Monitored Anaesthesia Care and Sedation (MAC Sedation) has developed
as a key component of modern ambulatory surgery and offers patients
the benefits of loco-regional anaesthesia with sufficient sedation
to permit the patient to tolerate the procedure. Used appropriately,
MAC sedation extends the repertoire of surgical procedures which
can be considered for ambulatory patients and may also permit
day surgery in patient groups who would traditionally be considered
unsuitable for outpatient general anaesthesia.
Currently, a range of drugs are used for MAC sedation with opioids, benzodiazepines and propofol being used most frequently. Although anaesthetists are familiar with managing the airway in anaesthetised or heavily sedated patients, these skills are not invariably possessed by other professional groups and the inappropriate use of sedatives has caused some well publicised disasters[1, 2]. In the UK, working parties of the Royal College of Anaesthetists, Royal College of Radiologists and Royal College of Surgeons of England have published guidelines for sedation by non-anaesthetists[3, 4] and offer advice on selection of patients, use of monitoring and appropriate staffing. The use of sedative "cocktails" is common with benzodiazepine plus an opioid an especially popular combination and the Royal College of Surgeons recognises the interaction between these agents and advises "Failure to modify dosage of these drugs, when used in combination, may lead to life-threatening complications." The continued use of these combinations reflects clinical experience that most surgical procedures, including those performed with some loco-regional anaesthesia include elements of patient discomfort and an opioid enhances patient tolerability of such stimulation.
The rapid onset of remifentanil (i.e. its rapid access to the "effect site"[5]) and rapid elimination by extra-hepatic metabolism makes remifentanil theoretically attractively for MAC sedation. Several groups have reported their experiences in this indication[6-9] (Table 1). Before this technique is generally adopted we should ask three questions. Is remifentanil effective for MAC sedation? Is it safe? How does it compare with the use of propofol and midazolam?
Other investigators[10,11] have evaluated the interaction between remifentanil and midazolam and concluded that the use of remifentanil alone did not provide optimal MAC sedation but the addition of midazolam 2 mg to an infusion of remifentanil 0.05-0.1 mcg kg-1 min-1 provided effective sedation and analgesia.
Remifentanil is undoubtedly efficacious as an agent for MAC sedation and is licensed to be used in this indication in many countries. Sedation is not the primary action of opioids and could reasonably be described as a side-effect. It may be argued that using a drug for a side-effect is poor pharmacology and that the well know dose related respiratory depression induced by all mu opioid receptor agonists makes conscious sedation of spontaneously breathing patients by means of an opioid infusion an intrinsically unsafe technique. These concerns are theoretically valid and they are partially supported by the clinical experience reported above with several authors describing respiratory depression in patients sedated with remifentanil. Furthermore, the use of pulse oximetry to confirm adequate respiration during remifentanil sedation has been criticised[12] and the published studies may therefore underestimate the magnitude of this problem. Serious consideration should be given to using a benzodiazepine or propofol as the hypnotic component of a MAC sedation technique with opioids reserved for provision of analgesia if the loco-regional technique is insufficient. Remifentanil is relatively expensive in comparison to propofol and much more expensive than midazolam however, drug acquisition costs form only a small portion of the total costs of a surgical episode and additional costs of a specific technique may, in certain circumstances, be offset by savings generated by swift patient recovery. There are few formal health economic evaluations in day surgery and there is currently no evidence that the use of remifentanil for MAC sedation offers overall economic benefits.
MAC sedation with remifentanil is an effective technique which has worked reasonably well in clinical trials. Its role in the large number of patients who routinely undergo this technique has not yet been convincingly demonstrated.
References
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2. Krippaehne JA, Montgomery MT. Morbidity and mortality from
pharmacosedation and general anesthesia in the dental office.
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3. Sedation and anaesthesia in radiology: Joint working party
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4. Guidelines for sedation by non-anaesthetists: Royal College
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remifentanil during monitored anesthesia care. J Clin Anesth 1997;9(2):148-54.
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surgery during monitored anesthesia care. Anesthesiol 1997;87(1):51-7.
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and remifentanil during monitored anesthesia care. Anesthesiol
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1998;88(4):1124-1125.
Table 1.
Summaries of comparative studies of remifentanil MAC sedation
| Reference | Surgery | Remifentanil | Comparator | Efficacy | Safety |
|
Mingus 1998[6] |
Orthopaedic and urogenital surgery |
n=72 (0.09 mcg/kg/min)* |
Propofol n=35 (53.8 mcg/kg/min) |
Fewer remifentanil patients had pain and less were over-sedated | Remifentanil was associated with more respiratory depression and short-term nausea |
|
Lauwers 1998[8] |
TURP and hand surgery |
n=14 (0.075 mcg/kg/min) † |
Propofol n=14 (50 mcg/kg/min) |
Remifentanil had less haemodynamic depression, similar scores for comfort and sedation in both groups | More respiratory depression and nausea with remifentanil |
|
Smith 1997[9] |
Breast biopsy |
n=22 (0.095 mcg/kg/min)* |
Propofol n=22 (50.6 mcg/kg/min) |
Both agents provided acceptable sedation, longer time to home readiness with remifentanil | Remifentanil was associated with more respiratory depression |
|
Lauwers 1999[7] |
Hand and hip surgery |
n=117 (ED50 = 0.043 mcg/kg/min) |
Placebo n=37 |
Satisfactory sedation in most patients given remifentanil | Nausea, pruritis, respiratory depression with remifentanil |