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|Year : 2010 | Volume
| Issue : 46 | Page : 26--36
A pilot study of sound levels in an Australian adult general intensive care unit
Rosalind M Elliott1, Sharon M McKinley1, David Eager2,
1 Faculty of Nursing, Midwifery and Health, University of Technology, Sydney, Australia
2 Faculty of Engineering and Information Technology, University of Technology, Sydney, Australia
Rosalind M Elliott
Intensive Care Unit, Level 6, Main Building, Royal North Shore Hospital, St Leonards NSW 2065
High technology and activity levels in the intensive care unit (ICU) lead to elevated and disturbing sound levels. As noise has been shown to affect the ability of patients to rest and sleep, continuous sound levels are required during sleep investigations. The aim of this pilot study was to develop a robust protocol to measure continuous sound levels for a larger more substantive future study to improve sleep for the ICU patient. A review of published studies of sound levels in intensive care settings revealed sufficient information to develop a study protocol. The study protocol resulted in 10 usable recordings out of 11 attempts to collect pilot data. The mean recording time was 17.49 ± 4.5 h. Sound levels exceeded recommendations made by the World Health Organization (WHO) for hospitals. The mean equivalent sound level (LAeq) was 56.22 ± 1.65 dB and LA90 was 46.8 ± 2.46 dB. The data reveal the requirement for a noise reduction program within this ICU.
|How to cite this article:|
Elliott RM, McKinley SM, Eager D. A pilot study of sound levels in an Australian adult general intensive care unit.Noise Health 2010;12:26-36
|How to cite this URL:|
Elliott RM, McKinley SM, Eager D. A pilot study of sound levels in an Australian adult general intensive care unit. Noise Health [serial online] 2010 [cited 2020 Dec 2 ];12:26-36
Available from: https://www.noiseandhealth.org/text.asp?2010/12/46/26/59997
International research reveals that technology and the high number of health care personnel within the intensive care unit (ICU) creates a busy noisy environment. ,,,, Elevated and disturbing noise levels, together with the symptoms of illness, have been shown to impact the patient's ability to rest and sleep. ,,,,,,, The sleep of ICU patients is distributed evenly between day and night;  therefore, continuous sound level recordings are required in order to interpret the effect of noise on the quality and quantity of patients' sleep. The aims of this pilot study were to examine international research related to noise levels in intensive care settings and to investigate sound levels that adult patients are exposed to within an adult Australian ICU. The results will inform a future substantive study aimed at improving sleep for intensive care patients. The paper provides a description of the instrumentation and set-up together with acoustical data.
Background: Investigations of sound levels in adult intensive care units
A search for relevant literature was performed in order to inform the development of the study protocol. The following databases were searched: PubMed, Ovid Medline, CINAHL and EMBASE. The search terms 'critical care unit' and 'noise' (text word) were used and the papers selected were restricted to those pertaining to those reporting studies of sound levels in adult intensive care units (as opposed to all critical care areas, for example post-anesthesia, high dependency and emergency care units) published in English after 1966. In addition, journals related to acoustics were searched using this strategy. Reference lists of the papers identified were scanned manually to identify other relevant papers. Publications regarding sleep in adult ICU patients were scanned manually to identify studies which recorded sound levels. The entire process yielded 27 papers which are briefly reviewed below.
The information presented in this section contains the main points extracted from published studies of sound levels in ICU and informed the development of the pilot study protocol described in the methods. A summary of the instrumentation and main findings of the studies is presented in [Table 1].
Two main study designs have been used in investigations of sound levels in ICU. The majority of studies are observational, with the primary aim of recording sound levels in ICU, while the aims of the experimental studies were to reduce sound levels using either behavioral or environmental changes or both. The experimental investigations used the preintervention and postintervention design as it suits the introduction of unit-wide global behavioral changes and architectural acoustic interventions. ,,,,,
Instrumentation and set up
Few of the reports of the studies fully describe the set-up and instrumentation for sound level recordings. However, the model and manufacturers of sound level meters and dosimeters are given for most studies. The sound level meters used are predominately Class 1 indicating that the instrument meets international measurement standards for research and legal purposes. 
It is common practice to attempt to capture the patient's experience of sound by placing the microphone close to the patient. In most studies that describe the microphone position, it was usually placed adjacent to the patient's head or bed. ,,,,,,,,,, For example in the observational study performed by Ryherd and Ljungkist  the microphone was 0.5 m above the patient's head. Distances of the microphone in relation to the patient were reported to range from 0.0 to 6.5 m. Information on the position of the microphone in relation to the floor, walls and other reflective surfaces is often omitted. Articles that provide plans of the patient rooms with the position of the microphone in relation to the patient offer the reader some indication of the possible effect of reverberation from the furniture and walls. ,,, The acoustic properties of architecture materials such as walls, ceilings and fitments in the ICU surrounds are commonly reported in interventional studies which have the specific aim of examining the effect of these materials on sound levels and reverberation. Calibration procedures (when described) follow the recommendations of the sound level meter manufacturers. Broadband parameter settings are often omitted from the study reports but the results suggest that the 'A' frequency-weighted decibel scale is used in all studies with 'C' frequency-weighting occasionally used for peak sound levels. Sampling frequencies are often omitted from study reports however when reported they range from 1 s to 2 min. ,,,,,,,
Results of published observational and interventional studies
The method of reporting sound level data differs. Mean L Aeq sound levels in the range of 49 to 65 dB are commonly reported and exceed international standards for sound levels in hospitals. (The World Health Organization recommend that sound levels should not exceed L eq 35 dBA in patient areas and the LAF max should remain below 40 dBA at night in hospitals.  ) Other sound parameters reported are mean peak levels (range: 78.1 to 126.2 dBA) and the mean number of peak levels >80 dBA per hour (range: 19 to 250). Minimum and maximum sound levels are also reported.
Noise sources in ICU
Common sources of noise for patients in the ICU were reported to be alarms emitted from monitors, sounds related to treatment, for example oxygen therapy, and equipment such as the X-ray machine. Talking amongst health care personnel can result in noise levels ≥80 dBA  and some equipment can emit up to 92 dBA (i.e. adjusting the bed rails).  Spectral analysis indicates the presence of predominately high frequency noise (rated 'hissy') in ICU. 
Effect of interventions to reduce noise
Some studies reporting noise reduction programs describe improvements in noise levels which are both statistically and clinically significant (mean range: 2 to 29 dBA). The remaining studies report trends toward lower noise levels. Effective interventions included sound reflective ceiling tiles, , staff behaviour modification ,, and noise attenuation strategies. , The use of white noise as opposed to noise attenuation shows promise. Its use in one study resulted in less sleep fragmentation in volunteers exposed to ICU noise despite the overall increase in mean noise level. 
Materials and Methods
We conducted an observational pilot study of noise level exposure in 11 patients in intensive care unit between April 2008 and September 2008.
The pilot study reported here was part of the preparatory work for the investigation "improving sleep for the ICU patient". The study was approved by the Human Research Ethics Committees of the University and Health Service. The setting was a 17 bed adult general intensive care unit in a metropolitan 600-bed hospital in Sydney, Australia. The hospital is a tertiary referral centre for several specialties, including burn injury, spinal cord injury, renal disease and cardiology.
Instrumentation and set up
A hand held sound level meter (SLM) and analyzer (Model 2250) (meeting international standard IEC 61672-1), microphone (Model 4189) attached to a 3.0 m extension lead and calibrator (Model 4231) (Brüel and Kjaer™) were used. The data were downloaded to a laptop computer (Compaq™, Windows XP Professional™ Version 2002 service pack 2) using BZ 5503 Utility Software for Hand Held Analyzers (Brüel and Kjaer™).
The microphone was placed 1.0 to 0.75 m above the patient's head and bed (this varied as the bed height and angle of the patient backrest were adjusted from time-to-time), 1.75 m above the ground and 1 m below the ceiling, with the nearest wall 1.5 m behind the patient. The two open plan six bedded spaces in which the recordings were made are divided by a 4 m solid brick wall extending from the exterior wall, with the other three bedded area being a mirror image of that shown in the diagram [Figure 1]. Thus the whole six-bedded ward area is open to sound throughout. Ceiling tiles are wet-formed mineral fiber covered with a vinyl latex paint, with acoustic properties as follows: noise reduction coefficient of 0.55  and weighted sound absorption coefficient, alpha w of 0.5.  All walls are solid brick structure. The floor is solid concrete with an overlay of polished tiles.
Five broadband parameters were set: LA eq , LC peak , LAF max , LAF min and LC eq along with LZ spectra recorded at a sampling and logging frequency of one sample per second. Maximum input level was 141.07 dB and 1/3 octave bandwidth was used for the sound spectra.
Patients were enrolled from the ICU for the pilot study of the larger investigation. The aim was to monitor patients' sleep, sound and other data for 24 h. The patients gave informed consent for sleep monitoring and for sound and light level measurements to be made in their surrounds. Sound and light level measurements were performed simultaneously with sleep monitoring in order to detect possible sources of sleep disturbance and to identify possible interventions to improve sleep, such as noise reduction. In order to reduce the likelihood of the transmission between patients of infectious microorganisms that are highly resistant to standard antibiotics (e.g. multiresistant Staphylococcus aureus - MRSA) patients treated in the individual isolation rooms of the ICU and patients at high risk of infection e.g. burn injured and immunocompromised patients were not enrolled, only patients in the two six bedded areas were enrolled. All sound recordings were made in these open plan areas
The sound level meter was calibrated by the company at the factory prior to the start of the study. The microphone was calibrated after fitting the 3.0 m extension cable before each monitoring period. Health care personnel were advised of the presence of the microphone and reassured that the sound level was being monitored and recordings were not being made of activity and speech. Sound level recording was started and terminated at the same time as sleep monitoring. In addition individual sound level recordings were made of common sounds emitted from equipment within the ICU on another day. In this instance in order to simulate the patient's experience of the sound the SLM and microphone was held by the researcher 1 m from the head end of a patient's bed while health care personnel conversed, alarms sounded and a dressing trolley was moved nearby.
Sound level data were transferred to a laptop computer and reports generated using the Utility software for Handheld Analyzers BZ 5503 (Brüel and Kjaer™). Summarized sound level and spectral data were then transferred to an Excel™ (Microsoft™) file for management. (In the main study the entire set of sound level data will be imported into an Access™ database for analysis).
Eleven sound level recordings were made between Monday and Friday. One recording was unusable. During sound level recording the microphone was moved closer to the patient during a time when the researcher was absent. On examination of the data, it appeared that the microphone had been repeatedly knocked. The duration of the remaining 10 recordings ranged from 13 h 33 min to 24 h (mean duration17.49 ± 4.50 h). Four recordings were made over 24 h, from midday to midday, three from early evening to early morning, three from midday/afternoon to mid morning. Recordings were made in eight different bedspaces within the two six-bedded areas. Mean values for each of the parameters for all of the recordings are provided in [Table 2]. The data were not divided into time periods (that is, day and night) but the standard deviations and a visual inspection of the sound level graph for each recording indicates that there was little variability in sound levels over the 24 hour period [Figure 2].
Background sound levels (L 90 ) ranged from 43.5 to 50.2 dBA (46.8 ± 2.46). Common sources of background noise were conversation, oxygen therapy and the electric floor polisher (characteristics of sounds are displayed in [Table 3]). Peak noises were generated by monitor and equipment alarms and elevated voices from health care personnel. Alarms on equipment typically located within 2.0 m of the patient, for example the intravenous pump, ventilator and air mattress were noted to generate sound levels up to LC peak 85 dB. Examination of the 1/3 rd octave bandwidth frequencies indicated that sound levels were higher at lower frequencies [Figure 3]. Intravenous pump and ventilator alarms tended to display spectra of higher frequency than the background noise, that is >2 kHz.
The protocols in many published studies on noise monitoring in intensive care settings often have insufficient detail to be replicable. However, the design of this pilot study resulted in a successful set-up and protocol for recording sound in an adult ICU. All data were usable with the exception of one recording, when the microphone was displaced and knocked. The protocol described in this paper will be used in the main study on sleep in the ICU patient.
Sound levels recorded in this Australian ICU exceed international standards for noise levels in Hospitals and are representative of levels found in some ICUs around the world. The LA eq indicates that sound levels exceeded annoyance levels which are generally considered to lead to sleep disruption in the healthy population, that is 37 to 40 dBA.  Perhaps more concerning is the high LAF max (again consistent with international reports) which was 90.89 dBA and far greater than the maximum value recommended by WHO for night time (40 dBA) in hospitals.  The mean LC peak indicates that patients were exposed to very high intermittent noise levels. Alarms were the predominant sources of loud intermittent noise while conversations amongst health care personnel and oxygen therapy were likely the main contributors to the background noise. In summary, the results of this pilot study indicate that there is scope for a noise reduction program which could potentially improve sleep for patients in this ICU.
This preliminary study highlighted a number of limitations which warrant consideration. For example a larger sample size (including more recordings of 24 h) would have enabled inferences to be made about sound levels at different time periods. Such data would provide useful information about sound levels at night and times when there is a high likelihood of noise disruption, for example shift change over. This limitation will be addressed in the main study when more sound level data will be collected in order to design an effective noise reduction program. In addition, the results would have been further enhanced by spectral analysis. It is well known that low frequency sound is more disrupting for humans than high frequency sound  and a more detailed analysis of this aspect of the sound measurement might reveal further possibilities for the design of an effective noise reduction program, for example the requirement to close the unit doors when the floor polisher, which generates low frequency noise, is used in the corridor. More sounds will be subjected to spectral analysis in the main study.
Further study is required not only to reduce noise but also to measure the effect on patient outcomes. Sleep data collected during the main study will not only provide additional information regarding the effect of these sound levels on sleep disturbance, but also the patient's perception of the quality of their sleep and disturbance factors. Further data will be collected regarding the patient's sleep during recovery at home and their memory of the ICU experience. This may contribute to the growing evidence that noise, and in particular its effect on sleep, affects the experience of being a patient in ICU.
We sincerely thank the Faculty of Engineering at the University of Technology Sydney for the loan sound level meter and the team at Brüel and Kjaer™ Australia in particular Neil Rawle (Applications Engineer) for technical assistance.
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