presentation will give a idea about management of thoracoabdominal aortic aneurysm, including detail of investigation and treatment options available today.
4. ANATOMIC PRINCIPLES
Arises distal to the origin of Left SCA.
TAA span the diaphragmatic hiatus at the level of Tl2
and introduce important considerations for pleural entry,
peritoneal access, and diaphragmatic conservation for
aortic repair.
In addition, phrenic nerve localization and preservation
are imperative within the pericardium as it crosses the
left atrium and terminates distally on the abdominal
surface of the diaphragm.
5. The critical vascular zone of the spinal cord from T4 to Ll vertebral levels is
characterized by the least prominent blood supply and is the zone at which
interference with the circulation is most likely to result in paraplegia.
The artery of Adamkiewicz is the largest anterior medullary feeder for the
supply of the lumbar cord and arises from the lower intercostal or lumbar
artery on left in 65% to 80% of cases between T6 and 14 levels.
The lower intercostal and lumbar artery supplying the artery of
Adamkiewicz should be preserved or reconstructed to maintain blood
supply to the lumbar spinal cord to minimize the risk of spinal cord injury.
Perfusion through medullary arteries maintains spinal cord blood supply
proximal to the aortic cross-clamp and determines postoperative
neurologic function.
6. Visceral branches are located on the ventral aorta as the celiac
axis, superior mesenteric, inferior mesenteric, and paired or
multiple renal arteries.
The anterior spinal artery is a principal component of the extensive
intraspinal and paraspinous collateral blood supply to the anterior
spinal cord, with 75% of all segmental arteries providing direct
anterior spinal artery-supplying branches.
This extensive collateral network imparts a responsibility to define
dominant intercostal and lumbar arteries for each individual patient
to guide operative planning for reconstruction and preservation of
blood supply to the spinal cord.
7. IMAGING, option available ??
Determined by following factors
1. patient-related factors
• hemodynamic stability
• renal function
• contrast allergy
2. institutional capabilities ( technologic capability, expertise).
CT-induced contrast nephropathy and magnetic resonance (MR) associated gadolinium
nephrogenic systemic fibrosis are principal considerations for patients with borderline
kidney function (serum creatinine > 1.8 to 2.0 mg/dl).
8. Chest X- Ray
specificity for acute aortic pathology of
86% in prospective study of patients
undergoing evaluation for acute thoracic
aortic disease.
However, it is insufficient to definitely
exclude thoracic aortic aneurysm in high-
risk patients and lacks anatomic detail
necessary for directed treatment.
9. CT angiography
(CTA)
CTA is accepted as the primary
diagnostic imaging modality for the
thoracic aorta with a demonstrated
accuracy of92% for all-inclusive
abnormalities of the thoracic aorta and
has an established efficacy in the
prediction of the need for hypothermic
circulatory arrest during surgical repair.
Image acquisition should include
ascending aorta, aortic arch,thoracic
branch vessels and femoral vessels to
determine aneurysm extension and to
guide potential endovascular access.
10.
11. MR angiography (MRA)
provides similar advantages to CTA without the limitations of radiation exposure or
iodinated contrast.
Phase-contrast techniques and two-dimensional time-of-flight modalities have
increased the application of MRA in the setting of thoracic aortic aneurysm and
dissection, with beneficial applications in the determination of flow dynamics within
the false channel.
First-line adoption of this imaging modality in the setting of thoracic aortic
aneurysm remains limited by institutional capabilities and the time required for
acquisition.
In addition to providing insight regarding aortic size and anatomic aneurysm
characteristics, both CTA and MRA guide the selection of safe sites for arterial
cannulation and cross clamp application.
18. Principle of medical therapy
The main aim of medical therapy in this condition is to reduce shear stress on the
diseased segment of the aorta by reducing blood pressure and cardiac
contractility.
Cessation of smoking is important, as studies have shown that self-reported
current smoking induced a significantly faster expansion (by approximately 0.4
mm/year).
Moderate physical activity probably prevents the progression of aortic
atherosclerosis but data are sparse.
To prevent blood pressure spikes, competitive sports should be avoided in patients
with an enlarged aorta.
19. It is mechanistically logical that medical therapy to reduce dP/dt and to control
blood pressure would be beneficial for the treatment of all patients with thoracic
aortic aneurysms.
In a randomized study of adults with Marfan syndrome, Shores et al found that
treatment with propranolol (versus no b-blocker therapy) over 10 years resulted in
a significantly slower rate of aortic dilatation, fewer aortic events, and lower
mortality.
There is some early experimental evidence to suggest that oxidative stress may
play a role in the pathogenesis of atherosclerotic thoracic aortic aneurysms and
that perhaps statin therapy and angiotensin II receptor blocker therapy may
potentially have a protective effect.
20. Once b- blocker therapy is maximized (or in the event that b-blockers are
contraindicated or not tolerated), any persistent hypertension should be treated
with other antihypertensive agents to bring the blood pressure down to a low-
normal range, eg, a systolic pressure of 105 to 120 mm Hg
Patients should be informed of the typical symptoms of acute aortic dissection.
Moreover, patients should be instructed that should they ever experience the
abrupt onset of significant chest, neck, back, or abdominal pain, they should
present immediately to an emergency department for evaluation.
In addition, patients should be instructed to inform the emergency physician of the
existence of a thoracic aortic aneurysm and explain explicitly that their physician
recommends an urgent CT scan of the chest (or transesophageal
echocardiography or MRI if a CT is contraindicated) to rule out acute aortic
dissection or rupture.
21.
22. ENDOVASCULAR REPAIR TECHNIQUE
Thoracic endo vascular aortic repair aims at excluding an aortic lesion (i.e.
aneurysm or FL after AD) from the circulation by the implantation of a membrane-
covered stent-graft across the lesion, in order to prevent further enlargement and
ultimate aortic rupture.
Careful pre-procedural planning is essential for a successful TEVAR procedure.
Contrast-enhanced CT represents the imaging modality of choice for planning
TEVAR, taking ,3 mm ‘slices’ of the proximal supra-aortic branches down to the
femoral arteries.
In situations involving important aortic side branches (e.g. left subclavian artery),
TEVAR is often preceded by limited surgical revascularization of these branches
(the ‘hybrid’ approach). Another option is a surgical de-branching or the use of
fenestrated and branched endografts or the ‘chimney technique’. An alternative
may be a single, branched stent-graft.
23.
24. In high-risk patients, preventive cerebrospinal fluid(CSF)drainage can be
beneficial, as it has proven efficacy in spinal cord protection during open
thoraco-abdominal aneurysm surgery.
Reversal of paraplegia can be achieved by the immediate initiation of CSF
drainage and pharmacological elevation of blood pressure to >90 mm Hg
mean arterial pressure.
Hypotensive episodes during the procedure should be avoided.
Follow up Ct scan to be done after 1 week to rule out endoleak.
25.
26. Type I and Type III
Endoleaks are regarded as treatment failures and warrant
further treatment to prevent the continuing risk of rupture.
Type II
Endoleaks are normally managed conservatively by a ‘wait-and-
watch’ strategy to detect aneurysmal expansion, except for
supra-aortic arteries.
Types IV and V
Endoleaks are indirect and have a benign course. Treatment is
required in cases of aneurysm expansion.
28. Anaesthesia and monitoring
General anaesthesia
Double lumen endotracheal tube.
Monitoring :-
Large-bore peripheral access, central venous pressure monitoring, continuous
arterial pressure assessment, pulse oximetry, and foley catheter are imperative to
guide intraoperative resuscitation and support.
Transesophageal echocardiography, continuous electrocardiographic monitoring,
and a pulmonary artery catheter provide additional adjuncts for intraoperative
cardiac evaluation and are routine in our institution.
Femoral artery access is needed with cardiopulmonary bypass to maintain
balanced pressures.
29. Temperature monitoring is achieved at two access sites to estimate
cerebral (blood, esophageal, tympanic membrane, nasopharynx) and
visceral (bladder, rectal) temperatures.
Cerebrospinal fluid (CSF) drainage is the principal modality for spinal cord
protection , due to the established benefit and low-risk of this protective
strategy.
Motor-evoked potential (MEP) and somato sensory evoked potential
(SSEP) monitoring may be applied in addition to CSF drainage for spinal
cord protection and monitoring.
30. Incision and Exposure: Thoracic
Aneurysms
An extended posterolateral thoracotomy is performed to expose the entire
length of the thoracic aorta.
The latissimus dorsi and a minimal portion of the serratus anterior muscles
are divided.
Aneurysms of the upper or middle thoracic aorta are accessed through a
single intercostal space, which may be facilitated by division of one of the
ribs posteriorly.
Two separate sites of entry through the fourth interspace and the seventh
or eighth interspace for more extensive descending thoracoabdominal
aneurysms can be obtained and recommended.
The fourth interspace is critical to proximal clamp application.
31.
32.
33. The thoracic duct and adjacent lymph vessels should be avoided. Intraoperative
lymph leaks should be immediately repaired.
The identification of the esophagus may be augmented by the direct palpation of
the nasogastric tube or transesophageal echocardiography scope to avoid
inadvertent injury.
FOR thoracoabdominal aneurysm-
Incision is started posterolaterally over the ribs of the seventh, eighth, or ninth
interspace dependent on the proximal extent of the aneurysm.
The incision is then advanced across the ninth interspace at the costal margin to
curve inferiorly to run parallel and left-lateral to the midline and rectus sheath.
The abdominal muscles are divided and the peritoneum is preserved. Special care
is needed at the lateral edge of the rectus abdominis muscle where the peritoneum
and transversalis fascia are closely apposed to the abdominal wall.
34. The diaphragm may be taken down with a
curved incision along the costal margin with
care to preserve a 3-cm rim along the
posterior aspect of the rib.
The tendinous center of the diaphragm is
then conserved when anatomically feasible
to improve postoperative respiratory recovery
and weaning time.
This limited phrenotomy technique allows
passage of the graft through the natural
hiatus of the diaphragm.
The incision is continued down to the crura,
and the left crus may be divided to expose
the aorta beneath.
A radial diaphragmatic incision may also be
utilized.
35. Progressive retraction of the peritoneum and its contents will facilitate exposure of
the retroperitoneum and a self-retaining retractor is necessary.
The aorta is located medial to the iliopsoas muscle.
Mobilization of the left kidney from the bed of the psoas muscle may provide
additional exposure.
Importantly, this step is deferred in patients with a retroaortic left renal vein.
Anterior visceral branches are identified and sharply dissected with attention to
mobilization should reimplantation or bypass be required.
Dissection is performed proximal and distal to the aneurysmal segment of aorta
and each site is tapped in preparation for cross-clamping.
36. Hemodynamic Support during Aortic
Cross-Clamping
Proximal aortic cross-clamp application induces a significant
increase in cardiac afterload.
Sudden afterload reduction following clamp release is
associated with an acute relative hypovolemia and systemic
hypotension.
37. Strategy:-
Approach to cross-clamp application and distal aortic perfusion involves active
distal aortic perfusion with femoral-to-femoral bypass for all but type IV and V
aortic aneurysms, for which we can minimize supraceliac clamp times with no
active distal perfusion.
maintenance of distal aortic blood pressure is imperative and is achieved through
the titration of pharmacologic agents and pump flow rates to maintain optimal
perfusion.
Infusion of nitroglycerine, trimethaphan, or sodium nitroprusside prior to the
application of the aortic cross-clamp may be performed to lower systolic blood
pressure to 70 to 80 mmHg.
38. Sodium bicarbonate, calcium, and rapid volume infusion may be initiated prior to
unclamping to prevent acute hypotension.
Vasopressor agents may also be utilized to augment these resuscitative measures
to maintain blood pressure upon clamp release.
Progressive clamp application and release over a period of 2 to 4 minutes may
blunt the imposed physiologic insult and hemodynamic response.
In assessment of end-organ ischemia, cross-clamp time is measured from the first
click of clamp application until its complete release.
39. Extracorporeal Circulation
Extracorporeal circulation support provides after load reduction and
continuous end-organ perfusion during the aortic cross-clamp period.
Techniques for the maintenance of extracorporeal circulation include
passive aorto-aortic shunt,
left atriofemoral bypass, and
femorofemoral cardiopulmonary bypass.
40. Spinal Cord Protection
Central to methods of cord protection is an understanding of the axial network and
the supplying segmental, subclavian, and hypogastric arteries and the protective
effect of permissive hypothermia on neural tissue.
This collateral network may increase flow through alternative routes when another
is reduced; however, this network may also result in steal that will result in
decreased nutrient flow to the cord.
Steal may occur secondary to the absence of visceral and iliac artery perfusion,
during the cross-clamp period, or as a result of pharmacologically induced
arteriovenous shunting when bleeding intercostals into an excluded aortic
segment.
41. liberal use of multi head
perfusion cannulae and
pediatric coronary sinus
catheters for the maintenance
of perfusion to the visceral and
subclavian aortic branches and
dominant intercostal arteries,
respectively.
42. The detection of potentially reversible delayed paraplegia may be achieved by
MEP and SSEP monitoring with immediate assessment of function postoperatively.
The adoption of the following provocative techniques for reduction of spinal cord
ischemic-induced injury has resulted in a significant decrease in the incidence of
paralysis following open repair that is dependent on the extent of repair.
15% for type I,
30% for type II,
7% for type III, and
4% for type Iv.
43. Predictors of delayed neurologic deficit
emergent operative status,
prolonged aortic cross-clamp time,
level of cross-clamp, hypogastric artery exclusion,
aortic rupture,
preoperative renal dysfunction,
prior abdominal aortic aneurysm repair,
acute dissection, and
extent II involvement.
44. Strategies
Distal aortic perfusion.
Lower body pressure monitoring is imperative to maintain appropriate cord
perfusion which may necessitate flow rates as high as 3 to 3.5 L/min.
Intrathecal vasodilators and topical cooling.
Experimental porcine studies have established the protective effect of
intrathecal administration of vasodilators during the aortic cross-clamp period.
This technique dilates spinal arteries and prevents spasm and may be
combined with local cooling of the cord with 4°C saline to extend the potential
aortic cross-clamp time.
Topical cooling of the spinal cord is associated with increases in CSF pressure;
however, this technique has proven to be a protective adjunct in the reduction
of postoperative paralysis and paraplegia.
45. Cerebrospinal fluid drainage.
In randomized prospective study, the incidence of paraplegia or
paraparesis was reduced with CSF drainage from 13.0% to 2.6%, P =
0.03.
CSF pressure is maintained < 10 mmHg with mean perfusion
pressures of 85 to 90 mmHg to enhance spinal cord perfusion.
Lumbar drains are generally removed on postoperative day 2 in
patients without neurologic deficit.
Preference in high-risk patients is to leave the lumbar drain inplace for
72 hours, while in select low risk patients one can consider removal at
24 hours.
46. Reattachment of intercostal and lumbar arteries.
acceptable rates of paralysis and paraplegia following sacrifice without
reimplantation of as many as 15 intercostal and lumbar arteries during
thoracoabdominal aneurysm reconstruction.
Prompt ligation of nonimplanted intercostal arteries is recommended to
avoid steal from the cord circulation.
While multimodality approaches have implemented complete intercostal
reimplantation.
47.
48.
49. Hypothermia.
Moderate (29 to 32°C) to profound (20%) hypothermia is associated with
improved outcomes following thoracoabdominal and descending aortic
operations.
The proposed mechanism of hypothermia-induced protection involves the
reduction of excitatory neurotransmitter release, decreased free oxygen radical
production, decreased postischemic edema, and stabilized central nervous
system blood flow.
50. Pharmacologic agents.
Mannitol (0.25 to 1.0 g/kg), high-dose barbiturates, methylprednisolone (30
mg/kg), calcium-channel blockers, adenosine 2A agonist, naloxone, and local
anesthetic agents have a demonstrated efficacy in experimental models of
spinal cord ischemia and multimodality clinical protocols.
The proposed mechanism of spinal cord protection involves decreased spinal
cord edema and improved free oxygen radical scavenging
Minimizing aortic cross-clamp times.
55. HYBRID APPROCH
Hybrid techniques that incorporate open and endovascular repair
techniques provide a promising approach to treatment in patients with
complex thoracic aortic aneurysms with or without concomitant dissection.
In patients with descending thoracic aortic aneurysms with proximal
extension into the aortic arch, we can successfully performed open arch
debranching and revascularization of branch vessels, followed by TEVAR
of the arch and descending thoracic aorta.
Similaraly, TAAA extending and involving viseral vessel, hybrid approch
can be tried.
56.
57.
58. SPECIAL FEATURES OF
POSTOPERATIVE CARE
Particular attention is paid to maintaining adequate ventricular preload by
volume infusions.
Amount of chest drainage is closely monitored.
close attention to pulmonary subsystem management is mandatory in
thoracotomy involving cases.
Prompt initiation of cerebrospinal
fluid drainage may, in some instances, reverse the neurologic deficit, and if
a drain is not already in place, it should be inserted when signs of spinal
cord ischemia develop postoperatively.
Avoiding prolonged periods of hypotension is also essential to
ensure optimal spinal cord perfusion.
59. FOLLOW-UP RECOMMENDATIONS
The current standard for postoperative endovascular and open
descending thoracic and thoracoabdominal aortic aneurysm
repair involves
physical examination,
Repeat imaging with CTA chest and chest radiography at 1, 6, and 12 months.
The initial interval to postoperative evaluation may be modified as determined by
the immediate in-hospital postoperative course.
60.
61. Literature rerview
What to look for
1. In hospital mortality
2. Morbidity
3. Type of different strategy developed over years.
