A profound prolongation of UNB of ∼60% was detected with perineural dexmedetomidine when added to 0.75% ropivacaine. The systemic administration of 20 µg dexmedetomidine resulted in a prolongation of ∼10% during UNB with 0.75% ropivacaine. Eudra-CT No.: 2012-000030-19.

Although the spread of LA was reproducible, the anesthetic effect was unpredictable, even with a standardized ultrasound-guided technique in volunteers. While it can be assumed that approximately 4 vertebral levels are covered by 20 ml LA, the somatic distribution of the thoracic paravertebral blockade remains unpredictable. In a significant percentage, the LA distributes into the epidural space, prevertebral, or to the contralateral side.

This is the first dedicated evaluation of dislocation rates of peripheral nerve catheters (PNCs) via US investigation. Both movement and time are considerable factors for perineural catheter displacement. US is useful for the performance of PNCs and for the continuous detection of the spread of fluid relative to the nerve and adjacent anatomical structures. Translational research is required to confirm the study results in the clinical practice.

Background: The efficacy of dexamethasone in extending the duration of local anaesthetic block is uncertain. In a randomised controlled triple blind crossover study in volunteers, we tested the hypothesis that neither i.v. nor perineurally administered dexamethasone prolongs the sensory block achieved with ropivacaine. Methods: Ultrasound-guided ulnar nerve blocks (ropivacaine 0.75% wt/vol, 3 ml, with saline 1 ml with or without dexamethasone 4 mg) were performed on three occasions in 24 male volunteers along with an i.v. injection of saline 1 ml with or without dexamethasone 4 mg. The combinations of saline and dexamethasone were as follows: control group, perineural and i.v. saline; perineural group, perineural dexamethasone and i.v. saline; i.v. group, perineural saline and i.v. dexamethasone. Sensory block was measured using a VAS in response to pinprick testing. The duration of sensory block was the primary outcome and time to onset of sensory block the secondary outcome. Results: All 24 subjects completed the trial. The median [inter-quartile range (IQR)] duration of sensory block was 6.87 (5.85e7.62) h in the control group, 7.37 (5.78e7.93) h in the perineural group and 7.37 (6.10e7.97) h in the i.v. group (P¼0.61). There was also no significant difference in block onset time between the three groups. Conclusion: Dexamethasone 4 mg has no clinically relevant effect on the duration of sensory block provided by ropivacaine applied to the ulnar nerve.

Dexmedetomidine mixed with ropivacaine produces a dose-dependent prolongation of sensory block and clinically relevant dose-dependent sedation. Dexmedetomidine 100 μg may represent a balance between efficacy and sedation.