Cervical Epidural Pressure Measurement Comparison in the Prone and Sitting Positions

Background: The hanging drop technique is used for identifying the cervical epidural space, using its negative pressure. However, it is doubtful whether the epidural space intrinsically exhibits a negative pressure. We designed this study to test the hypothesis that the cervical epidural pressure (CEP) is significantly higher in the prone position than in the sitting position. To evaluate this hypothesis, we measured and compared 30 CEP values in the prone and sitting positions. Methods: We measured and compared 15 CEPs in the prone group and 15 in the sitting group using a closed pressure measurement system under fluoroscopic guidance. Results: All CEPs in the prone group were consistently positive (median, 10 mmHg; range, 4.8-18.7; mean +/- SD, 10.5 +/- 4.4) in contrast to the sitting group (median, -0.3 mmHg; range, -2.4-7.9; mean +/- SD, 0.5 +/- 2.8). CEPs in the prone group were significantly higher than in the sitting group (P < 0.001). Conclusion: CEP was found to be significantly higher in the prone position than in the sitting position. Furthermore, CEPs were not consistently negative even in the sitting position. These results suggest that the hanging drop technique is inappropriate for identifying the cervical epidural space in either the prone or sitting positions.