Background and objectives: High-resolution ultrasound imaging (HRUI) allows real-time visualization of peripheral nerves, needle insertion, and the spread of local-anesthetic (LA) solution. We evaluated the feasibility of performing a high interscalene brachial-plexus block for carotid endarterectomy by means of HRUI, thereby limiting the amount of LA to the dose required to sufficiently surround the relevant nerve structures.
Methods: The interscalene brachial plexus was localized in the interscalene groove at its most cephalad point in 14 patients undergoing carotid endarterectomy by use of an ultrasound device with a 17.5 MHz transducer. Up to 20 mL of ropivacaine 0.5% was injected.
Results: In all patients, HRUI allowed clear delineation of the upper part of the interscalene brachial plexus at the level of the 4th cervical vertebra appearing as 1 hypoechoic, roundish, hypodense node located in a distance of 1.5 +/- 0.3 cm to the skin, 1.5 +/- 0.2 cm lateral to the common carotid artery, and 0.6 +/- 0.2 cm from the transverse process of the spine. Likewise HRUI allowed a clear delineation of minor blood vessels and adjacent anatomic structures, as well as accurate placement of the needle close to the nerves. Real-time observation of LA spread during injection was possible, even in increments of less than 1 mL.
Conclusions: High-resolution ultrasonic imaging allows clear depiction of the target tissues and facilitates accurate needle placement during high interscalene brachial-plexus blocks. This technique may minimize the risk of direct puncture-related complications, as well as accidental intravascular injection of LA. The observation of LA spread in all patients, even in small increments of less than 1 mL might enhance safety by limiting the injected LA to the actual demand. Well-placed LA spread could potentially avoid central nervous toxicity caused by intravascular injection or resorption of inadequately high dosages, in particular in nerve blocks of the highly vascularized neck region.