Truncal Cutaneous Temperature Changes and Anthropometry in Spinal Anaesthesia - An Observational Study

Objective: The predictability of onset of sympathetic block in spinal anaesthesia is poor. The role of the structures around the dural sac, in determining the spread of local anaesthetic in the subarachnoid space, is evaluated by studying the effect of the peri-spinal frustum volume on the change in cutaneous temperature and perception of cold sensation. Methods: In patients planned for spinal anaesthesia with 2.5 mL of 0.5% heavy bupivacaine intrathecally, volume of frustum between T8 and L3 was calculated using abdominal circumference at T8 and L3 and the distance between these spinous processes. The speed of onset at T8 level was measured as a change of 0.5 °C in cutaneous temperature probe and loss of cold sensation. Results: Of the 40 patients analysed, 22 patients had increase in cutaneous temperature while 14 had a decrease and 4 had no change. The onset time of loss of cold sensation in seconds was 327.68±169.65 (99% CI:234.51–420.85) and 232.64±75.47 (99% CI 180.69-284.60) in patients with increase and decrease of the skin probe respectively. The square of correlation coefficient (R2) of frustum volume was 0.55 (99% CI -0.15-0.88, p=<0.01) in the group with decrease in skin temperature and 0.03 (99% CI -0.51-0.55, p=0.46) in group with increase in skin temperature. Conclusion: The effect of peri-spinal volume on the speed of onset of block at T8 level is variable and somatic block correlates only in patients who had a decrease in skin temperature. Keywords: Anthropometry, skin temperature, spinal anaesthesia, sympathetic nerve block