Sound, acoustics and treatment spaces

In Denmark it is estimated that 10% of all patients get a bloodstream infection during a hospital stay – and there is a risk of 20% of dying because of that infection^[1].

Alone in American hospitals, the Centers for Disease Control (CDC) estimates that these healthcare-acquired infections (HCAI), also known as nosocomial infections, account for an estimated 1.7 million infections and 99,000 associated deaths each year and the annual economic impact was approximately US$ 6.5 billion in 2004 ^[2].

According to the WHO, HCAIs cause 16 million extra days of hospital stay in Europe and 37,000 attributable deaths, and contribute to an additional 110,000, every year ^[3]. In a world where the risk of ‘super bugs’ is increasing there is therefore a constant focus on overuse of antibiotics and on hygiene demands.

Recovery and sleep

What we seem to forget is how the sound environment contributes to recovery, medication intake and infection risks. Patients, no matter if they have just gone through a serious heart surgery or suffering from a pneumonia need to recover quickly to avoid infections – and a successful recovery is based on sleep.

In 2015 a group of Danish researchers investigated the suitability of the sound environment in a modern intensive care unit (ICU) in promoting sleep by analyzing continuous audio recordings captured over the course of three weeks. They focused on restorative periods (RP). RP is defined as a period that starts after 5 minutes without disturbance of the sleep and the chocking data showed that the mean restorative period in 3 weeks was 6.2 minutes ^[4]. Briefly, this means that you will get interrupted in your sleep 167 times in a 24hour period because of a highly disruptive noise environment! The study also revealed that only one third of the recorded days contained one or more RP ≥ 90 minutes. Knowing that the human sleep cycle is 90-110 minutes the study therefore concluded that an ICU patient rarely completed such a cycle.

Sound levels in the ICU

A study from Sweden conducted from 2012-2017 ^[5] showed similar results in regards to the sound environment in the ICU. To investigate how the patients experienced the sound environment of the ICU, they were interviewed 2–35 days after their discharge. All of the interviewed patients shared rooms with one or two other patients and the space was divided only by thin fabric curtain which made it possible for speech to be heard from one bed to another. One of the statements was:

The patients also described how they sometimes became involuntary listeners. They described how they heard parts of conversations concerning the other patient in the room and how these conversations woke them up and made them uncomfortable. Some of the patients also described the ‘hospital sounds’ as being scary and frightening and they felt like they had no way to shut off.

What is too much?

The big questions to answer in regards to healthcare and sound are: What is too much? When is sound affecting the patient? How is it affecting the patient? And how can we solve the problems?

In the before mentioned study from Sweden acoustic measurements were done and they revealed that the average sound pressure level in the ICU was 53 dB. It is of course debatable whether 53 dB really is loud or not. But the problem with analyzing an average SPL is that people react more to peaks – and it is the peaks that will wake patients up when they try to sleep. The average value actually doesn’t tell us much in regards to human perception (a lot of people can sleep for hours in an airplane that often has average SPL >70 dB). When it comes to the peaks in the investigated ICU – the numbers speak for themselves: The actual peak levels were 82–101 dB and they exceeded 55 dB 68–79% of the time!

There is no doubt when reading the interviews that the patients suffer in noisy surroundings, but can we put a number on HOW it affects them physically?

Noise and medication intake

Already in the 60s acousticians tried to investigate HOW patients were affected by noise and in 1968 a study revealed that medication intake could be related to sound pressure levels and noise in healthcare settings. In 5 random working days, investigations were made in a recovery room and in periods of heightened activity (presence of a large number of staff, overcrowding of patients, laughing, groaning, snoring, and ringing of telephones) noise levels were between 60 and 70 dB. – and this showed a correlation with the medicine intake ^[6].

Unfortunately, these findings are not only to found decades and decades ago and relates to 10-patient bedrooms. A newer study from 2005 showed the same tendency and revealed that something can be done!

The solution is room acoustics!

If patients suffer in noisy environments – what can we do to solve it? As mentioned above a newer study showed that room acoustic treatment can be linked to medication intake.

The study took place over eight weeks in a hospital in Huddinge, Sweden, with 94 patients suffering from chest pain. For the first four weeks the ceiling was a reflective type, and for the last four weeks the ceiling consisted of absorption class A tiles ^[7]. The results were clear. Just by changing the ceiling the sound level dropped by 5–6 dB in the patient rooms and the reverberation time dropped from 0.9 to 0.4 in the patient rooms. Finally, and most interesting, there was a significant rise in the need for extra intravenous beta-blockers in the group during the period with poor acoustics ^[8]!

The fragile cave man

^[5] Johansson et al: The sound environment in an ICU patient room – A content analysis of sound levels and patient experiences, 2012