• Thorsten Steinfeldt, Thomas Wiesmann, Wilhelm Nimphius, Valér Cornelius, Daniel Eismann, Thomas Kratz, Admir Hadzic, Hinnerk Wulf, and Tilmann Werner.
• From the *Department of Anaesthesiology and Intensive Care Therapy and †Institute of Pathology, Philipps University Marburg, Marburg, Germany; ‡St Luke's and Roosevelt Hospital Center, University Hospital of Columbia University, College of Physicians and Surgeons, New York City, NY; and §Department of Anaesthesiology, University of Regensburg, Regensburg, Germany.
• Reg Anesth Pain Med. 2014 Nov 1; 39 (6): 513-9.

Background And ObjectivesPerineural hematoma may occur during performance of peripheral nerve blocks. The aim of this study was to test the hypothesis that an iatrogenic hematoma in the immediate vicinity of a peripheral nerve may cause histologic evidence of nerve injury.MethodsFifty milliliters of autologous blood was injected adjacent to the right sciatic nerve in 20 anesthetized female pigs. In order to discern between blood-related volume and immune effects, 50 mL of albumin was injected at the same location in an additional 22 pigs. Either blood or albumin was injected in random order. The left sciatic nerve served as a negative control in all animals, that is, either no needle placement or needle placement without injection. After 48 hours, the nerves were resected. The grade of nerve injury was scored from 0 (no injury) to 3 (severe injury) by histologic analysis of myelin tissue and inflammatory cells.ResultsEighty-two nerve specimens were examined. Injury scores were significantly (P < 0.01) higher in the blood injection (n = 20; median [interquartile range] 2 [2-2]) and albumin injection (n = 22, 1 [1-2]) conditions compared with the no needle placement (n = 22, 0 [0-1]) and "dry needle placement" (n = 20, 1 [0-1]) conditions. Widespread inflammatory changes were seen in the blood injection group, in which 15% of nerve specimens showed damage to myelin.ConclusionsOur data suggest that hematoma adjacent to nerve tissue may result in structural nerve injury and inflammatory changes.

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