In Beagle cadavers, the volume of injected local anesthetic solution significantly affects cranial to caudal spread within the TAP during ultrasound-guided TAP blocks. The volume of local anesthetic injected could potentially be used to augment the spread of analgesic coverage for a given surgical procedure in dogs.
The purpose of this study was to evaluate the effectiveness of a novel fluorocarbon-based sevoflurane emulsion in dogs previously shown to produce short-term rodent anesthesia. On the basis of an unexpected allergic-type clinical reaction, we also tested the hypothesis that this type of formulation causes histamine release and complement activation. Physiological parameters, plasma histamine levels (radioimmunoassay), and complement activation (enzyme immunoassay) were quantified in response to emulsion components, including F13M5 (the emulsion’s fluorocarbon-based polymer) and methoxy poly(ethylene glycol) 5000 (the polymer’s hydrophilic block). Although the emulsion produced general anesthesia in dogs, they also experienced hypotension and clinical signs suggestive of an allergic-like response (i.e., vasodilation, urticaria, and pruritus upon recovery). Emulsions lacking sevoflurane failed to induce anesthesia but did elicit the allergic response. Plasma histamine levels were significantly increased following injection of micellar solutions of F13M5. Direct complement activation by the emulsion or its components was weak or absent. An allergic response leading to histamine release, likely initiated by the F13M5 component via an immunoglobulin pathway, is associated with an intravenous fluorocarbon-based emulsion of sevoflurane. Subsequently, its usefulness in medicine in its present formulation is limited.
The transversus abdominis plane (TAP) block is an innovative regional anesthetic technique using local anesthetic that is gaining popularity in the analgesic management of human patients undergoing abdominal surgery. Needle placement in the TAP block is within the facial plane between the internal oblique and transversus abdominis muscles and involves the abdominal and thoracic nerves. Successful blockade generally involves spinal nerves T10-L1 and may induce sensory blockade as far cranially as T7, thus producing analgesia for abdominal surgery. Human studies suggest that this regional anesthetic technique may provide postoperative analgesia of the abdominal wall for up to 48 hr. Because of the extent and duration of sensory blockade, this novel technique with bupivacaine was used on a Canadian lynx (Lynx canadensis), possibly providing 8-10 hr ofintra- and postoperative analgesia concurrent to exploratory laparotomy for removal of a gastric foreign body.
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