Ultrasound-Guided Two-Point Transversus Abdominis Plane in Adult Horses: An Experimental Study Assessing Wall Sensitivity

Ultrasound-guided transversus abdominis plane blocks may provide somatic analgesia for equine abdominal procedures, but evidence in adult horses remains limited. This prospective, blinded, randomized, paired study evaluated the feasibility, sensory effects, and motor effects of a two-point transversus abdominis plane block in eight healthy, standing, unsedated mares. Each horse received lidocaine 2% (2 mg/kg in 0.1 mL/kg per injection site) on one side and saline on the contralateral side. Responses to standardized mechanical stimulation were assessed at 21 sensory evaluation points per side for 300 min. The block was completed successfully in all horses without visible discomfort or procedural complications. No desensitization occurred on saline-treated sides. Following lidocaine administration, sensory blockade began at a median of 10 min, peaked at 30 min, and lasted a median of 258 (233–260) minutes. Desensitization was significantly greater at the stifle and intermediate horizontal levels than at the coxal tuberosity level. Transient motor impairment occurred in seven of eight horses and was severe in two. The technique produced multi-metameric desensitization, predominantly in the ventrocaudal flank, but limited dorsal coverage and frequent motor impairment may restrict its clinical application. Further dose optimization and clinical safety and efficacy studies are warranted.