Infraclavicular Brachial Plexus Block
The infraclavicular block (ICB) is very well suited to ultrasound guidance. Several factors have limited the popularity of the ICB with nerve stimulator techniques. These include poorly defined surface land-marks and the absence of an easily palpable artery together with the risk of arterial puncture and pneumothorax. These limitations are less relevant with US imaging. We have adopted the technique described by Dr N Sandhu and have now performed several hundred of these blocks. It is an excellent technique for surgery on the forearm, elbow and distal upper arm. Hand surgery may also be performed.
The infraclavicular area has the following boundaries. Superiorly lies the clavicle and coracoid process and inferiorly is the lower margin of the pectorlalis major (PM) muscle. The deltopectoral groove denotes the lateral border. Beneath the skin and subcutaneous muscles lies a fascial plane that covers the PM muscle. Deep to this is pectorlalis minor (Pm) muscle which is covered by the clavipectoral fascia. The axillary fossa lies deep to Pm and contains the neurovascular bundle. Typically the axillary vein is medial and the artery is lateral with the cords of the brachial plexus distributed around the artery in positions suggested by their names. The axillary artery commences at the lateral border of the first rib and continues as the brachial artery at the lower border of teres major. Medial and deep to Pm the ribs and pleura can be seen.
The ultrasound probe is placed in a parasaggital position below the clavicle and inferiomedial to the coracoid process. With a linear probe, a clear detailed view of the infraclavicular area is seen. Immediately deep to the skin, the PM muscle is seen as a thick dark wedge. The smaller thinner Pm muscle lies deep to the PM and is separated by a layer of fascia seen as a bright hyper echoic line with US. Pm muscle tapers superiorly towards its insertion the coracoid process. Deep to the Pm muscle is the Pm fascia. This overlies the axillary artery and vein.
The vessels assume a fairly standard position deep to the Pm muscle; the artery is superior and the vein inferior. Both are usually at about the same depth from the skin surface. The cords of the brachial plexus are distributed around the axillary artery. The lateral cord is usually the easiest to visualise and consists of a bundle of bright hyperechoic fascicles located superiorly and at the superficial border of the axillary artery (11 o'clock position). The posterior cord usually lies immediately posterior to the axillary artery. The medial cord is often more difficult to image as it usually lies between the axillary artery and axillary vein (1-2 o'clock position).
The patient lies supine with the arm abducted to 70-90 degrees. The arm should be supported on a small table or arm board. This ensures that the axillary vein is easily seen which helps with visualising the medial cord and avoids accidental venous puncture. The patient's head should be positioned at the very top of the bed. The head can lie on a low pillow and is turned slightly away from the side to be blocked. The patient's bed is raised to a height that allows easy access to the infraclavicular area without having to lean down or reach over the patients shoulder (about elbow level for the operator).
The operator stands at the patients head slightly towards the side to be blocked. The block trolley is positioned to the side opposite that to be blocked.
The US screen needs to be positioned so as to allow easy viewing of needle and probe and the US image. This is best achieved by using an LCD screen slaved to the US machine. The LCD screen can be swing out over the patient and allows an easy switch between observing needle/ probe alignment and the US image on the screen. If an LCD screen is not available the next best position for the US machine is between the patient's ipsilateral arm and the bed.
Two probes will provide good imaging in most situations - a high frequency (5-10MHz) linear probe or the medium frequency (4-8MHz) curvilinear probe. For a slender adult the linear probe will provide a good picture of the infraclavicular anatomy without any image distortion. However in larger patients, this probe is limited by its lack of imaging depth. In addition, in some individuals there is limited space between the US probe and the clavicle which makes needle placement difficult.
The curvilinear probe has several advantages. Firstly it is a lower frequency probe which allows for better imaging of deeper structures, especially useful in larger patients (>120 kg) where the target in more than 5cm deep. Secondly, the curvilinear probe allows more room for needle placement between clavicle and probe. Thirdly, the sector array of the probe makes needle imaging more reliable particularly with the steeper needle angles required for deeper nerves.
Prep and drape the area below the ipsilateral clavicle. Place a sterile sheath over the US probe after applying US gel to the inside of the sheath. Place US gel over the probe then apply to the patient. Optimise the image by selecting the appropriate depth and resolution setting for your machine. Use a 30 ml syringe for local anaesthetic (LA). Place a 3 way tap on the syringe then add a long length of narrow bore infusion tubing to the tap. Once the patient is prepped and draped, the syringe can be handed off the sterile field to an assistant who can aspirate and inject LA as directed. It is important to ensure that NO air is left in the syringe or tubing or needle; this will act as an acoustic barrier to the ultrasound waves and obscure the structures beyond.
Infiltrate the path of the block needle with a 5cm 25 gauge hypodermic. This is best performed with US imaging to ensure accurate infiltration and avoidance of inadvertent nerve / vessel puncture. We use a 10cm 16g Tuohy needle for the actual block. This has the advantage of giving a good image with US and allows some manipulation of the tissues to ensure optimal needle position. After ensuring good alignment between probe and needle, advance the needle towards the axillary artery. The posterior cord is blocked first. Avoid passing too close to the lateral cord by taking a steeper angle of approach initially and once past the lateral cord angle the shaft of the needle so as to pass just deep to the axillary artery. If imaging is difficult several techniques can be helpful -
- Firstly small movements of the needle generate tissue movement and can help localise the tip
- Secondly small injections of LA can clearly identify the tip of the needle
Once the needle position is in the desired position LA can be injected with the aim being to ensure good spread around the nerve. Once adequate LA is placed adjacent to the posterior cord, slowly withdraw the needle until it lies just deep to the lateral cord. Once again a series of small injections of LA can be made with minor adjustments of needle position to ensure good spread around the nerve. Ideally the LA is seen peeling away the connective tissue around the nerve leaving it surrounded in a black rim of LA. A final injection can be made adjacent to the medial cord. If there has been good spread of LA around the artery with the previous injections it may not be necessary. In order to perform this injection the needle must be withdrawn to the subcutaneous plane then redirected aiming to pass anterior to the axillary artery. It is important to penetrate the Pm fascia prior to injection but some care must be taken to avoid puncturing the axillary vein which lies in the path of the advancing needle.
Small injections of LA can help guide the needle advancement.
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