Systemic ropivacaine diminishes pain sensitization processes: a randomized, double-blinded, placebo-controlled, crossover study in healthy volunteers.

INTRODUCTION: Ropivacaine is a local anesthetic widely used for regional anesthesia. One of its advantages is low toxicity at plasma concentrations reached systemically during continuous peripheral or central nervous block. The objective of this study was to test the effect of systemic ropivacaine on pain, hyperalgesia, dynamic allodynia, and flare response. METHODS: This randomized, double-blinded, placebo-controlled, crossover study was carried out in at the Clinical Trials Centre, University of Zurich, Switzerland. Twenty healthy male volunteers were included in the study. Exclusion criteria were contraindications or hypersensitivity to local anesthetics, vulnerable subjects (intellectually or mental impaired), drug, alcohol or nicotine abuse, known peripheral neuropathies, diabetes mellitus and/or congestive heart disease. Ropivacaine and saline were infused intravenously during a subcutaneous electrical stimulation. The stimulation software adjusted the stimulus strength according to the rating on a numeric rating scale (NRS; 0-10) maintaining a NRS of 5. Areas of punctate hyperalgesia, dynamic allodynia, and flare response were measured before and after the infusion. RESULTS: The area of hyperalgesia increased significantly with saline (303 ± 380%, P < 0.05) and ropivacaine (186 ± 137%, P < 0.05). The area of allodynia (253 ± 299%, P < 0.05) and flare response (112 ± 24%, P < 0.05) increased only during the placebo infusion. CONCLUSION: The results of this study imply that systemic ropivacaine may diminish pain sensitization processes.

[Pharmacological treatment of chronic pain]. / Medikamentöse Schmerztherapie.

The pharmacological treatment of chronic pain differs from acute pain management. In chronic non-cancer pain patients pharmacological treatment is only one element of an interdisciplinary approach. Not pain reduction only but gain in physical and social functioning is mandatory for continuation of therapy. The developpement of a strategy is the most important and difficult step toward an individual and sustained pharmacological pain treatment. Simple practical guidelines can help to find an individual therapeutic straight. Outcome parameters have to be determined. Check-ups for discontinuation of the therapy have to be done periodically. Exact documentation of effect and side effects prevents ungrateful and potential dangerous treatments. The WHO ladder remains the cornerstone of pharmacological pain treatment. Further analgesics as antidepressants and anticonvulsants are important in treatment of neuropathic or mixed pain states. Special considerations have to be done in opioid treatment of non-cancer pain regarding the lack of evidence in long term outcome and possible side effects and risks.

Minimal local anesthetic volume for peripheral nerve block: a new ultrasound-guided, nerve dimension-based method.

BACKGROUND AND OBJECTIVES: Nerve blocks using local anesthetics are widely used. High volumes are usually injected, which may predispose patients to associated adverse events. Introduction of ultrasound guidance facilitates the reduction of volume, but the minimal effective volume is unknown. In this study, we estimated the 50% effective dose (ED50) and 95% effective dose (ED95) volume of 1% mepivacaine relative to the cross-sectional area of the nerve for an adequate sensory block. METHODS: To reduce the number of healthy volunteers, we used a volume reduction protocol using the up-and-down procedure according to the Dixon average method. The ulnar nerve was scanned at the proximal forearm, and the cross-sectional area was measured by ultrasound. In the first volunteer, a volume of 0.4 mL/mm of nerve cross-sectional area was injected under ultrasound guidance in close proximity to and around the nerve using a multiple injection technique. The volume in the next volunteer was reduced by 0.04 mL/mm in case of complete blockade and augmented by the same amount in case of incomplete sensory blockade within 20 mins. After 3 up-and-down cycles, ED50 and ED95 were estimated. Volunteers and physicians performing the block were blinded to the volume used. RESULTS: A total 17 of volunteers were investigated. The ED50 volume was 0.08 mL/mm (SD, 0.01 mL/mm), and the ED95 volume was 0.11 mL/mm (SD, 0.03 mL/mm). The mean cross-sectional area of the nerves was 6.2 mm (1.0 mm). CONCLUSIONS: Based on the ultrasound measured cross-sectional area and using ultrasound guidance, a mean volume of 0.7 mL represents the ED95 dose of 1% mepivacaine to block the ulnar nerve at the proximal forearm.