Healthcare guidance body NICE has today (21 November) published final guidance recommending the use of the Bispectral Index (BIS, Covidien), E-Entropy (GE Healthcare) and Narcotrend-Compact M (MT MonitorTechnik GmbH & Co) EEG-based depth of anaesthesia monitors as options in patients receiving total intravenous anaesthesia and in patients who are considered at higher risk of adverse outcomes during any type of general anaesthesia. This includes patients who are at higher risk of unintended awareness and patients who are at higher risk from excessively deep anaesthesia.

General anaesthesia is a reversible state of controlled unconsciousness achieved with intravenous or inhaled drugs. These drugs prevent awareness, recall, distress and movement in patients during surgery. It is estimated that 2.4 million people needed a general anaesthetic in England in 2007. The response to anaesthetics can vary between patients and occasionally complications associated with inadequate or excessively deep levels of anaesthesia can arise. These include patient awareness during surgery and recall after surgery as a result of inadequate levels of anaesthesia during surgery which can cause post-traumatic stress disorder, and potentially prolonged recovery, haemodynamic instability and respiratory complications (which can be fatal without cardiorespiratory support) as a result of excessively deep anaesthesia. Inappropriately deep anaesthesia has also been linked to an increased risk of post-operative complications such as myocardial infarction, stroke and cognitive dysfunction in older patients.

Patients who are considered at higher risk of unintended awareness during general anaesthesia include patients with high opiate or high alcohol use, patients with airway problems and patients with previous experience of unintended awareness during surgery. 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. Older patients, patients with comorbidities and those undergoing certain types of surgery are also considered at a higher risk of unintended awareness. This is because they are at greater risk of haemodynamic instability during surgery. In these patients, lower levels of anaesthetic are often used to prevent adverse effects on the cardiovascular system and these levels can be inadequate.

Patients who are considered at higher risk of excessively deep levels of anaesthesia include older patients, patients with liver disease, patients with a high body mass index, and patients with poor cardiovascular function.

Patients receiving total intravenous anaesthesia are not considered at higher risk of adverse outcomes from general anaesthesia than patients receiving inhaled anaesthesia. The use of EEG-based depth of anaesthesia monitors has been recommended in patients receiving total intravenous anaesthesia because it is cost effective and because it is not possible to measure end-tidal anaesthetic concentrationⁱ in this group.

In current NHS clinical practice, a patient's response to anaesthesia during surgery is assessed by clinical observations such as excessive tear formation (lacrimation), 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, a pulse oximeter to detect the pulse and estimate the amount of oxygen in the blood and, in the case of inhaled anaesthetic, the measurement of end tidal anaesthetic concentration. This NICE assessment focuses on three depth of anaesthesia monitors that use EEG (electroencephalography) data measuring electrical brain activity and compares them, in combination with standard clinical monitoring, to current NHS clinical practice. Their aim is to help the anaesthetist tailor the dose of anaesthetic used to the individual patient and therefore lower the risk of adverse outcomes from anaesthesia.

Professor Carole Longson, NICE Health Technology Evaluation Centre Director, said: "Uncertainties remain about how common unintended awareness during surgery is, and the benefits of avoiding excessively deep levels of anaesthesia. However, we do know that 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 therefore concluded that, although additional research on the benefits and costs of the products is desirable, the avoidance of uncommon but catastrophic events for patients is most likely to make depth of anaesthesia monitors of benefit and cost-effective in patients receiving total intravenous anaesthesia and in patients who are considered at higher risk of unintended awareness or the potential consequences of excessively deep levels of general anaesthesia."

The guidance for depth of anaesthesia monitors is available on the NICE website at dg6

Ends

Notes to Editors

Explanation of terms

i. End-tidal agent monitoring is used by modern anaesthetic monitors to calculate Minimum Alveolar Concentration (MAC). MAC is a measure of potency and is defined as the minimum alveolar concentration at steady-state that prevents reaction to a standard surgical stimulus (skin incision) in 50% of patients at 1 atmosphere (i.e. sea level)

About the guidance

1. The combination of standard clinical observation (of pupillary size and reactivity, lacrimation and sweating) and measurement of one or more clinical markers such as pulse, blood pressure and end-tidal anaesthetic gas concentration (for inhaled anaesthesia) constitutes standard clinical monitoring and is the comparator for this assessment.

2. Some common side effects of general anaesthesia include vomiting, headaches and dizziness.

3. Awareness during anaesthesia is a less common side-effect and results from under-dosing of anaesthetic. It is more likely during certain types of surgery in which lower levels of anaesthetic may be indicated, such as cardiac, airway, obstetric or emergency surgery for major trauma. For those who are aware during anaesthesia there can be long-term effects such as anxiety, nightmares, flashbacks, clinical depression and in some cases post-traumatic stress disorder.

4. Studies suggest that between 1 and 2 people in 1000 experience awareness or recall during general anaesthesia, with a third of these also experiencing pain and prolonged recovery.

5. The use of muscle relaxants can increase the risk of patient awareness because they allow a lower level of anaesthetic to be used. Muscle relaxants also prevent patients from moving. This limits the patient's ability to communicate with the surgical team and means that the anaesthetist has to use other clinical information to judge the patient's state of consciousness.

6. Side effects of excessively deep general anaesthesia include prolonged recovery and, in severe cases or in at-risk patient groups (for example, older patients, patients with liver disease,and patients with poor cardiovascular function), haemodynamic instability and respiratory complications (which can be fatal without cardiorespiratory support). Inappropriately deep anaesthesia has also been linked to an increased risk of post-operative complications such as myocardial infarction and stroke in older patients. There is some evidence to suggest a link between longer term morbidity (for example, cognitive dysfunction) and mortality, and the depth of anaesthesia.

7. Patients who are considered at higher risk of unintended awareness during general anaesthesia include patients with high opiate or high alcohol use, patients with airway problems, and patients with previous experience of unintended awareness during surgery. The risk of unintended awareness is also raised by the concomitant use of muscle relaxants, particularly with total intravenous anaesthesia. Older patients, patients with comorbidities and those undergoing certain types of surgery are also considered at a higher risk of unintended awareness. This is because they are at greater risk of haemodynamic instability during surgery. In these patients, lower levels of anaesthetic are often used to prevent adverse effects on the cardiovascular system, which can result in these patient groups receiving inadequate levels of anaesthesia.

8. Patients who are considered at higher risk of excessively deep levels of anaesthesia include older patients, patients with liver disease, patients with a high body mass index, and patients with poor cardiovascular function.

9. Patients receiving total intravenous anaesthesia are not considered at higher risk of adverse outcomes from general anaesthesia than patients receiving inhaled anaesthesia. The use of EEG-based depth of anaesthesia monitors has been recommended in patients receiving total intravenous anaesthesia because it is cost-effective and because it is not possible to measure end-tidal anaesthetic concentration in this group.

10. Current NHS clinical practice for monitoring the depth of anaesthesia consists of clinical observations such as lacrimation and sweating, and 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, a pulse oximeter to detect the pulse and estimate the amount of oxygen in the blood, a device to measure the patient's temperature, a device to monitor end-tidal anaesthetic concentration and provide a MAC value (measure of potency of inhalational general anaesthetics), a nerve stimulator (if a muscle relaxant is used) and a capnograph to monitor the inhaled and exhaled concentration of carbon dioxide. Additional monitoring equipment such as a cardiac output monitor may be used for some patients or certain types of surgery.

About the NICE Diagnostics Assessment Programme

11. Further information about the NICE diagnostics assessment programme can be found on the NICE website

12. Topics to be considered by the Programme are routed through the related Medical Technologies Assessment Programme.

About NICE

13. The National Institute for Health and Care Excellence (NICE) is the independent organisation responsible for providing national guidance and standards on the promotion of good health and the prevention and treatment of ill health.

14. NICE produces guidance in three areas of health:

• public health - guidance on the promotion of good health and the prevention of ill health for those working in the NHS, local authorities and the wider public and voluntary sector
• health technologies - guidance on the use of new and existing medicines, treatments, medical technologies (including devices and diagnostics) and procedures within the NHS
• clinical practice - guidance on the appropriate treatment and care of people with specific diseases and conditions within the NHS.

15. NICE produces standards for patient care:

• quality standards - these reflect the very best in high quality patient care, to help healthcare practitioners and commissioners of care deliver excellent services
• Quality and Outcomes Framework - NICE develops the clinical and health improvement indicators in the QOF, the Department of Health scheme which rewards GPs for how well they care for patients

16. NICE provides advice and support on putting NICE guidance and standards into practice through its implementation programme, and it collates and accredits high quality health guidance, research and information to help health professionals deliver the best patient care through NHS Evidence.