Posterior epidural space depth: safety of the loss of resistance and hanging drop techniques

We have compared skin to epidural space distance (SED) and tip to tip dista nce (TTD), a measure of posterior epidural space depth (PESD), in 40 patien ts with a 27-gauge Whitacre needle after identification of the epidural spa ce using the hanging drop (HD) or loss of resistance (LOR) to air technique . After the LOR technique, TTD was found to be 2 mm greater than that after the HD technique, whereas SED was the same. We conclude that identificatio n of the epidural space can be performed successfully with both techniques, but with a diminished risk of dural damage after LOR compared with the HD technique.