Pharmacological optimisation of ultrasound guided axillary brachial plexus block
Malladihalli Ranganath, Anil Kumar
University College Cork
Regional anaesthesia provide significant advantages in the perioperative care of the patient undergoing surgery, including improved postoperative analgesia, a reduction in adverse events, shorter recovery time, and expedited hospital discharge when compared to general anaesthesia. Safe performance of brachial plexus block warrants consideration of several factors, such as ⅰ. an understanding of relevant anatomy, ⅱ. effectiveness and potential adverse effects of brachial plexus approach for the intended site of surgery, ⅲ. methods of nerve localisation, and ⅳ. selection of pharmacological agents to enhance the quality of block. The choice of local anaesthetics in peripheral nerve block is dependent upon variables such as the desired onset and duration of motor and sensory nerve block, the expected duration of surgery and the requirement for post-surgical regional analgesia. Other factors that can modify the effectiveness of peripheral nerve blockade are the volume and concentration (and dose) of local anaesthetic injected and addition of adjuvants. The objective of this thesis is to evaluate the effect of local anaesthetic volumes, volume/concentration ratio (dose) and addition of adjuvants with a aim to optimise the clinical characteristics of the ultrasound-guided axillary brachial plexus block (USgABPB) for upper limb trauma surgeries. In the first study, we investigated the effect of two volumes (10 vs 30 mL) of lidocaine with epinephrine 1:200 000 on USgABPB. In the second study, we examined whether two different volumes and concentrations of a fixed dose of lidocaine with epinephrine by dilution influenced the characteristics of USgABPB. In the third study, we evaluated the effects of adding clonidine 1 µg/kg to 20 mL of lidocaine 2% with epinephrine 1:200 000 on the onset and duration of sensory and motor block following USgABPB. Our results added the following to the optimisation of the characteristics of the ultrasound guided axillary brachial plexus block. ⅰ. Higher volume (30mL compared to 10 mL) of lidocaine 2% with epinephrine resulted in longer overall duration of sensory and motor block and a shorter sensory and motor block onset time. ⅱ. Dilution of a fixed dose of lidocaine with epinephrine administered as 40 mL of lidocaine 1% (when compared to 20 mL of lidocaine 2%) with epinephrine resulted in faster overall onset of block. ⅲ. Admixture of clonidine 1µg/kg to lidocaine with epinephrine for ultrasound guided axillary brachial plexus block resulted in faster onset and longer duration of both sensory and motor block with extended duration of postoperative analgesia. On the contrary, the duration of lower volume group was similar when compared with the duration of block from our other studies (20 ml of lidocaine 2% with epinephrine 1:200,000). It seems that the relation between volume (dose) and duration of the block is not linear and any increase beyond the threshold volume, improvements in the block characteristics becomes less significant. Our findings indicate an optimal approach may comprise low (dose) volume (10 ml of Lidocaine 2% with epinephrine 1:200, 000) with adjuvant (clonidine 1µg/kg) to enhance the characteristics of USgABPB for patients undergoing upper extremity trauma surgeries. Our research findings also indicates that, dilution of this admixture to a greater volume can be utilised to improve the onset of the brachial plexus block and operator performance characteristics. In addition to this following original body of work a review article was published on Ultrasound guided axillary brachial plexus block.
Axillary brachial plexus block , Local anaesthetics , Clonidine
Malladihalli Ranganath, A. K. 2021. Pharmacological optimisation of ultrasound guided axillary brachial plexus block. MD Thesis, University College Cork.