Mapping sources of noise in an intensive care unit

Summary Excessive noise in hospitals adversely affects patients’ sleep and recovery, causes stress and fatigue in staff and hampers communication. The World Health Organization suggests sound levels should be limited to 35 decibels. This is probably unachievable in intensive care units, but some reduction from current levels should be possible. A preliminary step would be to identify principal sources of noise. As part of a larger project investigating techniques to reduce environmental noise, we installed a microphone array system in one with four beds in an adult general intensive care unit. This continuously measured locations and sound pressure levels of noise sources. This report summarises results recorded over one year. Data were collected between 7 April 2017 and 16 April 2018 inclusive. Data for a whole day were available for 248 days. The sound location system revealed that the majority of loud sounds originated from extremely limited areas, very close to patients’ ears. This proximity maximises the adverse effects of high environmental noise levels for patients. Some of this was likely to be appropriate communication between the patient, their caring staff and visitors. However, a significant proportion of loud sounds may originate from equipment alarms which are sited at the bedside. A redesign of the intensive care unit environment to move alarm sounds away from the bed‐side might significantly reduce the environmental noise burden to patients.


Introduction
Excessive ambient noise in hospitals adversely affects patients' sleep and recovery, causes stress and fatigue in staff and hampers communication. In critical care areas, disruption of patients' sleep patterns may contribute to the development of delirium [1,2]. Patients who experience delirium in hospital may have longer hospital stay and ongoing cognitive impairment after discharge home [3].
The US Environmental Protection Agency (USEPA) suggests sound pressure levels in hospitals should be limited to 45 decibel (dB)-equivalent continuous sound level (LAeq) during the day, and 35 dB at night [4]. The World Health Organization (WHO) advises sound pressure levels in hospitals should not exceed 35 dB [5]. For neonatal intensive care units (ICUs), an upper limit of 45 dB is recommended [6], with limits on transient loud sounds [7,8].
In a previous study of environmental noise in five general adult ICUs in the Thames Valley region of the UK, average sound pressure levels always exceeded 45 dB, and for 50% of the time exceeded 52-59 dB in individual units [9]. Although the WHO and US EPA guidelines are probably unachievable in any acute care area of a hospital, some reduction from these high levels should be possible. A preliminary step would be to identify the location and sources of noise.
As part of a project investigating initiatives to reduce noise in a single ICU, we installed a microphone array system in a single bay containing four beds in an adult general ICU. This continuously recorded the location, sound pressure levels and weighted 'loudness' values of environmental sound. This study summarises the results over one year.
Noise is usually described as 'unwanted sound'. In this article, we refer to 'sound' as raw, objective values (reported as sound pressure levels, measured in decibels); 'noise' signifies a subjective response. Features of sound, such as volume, frequency (Hertz), duration and time of occurrence are likely to affect subjective impression of sound. 'Loudness' is a weighted value (also measured in decibels) that allows the subjective perception of sound to be described and quantified.

Methods
This study focussed on environmental monitoring and did not involve patient recruitment or the use of any identifiable information. The system recorded sound pressure levels only; no audio recordings were made. The local ethics policy does not require formal review/approval for studies based on environmental data as they contain no identifiable information that can be traced back to individuals.
We used a four-bed bay in the general ICU at the John Radcliffe Hospital in Oxford (UK) for the study. In addition to beds and associated equipment, the bay contained equipment racks, trolleys and a built-in counter (nursing station) that housed two telephones and a computer. Two individual patient rooms opened into the bay on one side. These weighted values were calculated using the Zwicker method, which forms the basis of the ISO standard method for calculating loudness (ISO 532-1: 2017) [10]. The details of the system have been reported elsewhere [11]. The area monitored was 14. Temporal changes in loud sounds were summarised by similar plots of counts for one h corresponding to the loudest (19h00-19h59) and quietest (04h00-04h59) one-h periods identified in the earlier study [9].
The sound level monitoring system was installed as part of a range of measures to make the ICU quieter. One   This graphic can be interpreted as showing how loud, on average, noises were that originated from each 1 cm 2 of the monitored area. Louder noises originated from room peripheries and were generally centred on the head area of bed spaces. Noise originating from the centre of the room was on average less loud. Figure 3 shows a heat map of the frequency with which one of the five loudest sounds above 35 dB originated from each 1 cm 2 of the ICU bay between 19h00 and 20h00.
Counts were considerably lower than in Fig. 1, as this plot only represents about 1/24th of the data in Fig. 1.     Fig. 1, as this plot only represents 1/24th of the data in Fig. 1. source of the sounds directly. A machine learning approach was used to try to separate the sounds into classes (e.g. 'alarms', 'speech' or 'other'), but did not achieve reliable identification. However, an earlier phase of our project included an ethnographic study conducted between November 2014 and July 2015 [12]. This indicated that noise from equipment was pervasive. The volume of equipment-related noise was consistently high, and activity around patient bed spaces often led to alarms triggering, which were not silenced until patient care activity was concluded.

Discussion
Hospital noise is increasing. A systematic review suggested that the A-weighted SPL (corrected for the human hearing As reported elsewhere [12,14], our project utilised the AEBCD method [15] to design and deliver a number of interventions to reduce noise levels in the ICU. Briefly, these included soft-close plastic-lidded bins, better day/night differentiation, and alarm management guidelines that recommended 'personalising' alarm parameters and adjusting volume according to the wider environmental sound level. We also created a training package that delivered an online module and an experiential simulation Intensive care units are particularly noisy areas of hospitals [1]. Neonatal units have average sound pressure levels of 48-61 dB for up to 95% of the time [16][17][18][19], paediatric units average 53-73 dB [20][21][22][23][24] and adult units are 53-59 dB [25][26][27][28][29]. The unit at the John Radcliffe Hospital when measured in 2012 had daytime averages of 58 dB at the desk and 60 dB adjacent to the patient [9].
There seems to be considerable concordance between average sound pressure levels recorded in ICUs in different healthcare systems, and across levels measured in the wider hospital [13].
Excessive noise in ICUs disrupts patients' sleep [1,27,30], increases sleep medication use [2], sedation use [24] and the incidence of delirium [2]. Ambient sound markedly reduces the intelligibility of speech in acute care areas [13], which can contribute to avoidable errors in care. To be intelligible, speech needs to be about 15 dB above ambient sound pressure levels. Conversations, therefore, increase sound pressure levels which aggravates the problem (Lombard effect [31]). High ambient sound levels also have a range of deleterious non-auditory health effects on staff [32].
Acute care areas in hospitals rely heavily on alarms and pagers to signal urgent situations. It is, therefore, unsurprising that observational studies on ICUs identify these as major disruptive noise sources. Nearly 80% of disruptive noises are generated by monitor or ventilator alarms and speech [33,34]. However, a significant proportion of the noise coming from speech is not required for patient care [1,2], and almost 90% of alarms from physiological monitors are 'false positives', with no patient benefit [35].
The standard measure of environmental noise, the average daily sound pressure levels value (LAeq24), is insufficiently detailed to enable targeted noise-reduction interventions in an ICU. This may be one of the reasons why the majority of sound reduction studies conducted in ICUs have not resulted in significant change [36][37][38]. This study was designed to identify spatial positioning of sound sources within an ICU. This would enable interventions to be focussed on areas of high noise levels, which might lead to meaningful reduction in overall (averaged) sound levels.
Sound pressure levels increase logarithmically with proximity to the source of the noise. There is no reason for alarms from physiological monitors, ventilators or any other piece of equipment to be generated next to a patient. The primary function of alarms is to alert staff to a possible clinical problem. Arguably, there is no reason why patients need to hear these alarms at all. Hearing alarms may cause patients distress or contribute to disorientation [39]. With modern digital electronics and wireless networks, an ICU free from intrusive alarms is possible, although there are considerable commercial, regulatory and safety hurdles to overcome before this can be achieved [40]. In addition, changing a technology that has been in use for decades requires careful planning and detailed assessment of working patterns that may have evolved alongside the technology [41]. During the early phase of this project, the use of body-worn haptic alerts linked to monitoring equipment was suggested as an alternative to acoustic alarms. The nurses felt this approach would remove the multiple layers of redundancy that an alarm heard by all staff added to their practice, and would not consider this technological adaptation. Although they acknowledged the distress that alarms might cause, patients also expressed concern that urgent clinical situations might go unattended if this form of technology were adopted.
At the very least, conversations not directly involving patients or their visitors should occur away from the bed-side, and ideally outside the unit, if possible. A bodyworn electronic communicator has been successfully trialled in an ICU in the USA [13], although the major gain was a reduction in overhead paging calls, which are not used routinely in the UK. The sound location system revealed that the majority of noise in this four-bed ICU bay was generated immediately adjacent to patients' ears. This proximity maximised the adverse effects of high environmental noise, levels for patients. Paying attention to the locations of significant high noise, as well as the overall sound level, might improve both the patient experience of their ICU admission, and the general working environment for staff. The sound location system deployed for this study was both complex and expensive, and required minor building works to install. Although it would be ideal to repeat this work in other ICUs to test generalisability, this might not be practical. However, a simplified version of the system with single microphones near patients' heads at each bed space would be quite feasible. This would enable unit-wide evaluation of noise levels as experienced by individual patients.