Continuous spinal anaesthesia has a number of advantages, but there are a number of drawbacks as well: difficulties in threading the catheter, distribution of the local anaesthetics and the development of cauda equina syndrome. Spinaloscopy was done to visualize the fate of catheters during and after their insertion, as well as the distribution of local anaesthetics injected through these fine-bore catheters. METHOD. The studies were conducted in preserved and fresh cadavers donated to the Anatomic Institute for Medical Studies. The spinal column from T12 to S1, together with the back musculature (in order to preserve the normal curvature of the spine) were removed from the cadaver. Spinaloscopy was done with a 4 mm endoscope with a 0 degree optic (Storz, Tutlingen, FRG). All observations were made from the lumbosacral region of the dissected preparation. In this fashion, it was possible to observe the insertion of the spinal needle used to introduce the catheter into the subdural space. The distribution of local anaesthetics injected through a 22-gauge spinal needle or a 28-gauge catheter was shown by injecting 0.5% hyperbaric bupivacaine colored with a small amount of 1% methylene blue. Pictures were taken 15, 30 and 45 s after beginning the injection. RESULTS. Difficulty in threading the catheter: our observations indicate that the difficulty in inserting microbore catheters is most likely due to inserting the needle too far. It is impossible for the catheter to bend and be inserted into the subarachnoid space. In many cases the catheter encountered the anterior wall of the spinal canal and would slide along various structures. Distribution of the drug: the injection is better dispersed with a 22-gauge needle and it completely fills the subarachnoid space. The local anaesthetics injected through the 28-gauge nylon catheter (Kendall Healthcare, Mansfield, Mass.) are distributed in the dependent portions of the spinal canal. If high doses and a high concentration are injected, the distribution pattern may result in an overconcentration in some parts of the subarachnoid space. Possibility of trauma: the catheter stretches around the roots, the potential for trauma is that untoward stress may be applied to the root, either during full insertion of the catheter or during its withdrawal. CONCLUSION. Spinaloscopy was done in a non-fixated anatomic spinal column preparation with a 4 mm 0 degree endoscope (Storz, Tuttlingen, FRG). Based on our observations, we conclude: The catheter should only be inserted 2 cm into the subarachnoid space. This may decrease the risk of malpositioning. After the tip of the catheter has reached the subarachnoid space, the stylet should be with drawn 2 or 3 cm to minimize the risk of nerve injury and/or bleeding.
Möllmann, Holst, Enk, Filler, Lübbesmeyer, Deitmer, Lawin, , (1992). [Spinal endoscopy in the detection of problems caused by continuous spinal anesthesia]. Der Anaesthesist, 1992 Sep;41(9):544-7. https://www.ncbi.nlm.nih.gov/pubmed/1416010