1. Introduction

Sound is produced by air vibration and exists in all areas of life. Loud noise has harmful effects on both neonates and medical staff (Carvalhais et al. 2018). A great deal of research has focused on identifying and creating the ideal Neonatal Intensive Care Unit (NICU) environment (Meredith, Jnah & Newberry 2017). Specifically, attention has been dedicated to monitoring and regulating the acoustic environment in the NICU (Smith, Ortmann  & Clark 2018). 

Cochlear development and the growth of other terminal sensory organs occur in the 24th week of fetal life. Consequently, premature neonates hear sounds nearly similar to normal infants (Eggermont 2017). The range of hearing stimulation threshold in the 28-27 week is 40 dB and reaches 13.5 dB at 42 weeks of gestation, indicating continued evolution of the auditory nerve pathway through the term (Manske 2017; Santos et al. 2018).

The American Academy of Pediatrics (AAP) recommends that the noise level should not exceed 45 dB in NICUs and the US Environmental Protection Agency recommends that noises should be raised to 45 dB for the comfort and recovery of infants (Aggarwal et al. 2019). Despite these recommendations, existing analyses of the acoustic environment in the NICU have indicated that these noise standards are being violated regularly (Knutson 2012). 

Studies show that the average noise level in NICUs is 50-75 dB and reaches 105 dB at most. Although the benefits of noise reduction for neonates have been established, there is still no appropriate way to its implementation in the noisy parts of NICUs (Almadhoob & Ohlsson 2015).

Many recent studies have shown the need for sound reduction interventions to improve the environmental conditions of NICUs. 

Two systematic reviews with 5 years apart have been conducted on sound reduction interventions (Almadhoob & Ohlsson  2015). Many studies have suggested different ways to manage harmful sounds and obtained different results (Abdeyazdan, Ghassemi & Marofi 2014; Calikusu Incekar & Balci 2017; Fernández Zacarías et al. 2018).

Because of the rising trend of preterm births on the one hand, and the increased survival of these infants thanks to advances in technology and improved care, on the other hand, the importance of caring for these infants in a safe environment and treating them with minimal complications is paramount. 

This review article aims to evaluate the effectiveness of noise reduction interventions in neonatal intensive care units.

2. Materials and Methods

This review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for reporting on systematic reviews.

Search strategy

A literature search was conducted from 2012 to 2020 using Medline, Embase, CINAHL, SID IranDoc, and Magiran databases. The search words used were preterm infant, noise, and neonatal intensive care unit. Articles on sound levels and noise reduction interventions conducted at NICU were included. Conference proceedings and gray literature were also included. The articles were selected if they were in Persian/English languages, and interventional, or quasi-experimental in design. A total of 26 articles were found on noise levels, effects of noise enhancement, and noise reduction techniques; 19 articles included no interventions to reduce the noise in NICU and were excluded. 

Data collection and analysis

Title screening was carried out by the first author based on the agreed, pre-piloted structured forms. Full-text articles were assessed for eligibility by other reviewers with agreement by consensus. The included studies were assigned a grade based upon their level of evidence and critically appraised using several tools (Burns, Rohrich & Chung 2011; Evans 2003). Meta-analysis was not undertaken due to insufficient numerical data (Moher et al. 2016). Finally, six articles investigating different types of noise reduction techniques were reviewed. Papers that met the inclusion criteria were assessed in terms of performance and effectiveness of noise reduction interventions. 

3. Results

The results are shown in Table 1.


 

4. Discussion 

The noise level in the NICU consistently exceeds the recommended standards. Despite all interventions, the sound levels remained high. Noise reduction interventions were performed in the studied articles. The interventions used in the reviewed articles were the training of personnel and parents, changes in ward structure, use of low noise equipment, use of acoustics to alert loudspeakers, the implementation of quiet hours’ protocol, care of infants in separate rooms, and use of earplugs.  

The studies that assessed interventions found that continuous education was an important factor to reinforce suitable noise levels. The redesign of the NICU room has been recognized as one of the critical factors in maintaining a sound standard level. These findings led to effective strategies targeted environmental and behavioral modifications. Recent studies have shown that both structural changes and staff education have a significant impact on reducing NICU noise levels.

Implementing interventions to reduce noise levels may be attainable but requires a change in culture. Also, parents of newborns in NICUs will need education and reminders to maintain an appropriate level of silence within this environment. Proper placement of required equipment and careful evaluation of alarms are necessary. The implementation of such interventions should not inhibit the quality of care provided to this fragile population, but it should solely enhance it. Based on this review, nurses have a crucial role as leaders in affecting practice change to improve outcomes for the fragile population. Further studies focusing on implementing noise reduction strategies could enhance our knowledge base. 

Ethical Considerations

Compliance with ethical guidelines

All Ethical considerations in this systematic review article were observed.  Our reference was the rticle of  "Ethical Considerations of Conducting Systematic Reviews in Educational Research" by Suri (2020).

Funding

The present paper was extracted from the Master thesis of the first author from Department of Neonatal and Pediatric Nursing, School of Nursing & Midwifery , Iran University of Medical Sciences, Tehran.

Authors' contributions

Conceptualization, Original draft: Nasrin Gholami; Review and editing: Leili Borimnejad; Methodology: Reza jafari.

Conflict of interest

The authors declared no conflicts of interest.

Acknowledgments

The authors appreciate Iran University of Medical Sciences for its financial support.

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