[Techniques for identifying the epidural space]

A large part of the success of epidural anesthesia rests on correct identification of the epidural space. The last hundred years have seen the description of numerous techniques for locating the space in the most straightforward, effective, safe, and reliable manner. To evaluate the advantages and disadvantages of these approaches and the complications associated with each, we carried out a MEDLINE search using the following key words: "epidural analgesia," "epidural anesthesia," "epidural space," "identification," and "loss of resistance" (LOR). Traditional, complementary, and instrument-guided techniques used to identify the epidural space were analyzed. The results of clinical trials comparing different LOR techniques were evaluated. LOR with air, with isotonic saline, or a combination of both were the techniques shown to be simplest and safest. With respect to safety, LOR with air led to the greatest number of complications (pneumocephalus, air embolism, insufficient analgesia, higher incidence of dural puncture, nerve root compression, subcutaneous emphysema). When a small air bubble is created inside the syringe, LOR with saline solution is reliable and teachable, as well as safe and effective.