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LETTER TO THE EDITOR

The Posterior Epidural Space Is Largest at the Level of the Disc

University of Alberta Hospital; Edmonton, Alberta, Canada; btsui{at}ualberta.ca

In Response:

Dr. Aldrete commented on our case (1) involving spinal damage during placement of a thoracic epidural catheter, stating "puncture of the epidural veins and of the spinal artery is more likely when a near-lateral or paramedian translaminar entry is used." Although I appreciate that "thoracic epidural anesthesia is hazardous," I wonder how much safer it really would be to place a "high lumbar insertion" for upper abdominal and thoracic surgery. Such insertion can cause direct needle trauma to any part of the spinal cord during epidural insertion and result in devastating complications, albeit rarely.

Alternatively, if the anesthesiologist can safely and readily thread thoracic or cervical epidural catheters from the caudal or lumbar spaces, where the needle puncture site is well below the level of the spinal cord, the risk of spinal cord damage from direct needle puncture is reduced (2,3). Unfortunately, in patients beyond the age of 1 yr, it is difficult to thread an epidural catheter from the caudal/lumbar epidural space to the thoracic region because lumbar curvature has developed (4). The catheters often kink and coil as they encounter resistance in the lumbar region. Thus, as the anesthesiologist advances the epidural catheter from the lumbar epidural space (below the level of the spinal cord) into the thoracic or cervical space, he/she should verify the catheter tip position either via radiology (fluoroscopy) or via epidural stimulation (4). This verification will significantly advance patient safety, our ultimate goal as anesthesiologists. This strategy, epidural threading at vertebral sites below the spinal cord, will likely be more valuable than minor vertical changes or angular shifts in approaching the circumferentially variable depth of the epidural space.

REFERENCES

1. Tsui BCH, Armstrong K. Can direct spinal cord injury occur without paresthesia? A report of delayed spinal cord injury after epidural placement in an awake patient. Anesth Analg 2005;101:1212–4.[Abstract/Free Full Text]
2. Tsui BC, Entwistle L. Thoracic epidural analgesia via the lumbar approach using nerve stimulation in a pediatric patient with Down syndrome. Acta Anaesthesiol Scand 2005;49:712–4.[Web of Science][Medline]
3. Tsui BC, Wagner A, Cave D, Kearney R. Thoracic and lumbar epidural analgesia via the caudal approach using electrical stimulation guidance in pediatric patients: a review of 289 patients. Anesthesiology 2004;100:683–9.[Web of Science][Medline]
4. Valairucha S, Seefelder C, Houck CS. Thoracic epidural catheters placed by the caudal route in infants: the importance of radiographic confirmation. Paediatr Anaesth 2002;12:424–8.[Web of Science][Medline]

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