The characterization of noise levels in a neonatal intensive care unit and the implications for noise management
- Juan Carlos Fortes-Garrido1Email author,
- Andres Mauricio Velez-Pereira†2,
- Manuel Gázquez†2,
- Montserrat Hidalgo-Hidalgo†3 and
- Juan Pedro Bolívar†2
© Fortes-Garrido et al.; licensee BioMed Central Ltd. 2014
Received: 21 May 2013
Accepted: 30 June 2014
Published: 22 July 2014
The effects of noise are particularly harmful for the newborns, and therefore this study assesses and characterizes noise levels in a neonatal intensive care unit (NICU) in a medium-size hospital in the city of Huelva with the aim of optimizing the management and quality of care for newborns.
The equivalent continuous sound level was recorded as A-weighting curves using Type I sound level meters with levels measured during 100 milliseconds along to 15-day period in the both critical (in and out of incubators), and intermediate care units from a medium-size hospital. These devices were attached to a central beam 80 cm below the ceiling and into one of the incubators.
The maximum noise levels measured for critical (C-in), C(out) and intermediate (I) were: 88.8 dBA, 97.2 dBA and 92.4 dBA, respectively, while for the equivalent noise levels for the total measuring period (15 d) were 57.0 dBA, 63.7 dBA, and 59.7 dBA, respectively. The Fourier frequency analysis has demonstrated several typical periods related to both work activities and family visit, which were: 7 days, 24 h, 12 h, and 3 h.
The statistical analysis revealed a clear correlation between the noise level, the kind of care room, and the time of the day. The results show that the values recommended by international bodies and agencies (AAP, WHO) are surpassed by a large margin, thus making it crucial that certain norms are followed in order to reduce the noise level in the NICU, by means of physical alterations to the layout, and raising awareness of health care personnel and visitors in order to encourage noise prevention in the daily care work and conversation. And finally, has been demonstrated that by applying the t-Student test the mean noise values in both wards are significantly different, which leads us to state that the noise level for the critical wards are higher than in the intermediate care ward.
Recent studies on the quality and risks associated with admission to a medical center have established a relation between the increase in morbidity and mortality, in addition to alterations in the quality of life following discharge from the health center which are usually linked to greater exposure to environmental pathogens, a lowering of the body’s defenses and an increase in invasive techniques, among other reasons. Many authors have found a high correlation between noise levels in NICU and adverse effects arising from sleep disorders, underdevelopment of responses to stimuli, deterioration of the nervous system, etc. [1–6]. The noise that occurs in the NICU is linked to the monitoring and follow-up processes of the newborn’s state of health, such as alarm systems, electro-medical equipment and incubators, and the general human ambient noise .
Several studies have measured the noise levels in NICU, finding very different values depending on the management of the work activities or customs of the place, with equivalent continuous levels in ranges from about 55 up to 83 dBA. These noise levels are high enough to stimulate the newborn’s endocrinal and cardiovascular systems, resulting in significant alterations in sleep patterns [8–11]. Bushch-Vishniac et al.  determined that the average noise level for the John Hopkins Hospital has risen in the last 45 years by around 0.40 dBA a year, mainly due to the increase in audible alarm systems, the installation of air conditioning, control and surveillance systems and electro-mechanical therapeutics.
In terms of the legal framework, the World Health Organization (WHO) recommends that the newborn inside an incubator should not be exposed to noise levels higher than 35 dBA at night and 40 dBA during the day . As proposed by the US Environmental Protection Agency and supported by the American Academy of Pediatrics (AAP) Committee of Environmental Health, noise levels within the NICU should be kept below 45 dB . More specifically, the AAP recommends that hourly, a NICU’s loudness equivalent (LAeq) should be below 50 dBA, the sound level that is exceeded 10% of the time (L10) should be at or below 55 dBA, and the maximum sound (Lmax) should be below 70 dBA . In Spain, the Standards Committee of the Neonatology Society of the Spanish Pediatrics Association recommends a total background noise level in NICU of no more than 55 dBA, and should not exceed 70 dBA . However despite these recommendations, noise levels routinely oscillate between 65 dBA and 85 dBA, normally at low frequency .
In this study are correlated the temporal variations of the noise with its causes (Monitoring Systems, work activities, family visits, medical rounds, etc.). Spain is the second noisiest country in the world after Japan , according to the World Health Organisation (WHO), so this study is particularly important due to customs and the high noise level in the daily activities of the Spanish people.
With this in mind, the aim of our study is to identify, assess and make a space-time characterization of the noise levels in the NICU of a typical medium-sized hospital in Spain to find the main correlations with the noise sources, and, as consequence, to establish the right protection measures for noise reduction and elimination.
Two noise level meters used were the Type I Brüel & Kjäer model 2270 and 2250. The technical characteristics for two meters are: 4.2 HZ broadband linear frequency range with supplied microphone Type 4189, 16.6 – 140 dB A-weighted dynamic range with supplied microphone Type 4189. Outputs: Generator and Headphone. The third was the Rion NL-31, and the technical characteristics are: A weighting: 28-138 dB, C weighting: 33-138 dB, flat: 38-138 dB, Peak sound level: 141 dB, Ranges 100 dB dynamic, frequency 20-12,500 Hz (including microphone).
The sampling period lasted 15 days in order to ensure that the averages were representative and to offset the Hawthorne effect  of attention bias in which the study participants alter their behavior when they are aware they are being observed, and avoid interferences that can cause another unexpected variable to influence the study.
The collected data (individual data were for time intervals of 0.1 s) were recorder in the Secure Digital (SD) by Memory Card inside of the level meters and downloaded to PC and were treated and processed in the XLSTAT code developed by Addinsoft and SPSS 13.0.
Obviously there are more instances of intervention, monitoring and follow-up of newborns in the NICU-C ward where the most critical care takes place, with a consequently greater noise level throughout the day. The NICU-C-out ward recorded LAeq,1 h of 69 dBA at 08:00, which is when the biggest number of health care personnel starts work. Hence, the high noise level is directly attributed to talking by the staff, again verified by the second peak which occurs at 15:00 when the majority leaves work. This Figure also shows the close relation between the activities of the health care personnel in the NICU and the noise level in each ward.
By contrast, if we take a specific hourly period such as 00:00-01:00 in NICU-I, the resulting data set (N = 6 · 15 = 90 data) still has a normal distribution with 95% confidence. Likewise, if we apply the Shapiro-Wilk test we get W = 0.838 (p-value = 0.159), so the null hypothesis is acceptable at a significance level of 5% (alpha = 0.05) since the p-value obtained (0.159) is greater than the alpha considered (0.05). This result confirms our hypothesis that the noise level has a normal distribution if the sampling period is restricted to 1 hour, which is less than the shortest of the characteristic periods of the data series (3 hours or the newborns’ feeding time).
The results are consistent with those of other authors [20–28] in which the hours with the highest levels of noise are between 08:00 and 15:00, when care activity around the newborn in NICU is at its busiest. In terms of the maximum, minimum and average noise levels recorded, the studies in NICU that we have analysed present a wide range of values oscillating between 36-80 dBA [21–25]. The results of our study show that the noise levels in NICU at HJRJ fall within a similar range. However, our study recorded maximum values that exceeded those of other researchers, at 80 dBA in LAeq,10 min averages. The equivalent sound level in other studies has a broader range (between 40 and 90 dBA) than the one recorded in our study (between 48.8 and 72.2 dBA), and with an integrated hourly average of LAeq,24 h noise of 64.5 dBA, which easily surpasses international standards and recommendations for newborns in NICU [13, 14]: LAeq,1 h = 45 dBA, L10 (hourly) = 50 dBA and Lmáx = 65 dBA, which is a considerable problem that remains unresolved [29, 30].
The behavior of the hourly noise level in our study is consistent with that of Mackenzie , who established that the level of noise increased as the working day progressed and decreased in the afternoon. This is in accordance with Argote et al.  and Brandán et al.  who stated that noise levels rise at those times when the ward is cleaned in the mornings, and when relatives visit in the afternoons. Another characteristic that influences noise level relates to the health care work performed by personnel in shifts, with the night shift (22:00 – 08:00) showing the lowest levels and the morning and afternoon shifts registering the highest values, which is in line with various other studies [20–26].
This study has demonstrated the high levels of noise pollution that newborns and health professionals are exposed to in NICU. Noise varies according to the shift, with levels at their highest during the morning and falling substantially at night. The critical care unit endures the highest noise levels. Measures to reduce these high noise levels in NICU include sound insulation (design, walls, closed doors with silent locking), drawing up an preventative maintenance equipment programme, placing the newborn as far as possible from machines, which could also be removed from the ward (fridges, computers, medical case history trolleys, etc). It would be advisable to raise awareness among personnel of the noise they make during work, and achieve a gradual decrease in the noise emanating from alarms to acceptable levels. Also needed is a reduction in conversational noise among personnel and visitors to the wards, which could be achieved by hanging the appropriate warning signs in these areas. In addition, it would be needed to develop a guideline for noise mitigation, and educational preparation of the staff and patient’s visitors with the implementation of protocols and to assess the progress.
We would like to thank Dr Ricardo Hernández of the University of Cádiz for his support in obtaining the equipment and technical support necessary for this study, and Dr José Ceballos, Director of the Pediatrics Department at HJRJ, for allowing us to use its installations for our research.
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