Spinal anesthesia is a common technique in the practice of anesthesiology. Most often, it is the first choice of anesthetic for common surgeries like cesarean sections or hip/knee joint replacement surgeries. It is considered a relatively safe procedure.
A recent article (1) drew attention to the safety in practice of spinal anesthesia by reporting neurological damage in seven cases after a spinal or combined spinal-epidural anesthesia. All patients in this series had persistent unilateral sensory loss, some had foot drop and urinary symptoms as well. All patients had pain during placement of the spinal, which was believed to be at L2-3 space and free flow of CSF was reported before injection of local anesthetic. MRI imaging performed later revealed a normal length spinal cord with syrinx in the conus on the same side as the clinical symptoms, in six out of these seven patients.
The authors make some interesting observations that are important for those who perform spinal anesthesia. The clinical symptoms and subsequent imaging clearly show unilateral conus injury. The most probable cause of this is direct needle injury to the conus as evidenced by pain on placement of the needle and the symptoms restricted to the side of that pain. It is important not to inject when there is pain with placement of spinal needle but it is suggested that the needle itself can cause some damage to the closely packed terminal nerve roots without any injection.
Even though many experienced anesthesiologists believe that they can accurately identify the interspaces by palpation, it has been shown in studies (2, 3) that more than 50% of the times they are a space or two higher than intended. It has also been shown that anatomical landmarks such as Tuffier’s line (joining the iliac crests) are not very dependable either (4). This can lead to higher than intended placement of the spinal needle and subsequently increases the risk of conus injury.
During the placement of spinal anesthesia, the goal is to enter the subarachnoid space below the termination of the spinal cord which is usually at the level of L1 to L2. It has been noted that some of the textbooks also recommend performing the needle puncture in the second, third or fourth lumbar interspace. Taking into account the level of termination of the cord is not known, landmarks for identification of interspaces are not dependable, and that anesthesiologists identify interspace higher than intended, spinals should never be intended to be placed any higher than the L3-4 interspace.
Neurologic complications after a spinal anesthesia are very rare but dreadful and cause increased anxiety for both the patient and the anesthesiologist. Therefore it is prudent to practice safe methods in performing a spinal.
- Reynolds, F. “Damage to the Conus Medullaris Following Spinal Anaesthesia.” Anaesthesia 56, no. 3 (March 2001): 238–47. https://doi.org/10.1046/j.1365-2044.2001.01422-2.x.
- Broadbent, C. R., W. B. Maxwell, R. Ferrie, D. J. Wilson, M. Gawne-Cain, and R. Russell. “Ability of Anaesthetists to Identify a Marked Lumbar Interspace.” Anaesthesia 55, no. 11 (November 2000): 1122–26. https://doi.org/10.1046/j.1365-2044.2000.01547-4.x.
- Van Gessel, E. F., A. Forster, and Z. Gamulin. “Continuous Spinal Anesthesia: Where Do Spinal Catheters Go?” Anesthesia and Analgesia 76, no. 5 (May 1993): 1004–7. https://doi.org/10.1213/00000539-199305000-00015.
- Render, C. A. “The Reproducibility of the Iliac Crest as a Marker of Lumbar Spine Level.” Anaesthesia 51, no. 11 (November 1996): 1070–71. https://doi.org/10.1111/j.1365-2044.1996.tb15009.x.