New monitor can reduce patients experiencing awareness during an operation by more than 80%

May 31 2004

An Australian study headed by Melbourne’s Alfred hospital and published in The Lancet today is likely to change the way surgical anaesthesia is conducted throughout the world.

The B-Aware trial proved for the first time that by using a specially designed monitor, doctors can reduce the risk of patients experiencing awareness during an operation by more than 80 per cent.

Awareness is where a patient is conscious to varying degrees and may be able to hear or feel pain during surgery.

The monitor, known as the BIS monitor, uses complex algorithms to analyse the electrical activity of a patient’s brain and determine their exact level of unconsciousness, enabling anaesthetists to increase or decrease the amount of anaesthetic to maintain a safe level of unconsciousness.

Previous international studies have shown that patients experience some kind of awareness in 1 to 3 of every thousand surgical cases. This figure goes up to 1 in 100 for higher risk patients, including those undergoing procedures such as cardiac surgery, caesarean section and major trauma surgery, where light anaesthesia is preferable.

The B-Aware trial was supported by research funding from the Australian New Zealand College of Anaesthetists and The Alfred Hospital Trust, and was led by Alfred Director of Anaesthesia Associate Professor Paul Myles and Royal Melbourne Hospital Anaesthetist, Associate Professor Kate Leslie.

The study recommends that the monitor be used in all high risk surgical cases, which is about five per cent of all surgical cases around the world.

The study was the biggest of its kind ever conducted, involving 2500 patients, all classified as high risk, in 20 hospitals around Australia, New Zealand, South East Asia and the United Kingdom.

Half of the patients were monitored during surgery using BIS monitors and half of the patients received normal types of monitoring. Patients were followed up at four hours, one day and 30 days after surgery to see if they had any memories of surgery.

Eleven patients experienced awareness in the group of patients that received normal treatment, while only two patients experienced awareness in the group on which the BIS monitor was used.

A/Prof Paul Myles said that interestingly, in the two cases where BIS monitored patients experienced some kind of awareness, the monitor actually predicted that they would. The monitoring enabled anaesthetists to ensure that if awareness occurred at all, it was for a shorter period.

A/Prof Kate Leslie said: “The vital link between the BIS monitor and a new level of safety in anaesthesia is a vigilant anaesthetist who will act quickly on the information from the BIS monitor. Australian patients can be assured that the training of anaesthetists in Australia ranks with the finest in the world.”

“Many patients express concern about the possibility of awareness prior to surgery. Patients can now discuss with their anaesthetist whether they are at high risk and whether BIS monitoring can help,” A/Prof Leslie said.

”Becoming aware during an operation can be a terrifying experience. Although some patients take it in their stride, up to a half of patients who experience awareness suffer long term post-traumatic stress disorder, which can result in depression, anxiety, difficulty with relationships or substance abuse.”

A/Prof Myles said reducing the risk of awareness occurring should be among the highest priorities for anaesthetists world wide.

“Using the BIS monitor means we can assure our patients that the risk of this occurring is minimal, which we could not previously do.”

A/Prof Myles said that the other crucial outcome of the study was that doctors now have a proven way of ensuring they do not administer too much anaesthetic, reducing the risk of overdose and ensuring a faster, safer recovery for patients.

The patients that underwent BIS guided anaesthetic woke up significantly faster following the surgery than those patients that were not monitored.

“These findings are a water shed for anaesthetic medicine, giving anaesthetists new direction for how surgical anaesthesia should be carried out in the future,” A/Prof Myles said.

A/Prof Myles said there is still much to be learnt about the monitoring and when and how it should be used for best patient outcome.

“This opens the way for many new further research projects aimed at the prevention of awareness.”