Comparison of two neurostimulation techniques for axillary brachial plexus blockade

D. M. Coventry*, K. F. Barker and M. Thomson

Department of Anaesthetics, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK*Corresponding author

Accepted for publication: July 19, 2000


    Abstract
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
This prospective, randomized, double-blind study compared two techniques of axillary brachial plexus block using a peripheral nerve stimulator. Both groups received initial musculocutaneous nerve block followed by either a single injection on median nerve stimulation (group 1) or a double injection divided between median and radial nerves (group 2). All 60 patients received a total of 30 ml of lidocaine 15 mg/ml with epinephrine 5 µg/ml. Complete sensory blockade of all six peripheral nerves occurred in 53% and 97% of patients in groups 1 and 2, respectively (P<0.001), with a more rapid onset of blockade occurring in group 2 patients (P<0.001). Complete motor blockade was evident in 30% and 83% of patients in groups 1 and 2, respectively (P<0.001).

Br J Anaesth 2001; 86: 80–3

Keywords: brachial plexus, axillary approach; technique, nerve stimulation


    Introduction
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The many approaches used for brachial plexus block are well described. The choice usually involves personal preference based on the perceived efficacy of block in the surgical territory involved balanced against specific adverse effects in individual patients. The axillary approach avoids the more significant adverse effects of the more proximal approaches but suffers from inconsistency in achieving complete blockade. Recent improvements have centred around the use of the peripheral nerve stimulator to localize nerves accurately, while avoiding deliberate arterial puncture or the eliciting of paraesthesia.

The purpose of this study was to examine the extent of local anaesthetic blockade within all the nerves of the plexus using two different nerve stimulator techniques by the axillary approach.


    Patients and methods
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The study received approval from the Tayside Medical Ethics Committee. Sixty patients, ASA 1–3, aged >=17 yr, presenting for elective upper limb surgery were randomly allocated to receive one of two techniques for axillary brachial plexus block. Patients refusing a local anaesthetic technique were excluded, as were those with dementia, peripheral neuropathy or sensitivity to amide local anaesthetics.

All patients were visited before surgery and were given a full explanation; informed consent was obtained. On a patient’s arrival in the anaesthetic room, a 20G intravenous cannula was inserted in the hand not being operated upon and full non-invasive monitoring commenced (NIBP, ECG, SpO2). A small dose of midazolam (1–2 mg) was administered and oxygen 2 litres min–1 was delivered through a nasal cannula. With the patient lying supine, with their head placed on a pillow, the arm was abducted to 90° and the axillary artery palpated. The skin was cleaned and then anaesthetized with 1–2 ml of plain lidocaine 10 mg ml–1. Neural blockade was facilitated using a 22G insulated short-bevelled needle and peripheral nerve stimulator (Stimuplex; B. Braun Medical). All patients received a total of 30 ml of lidocaine 15 mg ml–1 with epinephrine 5 µg ml–1.

With both techniques, the musculocutaneous nerve was first located by eliciting maximal biceps contraction with a current of 0.5 mA and 5 ml of the local anaesthetic solution was injected. Then, from the same injection site in the distal axilla, 15–20 mm distal to the pectoralis major tendon, further injections were carried as follows (Figure 1). In group 1 (single-injection technique), the median nerve was located by eliciting the maximal flexor response in the fingers of the hand with a current of 0.5 mA and a total of 25 ml of lidocaine 15 mg ml–1 with epinephrine was then injected. In group 2 (double-injection technique), the median nerve was located as above and 15 ml lidocaine 15 mg ml–1 with epinephrine was injected. The radial nerve was then located by eliciting the maximal extensor response in the fingers and wrist with a current of 0.5 mA. A further 10 ml of lidocaine 15 mg ml–1 with epinephrine was then injected.



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Fig 1 Transverse section through the proximal humerus showing the relationship of the brachial plexus nerves to the axillary artery.

 
Cutaneous analgesia was assessed 10, 20 and 30 min after completion of injection by an independent and blinded observer. Using a short-bevelled 27G needle, all six upper limb areas—median, musculocutaneous, ulnar, radial and medial cutaneous nerve of arm and forearm—were tested for complete sensory loss. Inability to move the relevant muscle groups of the limb against gravity was taken as the motor block end-point. Analgesic failure was managed with peripheral local anaesthetic supplementation or general anaesthetic as appropriate. Intraoperative sedation was provided by an intermittent bolus of midazolam if requested.

Duration of surgery, tourniquet discomfort or any additional problems, such as vascular puncture, were noted. All brachial plexus blocks were carried out by one operator (D.C.) and assessed by one blinded assessor (M.T.). Assuming a success rate of 60% with one technique against 90% for the second, 29 patients in each group would be required to show a significant difference at 80% power. Statistical comparisons were made using the Fischer exact test.


    Results
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
There were no differences in patient characteristics between groups, nor any differences in type or duration of surgery (Table 1). It was possible to locate the desired nerves in all patients of both study groups. Sensorineural blockade of all six nerves occurred in 16 patients in group 1 (53%) and 29 patients in group 2 (97%) (P<0.001) (Table 2). The radial nerve was consistently blocked in all cases in group 2 but in only 18 patients (60%) in group 1 (P<0.001) (Table 3). Only one patient in group 1 had complete nerve blockade at 10 min compared with 14 patients in group 2 (P<0.001), and at 20 min, 27 patients (90%) in group 2 had complete sensory loss compared with seven (23%) in group 1 (P<0.001). Motor blockade was significantly better in group 2 than group 1 (P<0.001), with the radial being the nerve most difficult to block completely by the single-injection technique (Table 4). No patient required general anaesthesia, but three patients in group 1 required supplemental nerve blocks.


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Table 1 Patient characteristics
 

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Table 2 Pattern of sensory blockade. *P<0.001
 

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Table 3 Effectiveness of brachial plexus blockade. *P<0.001
 

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Table 4 Pattern of motor blockade. *P<0.001
 

    Discussion
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The axillary approach to brachial plexus anaesthesia is popular because of its ease of performance, clear vascular landmark and low incidence of complications.1 Many of the traditional approaches have, however, suffered from inconsistency in blocking the musculocutaneous and radial nerves in particular.2 Different agents and volumes of local anaesthetic, as well as a variety of methods for placing the local anaesthetic, have been described in an attempt to improve efficacy. These include feeling for ‘fascial pops’, trans-arterial methods and use of nerve stimulators.3

The trans-arterial approach appears to be both unnecessary and undesirable. Axillary block complicated by haematoma and nerve injury4 or by false aneurysm formation5 has been reported using this method and, as our study demonstrates; other methods avoiding this risk can be very effective. Another issue is whether large-volume single injections are as reliable as multiple-injection techniques. The failure rate remains significant for the ‘single-shot, high volume’ techniques often described in textbooks,6 even when specific blocking of the musculocutaneous nerve is included, and this is reinforced by the findings in our single-injection patients, even when performed with a peripheral nerve stimulator.

CT studies by Thompson and Rorie7 attributed this failure to anatomical variability in the septae within the neurovascular sheath creating a multi-compartmental structure which limits circumferential spread; they advocated the use of a multiple-injection approach. Vester-Anderson and colleagues8 showed, using a catheter technique, that even volumes of <=80 ml of local anaesthetic cannot reliably block the musculocutaneous nerve, which is essential for complete sensory analgesia of the limb and to prevent tourniquet discomfort and unwanted arm movement during surgery.

Some investigators have shown a favourable success rate with single-shot techniques with an end-point of ‘readiness for surgery’, but in these studies there may have been a predominance of palmar surgery. Lavoie and colleagues9 compared single and multiple injections using a nerve stimulator and demonstrated the benefit of considering the musculocutaneous nerve as a separate, preliminary part of any axillary brachial plexus block. However, despite correctly determining the sensory block of each nerve <=30 min after injection, they failed to detail those findings, confining themselves to recording adequacy for surgery as the study end point, rather than completeness of brachial plexus anaesthesia. Only 48% of the surgery in this study was restricted to the palmar surfaces of the hand, leaving radial nerve blockade desirable in 34% and essential in 18%.

The use of the peripheral nerve stimulator for brachial plexus block can improve success rates for both the regular practitioner of regional anaesthesia10 and the occasional user,11 combined with a reduced theoretical risk of nerve damage.12 We designed our study to start with the identification and blocking of the musculocutaneous nerve in both groups, as that nerve lies within the body of coracobrachialis muscle at the distal axillary level and is outwith the connective tissue sheath. Thereafter, we compared a single ‘intra-sheath’ injection (by identifying the median nerve), with a more specific localization of the median and radial nerves. The order in which each nerve is localized and blocked is important to minimize the theoretical risk of nerve injury. In this we disagree with Gaertner and colleagues,13 who suggested a sequence of nerve blockade as follows: median, ulnar, radial, musculocutaneous and medial (brachial and antebrachial) cutaneous nerves. This implies that whilst seeking the musculocutaneous nerve, the area of the median nerve may be recrossed some time after it has had local anaesthetic applied and risks transfixion of that nerve. In our study, the musculocutaneous nerve, outside the sheath, above and posterior to the artery, was blocked first. The needle was then withdrawn to and directed towards the artery to find the median nerve, and finally the needle was directed inferior to the artery to define the radial nerve (Figure 1). Following this sequence removes the risk of transfixing a nerve already partially blocked by a previous injection. Our experience with this double-injection technique is that there is little interference with localization of each nerve, even with the use of the more rapid onset local anaesthetic agents such as lidocaine.

This study revealed that the double-injection technique can have significant advantages over the single-injection technique in both speed of onset and pattern of block. Ninety per cent of blocks in the double-injection group and 23% in the single-injection group were deemed complete at 20 min. The pattern of sensory block showed the radial nerve to be incompletely blocked in 40% of patients having the single-injection technique, even after 30 min, compared with none in the double-injection group. It is also interesting to note that the ulnar nerve was blocked in 100% of the double-injection group despite no attempt to localize it. Motor blockade testing also showed significant advantage in the double-injection technique, 83% having complete motor blockade compared with 30% in the single-injection group. The double-injection technique in which the radial nerve is specifically identified has a faster onset and more complete sensory block.


    References
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
1 Fanelli G, Casati A, Garancini P, Torri G. Nerve stimulator and multiple injection technique for upper and lower limb blockade: failure rate, patient acceptance, and neurological complications. Study Group on Regional Anaesthesia. Anesth Analg 1999; 88: 847–52[Abstract/Free Full Text]

2 Vester-Anderson T, Christiansen C, Sørensen M, Eriksen C. Perivascular axillary block. I: Blockade following 40 ml 1% mepivacaine with adrenaline. Acta Anaesthesiol Scand 1982; 26: 519–23[ISI][Medline]

3 Brockway MS, Wildsmith JAW. Axillary brachial plexus block: method of choice? Br J Anaesth 1990; 64: 224–31[ISI][Medline]

4 Ben-David B, Stahl S. Axillary block complicated by haematoma and radial nerve injury. Reg Anesth Pain Med 1999; 24: 264–6[ISI]

5 Zipkin M, Backus WW, Scott B, Poppers PJ. False aneurysm of the axillary artery following brachial plexus block. J Clin Anesth 1991; 3: 143–5[Medline]

6 Hughes TJ, Desgrand DA. Upper limb blocks. In: Wildsmith JAW, Armitage EN, eds. Principles and Practice of Regional Anaesthesia. Edinburgh: Churchill Livingstone, 1993; 169–88

7 Thompson GE, Rorie DH. Functional anatomy of the brachial plexus sheath. Anaesthesiology 1983; 59: 117–22[ISI][Medline]

8 Vester-Anderson T, Christiansen C, Sørensen M, Kaalund-Jorgensen HO, Saugbjerg P, Schultz-Moller K. Perivascular axillary block. II: Influence of injected volume of local anaesthetic on neural blockade. Acta Anaesthesiol Scand 1983; 27: 95–8[Medline]

9 Lavoie J, Martin R, Tetrault JP, Cote DJ, Colas MJ. Axillary plexus block using a peripheral nerve stimulator: single or multiple injections. Can J Anaesth 1992; 39: 583–6[Abstract]

10 Tuominen MK, Pitkanen MT, Numminen MK, Rosenberg PH. Quality of axillary brachial plexus block. Comparison of success rate using perivascular and nerve stimulator techniques. Anaesthesia 1987; 42: 20–22[ISI][Medline]

11 Eifert B, Hahnel J, Kustermann J. Axillary blockade of the brachial plexus. A prospective study of blockade using electrical nerve stimulation. Anaesthesist 1994; 43: 780–85[ISI][Medline]

12 Salander D. Axillary plexus block: paresthetic or perivascular. Anesthesiology 1987; 66: 6–10.

13 Gaertner E, Kern O, Mahoudeau G, Freys G, Golfetto T, Calon B. Block of the brachial plexus branches by the humeral route. A prospective study in 503 ambulatory patients. Proposal of a nerve-blocking sequence. Acta Anaesthesiol Scand 1999; 43: 609–13[ISI][Medline]