The effect of noise on the neonatal unit and on neonatal transfer

Deafness Research UK supported a study led by Dr Lesley Jackson at the Glasgow Royal Infirmary to assess the risk to newborn babies of hearing loss after exposure to noise during neonatal care.

[Equipment grant: 2006-2008]

Neonates that have been admitted to intensive care are 10.2 times more likely to have a sensorineural hearing loss (“nerve” deafness) or mixed hearing loss (combining sensorineural and conductive hearing loss) than those who are not.

As noise-induced hearing loss is a well recognised phenomenon, the project aimed to address excessive noise in both the neonatal unit and on inter-hospital transfers.

Infants are transferred between hospitals by the Neonatal Transport Team for many reasons. These are often very sick or premature babies who are transferred by ambulance, plane or helicopter as required. Noise levels during transfers have been reported as high as 99 DbA, although the recommendations for noise levels on neonatal intensive care units themselves are set at 45-50 DbA.

In the first part of the study the team measured noise levels both inside and outside transport incubators in 30 transfers by a mix of ambulance, plane and helicopter. To assess the effect of noise on the inner ear, the team made recordings from the neonates of a particular type of otoacoustic emission (the noise that healthy ears emit). These emissions show changes after noise induced hearing loss.

Initial results showed no hearing loss for the babies but did find high levels of noise across some of the ambulance worker’s shifts. The research team then went on to investigate the noise levels staff are exposed to and measured the noise on the neonatal units.

They found that 20% of NHS worker’s shifts exceeded a lower exposure action level, 3% exceeded an upper exposure action level, 73% of shifts exceeded peak lower exposure action levels, and, 47% of shifts exceeded peak upper action exposure levels. If the action levels are exceeded, the employer (in this case the NHS) is required to provide information/training on hearing protection, or in some cases, take measures to reduce noise exposure. The research team concluded that the majority of shifts exceed legal limits for peak noise levels; however, the daily personal noise exposure level was exceeded only rarely.

Data from the study will be used to inform any new recommendations for safe levels of noise for both neonates and NHS workers.