 2.16)

• Height (cm) at 18 to 22 months' corrected age (MD 2.70, 95% CI -3.13 to 8.53)

• Days of assisted ventilation (MD -1.44, 95% CI -23.29 to 20.41)

• Days of initial hospitalisation (MD 1.36, 95% CI -31.03 to 33.75)

For all outcomes, we judged the certainty of evidence as very low.

We identified one ongoing RCT that will compare the effects of reduced noise levels and cycled light on visual and neural development in preterm infants.