Fig. 2

(a) The erector spinae muscle (ESM) was visualized superficial to the hyperechoic shadow of TP4 and TP5 and beneath the trapezius muscle (TM) and rhomboideus major (Rm) on the short axial view of US scan. (b) An epidural block cannula needle was inserted through the above-mentioned three muscles and advanced to the fascial plane between the TP and ESM using in-plane technique under the real-time guidance of US. Normal saline was administrated to dilate the fascia plane in order to confirm the correct position of the catheter in the targeted fascial space. (c) A epidural catheter was then inserted to the erector spinae plane through the cannula until the tip extended 5 cm beyond the tip of cannula according to the calibration. TP = transverse process; LA = local anesthetic