Considerable research has been carried out over the last 30 years to investigate whether regional anaesthesia improves the quality of postoperative analgesia compared with systemic opioids, and whether it influences the outcome from surgery. Some benefits, such as the quality of postoperative analgesia, are easy to demonstrate but the intuitive belief that regional anaesthesia improves the outcome from surgery is more difficult to prove. Many studies have been inconclusive, with methodological weaknesses making it difficult to compare the results of different studies. Nevertheless, the weight of evidence suggests that regional anaesthesia has the potential to improve outcome from surgery.
Regional analgesia versus systemic analgesia
It is difficult to isolate the analgesic benefits of regional anaesthesia (compared with systemic opioid-based analgesia) from the anaesthetic benefits (compared with general anaesthesia). Regional anaesthesia is most commonly used for surgery and early postoperative analgesia and most studies do not distinguish between these components. If an epidural injection or a major peripheral nerve block is used as the sole anaesthetic technique or is combined with a light general anaesthetic, the use of intra-operative opioids is unnecessary, or reduced, compared with general anaesthesia alone. The depth of general anaesthesia also differs because of the influence of the local anaesthetic technique. These differences influence the early indicators of recovery such as time to consciousness, the incidence of postoperative nausea and vomiting (PONV), return of full cognitive function, and time to first supplementary analgesic. Therefore, while it is possible to compare improvements in pain scores, other benefits may occur purely as a result of avoiding opioids (Figure 1). The quality of analgesia with regional anaesthesia is significantly better than that with systemic opioids. Central and peripheral nerve blocks can prevent or abolish the neural transmission of nociceptive signals; opioids can only modulate the transmission.
Can anaesthesia influence outcome from surgery?
Regional anaesthesia has been used in all three perioperative phases to try to improve postoperative analgesia and influence surgical outcome.
Preoperative: regional anaesthesia has little influence on postoperative outcome though it improves the management of pre-existing pain.
Pre-emptive analgesia is the ability to reduce the severity and duration of postoperative pain by instituting effective analgesia before the onset of the pain. It has been demonstrated in animal models, but does not exist as a clinical entity, based on current understanding. Initial studies suggested that regional anaesthesia and systemic analgesia, administered before surgery, would improve postoperative pain, but this was not borne out in later studies.
Intraoperative: the morbidity and mortality associated with surgery and anaesthesia continue to decrease with advances in techniques. In the absence of avoidable errors, there is little difference in intraoperative risk between regional or general anaesthesia. Serious adverse outcomes from anaesthesia are extremely uncommon (0.1–1.5 deaths directly attributable to anaesthesia per 10,000 procedures). Preoperative fitness, patient age and the surgical procedure remain the most important risk factors for major non-fatal morbidity or mortality.
Postoperative phase: effective, continuous, postoperative analgesia is a worthwhile target for humanitarian reasons and for improving outcome. A large number of publications confirm the advantages of regional anaesthesia (both peripheral and central neural blockade) compared with systemic opioids (Figure 2). Regional anaesthesia may also prevent acute pain becoming chronic. A significant number of patients (about 50% for major breast surgery or thoracotomy) develop chronic pain following surgery owing to neuropathic nerve injury. A study of paravertebral blocks following thoractomy showed a significant reduction in post-thoracotomy pain syndrome.1
Figure 2 (click to open larger image)
Regional versus general anaesthesia
In the last 30 years, numerous prospective, randomized, controlled trials have compared regional with general anaesthesia and their effects on outcome from surgery. In addition to improved analgesia, continuous lumbar epidural blocks for lower abdominal, pelvic and lower limb surgery significantly modify the surgical stress response, which is responsible for much postoperative morbidity (Figure 3).
The effects of thoracic epidural blockade on the stress response are not so marked because of less complete block of the lumbar autonomic nerve supply to the abdominal viscera and lower limbs. Intravenous patient-controlled analgesia (PCA) and other opioid-based analgesic techniques do not influence outcome from surgery despite satisfactory analgesia and a high degree of patient and staff satisfaction scores.
Regional anaesthesia, using local anaesthetic drugs alone or in combination with low doses of opioid drugs, has significant advantages over epidural or intravenous opioid-based analgesia.2
Figure 3 (click to open larger image)
A number of clinical benefits can be predicted from the effects that regional anaesthesia has on the stress response. It is easier to investigate the influence of regional anaesthesia on a single variable of the stress response than to investigate its overall influence. Consequently, stronger data are available to show that regional anaesthesia has a beneficial effect on single systems during and after surgery (Figure 4) than for its overall effects on outcome. The influence of regional anaesthesia on cognitive function remains unclear.
Figure 4 (click to open larger image)
The role of systematic reviews
It is difficult to measure differences in outcome between regional anaesthesia and general anaesthesia for rare but important variables such as perioperative mortality. A very large sample size is required for prospective randomized trials to demonstrate any significant differences (too large even for multi-centre trials when studying these rare outcome events). Systematic Reviews are a useful method of analysing large numbers of smaller studies to evaluate any potential benefits of regional anaesthesia.
Several important meta-analyses of the effects of regional anaesthesia on outcome from surgery have been published recently. A review of hip fractures showed reduced 1-month mortality in favour of regional anaesthesia plus a reduction in the rate of deep vein thrombosis,3 confirming earlier work that regional anaesthesia offers an early advantage over general anaesthesia, though this advantage reduces with time. At 3 months, mortality is the same as for general anaesthesia. Patients who had a thoracic epidural infusion for at least 24 hours postoperatively had improved postoperative analgesia and a reduction in postoperative myocardial infarction risk.4 Jorgensen showed improvements in the return of gastrointestinal function as well as improved pain scores.5 A meta-analysis of the effects of various postoperative analgesic regimens on pulmonary outcome confirmed the benefits of local anaesthetic-based epidural infusions.2 The largest and most significant meta-analysis6 evaluated 144 published papers, involved over 9500 patients, and confirmed several benefits of regional anaesthesia (alone or in combination with general anaesthesia) compared with general anaesthesia alone. There was a reduction in the risk of mortality from all causes after major surgery of 30% in the regional anaesthesia group compared with the general anaesthesia group.
Clinical relevance of regional anaesthesia
The important question is whether the benefits associated with regional anaesthesia lead directly to measurable clinical improvements such as fewer complications, lower mortality and better outcome from surgery. High quality analgesia is an important achievement but does not improve outcome directly. For example, an epidural infusion for postoperative analgesia following major abdominal surgery produces low pain scores, a shorter duration of ileus, a reduced need for postoperative blood transfusion and results in high levels of patient satisfaction. However, unless efforts are made to use the analgesia and other benefits of the epidural to mobilize the patient and encourage early return to full nutrition, there are no long-lasting benefits once the infusion is discontinued. Traditional surgical postoperative practice such as the routine use of nasogastric tubes, the slow return to enteral nutrition and other fixed determinants of the recovery pathway may also delay recovery and fail to maximize the potential improvements in surgical outcome that regional anaesthesia can offer.
The significant risks associated with spinals, epidurals and major peripheral nerve blocks must be balanced against the potential benefits if the anticipated improvement in outcome for an individual patient is to be realized. The key features of regional anaesthesia (quality of analgesia, avoidance of opioid side-effects and minimizing the impact of the surgical stress response), combined with new surgical techniques and ward routines, make it possible to reduce the incidence and severity of complications (e.g. hypoxaemia, fatigue, weight loss) and delayed recovery, and encourage early nutrition, increased mobility and reduced hospital stay.
1 Richardson J, Sabanathan S, Jones J et al. A prospective randomised trial of preoperative and balanced epidural or paravertebral bupivacaine on postthoracotomy pain, pulmonary function and stress response. Br J Anaesth 1999; 83: 387–392.
2 Ballantyne J C, Carr D B, de Ferranti S et al. The comparative effects of postoperative analgesic therapies on pulmonary outcome: cumulative meta-analysis of randomised controlled trials. Anesth Analg 1998; 86: 598–612.
3 Urwin S C, Parker M J, Griffiths R. General versus regional anaesthesia for hip fracture surgery: a meta-analysis of randomised trials. Br J Anaesth 2000; 84: 450–5. (Also published as a Cochrane Systematic Review.)
4 Beattie W S, Badner N H, Choi P. Epidural analgesia reduces postoperative myocardial infarction: a meta-analysis. Anesth Analg 2001; 93: 853–8.
5 Jorgensen S, Wettersler J, Moiniche S, Dahl J B. Epidural local anaesthetics versus opioid-based analgesic regimens on postoperative gastrointestinal paralysis, PONV and pain after abdominal surgery. Cochrane Database of Systematic Reviews 2000; 4: CD 001893.
6 Rodgers A, Walker N, Schug S. Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: results from an overview of randomised trials. BMJ 2000; 321:1493.
7 Does epidural analgesia improve surgical outcome? British Journal of Anaesthesia, 2004, Vol. 92, No. 1 4-6
Kehlet H. Modification of responses to surgery by neural blockade. In: Cousins M, Bridenbaugh P O, eds. Neural blockade in clinical anaesthesia and management of pain. 3rd ed. Lippincott-Raven, 1998, pp. 129–75.
PROSPECT procedure specific postoperative pain management
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