Truncal injection brachial plexus block: A Description of a novel injection technique and dose finding study

Brachial plexus (BP) blocks continue to be described with reference to anatomical landmarks (Interscalene and Supraclavicular), even after the introduction of ultrasound which enables us to directly identify the roots, trunks and divisions of the BP. The aim of this study was to describe a novel injection technique targeting trunks of BP and to determine the minimum effective local anaesthetic volume (MELAV) required to produce BP block with this approach.

Twenty-one male patients in the age group 20-40 years, undergoing elective forearm bony procedures received an ultrasound-guided truncal injection BP block. MELAV₅₀ was determined using the Dixon and Mood up-and-down method. Initial volume of local anaesthetic (LA; 50:50 mixture of bupivacaine 0.5% and lignocaine 2% with 5 μg/ml epinephrine) injected was 6 ml in each trunk, which was varied by 1 ml/trunk for each consecutive patient according to the response of the previous patient. The MELAV₅₀, MELAV₉₅ and MELAV₉₉ were calculated using Probit transformation and logistic regression.

Out of the 21 patients, 13 patients had a successful block. The MELAV₅₀, MELAV₉₅ and MELAV₉₉ were 7.41, 10.47 and 12 ml, respectively. Eight patients in whom block failed had sparing in the ulnar and median nerve territories.

Trunks of the brachial plexus can be identified and targeted for the injection of local anaesthetics. The MELAV₅₀ and MELAV₉₅ required for ultrasound-guided truncal injection brachial plexus block were 7.4 and 10.4 ml, respectively.