Regional anaesthesia — before or after general anaesthesia?

Many anaesthetists perform major regional blocks on anaesthetised patients as a matter of routine despite the views of some medical experts who strongly advise against the practice. Bromage [123] has consistently argued against performing central neural blocks, in particular thoracic epidurals, on anaesthetised patients, whereas others recommend it in thoracic surgery [4, 5]. A recent survey by the American Society of Regional Anesthesia showed that the practice was common in adults and children although the response rate was low [6]. The opinions of medical experts rightly carry great weight, so why is clinical practice at variance with this advice? A number of recent studies which examined very large patient populations [789] show that serious morbidity related to regional anaesthesia is extremely rare although the potential for serious spinal cord or major peripheral nerve damage focuses considerable, possibly disproportionate, attention on the risk. This, together with patient's innate dislike of needles, provides a background of suspicion towards regional anaesthesia, especially where the cultural experience has been to expect only a general anaesthetic. However, anaesthetists increasingly recognise the benefits of regional anaesthesia in the peri-operative period and may justify performing the block on anaesthetised patients for several reasons: greater patient acceptance (especially children), less impact on the throughput of the operating list, easier performance and better conditions for teaching and supervising trainees. The counter argument is that by removing verbal contact with the patient the most useful warning of impending nerve contact is lost and that no potential benefit to the patient is worth the risk of serious nerve damage. However, there are insufficient published data to lend support to the views of either side. There are no prospective randomised controlled studies which compare the relative risks of regional anaesthesia performed on anaesthetised or conscious patients. The data that do exist come from retrospective qualitative studies (critical incident reporting, closed claim analysis and case reports), where there has been a negative outcome. These studies have inherent weaknesses [10] including reporting bias, incomplete voluntary reporting and an increasing frequency of medicolegal claims which means that the numerator is unknown. Similarly, the total population at risk and the frequency with which different techniques are used (which form the denominator) are also unknown so that the incidence with which these rare but serious events occur cannot be calculated. Because of the time lag of up to 10 years between the closure of a claim and the subsequent analysis, original material may not be available for scrutiny and clinical practice can change radically, reducing the value of the findings [11]. A recent closed claim case report [12] highlights the difficulties of determining the exact cause of neurological damage. A 62-year-old female with a history of previous lumbar laminectomy had multiple unsuccessful attempts at a lumbar epidural under general anaesthesia, performed by a trainee. After a successful catheter placement above the level of the laminectomy scar by a more experienced colleague, several episodes of inadequately treated peri-operative hypotension occurred and the patient developed permanent paraplegia. MRI scans subsequently showed a small air bubble at the level of T10 and spinal cord infarction at T5. The pattern of injury suggested that anterior spinal artery ischaemia was the most likely cause rather than spinal cord damage so exactly which aspect of her management was responsible for the outcome? Technical difficulty, inexperience and serious hypotension are all major risk factors in adverse outcome from regional anaesthesia whether general anaesthesia is employed or not. Two major Medical Defence Organisations in the United Kingdom are currently unaware of any cases of neurological damage occurring where the sole risk factor was general anaesthesia being induced prior to the block being performed. The Medical Defence Union has a risk management analysis of cases where general anaesthesia preceded regional anaesthesia (spinal or epidural block) and serious neurological damage subsequently occurred. The prime risk factor was poor patient management, where the level of care fell below acceptable standards. Separate analysis of morbidity due to regional anaesthesia alone (spinal, epidural, thoracic sympathetic block, brachial plexus and paravertebral block) showed a similar profile of patient outcomes and risk factors, i.e. poor patient management (Goodwin H., personal communication). Neither organisation views the administration of a general anaesthetic before a regional anaesthetic as inherently bad practice. In a review of litigation against anaesthetists [13], Aitkenhead noted a recent increase in the number of claims from patients who have had regional anaesthesia, whether awake or under anaesthesia. There is a perception that nerve damage due to regional anaesthesia is becoming more common but given the weaknesses of currently available data it is difficult to establish whether any increase in complaints is due to bad practice, or is just a reflection of increasing usage and a greater tendency for resorting to litigation. In a frequently quoted review [11] of the American Society of Anesthesiologists closed claims analysis, 15% of all anaesthesia claims were for nerve damage. Of the 227 patients who suffered neurological damage, 61% received a general anaesthetic and 36% a regional technique, while there are no data on whether the techniques were combined. The ulnar nerve was damaged in 34% of cases, the brachial plexus in 23% and lumbosacral nerve damage in 16%. Ulnar nerve damage was predominantly related to general anaesthesia, lumbosacral damage was related to regional anaesthesia and brachial plexus damage was distributed between both techniques but it was not possible to assess the mechanisms of damage in the majority of cases. The frequency with which nerve damage occurs under general anaesthesia tends to be forgotten; poor patient positioning, inadequate padding, tourniquet compression, retractors and surgical technique have all been reported to cause peripheral nerve damage. Paediatric regional anaesthesia poses a particular problem for the critics of those who perform regional anaesthesia on anaesthetised or heavily sedated patients. In common with adult practice, there has been a sustained growth in the use of peri-operative regional anaesthesia in children and general anaesthesia is usually administered prior to the regional block [14, 15]. The incidence of complications in children up to the age of 16 years receiving this combined treatment is extremely low [16]. A prospective 12-month survey of paediatric anaesthesia in France and Belgium looked at data from over 85 000 anaesthetics which included 15 000 central neural blocks and 9300 peripheral blocks [9]. General anaesthesia preceded the regional block in 89% of patients, 6% were ‘sedated’ with intravenous induction agents or inhaled halogenated drugs — only 5% were fully conscious. There were 25 reports of complications with no deaths and no neurological damage. All the complications occurred in the central block group, with an incidence of 1.5 per 1000 and a zero incidence in the peripheral group. Auroy et al. [7] carried out a similar prospective survey in France of 103 000 adults receiving regional anaesthesia during 1994. Whilst there is no detail on the use of combined general and regional anaesthesia, of significance is the three-fold risk of complications associated with spinal anaesthesia (5.9/10 000) compared with epidural and peripheral nerve blocks (2.0 and 1.9/10 000, respectively). Spinal blocks are rarely performed on anaesthetised patients and thus nerve damage can occur despite verbal contact being maintained, although 33% of the patients who developed subsequent neurological problems felt no pain or paraesthesiae during needle placement, damage being due to other factors. Aromaa et al. [8] surveyed all the anaesthesia insurance claims made in Finland between 1987 and 1993, which included 25 cases of serious morbidity from a total of 550 000 spinals and 170 000 epidurals. The coincident use of general anaesthesia was not noted but the relative risk of complications was 8.6:1 for spinals compared with epidurals. The prime risk factors for nerve damage were pain on injection and pre-existing disease. Both these studies highlight the importance of recognising the role of pre-existing disease, technical difficulties and pain or paraesthesiae during needle insertion in the genesis of subsequent neurological complications. There are no large studies in adults which specifically look at peripheral blocks but an audit of 16 000 nerve blocks (9000 central and 7000 peripheral) performed in my department between 1991 and 1995 revealed that 85% of blocks were performed on anaesthetised patients with no serious neurological sequelae (unpublished data). So what conclusions can be drawn from the varied data and advice available? Clearly paediatric anaesthetists have no qualms about anaesthetising their patients prior to performing both central and peripheral blocks. The consequences of permanent neurological damage might reasonably be expected to be greater and last for longer in children, especially neonates whose nervous systems are still immature. Perhaps greater neuroplasticity and potential for healing in children markedly reduce the risks of combined general and regional anaesthesia. The same may not apply to adults in whom nerve damage is a rare risk of both general and regional anaesthesia. The major factors in preventing neurological sequelae are the experience and dexterity of the anaesthetist, proper training and supervision of trainees, detailed assessment of pre-existing vascular and neurological disease, avoidance of repeated attempts due to technical difficulties and prompt recognition and treatment of complications to prevent permanent damage. The issue of whether to administer a general anaesthetic prior to regional anaesthesia becomes less contentious if the correct systems are in place to ensure high standards of practice. Which blocks can be safely performed under general anaesthesia and which should only be performed on fully conscious patients? Infiltration techniques, field blocks and the discrete blockade of small peripheral nerves do not appear to cause problems and, in the absence firm data to the contrary, the weight of clinical practice suggests that the majority of larger peripheral nerve and plexus blocks, with the possible exception of the interscalene approach to the brachial plexus [17], can be safely performed under sedation or light general anaesthesia in spontaneously breathing patients. This assumes that the anaesthetist is painstaking in the execution of the technique, pays great attention to the feedback from the needle and has a high index of suspicion in the event of any difficulties. Although pain on injection cannot be verbalised by an anaesthetised patient, other cardinal signs do warn of neural contact: reflex muscle movement, increasing resistance to needle movement and, most importantly, any resistance to injection. Most peripheral nerves are surrounded by loose connective tissue and correctly placed needles should offer no appreciable resistance to flow. Some of these practical nuances are subtle and may escape the novice unless properly supervised, but they can be safely taught by skilled practitioners. Peripheral nerve stimulators are valuable teaching tools; they aid nerve location and improve success rates but there is no evidence that they reduce the potential for nerve damage in either anaesthetised or conscious patients. Epidural blocks may also be undertaken in lightly anaesthetised patients by suitably experienced anaesthetists who recognise and respond to any reflex movement generated by the needle in contact with a spinal nerve root, provided that patients do not receive muscle relaxants [18]. Caudal and lumbar epidurals performed below the conus medullaris cannot directly cause spinal cord damage and even thoracic epidurals are safe when carried out by experienced anaesthetists where the benefits to the patient justify the practice. Complications are an inherent part of medical practice and the risks and benefits of performing a regional block on an anaesthetised patient should be carefully assessed; the combination should not add to the overall risks of the anaesthesia and surgery. Without data, the experts can only advise caution but equally the onus is on the proponents to ensure that the quality of their practice is above criticism.