[Intended and actual paths of epidural needles. Investigations with a test tissue model]

Peridural anaesthesia needles (PDA) do not only differ in calibre or gauge but also vary in the design of the needle tip, which shows a special configuration to place a catheter in the epidural space. A laboratory model was performed to determine the influence of different types of virgin epidural needles concerning their path through tissue. In an additional test run we analysed the influence of a previous use on the path through tissue. We investigated 16 G and 18 G Tuohy needles for epidural anaesthesia and two different 18 G Tuohy needles for combined spinal-epidural anaesthesia. The experiments were performed in a standardised way using a precision drill press in order to make the test independent of the investigator. The test tissue was selected because of its close similarity to human tissue of the lumbar region. Every needle tested revealed a distinct deviation even after a 6 cm passage through the test tissue and regularly deviated away from the concave side of the needle tip. The comparison of the CSE needles tested revealed a significant deviation from the axis due to differences in cross-section and configuration of the needle tip. As expected, the average deviation of PDA needles depended on the diameter. No differences in the degree of deviation for virgin needles compared to previously used needles could be found. Thus, more than one application of the same needle in one patient is considered to be safe as long as the needle is not deformed in any way.