Interscalene plexus blocks are an important part of the peri-operative treatment in shoulder surgery. The nerve stimulation technique uses external landmarks for the definition of the injection site. Patient obesity is, therefore, one causative factor for a reduced success rate of the blockade.
Aim: This study investigated whether there are differences in visibility of the target nerves and in the success rate of the block between patients of normal weight (nw) and obese patients (ow), when portable sonography is used for guidance of the interscalene nerve blockade (ISB).
Methods: We investigated 70 patients routinely scheduled for shoulder surgery (ASA status I-III). The patients were allocated to group nw (body mass index BMI< 25) or ow (BMI > 25). The interscalene part of the brachial plexus was examined using high-frequency portable ultrasound. The blockade was performed under continuous sonographic monitoring. The quality of the ISB was tested post-operatively, and the time required for the procedure was documented.
Results: Identification of nerve structures in the obese patients did require slightly more time than in patients of normal weight, statistically (ow: 5 +/- 1 min versus nw: 4 +/- 2 min, p = 0.02). While in 33 patients (94 %) of group nw the plexus blockade was complete, in group ow 27 (77 %) of the blocks were sufficient. The difference in success, however, was not significant (p = 0.08). Visualisation of nerves was difficult in 3 patients in ow-group.
Conclusion: Portable ultrasound provides efficient depiction of the interscalene plexus structures in obese patients and, when used for guidance of regional blockade, renders similar results as in patients of normal weight.