Spinal
cord protection in the surgery of the descending aorta
(Portuguese
PDF version)
Henrique Murad *
*
Professor, Cardiothoracic Surgery, Universidade Federal do Rio de
Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil.
Correspondence:
Henrique Murad
Av. Alexandre Ferreira, 300/402
CEP 22470-220 - Rio de Janeiro, RJ, Brazil
E-mail: hmurad@hucff.ufrj.br
Phone: +55 (21) 2280.2693/2537.3525/22869317
J
Vasc Br 2005;4(1):3-5
Paraplegia
is a severe complication in the surgery of the descending aorta. The
incidence of paraplegia, according to the literature, varies from 3.5%
to 35%. Svensson,1 in successive series, showed a reduction in the risk
of paraplegia from 16% to 3.8% in thoraco-abdominal aneurysms.
The neurological
lesion in the spinal cord is a consequence of: 1) duration of aortic
clamping. The duration of aortic clamping has more influence in patients
with extensive aortic disease, such as those with Crawford type II thoraco-abdominal
aneurysm, and in patients with little development of collaterals, as
in the acute aortic dissection. 2) no reestablishment of spinal cord
blood flow after the aortic clamping increases the risk of spinal cord
injury. 3) The spinal cord injury depends on a second ischemic event
motivated by a postoperative hemodynamic instability.
Some perioperative
measures have proved to be important in order to avoid the occurrence
of permanent paraplegia or paraparesis after the surgery of the descending
aorta: 1) distal perfusion. Maintaining the descending aortic pressure
above 50 mmHg allows the spinal cord perfusion during aortic clamping.
This distal aortic perfusion can be obtained through left atrium-to-femoral
or femoro-femoral partial extracorporeal circulation. Von Oppell et
al.,2 in a great metanalysis of the English literature, observed a lower
incidence of paraplegia in cases of traumatic rupture of the aorta,
in which a left atrium-femoral partial extracorporeal circulation was
used. 2) Deep hypothermia and total circulatory arrest, as proposed
by Kouchoukos et al.3, it is an important method to be used in case
of aortic rupture or proximal aortic stump difficult to be approached.
Deep hypothermia around 18°C is obtained by extracorporeal circulation
through femoral vessels. 3) Intercostal arteries between T6 and the
celiac trunk must be reimplanted in the graft with Carrel aortic patches.
4) Passive hypothermia up to 32 °C before the aortic clamping. 5)
Cerebrospinal fluid drainage, in order to maintain the cerebrospinal
pressure below 10 mmHg. Since the spinal cord perfusion pressure represents
the difference between the distal aortic pressure and the cerebrospinal
fluid pressure, the increase in the cerebrospinal fluid pressure causes
a reduction in the spinal cord perfusion pressure. 6) In the postoperative
period, maintain a higher blood pressure (average of 85 mmHg of aortic
mean pressure) for 2 to 3 days.
A much
lower incidence of paraplegia has been shown with the endovascular treatment
of aneurysms and aortic dissections.4 The reason for this low incidence
is multifactorial, but certainly the fact that there is no aortic clamping
plays an important role.
There
are still several questions to be answered about the theme, so that
paraplegia stops being a sword of Damocles over the surgeon who operates
the descending aorta.
In this
issue of the Jornal Vascular Brasileiro, Mendonça et al.5
study the effects of the thoracic aorta clamping and the cerebrospinal
fluid drainage in the spinal cord blood flow and in the incidence of
paraplegia. They use the cerebrospinal fluid total drainage before the
aortic clamping in a canine model. The cerebrospinal fluid total drainage
before the aortic clamping prevented the occurrence of paraplegia. A
totally different fact from the control group, where all dogs presented
paraplegia after 60 minutes of descending aorta clamping. In the group
where the cerebrospinal fluid was drained, they observed a reduction
in the cerebrospinal fluid pressure, an increase in the spinal cord
perfusion pressure, and an increase in the spinal cord blood flow (measured
with Laser-Doppler technology). They also noticed that the dogs on which
there were cerebrospinal fluid total drainage presented a high-flow
reperfusion lower than the control group.
Maybe this
is an important method to avoid paraplegia in the surgery of the descending
aorta. The major prevailing question is knowing the consequence of the
abrupt removal of the cerebrospinal fluid. Dardik et al.6 described
eight cases of subdural hematoma in 230 patients submitted to the cerebrospinal
fluid drainage in order to maintain a cerebrospinal pressure lower than
5 mmHg. Based on this, Dardik et al.6 decided
to remove the liquor when the cerebrospinal pressure was higher than
10 mmHg. In this issue of the Jornal Vascular Brasileiro, the
study of Mendonça et al.5 found cerebrospinal
pressures of 7.4 mmHg negative after the liquor drainage.
The total
liquor drainage before the aortic clamping seems to be effective for
the prevention of paraplegia. However, there are doubts concerning the
method efficiency due to the potential complications related to this
therapy. Additional researches should complement this study.
1.
Svensson LG. Descending thoracic and thoracoabdominal aortic surgery.
In: Selke FW, Del Nido PJ, Swanson SJ, editors. Sabiston and Spencer
Surgery of the Chest. 7th ed. Philadelphia: Elsevier Saunders; 2005.
p. 1165-1194.
2. von Oppell DO, Dunne TT, De Groot WK, et al. Traumatic
aortic rupture: twenty-year metaanalysis of mortality and risk of paraplegia.
Ann Thorac Surg 1994;58:585-93.
3. Kouchoukos NT, Masetti P, Rokkas CK, et al. Safety
and efficacy at hypothermic cardiopulmonary bypass and circulatory arrest
for operations on the descending thoracic and thoracoabdominal aorta.
Ann Thorac Surg 2001;72:699.
4.
Buffolo E, Fonseca JH, Souza JA, et al. Revolutionary treatment of aneurysms
and dissections of descending aorta: the endovascular approach. Ann
Thorac Surg 2002;74:1815-17.
5.
Mendonça CT, Greca FH, de Paula JB. Efeitos do pinçamento
da aorta torácica e da drenagem do líquido cérebro-espinhal
no fluxo sangüíneo capilar da medula espinhal e na incidência
de paraplegia. Estudo experimental. J Vasc Br 2005;4:66-78.
6.
Dardik A, Perler BA, Roseborough GS, et al. Subdural hematoma after
thoracoabdominal aortic aneurysm repair: an underreported complication
of spinal fluid drainage. J Vasc Surg 2002;36:47-50.
