Evaluation of the surface thermal response of peripheral nerve blocks in dogs undergoing trauma surgery

Alejandro Casas Alvarado^1,2Daniel Mota-Rojas^2*PATRICIA MORA-MEDINA³Julio Martinez-Burnes⁴Ismael Hernández Avalos³Ana Zapata¹C. Ivan Serra- Aguado¹Rocío Fernández-Parra^1*

• ¹Universidad Catolica de Valencia San Vicente Martir, Godella, Spain
• ²Universidad Autonoma Metropolitana, Mexico City, Mexico
• ³Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
• ⁴Universidad Autonoma de Tamaulipas, Ciudad Victoria, Mexico

Locoregional anesthesia with local anesthetics has been proposed as a highly effective method for perioperative acute pain control because it prevents the generation of noxious impulses. However, a limitation of these techniques is the reliability of the block's effectiveness. Infrared thermography (IRT) has been suggested as a non-invasive tool to assess the success of peripheral nerve blocks by detecting temperature changes related to vasodilation. This study aimed to evaluate the effect of peripheral nerve blocks on the superficial thermal response of limbs in dogs undergoing trauma surgery. Twenty-six dogs of various breeds, classified as ASA 1 or 2, undergoing thoracic or pelvic limb, and abdominal surgery, were divided into two groups based on the analgesic technique used. In the experimental group (PNB, n= 20),composed of animals undergoing trauma or orthopedic surgery, bupivacaine was infiltrated into the brachial plexus or the saphenous and sciatic nerves. The control group (n= 6) underwent general anesthesia and surgery, and received conventional injectable analgesia. The variables assessed included maximum (Tmax.), mean (Tmean), and minimum (Tmin.) temperatures of the axillary region, groin, and lateral femoral area, as well as rectal temperature (T°C). Measurements were taken at baseline (TBasal), and 5 (T5min.), 10 (T10min.), and 15 minutes (T15min.) after treatment. Tmax., Tmean, and Tmin. were significantly higher in the PNB group (by 2–3 °C) compared to the Control group (P=0.01). In the PNB group, superficial temperatures decreased by approximately 1 °C from baseline (P=0.001), whereas the Control group exhibited a greater decrease of about 3 °C at the same time points (P=0.001). Rectal temperature was 2 °C higher in the PNB group compared to the Control (P=0.01), though only the Control group showed a progressive decrease over time (P=0.05). No significant correlation was found between surface and rectal temperatures. In conclusion, peripheral nerve blocks with bupivacaine induce localized vasodilation, resulting in increased superficial heat radiation. This thermal response may serve as an indirect indicator complementary of nerve block effectiveness, supporting the use of IRT as a clinical tool to evaluate peripheral nerve block success in dogs. Further studies are recommended to confirm and validate its clinical application.t