Skin temperature measured by infrared thermography after ultrasound-guided blockade of the sciatic nerve.

BACKGROUND: In the present study, we assessed the relationship between subgluteal sciatic nerve blocking and skin temperature by infrared thermography in the lower extremity. We hypothesized that blocking the sciatic nerve will lead to an increase in temperature, and that this will correlate with existing sensory block tests. METHODS: We studied 18 healthy individuals undergoing orthopaedic surgery of the foot under ultrasound-guided subgluteal blockade of the sciatic nerve with 30 ml ropivacaine 7.5 mg/ml. Skin temperature was measured on the toes, the dorsal and plantar side of the foot, the malleoli, and the lateral side of the lower leg, just before sciatic nerve blockade and at 10-min intervals thereafter. RESULTS: Baseline skin temperatures showed a significant distal-to-proximal gradient. After sciatic block, temperatures on the blocked side increased significantly in the toes and foot. When comparing pinprick to skin temperature in a receiver operating curve, there was an AUC of 85.9% (95% confidence interval = 83.7-88.2%, P < 0.001). The medial malleolus (not being innervated by the sciatic nerve) showed no significant difference to the lateral. CONCLUSIONS: After sciatic nerve block, temperatures of the foot increased significantly. There was a good correlation between pinprick testing and infrared temperature measurement. This makes infrared skin temperature measuring a good test in determining block success when sensory testing is impossible.