Evaluation of drug distribution, sensory and motor blockade regions in canine coccygeal epidural anesthesia

The distribution of anesthetic solutions, sensory blockade (SB), and motor blockade (MB) following coccygeal epidural anesthesia in dogs were evaluated. Six dogs received three different doses (0.1, 0.2, and 0.3 mL/kg) of a mixture containing equal volumes of ropivacaine and iohexol, administered via the first and second coccygeal intervertebral spaces. Drug spread was assessed using computed tomography, whereas SB and MB were evaluated using standardized scoring methods. The cranial extent of contrast medium spread reached L5, the L4-5 interspace, and L4 in the 0.1, 0.2, and 0.3 mL/kg groups, respectively, with no significant differences among groups. SB extended from the tail to the cranial femoral region in the 0.1 mL/kg group, to the caudal femoral-pubic region in the 0.2 mL/kg group, and to the cranial femoral-pubic region in the 0.3 mL/kg group. The 0.2 and 0.3 mL/kg groups showed significantly higher SB than the 0.1 mL/kg group did (P=0.039 and P=0.019, respectively). MB extended to the femoral nerve territory in dogs receiving 0.2 or 0.3 mL/kg, while dogs in the 0.1 mL/kg group maintained motor function. The 0.3 mL/kg group showed significantly higher MB than the 0.1 mL/kg group did (P=0.019). Despite the increased volume at 0.3 mL/kg, greater leakage through the neural foramina resulted in a net epidural dosage comparable to 0.2 mL/kg. These findings indicate that coccygeal anesthesia at 0.1 mL/kg provides SB from the tail to the perineal region while maintaining hindlimb motor function in dogs.