Project dates: 1 Jul 2011 – 31 Dec 2011

Past studies (in the '70s and '80s) have shown evidence of a relationship between the exposure of patients to high noise levels in intensive care units and their recovery time, but a definitive and systematic study (i.e. one that considers perceived characteristics of noise, that extend beyond simple energetic levels) is still lacking, mostly due to the absence of an appropriate metrology. This feasibility study builds on more recent research in terms of assessing soundscapes (i.e. acoustic environments as perceived by their users or designed to be perceived in a particular way), on the availability of distributed MEMS microphones measurement systems, conceived and developed by NPL, and on the existing relationship between the NPL and St. George's hospital. The aim was to determine a measurement protocol (featuring the correct measurands and the use of distributed sensors) to be tested by St George's personnel in at least one of their intensive care units.

A measurement protocol (measurands, pros and cons of distributed sensors etc.) was designed and tested, based on literature results. A preliminary assessment of the 'acoustic climate' at one of SGU's Intensive Care Units (ICUs) was conducted in November 2011. Since a 'classical' noise level meter was used, there was only one active measurement location at a time, which was moved in different locations across the site (Figure 1, Figure 2) to build a non-simultaneous acoustic picture. This survey allowed optimisation and testing of the measurement protocol, but will be used to benchmark future measurements with the distributed system. The results are at least of the same level of similar studies in the literature, but the level of detail used (e.g. we acquired at different time scales of 1 s, 1 min, 15 min; percentage levels were recorded; a preliminary correction from the measurement point to the patient's head was determined and the extremely valuable clinical insight from SGUL personnel, adding context to the noise measurements, made this study unique.

Figure 1: This map shows the position of the bed posts that will be used for the distributed monitoring (red circles) and the points used for the benchmarking study (blue diamonds). Also noted are Bed numbers, for reference in the graphs.

Figure 2: This graph shows that, with 15 minutes temporal acquisitions, there is very little difference between the locations. The graph also reports Lmax (the maximum value over 15 minutes), typically correlated with sleep disturbance, and L90 (the energetic value that is overcome for 90 % of the time, sometimes used as an indication of the background). As expected, values are quite high.

NPL staff involved with the project

Gianluca Memoli
Daniel Simmons
Ian Butterworth
Richard Barham

Collaborations

• St George's, University of London (Mike Grounds, Barbara Philips, Mark Hamilton)
• St George's Hospital (Deborah Dawson)

Publications

• Acoustic climate in a general intensive care unit
  D Dawson, G Memoli, R Barham, M Grounds, I Butterworth, D Simmons, B Phillips and M Hamilton
  Work in progress

Conferences and Presentations

• Distributed noise monitoring in intensive care units
  R Barham, G Memoli, D Dawson, M Grounds
  To be presented at Acoustics 2012 in Nantes

Further Opportunities

As part of this project, St George's also provided funding, covering equipment and additional staff time. This feasibility study will allow the partners involved to access further opportunities.