Limited spread may only block sympathetic fibers in the lower thoracic dermatomes,but rostral spread can easily extend to include the cardiac accelerator fibers (T1-T4).

• 有限的扩散可能只阻滞低于胸皮支交感神经纤维。但头端扩散很容易到达包括心脏加速纤维(T1-T4)的水平。