Ann Thorac Surg 2005;80:1833-1834
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Jan D. Galla, MD, PhD
111 Myrtle St, Haworth, NJ07641
(Email: jdgalla{at}optonline.net).
The most dreaded complication associated with thoracic aortic surgery remains paraplegia caused by spinal cord ischemia. The existence of this problem has been known since the early days of aortic surgery and much research, both clinical and experimental, has been devoted to the understanding and prevention of spinal cord injury. Intraoperative and perioperative adjuncts have included both pharmacological and surgical approaches. Varying degrees of success have been reported for each new approach, with some remedies coming and going in and out of fashion as continued research either supports or refutes their effectiveness. Rather than finding any one therapy that completely removes the threat of perioperative spinal cord injury, incremental improvements in surgical and anesthetic regimens have greatly reduced the incidence of this complication to an acceptable level.
Among the earliest adjuncts used in the battle against paraplegia was hypothermia. In studies dating back 50 years, Pontius and colleagues demonstrated that systemic hypothermia successfully allowed prolongation of the spinal cord ischemic interval in laboratory dogs [1]. For many years, the combination of moderate hypothermia, coupled with rapid surgical techniques, remained the mainstay of protection in aortic surgery. As more complex and extensive operations were attempted, profound hypothermic and circulatory arrest approaches were introduced, but for less comprehensive repairs this was thought to be overkill and was selectively used.
Hypothermic techniques, even when applied systemically in moderate or mild amounts, can adversely affect the conduct of the surgery. Prolonged operating times due to cooling and warming, the need for heaters and coolers in the circuits, and increased bleeding tendencies have all given pause to surgeons unfamiliar with these problems. Because of these issues, investigations were turned to eliminating the need for systemic hypothermia and limiting the cooling efforts to those tissues most directly affected, namely the spinal cord. Locally applied cooling blankets and appliances were found not to be effective due to the rapid rewarming by surrounding tissues and interference with the sterile fields of the procedure. Administration of iced saline solutions directly into the isolated aorta was shown to effect cooling of the spinal cord but, as one might expect, this was abandoned due to its complexity.
A more direct approach began to be explored experimentally; by installing a perfusion and drainage catheter system into the epidural or intrathecal spaces, localized sustained regional cooling could be generated. The necessity to perform a laminectomy to install this cooling apparatus as well as the direct installation of iced fluids into the epidural space made it unsuitable for aortic surgery, but alternative localized approaches continue to be explored. A cooling device that overlays the vertebral bodies without necessitating a laminectomy has recently been described, but the need for a separate incision overlying the spine as well as removing the spinous processes of several vertebral bodies also makes this an unacceptable adjunct to the routine aortic repair. The present study [2] is an advance from these two approaches, albeit necessitating open exposure of the vertebral bodies. By passing a catheter that remains closed into the epidural space containing the cooling fluid within, significant and effective cooling of the cord was achieved without exposure of the cord directly to chilled fluids. The effectiveness of the cooling was documented, and direct spinal cord temperature measurements and effectiveness of protection were also documented by both electrophysiological (EP) and clinical observations. The EP studies were performed using the more sensitive technique of direct measurements from the spinal cord, bypassing any involvement of the peripheral nerves. A direct correlate between the EP results and clinical observations confirmed the clinical usefulness of the former. A notable disadvantage of this technique was the size of the epidural catheter which mandated open exposure of the vertebral column. The authors suggest that with refinements, a percutaneous system may be developed.
Development of a closed, percutaneously placed system for epidural cooling would indeed permit the benefits of hypothermic protection for the cord without the adverse effects of systemic cooling. If a lumbar drainage system could be incorporated as well, this combined approach would address two central methods of cord protection in the current aortic surgical practice. However, as with everything else there is no free lunch. Post-lumbar puncture headaches are well known, and considering the size of the catheter system to be used, this could represent a significant postoperative morbidity: Perhaps the automatic use of a blood patch may be adopted to head this complication off at the pass. Correct placement of the catheter, without traumatizing the surrounding tissues (with the resultant epidural bleed that would generate its own set of problems), or the cord itself, may require a significant learning curve and would most certainly add time to the preoperative preparation of the patient. Anecdotal reports of meningitis or cerebritis after in-dwelling lumbar drain placement arise from the most active aortic centers, and one might expect an increase in such problems if manipulation of the (larger) catheter is a problem.
Despite the potential issues with future envisioned systems, the authors have demonstrated that systemic hypothermia is not necessary for cord protection and look forward to the day when truly localized hypothermia, delivered on demand, will be a useful and routine adjunct to the practice of aortic surgery.
 |
References
|
|---|
- Pontius RG, Brockman HLR, Hardy EG, et al. The use of hypothermia in the prevention of paraplegia following temporary aortic occlusionexperimental observations. Surgery 1954;36:33-38.[Medline]
- Mori A, Ueda T, Hachiya T, et al. An epidural cooling catheter protects the spinal cord against ischemic injury in pigs Ann Thorac Surg 2005;80:1829-1834.[Abstract/Free Full Text]
Top
References