Continuous regional analgesia: can we afford not to use it?

The history of regional anaesthesia and analgesia is littered with mishaps and setbacks that all too often remain more clearly in the mind of both the anaesthetic community and the public at large than its countless undoubted successes. In this respect, spinal and epidural anaesthesia have much to answer for. Messrs Woolley and Roe suffered permanent, painful paraparesis after spinal anaesthesia 54 years ago [1], most likely as a result of a mishap that had nothing to do with the anaesthetic technique itself [2]. Microspinal catheters were withdrawn from use in the US in 1992 because of their association with cauda equina syndrome. Later reflection on the aetiology of the condition laid the blame more at the feet of lidocaine 5% than the technique of continuous spinal anaesthesia itself [3]. Anxiety about spinal and epidural anaesthesia has been further stoked more recently by reports of spinal cord damage during thoracic epidural insertion in the anaesthetised patient [4] and by Reynolds' recent editorial in this journal [5]. This latter article invoked logic in its plea for the more distal placement of spinal injections and yet ignored the importance of the training, skill and experience of the operator in the generation of complications, and the potential role played by the design of spinal needle tips and needle-through-needle combined spinal–epidural equipment. Peripheral nerve blockade has a history as old and proud as that of spinal anaesthesia. The first brachial plexus block by Halsted preceded Bier's invention of spinal anaesthesia by 14 years and followed less than a year after Koller's original report of the local anaesthetic action of cocaine [6]. The names of Kulenkampff, Labat, Raj and Winnie stand out from a crowd of important innovators in regional anaesthesia. Regional anaesthetic techniques have been developed to an extent that now allows them a high success rate with a low complication rate. And yet, it often seems that the widespread embrace of regional anaesthesia by anaesthetists in general, and those in the UK in particular, is a revolution always just about to happen, but never quite happening. Sceptics claim the case for regional anaesthesia remains unproven, yet the evidence in its support is growing. Regional anaesthesia may have beneficial effects on coagulation, may improve blood flow to the site of surgery, reduces the ‘stress response’ and improves the patient's ability to breathe and move free from pain. A recently published meta-analysis of the results of 141 trials of neuraxial blockade concluded that these techniques, when compared with general anaesthesia, were associated with a one-third reduction in mortality, along with larger reductions in pulmonary embolism, blood transfusion requirements, pneumonia and respiratory depression [7]. Perhaps we are hampered by a misguided ‘concern about complication culture’ that leads us to practice defensive anaesthesia? In this, even our own masters do not help us. The March 2000 syllabus for the Primary and Final FRCA [8] lists 16 subspecialty areas in which candidates should demonstrate significant knowledge. These include vascular, paediatric, cardiac and regional anaesthesia. In only one area is the candidate obliged to learn the ‘recognition and management of (the) adverse effects’ of the techniques employed. We will leave you to guess which. Regional anaesthesia is all too often condemned by the occasional disastrous case report. The case report as an endangered species is the subject of another recent editorial [9] and it is indeed a vehicle for communicating ‘accounts of living anaesthesia from which real lessons can be learned’. However, it forms part of a reporting system that ignores the denominator. Yes, occasional devastating complications can occur at the hands of the regional anaesthetist, but without accurate data on the number of procedures being performed and, perhaps as importantly, the medical condition of those upon whom regional anaesthesia is conducted, the safety of regional anaesthesia cannot truly be judged. Just how safe is regional anaesthesia? In trained hands, it is very safe. The best currently available data are contained in a report of a prospective study of over 100 000 regional anaesthetics performed in France [10]. Peripheral nerve blocks were associated with the following complication rates: death, 0.5/10 000; neurological injury, 1.9/10 000. The same figures for spinal anaesthesia were 1.5/10 000 and 5.9/10 000. We hope that the above suggests that regional anaesthesia can confer significant benefits to the patient, and that neuraxial anaesthesia is safe, peripheral nerve blockade even more so. However, the use of peripheral nerve blocks for prolonged surgical procedures and postoperative analgesia has historically been limited by the duration of action of the block itself. This, of course, depends upon the local anaesthetic used, adjuncts such as epinephrine or clonidine, the dose administered and the anatomical location of the block. Thus, an interscalene brachial plexus block with plain lidocaine may last for only 2 h, whereas a sciatic nerve block with bupivacaine may last for up to 24 h [11]. The idea of continuous regional anaesthesia is not new. Ansbro described it first in 1948 [12]. He placed a needle through a cork and then into the brachial plexus by a supraclavicular route, fixing the cork to the skin with adhesive tape. By this means, he was able to prolong the meagre duration of procaine from minutes to hours. The advent of inert plastic cannulae and catheters, originally designed for intravenous or epidural placement, allowed pioneers to place these in nerve or plexus sheaths. In 1964, Winnie and Collins reported catheterisation of the brachial plexus sheath by both the axillary and the subclavian perivascular approaches [13]. Over the ensuing years, cannulation and catheterisation techniques for a variety of nerves and nerve plexuses have been described. More recently, purpose-designed equipment for plexus catheterisation has become available. Most of this equipment relies upon electrical nerve stimulation for the location of a peripheral nerve with an insulated needle, placement of a cannula over the needle into the sheath and the subsequent passage of a catheter through the cannula. Alternatively, a catheter can be passed through an insulated stimulating needle into the sheath. Once a catheter can be placed, prolonged anaesthesia and analgesia can be achieved. Further local anaesthetic can be administered by bolus injection, continuous infusion or patient-controlled analgesia (PCA) techniques [14]. Do continuous regional analgesia techniques provide effective pain relief? The answer is ‘yes’, but the published data can, as ever, be considered by some to be equivocal. The clinical success of peripheral catheter techniques appears to depend upon the following: the site of surgery being amenable to a single catheter technique; the pain after surgery being sufficiently severe to justify the use of a catheter [15]; the duration of pain lasting longer than a single shot of local anaesthetic. Studies show that continuous regional anaesthesia after upper limb surgery can be remarkably effective [16], often achieving a level of analgesia that can fairly be described as total. In addition to reduced levels of postoperative pain, the patients undergoing continuous regional analgesia of the upper limb enjoy a lower incidence of the side-effects of opioid analgesia, such as nausea, vomiting, urinary retention and pruritus. Studies on continuous regional analgesia of the lower limb do not always yield such convincing results. The infusion of local anaesthetic down femoral nerve catheters produces effective analgesia after operations on the anterior knee, e.g. anterior cruciate ligament repair [17]. However, procedures that include the posterior part of the knee do not enjoy the same degree of success [18]. The innervation of the lower limb is fundamentally different to that of the upper limb. The upper limb is almost entirely innervated by nerves that are contained in a single sheath, i.e. the brachial plexus, which passes close enough to the surface to allow the anaesthetist ready access. The lower limb is supplied by four nerves: the femoral nerve; the obturator nerve; the lateral cutaneous nerve of the thigh; the sciatic nerve. Although the first three of these nerves can be blocked with a single injection by a ‘three-in-one’ block anteriorly or lumbar plexus block posteriorly, there is no one place, apart from the neuraxis, where all four nerves can be blocked at the same time. A single catheter technique cannot therefore consistently provide perfect analgesia for procedures on parts of the leg where innervation is shared between the sciatic nerve and any of the other three nerves. However, analgesia for knee and foot surgery with single catheter techniques compares very favourably with that provided by continuous epidural analgesia [19], but with the promise of accelerated rehabilitation [20] and a lower incidence of side-effects of epidural anaesthesia such as contralateral nerve block, hypotension, urinary retention and late respiratory depression. This may allow clinicians to provide analgesia equivalent to that provided by epidural infusion but without the need to keep patients in a high-intensity nursing environment such as a High Dependency Unit. Such is the safety of continuous regional anaesthesia that it is now feasible to discharge patients from hospital with peripheral nerve catheters and infusion devices shortly after painful limb surgery [21]. However, there is no such thing as a ‘free lunch’, and catheter techniques are not without complications. First of all, the procedures are technically difficult and failure is common, even in experienced hands [22]. Fear of failure may be a significant factor in the reluctance of some anaesthetists to attempt regional anaesthetic techniques. Continuous regional techniques share all the complications of the single shot block on which they are based. In addition to these are potential complications that include nerve irritation or damage, infection, local anaesthetic toxicity, inadvertent incorrect drug injection, catheter migration into other structures [23] and difficulty with catheter removal [24]. However, in view of the increasing use of these continuous techniques, there are currently few adverse case reports to deter the enthusiastic user. The use of continuous regional analgesia presents the possibility of perfect analgesia for many patients and excellent analgesia for the majority of patients undergoing painful limb surgery. This is a goal that is difficult to achieve with other analgesic regimens, even with modern multimodal combinations of opioid and non-steroidal anti-inflammatory drugs. Although the technical difficulty of catheter insertion may put some anaesthetists off, there are continuing developments in equipment design that will make these techniques easier. The same leap of imagination and equipment that allowed anaesthetists to progress from single-shot epidural injections to continuous epidural analgesia now needs to be taken in the context of peripheral nerve blocks. The growth in the number of legal actions against doctors in general, and against anaesthetists in particular, continues apace. Anaesthetists have been sued for awareness during general anaesthesia and for pain during regional anaesthesia. As suits for inadequate postoperative analgesia emerge, anaesthetists must look to the most effective forms of analgesia that can be provided safely. If continuous regional analgesia can, with the right equipment in trained hands, provide perfect or excellent analgesia after painful limb surgery, can we afford not to use it?