By measuring the type of brain activity associated with perceptual awareness in anaesthetised patients, they have discovered the point at which a patient loses consciousness of their surroundings.
The research could lead to patients being given a personalised dose of anaesthetic during operations. Dr. Katie Warnaby, part of the research team based at the Centre for Functional Magnetic Resonance Imaging of the Brain at John Radcliffe Hospital in Oxford, said “Anaesthetists [currently] give a dose and will monitor not necessarily the brain, but the heart and vital organs, to see how the anaesthetic is affecting an individual and determine the dose on that basis, but we do not have a point where we know when the patient is unaware.
“This study, by showing that there is a change in the way that the brain processes information under anaesthesia, may define that point or at least get us closer to it.”
The team measured the brain activity of 16 patients under a standard anaesthetic. The time taken to send patients to sleep was extended to allow more accurate measurement of brain activity. Warnaby says, “It usually takes 10 minutes, or even 10 seconds, but we took 45 minutes for this stage so that we could see the exact point at which the patients stopped responding to stimulation.”
She stresses that this would lower the risk of patients being given excessive doses which affect the rate of recovery, saying, “Particularly if you’re older, you can get confusion which could persist over a period of time, and if people have problems with their heart and lungs, too much anaesthetic would put pressure on their systems.”
The current risks associated with general anaesthesia are low; in 2011, there were only 153 reported cases of accidental awareness out of 3 million operations, while deaths occur in the UK in only one out of every 200,000 patients given anaesthesia. However, this research offers a reliable method of ensuring that general anaesthetic would continue to be effective throughout an operation.
The research was part-funded by the Medical Research Council. Professor Hugh Perry, Chair of its Neurosciences and Mental Health Board, is excited by the prospect of safer treatment for vulnerable patients. He stated, “With the growing use of anaesthetics in the elderly and other at-risk groups, understanding the minimal dose required to induce the necessary level of anaesthesia is hugely important. This work… provides an excellent scientific foundation for new ways of treating vulnerable patients.”
It is possible that this research could lower the cost of surgery. Many hospitals have expensive monitors to measure the depth of anaesthesia, but only 2% of the anaesthetists questioned in a large survey conducted by the Royal College of Anaesthetists earlier this year said that they routinely used this technology. This simpler process could reduce the cost of each operation, while shorter recovery times as a result of personalised doses would relieve the pressure on post-operative care units.
