The relation between skin temperature increase and sensory block height in spinal anaesthesia using infrared thermography

Background and objectives To evaluate the feasibility of determining the extent of sympathetic blockade by skin temperature measurement with infrared thermography and relate the cranial extent of the temperature increase to that of the sensory block after spinal anaesthesia. Methods Before and 5, 10 and 20 min after the administration of spinal anaesthesia, skin temperatures were measured with infrared thermography at the dermatomes T2-L3, in 12 male patients scheduled for lower limb surgery. The most cephalad dermatome at which sensory blockade occurred was related to the dermatome at which the largest temperature jump (corrected for baseline temperature) occurred. Results The baseline temperatures showed considerable variation across the dermatomes, being lower below T12 than at the thoracic dermatomes. The mean difference between the level of the cephalad skin temperature elevation front (mean 1.03 degrees C, SD 0.8 degrees C) and cranial sensory block height was 0.10 dermatomes (SD 1.16), correlation coefficient (0.88, P < 0.001). Conclusion The varying baseline temperatures across the trunk, the limited sympathetic block-induced increase in skin temperature at the trunk and the difficult control of influences from the surroundings partly obscured the extent of the skin temperature increase and its correlation to sensory block height. These factors have to be controlled to improve the use of infrared cameras as an easy bedside tool for predicting the cranial extent of (sympathetic blockade during) spinal anaesthesia.