Comparison of thoracic epidural pressure in the sitting and lateral decubitus positions

Background: The hanging drop technique identifies the epidural space using the negative pressure of this space. Although the hanging drop technique is popular at the thoracic level, there is still controversy on the negative epidural pressure at this level. The authors hypothesized that the epidural pressure is more consistently negative in the sitting position than in the lateral decubitus position at the thoracic level. Methods: This study compared the epidural pressures of 28 awake patients in the sitting (sitting group, n = 14) or lateral decubitus (lateral group, n = 14) position. The T5-T6 epidural pressure was measured using a closed pressure measurement system connected to a Tuohy needle. Results: All of the thoracic epidural pressures in the sitting group were negative (median, -5 mmHg; range, -18 to -1; mean, -7.2; SD, 6.3), in contrast to the lateral group (median, 5 mmHg; range, -4 to 13; mean, 5.1; SD, 4.4). The thoracic epidural pressure in the sitting group was significantly lower than in the lateral group (P < 0.001). Conclusions: The thoracic epidural pressure is more negative in the sitting position than in the lateral decubitus position. These results suggest that the patient should be sitting when the hanging drop technique is used to identify the epidural space.