Fluoroscope guided epidural needle insertioin in midthoracic region: clinical evaluation of Nagaro's method

Abstract

Background: In the midthoracic region, a fluroscope guided epidural block has been proposed by using a pedicle as a landmark to show the height of the interlaminar space (Nagaro's method). However, clinical implication of this method was not fully evaluated. We studied the clinical usefulness of a fluoroscope guided thoracic epidural block in the midthoracic region.

Methods: Twenty four patients were scheduled to receive an epidural block at the T6-7 intervertebral space. The patients were placed in the prone position. The needle entry point was located at the junction between midline of the pedicle paralleled to the midline of the T7 vertebral body (VB) and the lower border of T7 VB on anteroposterior view of the fluoroscope. The needle touched and walked up the lamina, and the interlaminar space (ILS) was sought near the midline of the VB at the height of the pedicle.

Results: The authors could not insert an epidural needle at T6-7 ILS in two patients and it was instead inserted at T5-6 ILS. However, other patients showed easy insertion at T6-7 ILS. The mean inward and upward angulations were 25° and 55° respectively. The mean actual depth and calculated depth from skin to thoracic epidural space were 5.1 cm and 6.1 cm respectively. Significant correlation between actual needle depth and body weight, podendal index (kg/m) or calculated needle depth was noted.

Conclusions: The fluorposcope guided epidural block by Nagaro's method was useful in the midthoracic region. However, further study for the caudal shift of needle entry point may be needed.

Keywords: Analgesia; Epidural; Fluoroscopy; Thoracic vertebrae.

Fig. 1

This figure shows the interlaminar space, pedicle and vertebral body on AP radiograph. The needle entry point is the junction between the midline of the pedicle and the lower border of vertebral body. P: pedicle, VB: vertebral body, ML: midline, IE: inferior endplate of vertebral body, NEP:needle entry point.

Fig. 2

The figure shows the inward angulation, which represents the angle of the needle to the line of the spinous process on AP view. IA: inward angulation.

Fig. 3

The figure shows the upward angulation, which represents the angle of the needle to the line made by the posterior border of the vertebral body (white line) on lateral view. UA: upward angulation.

Fig. 4

A schematic representation that depicts the projection of a thoracic vertebra (T7) and shows the height of the interlaminar space and epidural needle tip relative to the pedicle and vertebral body. This figure is referred to in Nagaro's study, but ILS cannot be determined on AP view in this study. P: pedicle, VB: vertebral body, ILS: interlaminar space, EN: epidural needle, a: length of pedicle, b: distance from the lower border of the pedicle to the interlaminar space, c: length of vertebral body, d: distance from the lower border of vertebral body to the interlaminar space, e: distance from the lower border of the pedicle to the epidural needle tip, f: distance from the lower border of vertebral body to epidural needle tip.

Fig. 5

(A) The midthoracic computed tomography film (transverse plane). B: The distance from the epidural space to skin at the T6-7. (B) Principle of Pythagorean triangle trigonometry. Estimated depth = B / cos (IA)° × cos (90 - UA)°; B = Distance from the epidural space to skin at the T6-7 (CT transverse plane). IA: Inward anglulation (sagittal plane), UA: upward anglulation (axial plane), EN: epidural needle with paramedian approach.

Fig. 6

The figure shows the location of the epidural needle tips (hollow circle and solid circle) with fluoroscope guided epidural block. The hollow square refers to the ipsilateral side of the needle entry point, but the solid square is the contralateral side. Most needle tips are located at the space A and B. A: space between T6 lower border and upper border of the T7 pedicle, B: space between upper border and horizontal midline of the T7 pedicle, C: space between horizontal midline and lower border of the T7 pedicle, ML: midline, P: pedicle.