Thoracoabdominal aortic aneurysm (TAAA) repair and replacement
For patients with thoracoabdominal aneurysms, elective surgery is recommended if the aortic diameter exceeds 6.0 cm. However, in patients with a connective tissue disorder such as Marfan or Loeys-Dietz syndrome, surgery is recommended at a smaller diameter, particularly if an aneurysm is growing fast.
During TAAA surgery, the thoracoabdominal aorta is resected and replaced with a synthetic graft (see figure). The blood supply of the intestine, liver, kidneys and spinal cord originates from the thoracoabdominal aorta. During TAAA surgery, the vessels that supply blood to the organs above are disconnected from the diseased aorta and reconnected to the synthetic tube graft. This process results in a temporary interruption of the blood flow to these organs, and therefore, it can potentially lead to organ dysfunction.
One of the most serious complications that may result from thoracoabdominal aortic aneurysm repair is paraplegia—an impairment in the motor function of the lower extremities. The cause is an injury to the spinal cord, which is responsible for most sensory and motor activities of the lower body. Although several factors exist that may predict the onset of paraplegia after surgery, the most significant one is a lack of adequate blood flow (perfusion) to the spinal cord during surgery.
Spinal cord protection during thoracic and thoracoabdominal surgery
We have developed a unique clinical approach to spinal cord perfusion—one that puts our mortality and paraplegia rates among the best in the United States. This approach is dictated by the fact that healthy spinal cord perfusion depends on a network of small and integrated arteries rather than a single major spinal artery. As such, we employ a series of novel techniques that aim to optimize these connections and ensure as much perfusion to the spinal cord as possible.
Distal aortic perfusion (DAP)
During thoracic and thoracoabdominal aortic surgery, it is possible to cease temporarily blood flow to the diseased portion of the aorta using surgical clamping devices. However, to maintain adequate blood supply to the lower body, blood needs to be routed around the diseased aorta and circulated using an external pump device. This is the essence of distal aortic perfusion. Distal aortic perfusion is necessary for a variety of reasons. A primary one is that it allows for perfusion of the hypogastric arteries, which are an important source of collateral blood supply to the spinal cord. Without perfusion to these arteries, the risk of paraplegia would dramatically increase.
Cerebrospinal fluid drainage
The spinal cord exists in a chamber of protective liquid called cerebrospinal fluid (CSF). During aortic surgery, however, cerebrospinal fluid pressure elevates to a point in which blood flow to the spinal cord can be severely restricted. The result may be paraplegia. During TAAA repair, surgeons at the Aortic Wellness Center monitor CSF pressure continuously by having a small catheter inserted into the spinal canal and drain CSF if the pressure exceeds a critical level.
Spinal cord monitoring
Monitoring of the function of the spinal cord can be accomplished during surgery by recording and analyzing the somatosensory and motor evoked potentials (SSEPs and MEPs). These techniques record the electrical activity of the spinal cord which depends on the adequacy of the blood supply of the spinal cord. Changes in SSEPs and MEPs can be sensitive indicators of inadequate perfusion of the spinal cord with blood during descending and thoracoabdominal aortic repair. Continuous monitoring of these indicators is always done intraoperatively at Main Line Health to reduce the risks of paraplegia.
Also, monitoring of spinal cord perfusion pressure (SCPP) can be done during surgery to assess the level of spinal cord perfusion. In most cases, spinal cord ischemia can be immediately corrected during the operation by raising the arterial pressure or decreasing the CSF pressure. In selective cases, reimplantation of the blood vessels that directly perfuse the spinal cord may be needed.
Intraoperative drug use
Almost all techniques for thoracic and thoracoabdominal aneurysm repair involve brief, unavoidable intervals of spinal cord ischemia—lack of adequate perfusion to the spinal cord. However, when certain drugs are administered during surgery, the spinal cord appears to better tolerate these ischemic intervals.
Decreasing the body temperature (32C) during surgery has shown to increase the tolerance of the spinal cord to the temporary decrease of its blood supply by decreasing the metabolic demands of individual cells.
Postoperative Hemodynamic Stability
Spinal cord injury can occur not only during surgery but also in the post-operative period. We have developed special protocols to monitor and optimize the patient`s course after the operation to avoid problems that may lead to spinal cord dysfunction. Although it is impossible to protect completely against delayed paraplegia and other adverse effects, their risk of occurrence has decreased significantly at the aortic wellness center. By using these techniques, we have reduced the incidence of paraplegia to below three percent for all descending and thoracoabdominal aortic aneurysms-well below the national benchmark.
Selective perfusion of the renal and visceral arteries
During the period of the interruption of the blood flow to the kidneys, intestine and liver damage to these organs may occur. To prevent this damage, the blood vessels that supply these organs with blood are cannulated and perfused with cold blood utilizing an artificial pump.