Regional anaesthesia offers a number of advantages to the surgical patient, including quick post-operative recovery, low peri-operative morbidity, and maintenance of consciousness and protective reflexes. Surgery is an intrinsically stressful experience, and many patients will be anxious and agitated. Effective sedation is, therefore, an important aspect of the management of patients undergoing regional anaesthesia. In contrast to general anaesthesia, where sedation is only required prior to induction of anaesthesia, sedation with regional anaesthesia is required preand intraoperatively.
The aim of sedation during regional anaesthesia is to ensure that the patient is comfortable, free from anxiety and pain, and able to sleep if he or she desires. This can be achieved by using combinations of agents with different properties to meet the anxiolytic and analgesic needs of individual patients - the balanced sedation approach.
The need for sedation
Sedation during regional anaesthesia may be necessary to relieve anxiety and agitation, to ensure effective pain relief, or because of the nature of the surgical procedure (Table 1). Patients may become anxious if they hear sounds during the procedure, or if they are able to see the procedure; they may also fear pain, or have unpleasant memories of previous surgery under regional anaesthesia. In addition, patients may be uncomfortable on the operating table, particularly if they have to lie in an awkward position for prolonged periods, or if the theatre is cold. Chronic lower back pain, hypoxia, a full bladder, or infusion of cold fluids can also cause discomfort.
Pain may occur during regional anaesthesia if the block is incomplete, producing areas of inadequate anaesthesia. Moreover, if the regional block produces only analgesia, rather than anaesthesia, some patients may feel touch as pain because of activation of central mechanisms. The use of tourniquets may also lead to pain.
A number of non-pharmacological measures can be used to reduce anxiety and discomfort. For example, headphones can be used to prevent the patient hearing operating theatre noises, while effective screening will prevent the patient from seeing the procedure. A soft mattress on the operating table, and optimal positioning of the patient, can prevent discomfort; similarly, the patient can be allowed to urinate during the procedure, and oxygen should always be administered to prevent hypoxia. Infusion of cold fluids can often be avoided, and the patient warmed by convective heating. If, however, the patient's anxiety is a result of pain or previous unpleasant experiences, or if the patient does not wish to remain awake during the procedure, pharmacological sedation should be considered.
Pharmacological options for sedation
A variety of options is available for sedation during regional anaesthesia (Table 2). Although barbiturates can be used as premedication before general anaesthesia, they are not suitable for sedation during regional anaesthesia because they have long half-lives and thus may accumulate, and they also carry the risk of dose-related cardiorespiratory depression. Low-dose benzodiazepines are the drugs of choice for the treatment of anxiety, but these agents may sometimes cause paradoxical excitation reactions, with agitation, confusion and unco-operativeness. The incidence of such reactions has been estimated to be between 1% and 7% [1-3]. Sexual fantasies have also been reported during sedation with midazolam . Etomidate and, to a lesser extent, propofol may cause a burning pain on injection .
Sedation with benzodiazepines may lead to a reduction in oxygen saturation during use. In a study by Tay et al. involving 52 patients, no patient had an oxygen saturation less than 90% before sedation with midazolam, whereas 15% of sleeping patients, and 40% of those requiring vigorous stimulation to awaken them, had low oxygen saturations after sedation . The risk of desaturation is further increased by the use of combinations of benzodiazepines and opioids. In one study, over 90% of patients treated with low doses of midazolam (0.05 mg kg−1) and fentanyl (2 μg kg−1) had oxygen saturations below 90% (P<0.05), and 40% had apnoea (P<0.05) . For this reason, the use of opioids should usually be avoided in patients undergoing regional anaesthesia.
Ketamine at low doses (less than 0.5 mg kg−1) may provide an alternative to opioid analgesia in patients with surgical pain. Concomitant administration of benzodiazepines is effective in preventing the psychotomimetic emergence reactions that affect up to 30% of ketamine-treated patients . Moreover, the sedative effects of ketamine are synergistic with those of benzodiazepines. Combination treatment with ketamine and benzodiazepines, therefore, offers a number of advantages over other agents. In a comparative trial involving 40 patients undergoing peribulbar anaesthesia, fewer patients treated with ketamine (maximum dose 15 mg) plus midazolam (maximum dose 2 mg) moved during surgery compared with patients who received methohexitone 0.5 mg kg−1 (10% versus 45%, respectively; P=0.013). Respiratory depression was also significantly reduced in patients who received the combination treatment (5% versus 30%; P=0.046) . Thus, low-dose treatment with ketamine plus benzodiazepines provides adequate analgesia and sedation without affecting respiratory function.
Propofol is a useful sedative. Comparative studies with benzodiazepines have shown that propofol offers a number of advantages. Compared with midazolam, for example, propofol offers more predictable sedation and better post-operative recovery. In a study by Dertwinkel & Nolte, awakening time was significantly shorter with propofol 1-2 mg kg−1 h−1, compared with midazolam 0.03-0.06 mg kg−1 h−1 (0.2-2.2 min versus 10-26 min, respectively), and the incidence of pulmonary obstruction was lower (23-39% versus 50-62%) . In this study, the incidence of agitation was higher with propofol than with midazolam (15-39% versus 7-13%). While propofol was associated with a higher incidence of post-operative nausea and vomiting than midazolam , these findings are inconsistent with other studies which have shown low incidences of nausea and vomiting in patients treated with propofol . Moreover, other studies have shown that low doses of propofol do not usually cause respiratory depression . However, oxygen saturation was not measured in the present study.
Intra-operative, and occasionally pre-operative, shivering occurs in approximately 30-40% of patients during regional anaesthesia. This appears to be due to anaesthetic-induced changes in the temperature distribution across the skin without any change of core body temperature. While pethidine (meperidine) is useful in preventing intra-operative shivering, in common with other opioids this agent produces respiratory depression and thus is unsuitable as a sedative. The α2-adrenoceptor antagonist clonidine is a useful alternative, which is believed to act by the same mechanisms as pethidine without producing respiratory depression. In a placebo-controlled trial, treatment with clonidine 150 μg significantly reduced the incidence of shivering within 5 min of administration . Convective heating, though effective, is significantly slower than clonidine in reducing shivering in patients during regional anaesthesia (unpublished observation).
Choice of sedative in individual patients: balanced sedation
Clearly, of the sedative agents available each has its own advantages and disadvantages. How, then, should these agents be used to provide balanced sedation?
Anxious patients should be premedicated with oral benzodiazepines where possible; only the benzodiazepines have anxiolytic activity. Long-acting agents with strong anxiolytic effects, such as nordiazepam and potassium clorazepate, are preferable. Benzodiazepines also produce amnesia to a greater extent than other agents and this may be a desirable effect in some patients [14,15]. In contrast, propofol has a greater hypnotic effect than other agents including benzodiazepines.
If analgesia is required, low-dose ketamine may be appropriate. This is particularly useful in cases where there is 'spotty' analgesia or incomplete regional block. Propofol can be used in situations where a deeper level of sedation is required, for example in patients who have expressed a wish to sleep during the procedure.
Clonidine, 50-150 μg, has been shown to act synergistically with propofol, ketamine and benzodiazepines . Thus concomitant treatment with propofol and clonidine allows the use of lower doses of propofol (0.5-2 mg kg−1). Such doses produce effective sedation throughout the procedure.
In the author's experience, certain patients with psychotic problems, such as alcoholics, may benefit from low doses of neuroleptic drugs, for example haloperidol or droperidol, 2.5-5 mg. These drugs may also be useful in agitated elderly patients.
Balanced sedation in practice
Table 3 summarizes the use of sedatives in a consecutive series of 500 patients who underwent surgery under regional anaesthesia at University Hospital Bergmannsheil, Bochum, Germany. Although the need for sedation varied according to the procedure and type of anaesthetic used, approximately 50% of patients did not require any sedation besides routine premedication with benzodiazepines. Analgesia with ketamine, clonidine or propofol, for example, was required in only 10-15% of patients undergoing ankle blockade.
Midazolam and ketamine were the most commonly used drugs in patients undergoing axillary plexus block; this combination is useful during induction and the early phase of surgery as some patients interpret touch as pain. Clonidine was also used in these patients to control shivering.
Epidural and spinal anaesthesia present different requirements for sedation. Spinal anaesthesia generally produces anaesthesia rather than merely analgesia, and thus the use of ketamine, propofol and midazolam was lower among patients undergoing spinal anaesthesia than in those undergoing epidural anaesthesia. The incidence of shivering, however, is comparable with the two techniques, and clonidine was used to a similar extent in both groups of patients.
The advantages of balanced sedation are illustrated by the experience obtained at University Hospital Bergmannsheil in over 1000 patients who underwent supplementary short-term (i.e. less than 30 min) general anaesthesia during prolonged procedures, such as bone, vessel or skin grafting, under regional anaesthesia. Such an approach presents a number of potential problems. Volatile anaesthetics or barbiturates can produce excitation, and volatile anaesthetics also lead to shivering. Pain can occur if analgesics are not used, while the use of muscle relaxants may cause respiratory depression or prolonged muscle relaxation. These problems can be avoided by the use of balanced sedation. Excitation and shivering can be avoided by using propofol 1.5-2 mg kg−1 and clonidine 150 μg. Where necessary, pain can be controlled by a small dose of fentanyl (0.1 mg); the addition of clonidine may be useful in some patients.
It should be noted that the same standard of care required for general anaesthesia is mandatory for effective regional anaesthesia. In the routine protocol used at University Hospital Bergmannsheil, oxygen saturation and heart rate are measured continuously by pulse oximetry, together with ECG and non-invasive blood pressure every 3-5 min.
By exploiting the relative advantages of different sedatives, a balanced sedation technique can achieve the ideal goal of a comfortable patient who is free from anxiety and pain, and is able to sleep if desired. Benzodiazepines, such as midazolam, provide basic sedation, relieve anxiety and produce amnesia, and propofol can be used to achieve a deeper level of sedation. Opioids provide only analgesic effects and, because of the respiratory depression and desaturation they produce, should not be used for sedation.
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