Comparison of Rostral Spread of Lumbosacral Epidural Volume Calculated by Body Weight or Length of the Vertebral Column in Dogs

Abstract

This thesis evaluated in dogs the rostral spread of a lumbosacral epidural volume calculated by body weight or by length of the vertebral column. In phase I of this study, cadaver dogs (4.6–52 kg; 39-99 cm in length) were paired and matched within < 10% for body weight, length of the vertebral column from the sacrococcygeal space to the occipital crest, and body condition score. Within each pair, one dog was randomly allocated to receive an epidural volume by weight and the other dog by length of the vertebral column, using a mixture of dye and contrast medium. Within 5 minutes, the rostral spread of the contrast medium was assessed by computerized tomography (CT), and within one-hour the rostral spread of the dye was assessed by anatomical dissection. In phase II, research Beagle dogs (7.5–10.2 kg; 46–56 cm in length) were used in a randomized crossover design to receive a 1:1 epidural volume of contrast medium and bupivacaine 0.5% based on body weight or length under isoflurane anesthesia, with at least 5 days between doses, and assessed for rostral spread of the contrast medium by CT within 5 minutes of injection. Cardiorespiratory function assessments started immediately after injection, and sensory and motor block from the bupivacaine at 30 minutes post injection and while dogs were conscious. Phase I and phase II demonstrated a larger volume of injectate using length than for body weight. In cadaver dogs of all sizes this difference was not significant and resulted in a similar number of vertebrae reached by the indicator (dye or contrast medium) between the two methods. In live dogs and their small size, the larger volume was significantly different and resulted in a significantly greater number of vertebrae reached by the indicators. In phase I, the number of vertebrae reached by dye was significantly greater than for contrast medium. In phase II, the resultant concentration of bupivacaine (0.25%) resulted in sensory and motor blockade of short duration. Cardiorespiratory function was within normal limits and similar for both dosing methods.