By: 2 August 2012

Draft guidance from NICE’s Diagnostics Assessment Programme issued for consultation recommends the use of the Bispectral Index (BIS) depth of anaesthesia monitor as an option for reducing adverse outcomes from anaesthesia in patients receiving total intravenous anaesthesia and in patients who are at higher risk of complications from any type of general anaesthesia such as unintended awareness, cognitive dysfunction, and the adverse physiological effects of deep anaesthesia. Although there is more uncertainty about the E-Entropy (GE Healthcare), and Narcotrend-Compact M (MT MonitorTechnik GmbH & Co) depth of anaesthesia monitors, the draft guidance also recommends them as options for the same patient groups.
It is estimated that 2.4 million people needed a general anaesthetic in England in 2007. Individual variation in response to anaesthetics can lead to occasional complications associated with inadequate or excessively deep levels of anaesthesia. These include patient awareness during surgery and recall after surgery which can cause post-traumatic stress disorder as a result of inadequate levels of anaesthesia during surgery, and potentially fatal cardiac and respiratory collapse, prolonged recovery and cognitive dysfunction as a result of excessively deep anaesthesia.
In current NHS clinical practice, a patient’s response to anaesthesia during surgery is assessed by clinical observations such as crying, sweating, pupillary size and reactivity, and by the use of supplementary monitoring devices. These include an electrocardiograph (ECG) to measure the speed and rhythm of the heart, a non-invasive blood pressure monitor, and a pulse oximeter to detect the pulse and calculate the amount of oxygen in the blood. The monitors that NICE is currently assessing measure electrical brain activity, providing a further indication of how the patient is reacting to the anaesthetic.
Patients who are considered at higher risk of complications from general anaesthesia include older patients, those with a high body mass index, patients with airway problems, patients who have comorbidities and those undergoing certain types of surgery in which lower levels of anaesthetic are often used (for example, cardiac surgery, airway surgery, obstetric surgery or emergency surgery for major trauma). The use of muscle relaxants can also increase the risk of patient awareness because they allow a lower level of anaesthetic to be used and prevent patients from moving. This limits the patient’s ability to communicate with the surgical team about any awareness that may develop. This assessment focuses on three depth of anaesthesia monitors that are based on algorithms using EEG (electroencephalography) data and compares them, in combination with standard clinical monitoring, to current NHS clinical practice.
Professor Carole Longson, NICE Health Technology Evaluation Centre Director, said: “Although relatively rare, inadequate or excessively deep levels of anaesthetic can be traumatic and have far-reaching consequences for patients, including post-traumatic stress disorder, cognitive dysfunction and an increase in the incidence of stroke and heart attack. The Committee considered that whilst additional research on the benefits and costs of the products is desirable, they concluded that the size, complexity, cost, and time requirements of such studies could unduly delay the uptake by the NHS of a technology that is likely to be of benefit to patients at high risk of the complications of anaesthesia.”
The draft diagnostics guidance for depth of anaesthesia monitors is available on the NICE website at