The specific indications are slightly different for each block but are to provide analgesia or anaesthesia of the upper limb. In skilled hands these blocks can provide an alternative to general anaesthesia for upper limb surgery. Introduction of catheters instead of a single-shot injection can allow for a more prolonged infusion and analgesia in significant surgery.
Blocks can be done through a variety of techniques, with ultrasound guided blocks becoming the most common approach due to benefits in terms of speed of onset and better quality block (level 1b evidence). There are also theoretical advantages in safety from being able to visualise key structures, but there isn’t yet strong evidence of this. Landmark techniques with nerve stimulation have also been used. The addition of nerve stimulation to the ultrasound guided technique is not thought to add any additional benefit.
The general principles of regional anaesthesia all apply, with certain additional components for some blocks.
An understanding of the anatomy of the brachial plexus and its relationship with surrounding tissues is essential for safe and effective regional anaesthesia.
The ISB blocks the superior roots/trunks of the brachial plexus close to their origin. As such, it is the block of choice to capture the nerves that leave the brachial plexus early in its course e.g. suprascapular nerve. This makes it the block of choice for shoulder surgery as it is more likely to catch all the required nerves. However, the inferior trunk is less well blocked by this block, and so it is less effective for surgery more distally on the limb - ulnar sparing is common (C8,T1)
Contraindications (in addition to general):
Contralateral phrenic nerve impairment e.g. contralateral ISB
Severe respiratory disease
The ISB has a very high rate of blockade of the ipsilateral phrenic nerve - nearly 100% if large volumes (>20ml) are used. As such, the impact of this on the patient must be taken into account, and it means that bilateral ISBs are contraindicated. However, careful, low volume ISB to allow avoidance of GA may be better in patients with severe lung disease, and so is a balance.
The equipment is similar to most regional anesthetic blocks:
Linear probe of US machine
50mm 22g block needle
20ml local anaesthetic
The volume of local anaesthetic will vary depending on the goal of the block (anaesthesia vs analgesia) and the technical ease. Very low volumes (if carefully placed) can be used to excellent effect and have a reduced chance of resulting in phrenic nerve blockade.
Positioning The patient is commonly positioned semi recumbent with the head turned away from the side of the block. The use of a head ring rather than a pillow may make the block easier, as the approach angle can be quite posterior and may be impeded by a pillow. As with all blocks the positioning of US screen should be optimal.
Performance The block starts with ultrasound imaging of the neck and the important structures identified. This can be identification of the trachea centrally, followed by lateral movement of the probe with identification of the carotid artery and internal jugular vein. Continuing to move the probe laterally should allow identification of the brachial plexus between the anterior and middle scalene muscles. The nerves will often appear as a ‘traffic light’ appearance. The usual level is about 2-3cm above the clavicle, or around the level of the cricoid cartilage. An in-plane approach, usually from lateral to medial is then used , keeping the needle tip in view at all times. The plexus is surrounded by a fascial sheath and this is often punctured (with a tactile ‘pop’ sensation). Injection of local anaesthetic can then be commenced, ensuring negative aspiration and low resistance to injection, as well as visualising the spread of local anaesthetic. If the fascial sheath is punctured then it is important to ensure that the needle tip is not intraneural, and so visualising the LA spread is a key step.
In cases of difficulty identifying the correct space, a recommended approach is to identify the brachial plexus at the supraclavicular location. It can then be tracked up the neck to the interscalene position.
Specific to this block include:
Phrenic nerve paralysis
Horner’s syndrome (stellate ganglion blockade)
Hoarseness (recurrent laryngeal nerve blockade)
Total spinal (accidental dural puncture of nerve root)