Paraplegia is a devastating complication which may occur following surgery on the thoracic aorta. Spinal fluid drainage may reduce the paraplegia risk in thoracic and thoracoabdominal aortic aneurysm repair by reducing the cerebrospinal fluid pressure and hence increasing the spinal perfusion pressure.
The pathophysiology of spinal injury after thoraco-abdominal aneurysm repair is complex. It is a result of interruption of the blood supply to the spinal cord including; intercostal and lumbar arteries, the artery of Adamkiewicz, the internal iliac arteries and the spinal arteries via the subclavian/vertebral artery.
If there is a significant interruption of the spinal cord blood supply, there is ischaemia (lack of perfusion) of the anterior column of the spinal cord which transmits the signals for movement of muscles of the lower limbs.
If there is no transmission of the signals from the brain to the muscles of the lower limb then there will be an absence of movement and hence paraplegia - an absence of movement of the lower limbs.
Whilst spinal fluid drainage implemented post-aneurysm repair reduces the risk of spinal injury, it should be borne in mind that complications can arise following drainage itself.
The major complications of spinal drainage include occlusion, bleeding and infection.
If a spinal drain is occluded the pressure in the spinal canal may increase, spinal perfusion may fall, and infarction of the spinal cord may result.
Bleeding may occur in the brain with excessive drainage of cerebrospinal fluid, which causes headache and neurological signs. Bleeding may occur directly in or around the spinal cord itself leading to intradural haematoma or epidural haematoma. This causes pressure on the spinal cord and damage to the nerves.
The drainage of cerebrospinal fluid should be closely monitored. With cessation of drainage, the drain should be aspirated and checked patent. If excessive drainage ensues at any point, then clamping of the drain is advised. Removal of drains should only be undertaken once the clotting profile of the patient is normal and at least 12 hours after heparin or anticoagulant administration.
A spinal drain, if left for an extended period of time, will risk infection in the spinal cord and abscess formation which may require long term antibiotic therapy and drainage.
Spinal drains may be set up and managed in different ways, which is acceptable practice. Spinal drains should be managed according to strict protocols by well trained staff. The drain management should only occur on a specialised unit such as a suitable high dependency unit.