Introduction

Over the last few decades, noise pollution has grown mainly due to urban expansion and the increasing size of vehicle fleets, which is considered an aggravating factor for public health (Hanninen et al. 2014). Several problems related to human health and cognitive activities are attributed to noise, such as sleep disturbance (Muzet 2007; Basner and McGuire 2018), annoyance (Miedema and Oudshoorn 2001; Licitra et al. 2016; Guski et al. 2017; Paiva et al. 2019), cardiovascular diseases (Babisch et al. 2005; Dratva et al. 2012; Sorensen et al. 2017; Héritier et al. 2018; van Kempen et al. 2018; Lin et al. 2020), perception, and learning (Erickson and Newman 2017; Minichilli et al. 2018).

There is even a greater concern in areas considered sensitive to noise, such as hospitals, where noise affects the well-being of patients, slowing their recovery, reducing the productivity of professionals, and increasing the occurrence of medical errors (Hsu et al. 2012; Loupa et al. 2019; Montes-González et al. 2019; Loupa 2020). Moreover, noise can also have a negative effect on visitors and the hospital as a whole (Zannin et al. 2019) and can increase the incidence of rehospitalization (Hagerman et al. 2005). The main factors involved in noise audible inside hospitals may originate outdoors, e.g., vehicle traffic, or indoors, e.g., conversations among employees and/or patients (Ravindra et al. 2016).

Several studies on environmental noise measurements in hospitals that have been carried out around the world (Busch-Vishniac et al. 2005; Fortes-Garrido et al. 2014; Zannin and Ferraz 2016; Montes-González et al. 2019) have revealed noise levels exceeding those recommended for a healthy environment. The World Health Organization (WHO) suggests that sound levels should not exceed Leq 35 dB (A) in the daytime and Leq 30 dB (A) to Lmax 40 dB (A) at night in hospital environments (Berglund et al. 1999). The United States Environmental Protection Agency (USEPA) recommends daytime and nighttime sound levels of less than Leq 45 and 35 dB (A), respectively (USEPA 1974).

In practice, even with technological advances in hospital equipment and construction processes, noise levels inside hospitals have gradually increased from the 1960s to the present day (Busch-Vishniac et al. 2005; Busch-Vishniac and Ryherd 2019). Sound level assessments in hospitals are performed in various ways, given the complexity of hospital environments (Wallis et al. 2019).

The purpose of this systematic review was to survey research conducted between the years 2015 and 2020 pertaining noise measurement in hospitals around the world by examining top ranking scientific and academic journals.

Methods

The systematic review of the literature in electronic format involved three databases, Scopus, Web of Science, and ScienceDirect. The first filter employed in the search selected articles published in the last 6 years (from 2015 to 2020), only articles in English, research articles (excluding technical and review notes), and keywords “Noise” and “Hospital.” The second filter excluded duplicate articles, while articles found in the Web of Science database were kept as reference (without excluding them). The third filter removed articles containing titles outside the context of the research, such as other types of interventions in hospitals or noise from hospital imaging equipment (e.g., X-ray machines). The fourth filter excluded articles whose abstract did not contain elements that met the objective of this review, such as those that did not measure sound pressure levels outside or inside hospitals. Lastly, in the fifth filter, after the articles were read in full, those stating that their authors had taken measurements using noise dosimeters (that evaluated only the noise dose) were excluded, since this is a special device for measuring individual exposure to sound pressure levels. Research that used class 2 equipment was excluded in order to equalize the work in terms of quality and quantity of resources of class 1 equipment. Also excluded were articles involving only simulations and modeling, but not measurements.

The articles selected after applying the five filters revealed the following information: (a) the databases containing the largest number of published articles; (b) the areas of knowledge of the journals in which the articles are published; (c) the countries whose hospitals have been studied and the laws/standards used as reference; (d) the authors’ profession/area of expertise and the main focus of their studies (areas outside or inside hospitals); (e) measurement methods and parameters that were used; (f) works that adopted/proposed noise mitigation measures; and (g) future perspectives for the area. Figure 1 summarizes the literature review filtering scheme, while Appendix 1 Table 6 provides information about all the final articles selected.

Fig. 1
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Literature review filtering scheme

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Results and discussion

Databases and areas of knowledge of journals

After applying the filters, the database found to contain the largest number of articles was Web of Science, with 73%, followed by Scopus with 21% and ScienceDirect with 6%. Figure 2 shows the areas of knowledge of the journals (SCImago 2020) in which the articles were published.

Fig. 2
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Areas of knowledge of scientific journals. Areas of knowledge of scientific journals extracted from the site: https://www.scimagojr.com

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Figure 2 shows that 28% of the articles were published in medical journals, followed by 21% in engineering, 18% in environmental sciences, 15% in acoustics, 9% in nursing, 6% in pediatrics, and 3% in multidisciplinary journals, indicating the interdisciplinarity of the subject and its importance in several fields of science.

Countries where the studies were conducted

Among the 33 studies selected in this review, the countries with the highest participation rates were the USA (n = 3), Brazil (n = 3), China (n = 3), England (n = 3), Portugal (n = 3), and Turkey (n = 3) (9% each), followed by Colombia (n = 2) and Iran (n = 2) (6% each one), Germany, Australia, Bosnia and Herzegovina, Canada, South Korea, Spain, Greece, the Netherlands, India, Peru, and Taiwan (each with 1 study, corresponding to approximately 3% each) (see Fig. 3).

Fig. 3
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Global map showing the distribution of countries where studies were performed

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Approximately 42% of studies are located in Europe (although Turkey is geographically situated between two continents, for the purpose of this review it was considered in Europe), 18% in South America, 12% in North America, 24% in Asia, and 4% in Oceania. Research on the African continent does not exist for the period and the criteria adopted in this review. One of the hypotheses for the paucity of studies on noise in hospitals in the African continent is that there are other more urgent needs, such as access to drinking water and treatment of some diseases, such as HIV and Ebola. Several researchers cite the lack of noise-related research in Africa (Okokon et al. 2018; Sieber et al. 2018). In a review study on noise pollution, Khan et al. (2018) found that most research on the subject has been conducted in Europe, demonstrating a potential gap for studies in this area in Africa, Oceania and South America. In a review study on noise in hospitals, Wallis et al. (2020) found that 33% of research was performed in Europe (in twelve countries), 38% in North America (in two countries), 5% in South America (two countries), 17% in Asia (four countries), 5% in Oceania (one country), and 2% in Africa (one country). In addition to the global geographic gap, if one considers, for example, that the USA has 6090 hospitals (AHA 2021), there is also a regional/local gap, since hospitals have different configurations, activities, layouts, etc.

Standards/laws used as references in studies

Although several countries have noise pollution laws and/or standards, many studies use other references as a parameter to assess whether or not measured noise levels pose risks to human health. Table 1 describes the main characteristics of laws and standards used as references in the studies.

Table 1 Laws and standards used as references
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It was found that 45% of the studies cited the WHO as a reference for noise values, followed by the United States Environmental Protection Agency (EPA) with 15% and the American Academy of Pediatrics (AAP) with 12%. The WHO has more restrictive noise values than the other laws/standards cited in other studies, since it considers overall well-being. Taken together, WHO and EPA are the pioneer institutions in creating standard values for hospital noise (Baqar et al. 2017). Other studies have shown that the values recommended by the WHO are widely used as a reference for noise levels in hospitals (Wallis et al. 2019), although these levels are often exceeded and unlikely to be achieved (Loupa 2020).

Other countries and/or cities had their own particularities when they created their reference laws and considered not only the general health and well-being of the population. Most of these laws/standards are quite old, dating back to the 1970s, 1980s, or 1990s, when cities were less crowded and vehicle fleets smaller. Jahan et al. (2016) state that noise pollution was not a major concern for the population of Bangladesh in the 1970s and early 1980s, but that the risk of noise pollution increased and exceeded the level of tolerance in response to the growing number of motor vehicles in the country. Urban and demographic growth is not always planned, and it is difficult to adjust external environmental noise emission standards to acceptable levels.

To assess the effect of noise exposure of people in different countries, other factors must be considered as well, such as psychological, economic, social, cultural, climatic, and others not yet identified (Sieber et al. 2018).

Table 2 shows the range of equivalent sound pressure levels (Leq) for indoor and outdoor environments observed in the studies.

Table 2 Equivalent internal and external noise levels from studies
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The indoor daytime Leq values in hospitals ranged from 37 dB (A) (Cho et al. 2019) to 88.6 dB (A) (Pirsaheb et al. 2016), while the nighttime levels varied from 38.7 dB (A) (Bevan et al. 2018) to 68.8 dB (A) (Filus et al. 2015). The outdoor noise level (Leq) was 74.3 in the daytime and 56.6 dB (A) at night. For measurements lasting 24 hours or longer, the values ​​ranged from 39.7 (Zijlstra et al. 2019) to 71.7 dB (A) (Carvalhais et al. 2015; Santos et al. 2017). As for studies of outdoor noise levels, these varied from 83.3 to 88.6 dB (A) in the daytime (García-Rivero et al. 2020), from 58.3 to 65.4 dB (A) at night (Predrag et al. 2018), and from 62.7 to 84.7 dB (A) in a 24 h period (Tezel et al. 2019).

Even in countries that have technical guidelines for measuring indoor sound levels, such as Brazil through the NBR 10152 standard, it was found that the levels exceeded recommended ones (Filus et al. 2015; de Araújo Vieira et al. 2016).

Authors’ field of expertise

Like the journals that publish articles on noise in hospitals, the main authors of the publications also have different areas of expertise. In Table 3, note that the total of 33 selected articles were divided into 21 distinct areas. Areas such as architecture and engineering, which represent 27% of the authors’ specialties, contribute to the quality and interpretation of noise assessments in hospitals. Among the authors’ areas of expertise, 36% are in medicine, nursing and other related areas such as pediatrics, communication disorders, public health, health sciences, health and environment, and experimental clinical sciences. One of the explanations for these numbers is that most of the authors have some connection with hospitals (medical, nursing, pediatrics, and other departments, as well as medical laboratories). This facilitates not only the development of the study, in terms of bureaucracy, but also the methodology (choice of noise measurement points, authorization from specific departments, and analysis in different layouts, among others). The areas of expertise of the remaining 37% of authors are in environment, physics, and acoustics. This indicates that the subject has attracted increasing attention from different areas (Loupa 2020), since noise is often underestimated.

Table 3 Areas of expertise of the main authors of scientific papers
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Focus of the studies (areas outside and/or inside hospitals)

Table 4 describes the focus of the studies in terms of location, which may be outside or inside the hospital building, as well as the number of studies.

Table 4 Focus of studies and number of studies conducted outdoors and indoors
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Eighty-two percent of studies measured noise levels inside hospitals, while 15% measured noise outside hospital buildings and 3% took measurements both outdoors and indoors. Indoor measurements are important to evaluate the level of acoustic comfort of patients and medical staff, since a quiet environment is beneficial for both, lowers the physical and mental stress of hospital staff, and contributes to hasten patient recovery (Mousavi and Sohrabi 2018). Outdoor measurements are normally taken to draw up acoustic maps, which are useful tools for diagnosing and evaluating urban noise and indicating the noise levels that reach the hospital facade (Fiedler and Zannin 2015; Zannin and Ferraz 2016). Studies combining outdoor and indoor noise measurements are more laborious, but they can better describe the stressors that may originate outside buildings, such as vehicle traffic, or inside, such as medical equipment and loud conversations (Zannin and Ferraz 2016). Hospitals are environments where patients need to rest and recover and should therefore be quiet indoors and outdoors (Ramadhan and Talal 2015).

Measurements taken outside hospitals usually evaluate traffic noise generated by light vehicles, e.g., motorcycles and cars, and by heavy vehicles, e.g., buses, trucks, and trains. The studies conducted inside hospital environments in specific locations or in various departments are listed in Fig. 4.

Fig. 4
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Hospital environments and number of studies conducted

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Most of the studies available in the literature that involved measuring noise inside hospitals prioritized departments where patients are most vulnerable. Of the total of studies carried out indoors, 26% were conducted in neonatal ICUs, 22% in various different ICUs, and 19% in multiple locations inside hospitals. In addition, 22% were carried out in private and waiting rooms and 11% in emergency rooms, infusion center, and dental clinic. In another review of the literature on noise in hospitals, the authors found that 70% of the studies involved measurements taken in ICUs, and the remainder in different hospital departments (Wallis et al. 2019).

Measurement methods and parameters used

Table 5 describes the criteria adopted in the studies for installing the microphone of the sound level meter, such as height and distance from reflective surfaces, measurement time, and evaluated parameters. Most of the studies examined in this review used Leq dB (A) as a parameter. Other parameters such as Lmax are present in 39% of the studies, followed by Lmin with 27%. Some studies consider the statistical indices most commonly employed, such as L5, L10, L50, L90, and L95 (employed in approximately 73% of the studies), and others less common ones, such as L1, L70, L30, and L33 (used in 12% of the studies). It is noteworthy that 27% of the studies also performed frequency analysis (Carvalhais et al. 2015; Chen 2015; Lahav 2015; Ai et al. 2017; Galindo et al. 2017; Santos et al. 2017; Bliefnick et al. 2019; Loupa et al. 2019; Hasegawa and Ryherd 2020). In addition, 30% performed subjective analysis with questionnaires (Chen 2015; Oliveira et al. 2015; de Araújo Vieira et al. 2016; Ai et al. 2017; Santos et al. 2017; Cho et al. 2019; Wu et al. 2019; Zijlstra et al. 2019; Astin et al. 2020; Tang et al. 2020), or used reverberation time measures such as RT30, RT20 (Chen 2015; Cho et al. 2019), or the Speech Intelligibility Index (SII) (Bliefnick et al. 2019).

Table 5 Microphone installation height, distance from reflective surfaces, measurement time, and evaluated parameters
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Distance of measurements from ground height ranged from 0.75 to 4 m, with some studies installing microphones on the ceiling or objects in order to protect the equipment, not disturb the hospital routine, or avoid the Hawthorne effect, enabling them to take long-term noise measurements (D’Souza et al. 2017; Cho et al. 2019; Zijlstra et al. 2019; Astin et al. 2020). As for the distance from reflective surfaces, 18% of the studies adopted 1 m.

Measurement times varied widely, ranging from 2.5 min to 52 days of uninterrupted measurement (Filus et al. 2015; Astin et al. 2020), although 21% of the studies took 24-h sound level measurements.

Studies that adopted/proposed noise mitigation measures

Some studies proposed or adopted measures to mitigate noise in hospitals, as indicated in Fig. 5. Studies that proposed measures for possible noise mitigation in hospitals represent 36% of the total number of studies analyzed in this review, while 52% of studies did not adopt or propose measures and only took measurements. Studies that adopted measures in order to make “before and after” comparisons represent 3% of the total, while 9% proposed and adopted noise mitigation measures.

Fig. 5
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Studies that proposed or adopted noise mitigation measures

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Luetz et al. (2016) adopted ICU room modification measures, achieving noise reductions in the order of 2.8 dB (A). The main measures proposed by the studies for noise reduction in hospitals involve preventive and educational actions (Filus et al. 2015; Disher et al. 2017; Santos et al. 2017; Astin et al. 2020); use of sound absorbing materials (Chen 2015); adoption of barriers and architectural designs (Monazzam et al. 2015); simulations (Fiedler and Zannin 2015; Montes-González et al. 2019); changes in equipment; physical installations, and procedures (Pirsaheb et al. 2016; Shield et al. 2016); and more studies in different locations and hospitals (Hasegawa and Ryherd 2020; García-Rivero et al. 2020).

Studies that proposed and adopted noise control measures involved a training program (Carvalhais et al. 2015) in which the noise levels showed no variation after implementation of the program, a non-talking rule (Zijlstra et al. 2019) whose implementation led to a noise reduction of 1.1 dB (A), and a quiet hospital environment (Bliefnick et al. 2019).

Vehicle traffic noise is what most affects the modern human lifestyle (Ruiz-Padillo et al. 2016). Changes in driver behavior can contribute to reduce noise levels that reach hospital facades. However, some studies have indicated that despite the significant reduction in the number of vehicles circulating during the COVID-19 pandemic, reductions in noise levels were lower than expected, a fact that is attributed the high driving speed of the remaining vehicles (Asensio et al. 2020). Other factors that contribute to traffic noise levels and that deserve attention are the types of tires (Licitra et al. 2017) and of paving (Praticò and Anfosso-Lédée 2012; Praticò 2014; Licitra et al. 2015; Licitra et al. 2019; Del Pizzo et al. 2020).

Future perspectives in this field

Noise measurements are extremely important for assessing the level of exposure to which people are subjected, given the risks associated with this type of pollution. In hospitals, these measurements are even more important, given the physical and emotional vulnerability of patients and the stress to which hospital staff are subjected daily. Hence, working in extreme situations while subjected to noise levels exceeding those established by laws, standards, or agencies such as the WHO can delay the recovery of patients and impair the performance of healthcare professionals (Zannin and Ferraz 2016; Zannin et al. 2019; Busch-Vishniac and Ryherd 2019; Loupa 2020).

An average of 5.5 articles per year were published in the period studied in this review, as illustrated in Fig. 6.

Fig. 6
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Number of studies conducted in the last 6 years

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In order to improve noise assessments in hospitals, research must contain as much information as possible, e.g., locations where equipment was installed, measurement height from ground level, distance from reflective surfaces, measurement time, noise sources, and measurement period (Wallis et al. 2019). As can be seen in Table 5, the information provided by some studies is insufficient for a careful reproduction or analysis, even those that took measurements for 24 h or more. Studies published in journals in the area of ​​acoustics (e.g., Bliefnick et al. 2019; Hasegawa and Ryherd 2020) offer more complete information, extracting the maximum quality and diversity of resources provided by the equipment used, thus enabling the analysis of a series of interventions and improvements in the quality of the environment. Given the diversity of ways in which the studies are conducted, perhaps a more comprehensive standardization strategy is needed in order to balance noise measurement procedures in indoor hospital environments, considering that the forms of noise measurements in outdoor environments with validation on maps ensure more reliable results.

Conclusions

Several scientific journals have published studies on environmental noise assessment in hospitals, mainly in the areas of medicine, engineering, environmental sciences, acoustics, and nursing. The areas of expertise of the authors of these studies correspond to those of the journals, since most of them are doctors, nurses, and engineers. The studies are concentrated mainly in Europe, the Americas, and Asia.

Most of the studies use the noise levels recommended by WHO as a reference to determine whether the measured noise levels may be harmful to human health in the hospital environment. However, it should be noted that the levels recommended by WHO are the most restrictive possible and that the noise levels measured in practically all the studies selected for this review were much higher. The Leq levels measured in indoor hospital environments varied from 37 to 88.6 dB (A) in the daytime and from 38.7 to 68.8 dB (A) at night, while the outdoor noise levels were 74.3 in the daytime and 56.6 dB (A) at night.

The main focus of the studies was the internal part of the hospitals, and most of them took measurements in only one hospital. Departments treating more sensitive and vulnerable patients that require greater attention from health care professionals, such as ICUs, were preferred environments for environmental noise measurements.

A considerable number of the studies only indicate if the measured noise levels are in conformity with some reference standard or law, but do not adopt or propose measures to reduce the levels.

This is a field of research with a potential for growth. However, there is a need for a more critical assessment of the quality of studies, aiming at scientific advances and reliable dissemination of information to the community in general.