Improving efficacy of regional anaesthesia

The introduction of new surgical techniques and rapid, short-acting anaesthetic agents has facilitated fasttrack surgery.1 Minimally-invasive approaches have been shown to reduce post-operative morbidity, lessen pain and enhance patient recovery, all leading to a reduction in length of hospital stay.1 Although associated with less tissue damage and inflammation than traditional surgery, laparoscopic techniques do little to address the hormonal and metabolic changes triggered by the stress response to surgery.2 These responses can lead to organ dysfunction, nausea and vomiting, hypoxaemia, sleep disturbances, fatigue and immobilisation and ultimately delay recovery.1 However, research has shown that use of regional anaesthesia, whereby a region of the body is kept “numb” and pain free for several days using local anaesthetic drugs, can attenuate the hormonal and catabolic responses to surgery, leading to improvements in pulmonary function and a reduction in the incidence of thromboembolic complications.2,3 Evidence for the benefits of regional anaesthesia on surgical outcome comes largely from a meta-analysis conducted by Rodgers et al.3 The authors systematically reviewed all trials with randomisation to intraoperative spinal or epidural anaesthesia (neuraxial blockade) or not and showed that overall mortality was reduced by approximately a third in those patients allocated to neuraxial blockade. The authors also reported significant reductions in the incidence of deep vein thrombosis (DVT), pulmonary embolism, transfusion requirements, pneumonia and respiratory depression, as well as reductions in the incidence of myocardial infarction with neuraxial blockade (MI).3

Barriers to wider use of regional anaesthesia

The clinical benefits of regional anaesthesia suggest that it should be used more routinely. However, there are a number of barriers preventing its wider implementation. Nerve block involves the administration of local anaesthetic in the spinal or epidural space or the use of local anaesthetic techniques that block nerve impulses from a specific limb. When performed blind, there is a risk of intraneuronal injection and possible nerve damage. There is also a risk of intravascular injection leading to grand mal seizures, malignant arrythmias, and cardiac arrest.4 While injecting slowly and adhering to the upper dose limits for anaesthetic agents is an important factor, the risk of intraneuronal and intravascular injection can be reduced by the use of a nerve stimulator, which finds the nerve electronically using a small current passed directly through the needle tip, stimulating a specific muscle group. Unfortunately, nerve stimulator settings do not lead to accurate and consistent placement of the needle close to the nerve and success rates are variable. Studies involving single- and multiple-nerve stimulation report variable success rates of complete block between 40% and 91%.5-8 A number of factors can cause ineffective nerve stimulation and failure to produce a peripheral nerve block. Patient factors, such as obesity or unusual anatomy, can prevent the needle from reaching the intended location, or vascular diseases such as diabetes, can diminish the response to the nerve stimulator. Whatever the cause, failure to produce a block leads to procedural delays causing frustration for the anaesthetist, surgeon and patient. Relying solely on nerve stimulation to position the needle in regional anaesthesia can also lead to a lack of predictability regarding the extent and duration of a block. For example, during lumbar plexus block for hip surgery, local anaesthetic can track back along tissue planes and spread bilaterally or into the epidural space. This can also occur if the needle moves out of position during the procedure or if too high a volume of local anaesthetic agent is injected. All these events generally lead to unexpected complications for the patient and the risk of extended stay in hospital. Successful use of epidural anaesthesia and analgesia is dependent on the ability to accurately locate the epidural space. Traditional approaches have involved the use of surface anatomical landmarks and loss of resistance (the LOR technique). However, both these “blind” techniques are inconsistent in terms of efficacy.9 The success of the former is limited by its inability to take into account anatomical variations or abnormalities for example, in those patients who are obese or have oedema in the back, Broadbent et al9 showed that use of anatomical landmarks frequently leads to incorrect identification of a given lumbar intervertebral space. Similarly, using the LOR technique alone does not provide confirmation of correct positioning of the needle, which may lead to repeated attempts at puncture and cause pain for the patient.11