Paving the way to ever-safer anaesthesia

The breakthrough could help to provide a new guide for anesthetists and lead to much quicker recovery times for patients following operations as greater optimisation of dosage could lead to drugs being significantly reduced.

If drug levels are judged incorrectly this has led to well documented, albeit very rare, cases of patients becoming aware or feeling pain during surgery due to insufficient dose of anesthetic drugs. Also, overdosing of drugs may be harmful, resulting in cardiovascular malfunction and prolonged delay in awakening after surgery.

In a study published in the journal anesthesia (September 9) researchers tested a new more nuanced form of investigating the subtle clues sent out by the human body during anesthesia -- particularly the cardiovascular signals that can indicate the state of the pain-monitoring autonomous nervous system . The results have proved more reliable than existing methods.

The journal article -- 'The Discriminatory value of Cardiorespiratory Interactions in distinguishing awake from anesthetized states: A randomised observational study' -- found that by looking at how key indicators -- such as ECG, respiration, skin temperature, pulse and skin conductivity -- interacted with one another researchers could much more accurately predict whether a patient was awake or anesthetized. They also helped distinguish between the effects of two commonly-used anesthetic drugs, propofol and sevoflurane.

The study measured the depth of anesthesia of 27 patients in good health during surgery in the United Kingdom and in Norway. Readings were taken at a high frequency -- several hundred samples per heart beat -- for 30 minutes while the patients were awake before their surgery and for up to 30 minutes during general anesthesia. The signals showed, with a high degree of accuracy, how the patients reacted to the anesthetics.

Lancaster University's Professor Aneta Stefanovska said: "We have developed new methods to study complex interactions between ever changing processes such as the processes in our heart, lungs and vasculature. These physiological processes constantly interact with one another but anesthetic drugs change the level of these interactions. By applying our new methods, in this study we were able to get a very accurate picture of what was going on, leading to the most reliable predictions of the state of anesthesia obtained from cardiovascular signals to date of closer to 97 per cent."

The study has been welcomed by the Association of Anesthetists of Great Britain and Ireland (AAGBI).

Professor Andrew Hartle, President of the AAGBI, explained: "Anesthesia is a complex process based on physiological measurements, combined with the skill and expertise of anesthetists to keep the patient at the right depth of unconsciousness through the correct dosing of potent drugs. We warmly welcome any new research which further improves patient care."

Professor Peter McClintock, also of Lancaster University said: "The likelihood of waking up during surgery is extremely small but, if it happened, it could be a distressing experience. So we are delighted to pave the way to a new tool for gauging depth of anesthesia."

The collaborative research involved consultant anesthetists from University Hospitals of Morecambe Bay NHS Trust in North West England.

Professor Andrew Smith, Consultant Anesthetist, Royal Lancaster Infirmary said: "This publication is highly topical given the recent audit on accidental awareness under general anesthesia conducted by the Association of anesthetists of Great Britain and Ireland (AAGBI) and the Royal College of anesthetists. Whilst it is early days, the prospect of a monitor of anesthetic depth that relies on measurements of the circulation and respiration is very attractive. I look forward to further collaboration with Lancaster University in the interests of enhancing the care of patients in the NHS locally and nationally in the future."

Johan Raeder, Professor in Anesthesiology at Oslo University Hospital, who also took part in the study, said: "This very complex work is a logical step further in the search for specific and sensitive methods of objectively detecting the state of anesthesia.

"While so far most methods have relied on a single kind of measurement, our work tries to integrate information from many different physiological processes at the same time, thus adding an entirely new perspective. Namely how the different processes interact with each other and synchronise."