Sound medicine (part 2)
publication date: Jun 3, 2008
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author/source: David Harris
To give an idea of the magnitude of sounds that can be found in hospital environments, the decibel level of a portable X-ray machine is roughly equivalent to that of motorcycle; while a bedside monitor alarm approaches the intensity of sound created by heavy lorry traffic. While sound can be measured objectively, noise is a subjective phenomenon and not an acoustic property. At the wrong time or place the sound of laughter may be more disturbing than the louder but more appropriate sound of an infusion pump or heart monitor. It’s also important to understand, acoustics experts say, that when it comes to sound management silence is not golden - or the goal. If the level of continuous sound or noise floor of a space is too low, conversations can be easily overheard and sharp sounds like a cabinet door slamming or a glass breaking can startle people unnecessarily.
Noticeable changes in sound levels over time and in different areas of the hospital facility make it harder for patients and caregivers to block out unwanted sound. A continuous and consistent noise floor ranging between 42 and 48 dBA can help preserve speech privacy and protect concentration. All noise is sound, but all sounds are not necessarily noise. The sound of carers moving quietly through the corridors can be reassuring to patients in their rooms. The sound of a harp playing in the background can be soothing, even healing.
Hospitals need auditory environments that promote clear and timely communication while also protecting proprietary information from being overheard and possibly misused or misunderstood. Closed doors and other visual barriers can hamper staff accessibility without assuring that patients and their families won’t hear proprietary information or preventing nurses and physicians from exchanging critical information at the right time but in the wrong place.
Designing sound environments for hospital facilities, then, must include considerations of intelligibility levels as well as decibel levels. The first step in reducing noise in hospital environments is identifying its sources. A digital decibel meter is an effective tool for measuring the sound levels of specific areas of the hospital at different times of day. In addition to quantitative measurements, of course, it is important to assess the perception of noise by patients and their families.
Once noise sources have been identified, a variety of noise-abatement strategies, from sophisticated sound-masking systems to “Quiet, Please!” signs, may be employed. In general, studies of the effectiveness of different measures suggest that design interventions are more successful than organisational or behavioral interventions.
However, policy changes regarding use of communications devices can be effective. Switching from loudspeaker paging to vibrating beepers and setting standards governing the use of cell phones, nurse call systems, and the discussion of confidential information in public spaces can go a long way toward reducing unwanted sound and protecting patient privacy.
Environmental design strategies for noise reduction include the maintenance and replacement of hospital equipment, the layout and acoustical treatment of patient rooms, nurses’ stations, and corridors, and the implementation of emerging technologies to mask sound, reduce speech intelligibility, and introduce healing sound into the environment.
With all the rolling carts and machines in hospitals today, considerable noise reduction can be achieved by simply fixing or replacing squeaky wheels and scheduling regular maintenance to keep mobile equipment in quiet working order. The noise level of heavy rolling equipment can be reduced by as much as 30dB just by lubricating the moving parts. Other effective strategies include padding chart holders and pneumatic tube systems, and lowering volume levels on clinical and communication equipment.
Walls are still the first line of defense in acoustic design. Physical barriers between patients and noise sources will block sound movement fairly effectively if they are of the proper height and constructed of sound-absorbing materials. However, the floor and ceiling can do more to collar noise. Together they typically account for 70 to 80% of the acoustical properties of a patient room. Noise levels are much lower in single-bed rooms than in shared rooms or bays. In new hospital construction, there is already a trend toward single-bed rooms. In areas like ICUs and nurses’ stations, where visual access is essential, clear plexiglass or non-breakable glass is a workable alternative to architectural walls or freestanding partitions. While naturally more sound-reflective than acoustically treated opaque sound baffles, transparent barriers between patient rooms and corridors or nurses’ stations can provide a level of noise control and speech privacy while maintaining an open line of sight.
"The noise level of heavy rolling equipment can be reduced by as much as 30dB just by lubricating the moving parts"
Of course, it’s impossible to erect barriers of any kind between patients and the sound sources within their rooms. Here, the replacement or treatment of hard, reflective surfaces with soundabsorbing materials can dramatically reduce noise levels. Hospitals that have replaced “hard-lid” ceilings with high-performance acoustical tiles and tiled floors with sound-absorbing carpet report that they have been able to reduce decibel levels and improve patient sleep without sacrificing cleanliness or infection control.
Distance is another separation strategy that can be employed. Sound intensity decreases by 6 decibels every time the distance between the sound source and the listener doubles. Locating noisy as far as possible from patient rooms (and acoustically treating those locations and connecting corridors to prevent their racket from reverberating its way back to patient rooms) is an obvious but often overlooked plan of action. The location of nurses’ stations is also an important design consideration. Decentralizing nurses’ stations, if space allows, disperses people and reduces the concentration of sound emanating from their activities. However, central workstations are likely to remain for several functions on the nursing unit, even with the use of decentralized nurses’ stations. To keep noise in check, careful planning of work zones and locating equipment according to who uses it must be considered.
Another method for controlling noise involves actually adding sound to the environment. Soundmasking systems work to reduce the distance over which speech and other distracting sounds can be heard by raising the decibel level of the “noise floor” in a controlled fashion. A series of speakers installed in the ceiling distributes electronically generated background sound that serves to cover or reduce the impact of noise spikes. This specially engineered sound creates an ambient environment that is perceived to be quieter and that enhances speech privacy in healthcare facilities. Emerging technologies that use computing technology to shape sound offer the possibility of localized sound-masking that can be customized for specific situations. Perhaps eventually individual patients and caregivers will be able to control them. These technologies are particularly effective in masking conversations.
Acoustics experts caution that noise is not a problem that can be fixed once and for all, but an ongoing issue that requires continual attention in healthcare facilities. Regular sound assessments and acoustical maintenance of equipment are essential to sustaining an auditory environment that promotes the effectiveness of caregivers and patient rest and healing.
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