Sounds in the NICU


Babies born prematurely often suffer from stress, which can have negative effects on the development of the brain. This is caused, alongside other things, by exposure to loud noise. This research was conducted to find out how it can be ensured that the noise level at the Neonatal Intensive Care Units (NICU) remains below 45 dB. This has been accomplished by observing and noting why and how many times the SoundEar in the NICU turns orange or red. In this way the most significant cause of high noise levels in the NICU will be found. This study has shown that the noise level at the NICU is too high, but there are some simple solutions that could make sure that the noise level stays below 45 dB, although they were not tested during the study. Placing felt pads on cabinets, changing staff outside the NICU and lowering the sounds of the monitors are a few examples. These solutions can contribute to lowering the amount of stress that the babies experience.


In the Netherlands, 15,000 babies are born prematurely every year.[1] These babies lack the comfort and protection from the womb for the last few weeks of pregnancy. Very premature babies or babies with serious problems will be placed in the Neonatal Intensive Care Unit (NICU), where they are cared for day and night. In the womb, it is dark and quiet, while in the hospital, it is light and noisy. Moreover, these babies are exposed to many examinations. This increased level of stimuli can cause stress for a baby.

Neonatal Intensive Care Unit (NICU)

Children who require additional care after birth, including premature babies who are born at a gestational age of 24-30 weeks, are admitted to the hospital’s neonatology department. There are three different levels of care in this department: Medium Care, High Care, and Intensive Care. Eight babies are housed in one unit in a high-tech environment where they are constantly monitored for the best possible care.[2]


The brain triples in size during the first five years of life. If the experiences of a baby or child during this period are abnormal, traumatic and/or chronically stressful, they can result in permanent damage to the structure and mechanisms of the functioning brain.

The stress response system is activated by a centrally located area in the right hemisphere, which is dominant in controlling the functions used to survive, to process physical information, and to regulate and receive emotion. In the early development of the brain, the right hemisphere of the brain is also deeply connected to all areas of the brain that are important in controlling stress. When a baby experiences stress, these brain areas provide instructions about how to respond. As a result, hormones are released and the heart rate increases.

If babies experience chronic stress or trauma, this can have both psychological and biological adverse consequences. While the brain is structurally developing and mapping its nerve pathways, stress and trauma often force these routes to follow abnormal directions. This results in abnormal brain function.[3] As a result, children who have experienced this, often react differently and more strongly to stress at a later age. The possible consequences are chronic childhood trauma and difficulty in processing sensory, emotional, and cognitive information in a coherent way.[4] The POPS-19 study[5] also shows that 24% of prematurely born babies had received special education until the age of 19.


The hearing system begins to develop early in pregnancy. All main structures are in place between 23 and 25 weeks, allowing most premature babies to hear as soon as they are born. Between 26 and 30 weeks of pregnancy, hair cells in the cochlea of the ear are tuned to specific frequencies, so that sound can be translated into a signal that is sent to the brain. After 30 weeks, the baby can distinguish between different sounds. As long as the hearing system is not fully developed, which is the case with prematures, loud noise has a higher chance of causing hearing damage.[6]

Hearing disorders are diagnosed in 2% to 10% of premature babies, while this is, on average, 0.1% for mature babies.[7] Recent studies have shown that loud noise, in addition to causing auditory disturbances, also causes stress in prematures. This has negative effects on the brain and can cause damage to the entire body.[6, 7, 8, 9] For instance, it can cause heart rate accelerations, heart rhythm disturbances, sleep disturbances, and increases in muscle tension and blood pressure. These disruptions consume an increased amount of energy, which has a negative impact on growth and development and can cause physical instability.

In the NICU, disturbing noises of short duration are present at irregular intervals. In the womb, these sounds are muted by amniotic fluid, among other things.[9] These noise levels often exceed the maximum acceptable level of 45 decibel (dB), which is the recommended limit by the American Academy of Pediatrics.[10] This nuisance is mainly due to “competing auditory signals.” For example, an increased speech level between the nurses is needed to be able to understand each other over the alarms. In addition, high noise levels are associated with reduced performance among staff, as they cause lower concentration levels and more errors.[7]

The risk of loud noise has been demonstrated by a study with rat juveniles who grew up under different sound conditions. These animal studies show that exposure to loud noise has a negative effect on the development of the hearing system and that changes in sound can have many effects on the development of the cerebral cortex, showing that noise is a risk factor for the development of prematures.[6]

SoundEar II

The SoundEar II is a device that measures the noise level in the environment. It is used in places where it is important that the noise level is regulated. On the device, three lights can be seen: green, orange, and red. The threshold value can be set to a value from 40 to 115 dB.[11] If the environmental sound exceeds the set value, the red light is on. If it approaches the value, the orange light is on. Otherwise, the green light is on. The SoundEar is preferably positioned at a height of approximately 1.8 meters and reaches up to 30 m2. It has a margin of error of ± 3.0 dB. Sounds closer to the device give a higher result than sounds further away. Hence, it is very important that the SoundEar is carefully placed in the room. The SoundEar does not work properly if it is close to absorbent materials.[12, 13] The results of the SoundEar are converted into graphics in SoundLog, an accessory to the SoundEar.

To prevent as much stress as possible, it is therefore important that the sound level and the conditions in the womb are as closely as possible. The research question that follows is: how can it be ensured that the noise level at the NICU remains below 45 dB? The hypothesis is that the noise level of 45 dB will be exceeded. This is partly due to the staff change after each work shift, the sounds of the monitors, and consultations between medical staff.

Material and method

The research took place at the Wilhelmina Children’s Hospital (WKZ) in Utrecht, the Netherlands. The WKZ has four level 3C NICUs; this is the highest care level that exists. Each NICU has had a SoundEar II for several years.

First, SoundEar data about the average sound level per minute from NICU 1, NICU 2 and NICU 3 were collected. The data was measured a week prior to the main focus of the research. These data were used to create a graph of the average sound level during the day. The SoundEar was set to 65 dB, and this value was not changed, so that the SoundEar would behave the same way during our research as the week prior. Also, according to the SoundEar, the noise level in the NICU was always above 45 dB. If the threshold was lowered to, for example, 45 dB, the red light would be on constantly. The device turns orange when the sound level approaches 65 dB and turns red when the sound exceeds 65 dB. The graph shows a possible relation between the average sound level and the moment of the day. It also shows the overall average sound level per NICU.

This image has an empty alt attribute; its file name is NICU.png

Next, the data that is discussed in diagram 1 and 2 in the Results section were collected by sitting in NICU 2 and noting when the SoundEar II turned orange or red. The experiment was conducted at the centre of the unit, as it can be seen in Figure 1. This way, there was a clear sight of the SoundEar, the babies, and the staff. Sounds such as alarms, talking, opening and closing of cabinets and packaging, etc. were observed and noted. With these data, the causes of the extensive noise were determined. In total, research was collected over eleven hours.

As a follow-up to this research, there were also various specific sounds measured with a decibel meter from within the closest incubator. These measurements were made to see if the SoundEar works properly and is placed correctly.

Lastly, there was a survey conducted among the nurses. This gave an impression of the opinion of the nurses about the SoundEar and how they appreciate it.


Type of answer

Do you pay attention to the SoundEar?

Answer on a scale of 0 to 5.

How useful do you think the SoundEar is?

Answer on a scale of 0 to 5.

What do you think is the scientifically determined maximal sound level in the NICU, at which babies experience as little stress as possible?

Multiple choice question, options from 40 to 70 dB in steps of 5 dB.

What do you think makes unnecessary noise?

Multiple choice questions with space for their own answers, the options were: alarms, visitors, cabinets/packaging/doors, staff, telephones and other, for example: ………

Table 1: Questions of the survey


Chart 1 shows the sound levels that the SoundEar measured at the different NICUs the week before the study. The days have been combined and the sound levels are averaged per 10 minutes. The plot shows the average sound against the time of the day.

The average noise level was 49dB in NICU 1, 50 dB in NICU 2, and 48 dB in NICU 3. Most striking in the graph are the peaks around 8 AM, 4 PM and midnight. Only in NICU 3, the peak at 8:00 AM seems to be significantly lower, and in NICU 1 there is an extra peak around 10:00 AM.

The diagrams below show what factors cause the most noise disturbance in NICU 2. The first diagram shows how often the orange light on the SoundEar turned on. The second diagram shows how often the red light of the SoundEar turned on.

As you can see in diagram 2, the staff(labelled as personnel) caused the red light to turn on the most, followed by the alarms. Both diagrams show that research day 2 is much louder than research days 1 and 3.


This survey was completed by 15 nurses.

Diagram 3 shows what the nurses at the NICU think is making too much noise, which recognizes that they believe the staff makes too much noise. The noise from the alarms and the telephones is also unnecessary, according to the nurses. Furthermore, they think that visitors do not cause an unnecessary noise disturbance. The nurses added that the trolleys make too much noise.

Diagram 4 shows that 75% of the nurses think the noise level at the NICU should be low, 40 or 45 dB.The other questions show that the staff knows that the SoundEar is in the NICU, but they do not find it very useful (Appendix).


The peaks in chart 1 can be explained logically because they mark the points in time where the staff changes. There is no peak around 8:00 AM in the graph for NICU 3, while this is the case in the graphs of the other NICUs. Changing staff in the morning in room 3 is, therefore, quieter than in the other rooms.

It is a surprising result that the paper shredder causes the least noise disturbance because it was expected that this would be one of the loudest noises. The same applies to staff talking behind the counter and ringing telephones; these made less noise than expected. It is striking that the sounds which turned the SoundEar red are not the loudest sounds for the babies. Opening the incubator doors is something that happens very close to the baby, but while it is a loud noise for the baby, the SoundEar does not capture it (Appendix). The survey results show that the nurses know that the noise level must be low and that they think that they themselves cause the most disturbance. However, they did not pay much attention to the SoundEar and did not actively reduce the sound level.

The article, “Noise level in the NICU: Impact of monitoring equipment”, is one of the articles that is similar to the research in this study. In their research, the authors introduce the SoundEar at a NICU. They compare the noise levels in the rooms before and after the introduction. This research shows that the sound level decreases shortly after the introduction of the SoundEar. However, after three months, the noise level returns to the original level. This matches the findings from this study, as the SoundEar in the WKZ has been there for more than three months, and it does not seem to affect the average sound level.[14] Another article that is comparable to this research is “Examining the effects of a targeted noise reduction program in a neonatal intensive care unit”. This research was conducted in three phases. First, the authors measured the noise level without the staff being aware of it. Then, the authors gave information and again measured the noise level. In phase three, a SoundEar was installed, so that everyone became aware of the excessive sound level. The results are consistent with the results obtained in this study, as the average noise level is also 49 dB. In their research, the authors focus more on the influence of the SoundEar, while this study focuses more on what causes the noises.[15]

The results can be applied well to a neonatal intensive care unit. It is hypothesized that the excessive sound level can be solved by placing all babies in separate rooms. This is not a realistic solution, because there is not enough money and space available for this. A better alternative is to place fewer babies in one room. As a result, the babies are less troubled by each other’s alarms, allowing them to experience less stress. There would also be fewer nurses present in each room, which reduces the noise disturbance from the staff. Other simple feasible solutions were found for a number of noise sources, such as reducing the noise of cabinets with felt pads.

The research does have a number of weaknesses. The SoundEar in the NICU was not installed in the most convenient place. It now hangs above the place where the nurses are, while the research involves the sound that reaches the babies. So, there should be a SoundEar microphone in every incubator to get a more realistic indication of the sound level near the babies. However, this costs a lot of money and is therefore not a solution that can be easily applied. Another limitation is that the SoundEar measured no lower than 47.5 dB while it should actually measure sound as low as 45 dB, for this research question and hypothesis. The accuracy of the SoundEar may be limited, because considerable differences were visible when comparing a decibel meter to the SoundEar. The decibel meter is more accurate, and brief loud noises that were measured by the decibel meter were not picked up by the SoundEar.

The research and the results are relevant because hearing disorders are diagnosed in 2% to 10% of premature babies, while this is only 0.1% for mature babies. Animal studies have also shown that various changes in the sound around the animals negatively affect the development of the cerebral cortex.

For further research, the measurements could be carried out again, using a newer version of the SoundEar. The latest SoundEar shows the decibel level on a display and has a greater accuracy of ± 0.5 dB. It could also be performed again if the SoundEar is positioned in a different and better place, for example, above the babies. Another study could focus on how the alarms can be passed on to the nurses, for example through earphones, so that the noise level becomes even lower. In addition, the study “Cum laude for contactless and efficient monitoring of premature babies”[16] is a good follow-up to this study. That study looks for contactless monitoring of the babies, which reduces stress.


This study focussed on finding an answer to the question: “How can it be ensured that the noise level at the NICU remains below 45 dB?” To come to an answer, a quantitative study was conducted as the noise level in the NICU was examined.

The data from the SoundEar shows that the average sound level is 49 dB, above the desired level of 45 dB. The results show that the alarms and staff cause the most noise disturbance, which is consistent with the hypothesis.
This study has shown that the noise level at the NICU is too high, but that there are solutions to reduce this. The most logical and easily applicable solutions are changing staff outside the room, lowering the sounds of the monitors, placing the babies in separate rooms as much as possible, and consultation outside the units. These solutions can reduce the amount of stress that premature babies have, and therefore possibly lower the negative effects this has on the babies.


Thanks to the WKZ for their hospitality and to our researcher and supervisor Jeroen Dudink for his help with our research.


[1]. Couveuseouders. (n.d.). Neonatologie en NICU – Couveuseouders. Accessed November 18, 2019.

[2]. Wilhelmina Kinderziekenhuis. (n.d.). Neonatologie. Accessed October 1, 2019.

[3]. Eckstein Grunau, R. (2013). Neonatal Pain in Very Preterm Infants: Long-Term Effects on Brain, Neurodevelopment and Pain Reactivity. Rambam Maimonides Medical Journal, 4(4).

[4]. Maroney, D. I. (2003). Recognizing the Potential Effect of Stress and Trauma on Premature Infants in the NICU: How are Outcomes Affected? Journal of Perinatology23(8), 679–683.

[5]. Wolthuis, A., van der Pal, S., Janssen, Y., & TNO. (2008 november). Vervolgonderzoek levenslange zorg voor te vroeg geboren kinderen. POPS-19. Accessed September 3, 2019.

[6]. McMahon, E., Wintermark, P., & Lahav, A. (2012). Auditory brain development in premature infants: the importance of early experience. Annals of the New York Academy of Sciences, 1252(1), 17–24.

[7]. Almadhoob, A., & Ohlsson, A. (2015). Sound reduction management in the neonatal intensive care unit for preterm or very low birth weight infants. Cochrane Database of Systematic Reviews.

[8]. Chang, Y.-J., Pan, Y.-J., Lin, Y.-J., Chang, Y.-Z., & Lin, C.-H. (2006). A Noise-Sensor Light Alarm Reduces Noise in the Newborn Intensive Care Unit. American Journal of Perinatology, 23(5), 265–272.

[9]. Couveuseouders. (n.d.). Geluid – Couveuseouders. (2017). Accessed June 18, 2019.

[10]. Committee on Environmental Health. (1997). Noise: A Hazard for the Fetus and Newborn. PEDIATRICS, 100(4), 724–727.

[11]. SoundEar. (n.d.). Accessed November 18, 2019.

[12]. Iversen, S. (2018, 5 april). How does a SoundEar noise meter work? Accessed November 18, 2019.

[13]. SoundEar A/S. (n.d.). SoundEar II – Lower your Noise Levels by Making Noise Visual – SoundEar. Accessed October 4, 2019.

[14]. Degorre, C., Ghyselen, L., Barcat, L., Dégrugilliers, L., Kongolo, G., Leké, A., & Tourneux, P. (2017). Nuisances sonores en réanimation néonatale : impact d’un outil de monitorage. Archives de Pédiatrie24(2), 100–106.

[15]. Wang, D., Aubertin, C., Barrowman, N., Moreau, K., Dunn, S., & Harrold, J. (2013). Examining the effects of a targeted noise reduction program in a neonatal intensive care unit. Archives of Disease in Childhood – Fetal and Neonatal Edition99(3), F203–F208.

[16]. Bonito, V. (2019, 26 augustus). Cum laude voor contactloos en efficiënt monitoren van vroeg geboren baby’s. Accessed September 3, 2019.


Figure 2: Results of the survey question “Do you pay attention to the SoundEar?” on a scale of 0 to 5.

Figure 3: Results of the survey question “How useful do you find the SoundEar?” on a scale of 0 to 5.


Sound at baby (dB)

Opening the diaper cloths


Put something on the incubator


Alarm of CPAP-machine


Moving the breastfeeding pumps around


Tearing open the water bags


Open incubator doors


Close Microwave


Aspiration catheter


Opening of the staff lockers


Talk next to the incubator


Turn CPAP device on / off


“Goes bad” alarm


Moving the scales around


Switching spray pumps on and off


Use of the bedside tables


Heat pump


Opening and closing trash can


“Goes too well” alarm


Open microwave


Scanning sounds




Talk behind the counter


Printer on unit 2 of the MC






Paper shredder


Table 2: Noise measurements of different actions in the unit, measured from the nearest baby.

About the Authors

Marijn Jonkman, 17 years old, Joost Verhoeven, 17 years old, and Laure Babeliowsky, 18 years old, are three students who are in their final year at De Amersfoortse Berg in the Netherlands. During high school they also followed an extra program, The U-talent Academy at the University of Utrecht.

Marijn is going to study Mathematics at the University of Utrecht. In her free time, she likes to play games with her family, watch a relaxing show on Netflix, do arts and crafts, and play Minecraft with friends.

Joost is interested in medical sciences, but also likes technical subjects. After high school he is going to study Biomedical Technologies, a perfect combination of the two for him. In his free time, he likes to sail, watch series on Netflix and play videogames with friends.

Laure is going to study Medicine next year at the University of Nijmegen. She’s really interested in the human body and likes to help people a lot. In her free time, she likes to play hockey, hang out with friends or cook.

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