Thermography as an early predictive measurement for evaluating epidural and femoral-sciatic block success in dogs.

OBJECTIVE: To evaluate skin temperature increase as an early predictive measure for evaluating epidural and femoral-sciatic block success in dogs. STUDY DESIGN: Prospective clinical trial. ANIMALS: A total of 29 dogs undergoing orthopaedic surgery on one hindlimb. METHODS: Dogs were anaesthetized and placed into lateral recumbency with the affected limb uppermost and the coat was clipped. Baseline infrared thermographic images (T0) of the affected limb, of the paw pad of the affected leg and of the ipsilateral paw pad were taken. Subsequently, dogs were administered either an epidural (EPI; n=11) or a femoral-sciatic block (FS; n=18) using bupivacaine 1 mg kg-1. Then, 2 minutes after placement of the block, thermographic images were obtained every 3 minutes for a total of four measurements (T1-T4) and surgery was commenced. Rescue analgesia consisting of fentanyl 1 µg kg-1 was administered if needed. A regional block was considered successful if the dose of fentanyl administered was less than the lower 95% confidence interval of the geometric mean of the total fentanyl used in each group. A ≥ 1 °C increase of skin temperature was considered as the minimum increase required for detection of a successful block. RESULTS: A total of 12 out of 18 blocks in the FS and eight of 11 in the EPI group were considered successful based on fentanyl consumption. Out of these, only four of 12 in the FS and one of eight in the EPI group developed an increase in temperature of ≥ 1 °C. Contrarily, four of six of the nonsuccessful cases in the FS and three of three in the EPI group developed an increase in temperature of ≥ 1 °C. CONCLUSIONS AND CLINICAL RELEVANCE: Contrary to reports in humans, thermography did not indicate regional block success prior to surgery in dogs. However further studies under more controlled conditions are needed to determine whether thermography can be used to indicate failure of regional blockade.