A reply

Abstract

We are grateful to Drs Troy and Kinirons for their interest in our case report and for their comments. The choice of approach to the brachial plexus in a patient who needs elbow surgery, but who has minimal ventilatory reserve, is a difficult one. The incidence of phrenic nerve paralysis approaches 100% with techniques aimed at the upper reaches of the brachial plexus [1], decreasing progressively with techniques that aim at lower portions of the plexus. Anaesthetic efficacy for elbow surgery also varies with different approaches to the brachial plexus, being relatively low with single-injection techniques in the distal axilla, increasing as one approaches a target area between the coracoid process and the first rib, and then decreasing again above this level, as the lower roots and trunks of the plexus are often missed by blocks such as the interscalene or subclavian perivascular. Variations in technique that may encourage local anaesthetic spread to this ‘coraco-costal’ area (the part of the plexus that can provide anaesthesia of the entire upper limb) have been described: distal pressure and high volume with an axillary approach [2, 3], proximal pressure and high volume with an interscalene approach [4]. As an increased volume of injectate will most likely result in an increase in both proximal and distal spread (even with digital pressure [5]), and if it is accepted that the mechanism of phrenic block is the proximal passage of local anaesthetic within the plexus sheath to the cervical roots, logical choices for anaesthesia in the described circumstances include a distal plexus block with a high volume or an accurately placed ‘coraco-costal’ block with a lower volume. The solutions suggested by your correspondents (multiple injection technique at the axilla or a coracoid-level block) are also wholly acceptable. However, the technique used in a particular situation depends not only on the anatomy, the techniques and the patient, it also depends upon the skills and experience of the operator. We were not experienced in coracoid-level blocks and had had unsuccessful experiences of single-shot axillary blocks for elbow surgery in the awake patient. We therefore chose a technique with which we were becoming increasingly familiar and which targeted the appropriate area of the brachial plexus: the vertical infraclavicular block. We chose a volume of 20 ml of local anaesthetic solution for two reasons: firstly, in order to minimise the proximal spread of local anaesthetic, and thus, we hoped, to reduce the chances of phrenic nerve paralysis; second, it is our contention that 20 ml of local anaesthetic is all that is needed to produce arm, as opposed to arm and shoulder, anaesthesia at a plexus level behind or close to the clavicle. This view is supported by Winnie's demonstrations of the relationship between injection volume and extent of anaesthesia in upper limb blocks [6].