Neuro-anatomical studies in advanced techniques of ultrasound- guided peripheral nerve blocks for increasing quality, efficacy and safety, through objective evaluation
29 May 2017
Antwerp University Hospital (UZA), Auditorium Kinsbergen (route 12) - Wilrijkstraat 10 - 2610 WILRIJK
Prof M. Vercauteren & Prof G. Hans
PhD defence Luc Sermeus - Faculty of Medicine and Health Sciences
During our study period (2009-2016), general guidelines were published in Belgium to improve safety when performing PNB. These guidelines were elaborated by the “Peripheral Nerve Block Working Group” of the BARA (Belgian Association for Regional Anesthesia) in order to give practical information to all anesthetists interested in regional anesthesia (Chapter 2).
Since the aim of our different studies was to improve the efficacy and safety of PNB, we were interested in finding a reproducible, safe technique for nerve blockade, without placing the needle tip sub-epineurally. Avoiding sub-epineural injection was not only important for minimizing nerve lesions, but also for producing similar blocks whose clinical characteristics could be readily compared. Our tangential approach to the nerve led to a study on cadavers aimed at avoiding intra-neural injections. We showed that this approach considerably reduced the sub-epineural positioning of the needle and subsequent intra-neural injection. This tangential needle approach to the nerve was important enough to be added to the safety algorithm for performing PNB (Chapter 3).
We evaluated thermal QST as a suitable method for assessing PNB characteristics on a graded scale – we observed the effects of local anesthetics, with or without adjuvants. For this purpose, we used the technique to compare three long-lasting local anesthetic solutions in interscalene block. We compared onset time, block intensity, duration and recovery times. In the interscalene groove, the roots lie close to each other allowing comparison of block characteristics in the different root territories following one single injection in a peri-plexus approach close to C5. Our results proved thermal QST to be a valid method for graded measurement of PNB efficacy (Chapter 4).
Following validation of the QST method, the effect of low volumes of three different local anesthetics for PNB could be tested. Here, besides comparing the 3 LA, the technique was used to evaluate the spread of local anesthetic to adjacent roots, when injected in a peri-plexus approach close to the root of C5. Low volume injection led to a reduction of block intensity in the adjacent roots at distance from the injection site, demonstrating the importance of volume in block efficacy (Chapter 5).
In the third study using thermal QST evaluation, we studied the modulation of somatic pain transmission by concurrent sympathetic fiber block. We compared and quantified the characteristics of an interscalene block alone and with interscalene block plus stellate ganglion block. In non-fractured shoulders, neither positive nor negative modulation could be demonstrated with PNB. It seems, when compared to studies where the shoulder has been fractured, somatic modulation is linked to an activation of the sympathetic chain prior to the induction of the block (Chapter 6).
The last chapter deals with adjuvants added to local anesthetics and their possible influence on improving PNB. In future studies, the effect of adjuvant substances in a local anesthetic solution, especially dexmetedomedine, might be evaluated with QST. This drug seems to have promising properties for PNB. We reviewed the literature regarding the different adjuvants already used along with possible candidates for the future. Evaluation of these adjuvants with thermal QST might be a useful tool to demonstrate increased intensity and/or duration of PNB. A further important role for this methodology might be the documentation of full functional nerve recovery, since adjuvant drugs are used off-label in this setting. (Chapter 7).