Deltoid, triceps, or both responses improve the success rate of the interscalene catheter surgical block compared with the biceps response.

BACKGROUND: The influence of the muscular response elicited by neurostimulation on the success rate of interscalene block using a catheter (ISC) is unknown. In this investigation, we compared the success rate of ISC placement as indicated by biceps or deltoid, triceps, or both twitches. METHODS: Three hundred (ASA I-II) patients presenting for elective arthroscopic rotator cuff repair were prospectively randomized to assessment by biceps (Group B) or deltoid, triceps, or both twitches (Group DT). All ISCs were placed with the aid of neurostimulation. The tip of the stimulating needle was placed after disappearance of either biceps or deltoid, triceps, or both twitches at 0.3 mA. The catheter was advanced 2-3 cm past the tip of the needle and the block was performed using 40 ml ropivacaine 0.5%. Successful block was defined as sensory block of the supraclavicular nerve and sensory and motor block involving the axillary, radial, median, and musculocutaneous nerves within 30 min. RESULTS: Success rate was 98.6% in Group DT compared with 92.5% in Group B (95% confidence interval 0.01-0.11; P<0.02). Supplemental analgesics during handling of the posterior part of the shoulder capsule were needed in two patients in Group DT and seven patients in Group B. Three patients in Group B had an incomplete radial nerve distribution anaesthesia necessitating general anaesthesia. One patient in Group B had an incomplete posterior block extension of the supraclavicular nerve. No acute or late complications were observed. CONCLUSIONS: Eliciting deltoid, triceps, or both twitches was associated with a higher success rate compared with eliciting biceps twitches during continuous interscalene block.

In vitro exposure of human fibroblasts to local anaesthetics impairs cell growth.

Lidocaine, bupivacaine or ropivacaine are used routinely to manage perioperative pain. Sparse data exist evaluating the effects of local anaesthetics (LA) on fibroblasts, which are involved actively in wound healing. Therefore, we investigated the effects of the three LA to assess the survival, viability and proliferation rate of fibroblasts. Human fibroblasts were exposed to 0·3 mg/ml and 0·6 mg/ml of each LA for 2 days, followed by incubation with normal medium for another 1, 4 or 7 days (group 1). Alternatively, cells were incubated permanently with LA for 3, 6 or 9 days (group 2). Live cell count was assessed using trypan blue staining. Viability was measured by the tetrazolium bromide assay. Proliferation tests were performed with the help of the colorimetric bromodeoxyuridine assay. Production of reactive oxygen species (ROS) was determined, measuring the oxidation of non-fluorescent-2,7'-dichlorofluorescin. Treatment of cells with the three LA showed a concentration-dependent decrease of live cells, mitochondrial activity and proliferation rate. Group arrangement played a significant role for cell count and proliferation, while exposure time influenced viability. Among the analysed LA, bupivacaine showed the most severe cytotoxic effects. Increased production of ROS correlated with decreased viability of fibroblasts in lidocaine- and bupivacaine-exposed cells, but not upon stimulation with ropivacaine. This study shows a concentration-dependent cytotoxic effect of lidocaine, bupivacaine and ropivacaine on fibroblasts in vitro, with more pronounced effects after continuous incubation. A possible mechanism of cell impairment could be triggered by production of ROS upon stimulation with lidocaine and bupivacaine.