Customising anaesthetic to patient need

Measuring the body’s response to sound could ensure that patients receive the correct dose of anaesthetic during surgery, researchers at the University of Southampton have announced.

At present, anaesthetists must judge the correct level of drugs given to patients to ensure they are fully asleep yet not too deeply anaesthetised, based on criteria such as their physical build.

However, people’s susceptibility to doses varies, making the process highly subjective and the anaesthetist must depend on his or her experience to make a judgment. This is further complicated as some operations require the patient’s level of consciousness to be varied at different stages of the procedure.

‘The mix of drugs used during anaesthesia includes muscle relaxants and pain relievers,’ said project leader Prof Robert Allen of the University of Southampton’s Institute of Sound and Vibration Research this week.

‘This interferes with patients’ normal response to stimulation, leading to the possibility that they may be immobile but awake. To make sure they are fully under you must use additional anaesthetic, but this is expensive and the longer it takes to wake the patient the more dangerous it becomes.’

To accurately measure the patient’s condition, Allen placed electrodes on the patient’s scalp coupled with a microphone earpiece to delivers a chirp signal similar to a dolphin’s sound.

This creates a response from the cochlear middle ear as well as changing the brain’s alpha wave patterns as the noise is processed by the body, a response known as Auditory Evoked Potential (AEP).

The patient’s response to chirps can be displayed on a computer screen and analysed to assess their level of consciousness, taking factors such as hearing problems into account.

The team recently completed trials on 10 patients during normal operating conditions and says the results are very promising.