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
Anaesthesia for limb surgery
One of the challenges of limb surgery is providing effective pain relief that does not limit the mobilisation of the patient. Ideally, post-operative analgesia techniques should provide sufficient relief to allow early function, physiotherapy and movement. However, lack of standardisation means that many regional anaesthesia procedures fail to provide these benefits. This is particularly the case with total knee replacement, where the anaesthetic management of patients undergoing this procedure is still not standardised. Epidural analgesia is common, but is associated with bilateral lower limb motor block, limited mobilisation and the need for bladder catheterisation. Spinal anaesthesia with intrathecal morphine provides good pain relief, but only for 12 to 16 hours, and it is often associated with nausea and vomiting. Combined single-injection femoral/sciatic blocks provide good pain relief, but for a variable length of time (between 12 and 24 hours) and often result in excessive block when commercial concentrations of ropivicaine and levobupivicaine are used.12 Recently, our department has been looking at techniques that assist the optimal placement and minimal dosing of anaesthetic agents for total knee replacement; the overall aim being to develop a local anaesthetic regimen that offers complete pain relief for at least 48 hours, yet allows full mobilisation within 24 hours of surgery.
Ultrasound-guided epidural and regional anaesthesia
There has been increasing interest in the use of ultrasound to guide needle placement when administering epidural and peripheral nerve blocks13 in order to improve efficacy and procedural outcomes. It provides an opportunity to see the relevant anatomy and distribution of the local anaesthetic in real-time14-16 and the real possibility of higher success rates and avoidance of the recognised complications associated with needle misplacement during blind procedures.11,13 In addition, using ultrasound to accurately identify the nerve to be blocked could lead to the use of a lower dose of local anaesthetic, enhancing postoperative mobility without compromising pain relief.12 Similarly, when administering epidural anaesthesia, ultrasound can be used to preview the epidural space and flag technical problems in advance as well as facilitate successful access and minimise the need for multiple punctures. The ultrasound machine we use, the Zonare Z.one Ultra, offers a new approach to ultrasound image and acquisition. Unlike conventional ultrasound systems, which acquire echo data line-by-line, zone sonography rapidly acquires echo data in a relatively small number of large zones, each of which contains a volume of data equivalent to many “lines” in a conventional system. The use of a broad transit beam to acquire this data means that image formation is not directly linked to the speed of sound through tissue, dramatically reducing the time required for image acquisition. The system also differs from conventional systems in terms of software use. In conventional ultrasound, only the “back-end” processing of scan conversion and image acquisition is implemented in the software. However, it also uses software in its “front-end” implementation. As a result, the system is small and light, offering an online upgrade or update every six months which is both cost-effective and convenient, and has the potential to become more powerful as the technology develops.
Efficacy of ultrasound-guided regional anaesthesia
Clinical studies of ultrasound-guided regional anaesthesia show that success rates are improved. Although traditionally studies include small numbers of patients, Sandhu et al17 analysed the use of ultrasound-guided infraclavicular brachial plexus block (ICBPB) in 1,146 cases over 32 months. Data from this retrospective study show that ultrasound guidance improved the success rate (99.3%) compared to previously published findings and the safety for ICBPB, with no reported cases of nerve injury, pneumothorax or local toxic reactions to the anaesthetic. A more recent, qualitative systematic review of the evidence for superior risk to benefit profiles of ultrasound-guided regional anaesthesia and analgesia was conducted by Liu et al.18 The review failed to show any superiority associated with the technique, mainly due to too few patients and diversity (type of block, anaesthetic and analgesic agents) of the RCTs but it did identify a number of patient-focused benefits. These included faster block performance, fewer needle passes, and less discomfort and minor side effects from block performance. The authors speculated that use of ultrasound allowed for closer positioning of the needle and local anaesthetic to the nerve, leading to faster onset of block. In addition, the resulting lower dose of anaesthetic reported potentially influenced the incidence of toxic systemic reactions to the local anaesthetic. A recent systematic review and metaanalysis of all randomised controlled trials comparing epidural analgesia with perineural block for major knee surgery conducted by Fowler et al20 shows that perineural block is associated with equivalent pain relief to epidural analgesia, but is associated with significantly fewer side effects, including a reduction in the incidence of hypotension, respiratory depression, pruritus and restriction of movement.
Local experience
The axillary block is the most common nerve block technique used in forearm and hand surgery; it is often the first block that trainee anaesthetists perform. The median, ulnar, radial and musculocutaneous nerves are all easily visible (see Fig. 1) and, in our experience, lead to improvements in the accuracy and outcomes of the block. In the systematic review conducted by Liu et al,18 ultrasound-guided axillary block was found to reduce the number of needle passes and shorten the time for block performance in upper limb procedures. This superior imaging capability has also facilitated our research into the tracing of distant nerves such as the lumbar plexus and sciatic nerve (Fig. 2a, 2b, 2c). Ultrasound helps us to visualise the anatomy and select the best site for administering the block to these previously difficult sites. Ultrasound guidance has facilitated the use of continuous femoral perineural infusion of local anaesthetic at Ninewells Hospital. Under ultrasound guidance, a small plastic catheter is accurately inserted into the space between the femoral nerve and its connective tissue sheath, then a bolus of local anaesthetic injected. Pain relief is maintained by a constant infusion of local anaesthetic using an elastomeric ball. To date, we have administered approximately 500 femoral blocks using this technique, with a high success rate (>99.5%) and high degree of patient satisfaction. Infusion of local anaesthetic via a femoral perineural catheter provides pain relief that is equivalent to epidural analgesia but associated with earlier mobility and a shortened period of time spent in rehabilitation. Our findings support those of Chelly et al19 who studied the effects of continuous femoral infusion (CFI) on recovery following total knee arthroplasty. The authors found that patients who received sciatic blocks followed by CFI significantly reduced postoperative morphine requirements and postoperative bleeding. Continuous femoral infusion was also associated with better performance on continuous passive motion as well as a 90% decrease in serious complications and a 20% decrease in the length of hospitalisation.
Ultrasound-guided epidural anaesthesia
Data supporting the use of ultrasoundguided needle placement in epidural and peripheral blocks is limited mainly to small prospective studies. Karmakar et al11 evaluated the feasibility of performing real-time ultrasound-guided paramedian epidural access in 15 patients undergoing groin or lower limb surgery under an epidural or combined spinal-epidural anaesthesia. The authors reported being able to visualise the forward movement of the plunger and expulsion of the saline from the syringe (the LOR) as the needle tip entered the epidural space. They also highlighted the greater precision in achieving epidural access with ultrasound when compared to use of the LOR technique alone. A series of case reports by the same author14 showed that local anaesthetic injected via a needle positioned close to the lumbar plexus under real-time ultrasound guidance is effective in producing ipsilateral lumbar plexus block. The technique also improved the quality of the block and reduced the incidence of minor and major side effects. Grau et al15 evaluated the clinical efficacy of ultrasound diagnostics in obstetric anaesthesia in 300 patients. Using ultrasound for structure detection significantly reduced the rate of puncture attempts and the mean rate of necessary puncture levels. It was also associated with significantly greater achievement of complete analgesia, a lower VAS pain score and a reduction in the incidence of side effects.15 In a later study, Grau et al16 compared the impact of online ultrasonic imaging of the lumbar region during epidural puncture on the efficacy of puncture of the epidural space with conventional combined spinal-epidural anaesthesia and offline ultrasonic scans in a study involving thirty women scheduled for Caesarean section. The authors reported a significant reduction in the number of attempts at puncture, the number of interspaces necessary for puncture and the number of spinal needle manipulations in the group of patients receiving online imaging compared to patients in the other two groups. Our own experience is with a small curvilinear probe with a frequency range between 3 MHz and 9 MHz. A typical image of the lumbar neuraxial structures is seen in Figure 3.
Continual improvement of techniques
One of the challenges of using perineural block for knee replacement surgery is that high concentrations of the local anaesthetic levobupivicaine ensure good pain relief but are associated with unacceptably dense motor block. In contrast, providing lower concentrations of levobupivicaine allows some movement but patient movement is restricted due to severe pain. To date, we have managed to reduce the concentration of the femoral, obturator and sciatic boluses of levobupivacaine from 0.375% to 0.3%, and reduced the concentration of levobupivacaine infusion to 0.024%, a five-fold reduction from commercial solutions. These changes have maintained pain relief, further reduced motor block and allowed the sciatic block to wear off within 18 hours (no foot numbness), promoting early morning physiotherapy. Research is now underway to determine the sensory-motor split of two local anaesthetics – levobupivicaine and ropivicaine – in an attempt to identify which of the two is most effective for femoral perineural block, particularly as ropivicaine offers a more advantageous pharmacological profile than levobupivicaine. Although molar differences between drugs often seem slight, a small reduction in molar concentration may provide similar pain relief, but result in a large reduction in side effects due to the shape and position of the efficacy and side effect dose response curves of each local anaesthetic.
Future directions
A recent review article in Regional Anaesthesia and Pain Medicine made several proposals as to the future direction of regional anaesthesia research and practice. The most important proposal was the quantification of local anaesthetic spread around nerves in order to objectively confirm correct local anaesthetic placement and spread, guaranteeing safe and effective block. Traditionally, testing of invasive techniques has been difficult because of the lack of a reproducible model. Ideally, a regional anaesthesia model should simulate the passive and dynamic components of nerve block such as nerve anatomy, needle movement, fascial penetration, perineural fluid injection and inadvertent intraneural injection. Fortunately, the anatomy department of the University of Dundee was the first in the UK to introduce Thiel cadavers in mid 2009 in order to assess their suitability for teaching and simulating surgical procedures. A novel preservation technique developed by Professor Thiel of the University of Graz, allows complete flexibility of limbs, and realistic simulation of needle passage. The Thiel cadaver has allowed our research group based at the Institute for Medical and Surgical Technology (IMSaT), consisting of anaesthetists, engineers and medical physicists, to investigate local anaesthetic spread around nerves by using research software which allows alteration of ultrasonic images on our ultrasound machine, and enables translation of pre-clinical data to the operating room. In the near future, we hope to see mapping of local anaesthetic spread, and greater confidence in differentiating between perineural and intraneural injection. Ultimately, ultrasound will have a role in imaging regions previously regarded as inaccessible. This may have particular relevance to administration of spinal anaesthesia in the elderly, especially those presenting with crush fractures or osteophytes. In addition to providing a superior image quality when compared to conventional ultrasound, viewing modalities can be combined to enhance penetration and image quality, which has particular application when imaging obese patients. With further research, the system may also offer advantages in imaging elderly patients for regional anaesthesia and overcome the increased echo density of muscles seen in this age group. In the future, we will see greater use of ultrasound in the administration of epidural anaesthesia during labour. There is currently a 20% partial failure rate in administration of epidurals in our obstetric unit and long delays but using ultrasound to pre-scan the patient should help us to pre-empt problems so that failures can be avoided and waiting times reduced. In addition, achieving good visualisation of the needle using new modalities should help improve real-time injection into the epidural space.
References
1 Wilmore D.W., Kehlet H. Recent advances: Management of patients in fast track surgery. Br Med J 2001; 322:473-6. 2 Desborough J.P. The stress response to trauma and surgery. Br J Anaesth 2000; 85:109-17. 3 Rodgers A. et al. Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: results from overview of randomised trials. Br Med J 2000; 32:1-12. 4 McLeod G.A., Wildsmith J.A.W. Systemic Toxicity In: Bridenbaugh, Cousins, Carr, Horleker Eds. Neural Blockade Lippincott 2008. 5 Gaertner E. et al. Infraclavicular plexus block: multiple injections versus single injection. Reg Anesth Pain Med 2002; 27:590-94. 6 Koscieiniak-Nelson Z. et al. A comparison of coracoid and axillary approaches to the brachial plexus. Acta Anaesthesiol Scand 2000; 44:274-79. 7 Borgeat A, et al. An evaluation of the infraclavicular block via a modified approach of the Raj technique. Anesth Analg 2001; 93:436-41. 8 Desroches J. The infraclavicular brachial plexus block by the coracoid approach is clinically effective: an observational study of 150 patients. Can J Anaesth 2003; 50:253-57. 9 Broadbent C.R. et al. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000; 55(11):1122-6. 10 Furness G. et al. An evaluation of ultrasound imaging for identification of lumbar intervertebral level. Anaesthesia 2002; 57(3):277-80. 11Karmakar M.K. et al. Real-time ultrasound-guided paramedian epidural access: evaluation of a novel in-plane technique. Br J Anaesth 2009; 102(6):845-54. 12 McLeod G.A. et al. Determination of the EC50 of levobupivicaine for femoral and sciatic perineural infusion after total knee arthroplasty. Br J Anaesth 2009; 102:528-33. 13 Hopkins P.M. Editorial: Ultrasound guidance as a gold standard in regional anaesthesia. Br J Anaesth 2007; 98(3):299-301. 14Karmaker M.K. et al. Ultrasoundguided lumbar plexus block through the acoustic window of the lumbar ultrasound trident. Br J Anaesth 2008; 100:533-7. 15 Grau T. et al. Efficacy of ultrasound imaging in obstetric epidural anesthesia. J Clin Anesth 2002; 14(3):169-75. 16 Grau T. et al. Real-time ultrasonic observation of combined spinalepidural anaesthesia. Eur J Anaesthesiol 2004; 21(1):25-31. 17 Sandhu N.S. et al. Sonographically guided infraclavicular brachial plexus block in adults. J Ultrasound Medicine 2006; 25:1555-61. 18 Liu S. et al. Ultrasound-guided regional anaesthesia and analgesia. Reg Anesth Pain Med 2009; 34:47-59. 19 Chelly J.E. et al. Continuous femoral blocks improve recovery and outcome of patients undergoing total knee arthroplasty. J Arthroplasty 2001; 16:436-45. 20 Fowler S.J. et al. Epidural analgesia compared with peripheral nerve blockade after major knee surgery: a systematic review and meta-analysis of randomized trials. Br J Anaesth 2008; 100:154-64. 21 Sites B.D., Neal J.M., Chan V. Ultrasound in Regional Anesthesia: Where Should the ‘‘Focus’’ Be Set? RAPM 2009; 34:531-533.
Author
Graeme McLeod, MD PGCertMedEd MRCGP FRCA FFPMRCA, is a consultant and clinical reader at the University Department of Anaesthesia, Ninewells Hospital Medical School, Dundee.