One size does not fit all: Proposal of an algorithm for the practice of ultrasonography in combination with nerve stimulation for peripheral nerve blockade
- Hervé Bouaziz
- [Denis Jochum], [Attila Bondar], [Laurent Delaunay], [Michael Egan], [Hervé Bouaziz]
Several articles have been published recently comparing the use of ultrasound (US) to that of peripheral stimulator (PNS) as nerve blocking techniques. We have read the meta-analysis by Abrahams et al. of randomized controlled trials, which suggests the greater efficacy of US compared
More... Several articles have been published recently comparing the use of ultrasound (US) to that of peripheral stimulator (PNS) as nerve blocking techniques. We have read the meta-analysis by Abrahams et al. of randomized controlled trials, which suggests the greater efficacy of US compared to PNS [1]. Though there are many interesting points to the meta- analysis, Abrahams acknowledges in Appendix A of his review and in the subsequent correspondence, that of the 9 studies used, 3 used an inappropriate motor response as an endpoint and others opted for too high a minimal stimulating current [1]. These practices greatly reduced the effectiveness of nerve blocks using PNS. Perlas et al. for example described a 40% failure for popliteal block [1]. We would suggest that on balance, it is neither necessary nor desirable to persist in attempts to establish the superiority of one technique over the other and would rather encourage the view that there are advantages as well as limitations pertaining to both. Consideration therefore should be given to a practice which is based on how both PNS and US approaches might be complementary rather than choosing one to the exclusion of the other. We submit that the algorithm we describe is a practical way to combine the two approaches and should result in a more favourable risk-benefit ratio for nerve localization.
In a series of steps as illustrated in the algorithm, the first (and essential) is to obtain adequate training in both techniques [2]. In accordance with best practice, the procedure is performed on an awake or lightly sedated patient in order to maintain continuous verbal contact [3]. A sterile technique is mandatory. An initial ultrasound scan of the target anatomical area must be undertaken [4]. The scanning should be systematic and should cover a large area in order to accurately identify the anatomical components, particularly the neurovascular structures. The initial aim is to plan the needle trajectory and develop a strategy to optimise performance of the block. Whether an in-plane or out-of-plane technique is used it is essential that the full extent of the needle be visualized. Meanwhile the nerve stimulator should be set at 1 mA current intensity and 0.1 ms for the impulse duration. Nerve stimulation has a high specificity and low sensitivity [5] and it should always be kept in mind that in case of needle to nerve contact, it is still possible to increase current intensity without eliciting a motor or sensory response.
During the procedure the needle tip position can be confirmed by hydrolocalization. This consists of repetitive injections of a small volume (usually less than 1 ml) of either the local anaesthetic itself, saline or dextrose 5% water (D5W). We recommend the use of D5W or saline as safer during needle positioning, when the needle tip may contact the nerve(s). Gentili et al. has shown in an experimental study that no neural damage occurred after saline injection, even if it was administered intrafascicularly [6]. D5W is preferred as it is a nonionic solution and in contrast to saline it potentiates the electrical field for the nerve stimulator [7].
Priority should be given to US, when the quality of the image is good and the anatomical structures can be easily identified. A tangential rather than a direct approach will provide optimal spread of the local anaesthetic and should therefore be chosen. In the tangential approach, when the needle is positioned slightly beyond the nerve (in order to obtain a circumferential spread of local anaesthetic) the minimum current intensity will be inevitably increased. If the quality of the image is poor, nerve stimulation assumes greater importance. In both cases, finding the minimum stimulating current intensity is essential [3] as it indicates the distance between the needle tip and the nerve (more precisely, the nearest nerve fascicle) as well as providing functional information.
Strict adherence to safe practice should be maintained [3] and as with any regional technique it is essential to aspirate before injecting the solution and be aware that US images may give a false sense of security. Manoeuvres of the probe such as applying and then releasing pressure on the tissues can localise venous structures and define the relationship of the needle to the vein. While the width of the US beam is in the order of 1mm, it is essential to position the US field exactly over the needle tip to allow visualization of the first millilitre of hypoechoic fluid injected [4]. Nerve stimulators, e.g. Stimuplex HNS 12 (B Braun), that display the electrical impedance on their screen provide valuable information and should be used [8]. At a constant stimulating current intensity, any modification of the electrical impedance observed may be indicative of pre-injection intraneural needle placement. Absence of variation or a mild increase in electrical impedance during the injection of a few millilitres of D5W indicates intravascular needle position [9]. Extrafascicular injection should be of low resistance and painless. Whether needle repositioning is required depends on the pattern of fluid spread seen on the US image. An optimal spread, in contact with and circumferential to the nerve will permit a reduced injection volume of local anaesthetic, provided that it is dispersed along the nerve. When this is not the case, the needle should be repositioned.
The overall aim should be to inject the local anaesthetic at the correct site, to minimise the dose while administering an adequate volume of solution. Throughout the procedure the operator should continuously assess the advantages and limitations of both techniques to obtain the most favourable risk-benefit ratio for the patient.
In our view, it is necessary to combine techniques using a rigorous procedure for the optimum result. The algorithm we propose may be simplified and individualized according to preference but it should be kept in mind that each step removed is a loss of potentially useful information.
References: 1. Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta- analysis of randomized controlled trials. Br J Anaesth 2009;102:408-17. 2. Sites BD, Chan VW, Neal JM, Weller R, Grau T, Koscielniak-Nielsen ZJ, Ivani G. The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anaesthesia and Pain Therapy Joint Committee Recommendations for Education and Training in Ultrasound-Guided Regional Anesthesia. Reg Anesth Pain Med 2009;34:40- 46. 3. Les blocs périphériques des membres chez lâÂÂadulte. Recommandations pour la pratique clinique. RPC publiées par la SFAR.
http://sfar.org/t/spip.php?article184 (Mis en ligne le 2 mars 2003). 4. Brull R, Perlas A, Cheng PH, Chan VW. Minimizing the risk of intravascular injection during ultrasound-guided peripheral nerve blockade [Letter]. Anesthesiology 2008;109:1142. 5. Perlas A, Niazi A, McCartney C, Chan V, Xu D, Abbas S. The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound. Reg Anesth Pain Med 2006;31:445-50. 6. Gentili F, Hudson A, Kline DG, Hunter D. Peripheral nerve injection injury: An experimental study. Neurosurgery 1979;4:244-53. 7. Tsui BC, Kropelin B, Ganapathy S, Finucane B. Dextrose 5% in water: fluid medium for maintening electrical stimulation of peripheral nerves during stimulating catheter placement. Acta Anaesthesiol Scand 2005;49:1562-5. 8. Jochum D, Iohom G, Diarra DP, Loughnane F, Dupré LJ, Bouaziz H. An objective assessment of nerve stimulators used for peripheral nerve blockade. Anaesthesia 2006;61:557- 64. 9. Tsui BCH, Chin JH. Electrical impedance to warn of intravascular needle placement. Reg Anesth Pain Med 2008;32:A-51.
*****(Authors request Algorithm to be attached here)****
Published August 7, 2009