1. Anesthesia for Patients With Aortic Aneurysm
Undergoing Endovascular Stenting
Benjamin Drenger, MD and Sudheer Jain, MD
Department of Anesthesiology and Critical Care Medicine
Hebrew University - Hadassah Medical Center
Jerusalem, Israel
Department of Anesthesiology
New York University Langone Medical Center
New York, New York
aortic surgery, thoracic aortic repair carries an even higher
Learning Objectives:
risk for postoperative morbidity and mortality. Although
As a result of completing this activity, the participant
these risks have diminished in recent years with the
will be able to
significant advances in perioperative care and surgical
Evaluate the risks, different approaches to anesthe-
techniques, aortic aneurysm surgery is still considered a
sia, outcome and anesthesia, motor evoked poten-
high-risk procedure. The introduction of less invasive and
tials, and anesthetic considerations, for patients
potentially safer stent grafts as an alternative to open
undergoing endovascular stenting
surgical repair has led to new perspectives in the treatment
Describe the important role of transesophageal
of aneurysms and aortic dissections.
echocardiography in diagnosing abnormalities and
guiding endovascular stenting procedures Endovascular grafting has the distinct advantage of
Discuss mechanisms of cerebrospinal fluid (CSF)
being a much less traumatic technique compared with
pressure rise, indications and risks of CSF drainage, conventional arterial reconstruction, owing to the unique
the risk of cerebral hemorrhage, and blood patch ability of being able to insert these grafts through small
incisions in remote arterial access sites. In patients with
Author Disclosure Information: multiple comorbidities, avoiding the need for extensive
The authors have disclosed that they have no periaortic dissection, prolonged aortic occlusion, sig-
financial interests or significant relationship with nificant fluid shifts, and substantial blood loss has special
any commercial companies pertaining to this educa- significance in patient outcome. Proper placement of an
tional activity. endovascular stent may reduce the incidence of aortic
rupture, whereas in cases of dissection, it will seal the in-
timal tear, decompress the false lumen, and may even re-
ortic aneurysm surgery is a formidable burden for
A every patient and carries substantial risks for serious
complications. When compared with abdominal
place conventional medical therapy for this condition. In
recent years, the accumulated experience in endovascular
stent surgery has allowed long-term outcome comparisons
with open surgery. The common conclusion of these stu-
dies is that the significantly lower operative mortality of
Supplemental digital content is available for this article. Direct URL stent-graft surgery in the short term (30 days post-
citations appear in the printed text and are available in both the HTML operatively) is offset in the long term by higher rates of
and PDF versions of this article. Links to the digital files are provided in
graft-related complications and costlier reinterventions for
the HTML and PDF text of this article on the Journal’s Web site
(www.asa-refresher.com). endovascular repair.1,2
41

2. 42 Drenger and Jain
The current indications for endovascular treatment of echocardiography—transesophageal echocardiography (TEE)
thoracic and abdominal aortic lesions are no longer limited for thoracic aortic lesions—is performed to confirm that
to patients who are unfit for open surgical repair due to the endovascular stent graft has successfully excluded the
older age and severe systemic concomitant diseases (sub- lesion from central aortic flow.
stantial cardiac, pulmonary, and renal dysfunction). An In aortic arch pathology and in descending thoracic
open surgical repair is still recommended for patients with dissection, special consideration is taken to exclude the
thoracoabdominal aneurysms, for whom endovascular initial intimal tear. Excluding the intimal tear with a short
stent graft options are limited.3 Most aortic aneurysms and endoluminal stent is usually followed by rapid thrombosis
type B aortic dissections can be treated by endovascular of the false lumen; however, because long-term sealing of
procedures as long as they meet the technical criteria for the secondary lumen is less certain, longer grafts are
safe advancement and deployment of the stent. In younger usually needed. By inhibiting the continued flow of blood
patients with minimal or no medical comorbidities, an open into the false lumen, end organ ischemia, infarction, and
surgical repair is indicated because of its established track risk of rupture are prevented and future aneurysm forma-
record of low complications and because the long-term tion is retarded. In cases of aortic arch pathology, addi-
outcome of endovascular stenting remains uncertain.4 tional surgical interventions might be needed to preserve
A patient is considered to be a candidate for a stent-graft carotid flow, such as carotid to carotid bypass, carotid to
procedure if the major prerequisites are met: (a) The mor- subclavian bypass, or femoroaxillary bypass.5 When the
phology of the aneurysm, with special attention to the whole arch is in need of repair, reimplantation of the bra-
‘‘landing zone,’’ will allow the graft to be anchored. A chiocephalic artery and the left carotid artery is performed
minimum of 20 mm of normal aortic wall is required for first, followed by arch endograft implantation either im-
safe stent deployment, secure anchoring, and avoiding the mediately or two weeks later. These aortic arch endografts
obstruction of major branch-artery ostia. (b) Distal vas- are currently not approved by the U.S. Food and Drug
cular access of sufficient size is present. Severe stenosis or Administration and their use is limited to centers partici-
occlusion of the abdominal aorta or the iliac arteries may pating in studying this evolving technique.
prevent the passage of the endograft delivery system. (c)
There is limited tortuosity of the aorta. Substantial kinking
may result in arterial dissection after insertion of the vas- By inhibiting the continued flow of blood into
cular sheath (see Supplemental Digital Content 1, http://
the false lumen, end organ ischemia, infarc-
links.lww.com/ASA/A108). Thoracic aneurysms are con-
sidered for repair in cases of pain symptoms and when the tion, and risk of rupture are prevented and
maximum diameter is more than 5.5 cm (smaller diameter
limit in Marfan syndrome). In cases of aortic dissection, future aneurysm formation is retarded.
continuing pain despite ‘‘optimal’’ medical treatment, sus-
picion of end organ or lower extremity ischemia, and acute Most of the acute complications of thoracic endograft
aneurysmal expansion of the false lumen are all indications procedures are related to problems with access to the im-
for endovascular intervention. Aortic transection from plantation site and with device implantation. Major ad-
blunt trauma and acutely ruptured aorta are emerging as verse events related to the device occur in 10% to 12% of
additional indications for endograft repair. patients in the initial 30-day perioperative period with
stroke rate between 2.5% and 8%, spinal cord ischemia in
1.5%, acute renal failure in 1.3%, and endoleaks in 10%
SURGICAL TECHNIQUE
to 20% of the patients.4 Blood loss ranges from approxi-
During endovascular aortic repair, a remote arterial site mately 300 to 500 mL; it may be considerably higher,
(usually the femoral artery) is exposed and isolated however, as in many cases it is not readily apparent. Cat-
through a small groin incision. More aggressive retro- astrophic bleeding is rare, but when it occurs, the an-
peritoneal dissections may become necessary to expose the esthesiologist must be ready with large bore venous access
external iliac artery if the femoral artery is small, stenotic, and available blood products.
or severely calcified. The aortic anatomy is defined using
fluoroscopy with particular attention toward the selection
PREOPERATIVE PATIENT EVALUATION
of appropriate ‘‘landing zones’’ for the endovascular stent
graft. After heparinization (5,000 IU), a large endovas- As in open abdominal aortic aneurysm surgery, the pri-
cular stent-graft delivery system is introduced into the re- mary goal of perioperative evaluation is to achieve
mote artery over a stiff guide wire and is advanced under accurate estimation of the patient’s current condition
fluoroscopic guidance to the diseased aortic segment. and the expected risk to organ function. Comorbidities
When the final position of the stent graft is achieved after tend to be similar in patients scheduled for endovascular
confirming patency of important branch arteries, the de- stent insertion as in those planned for open repair. The
livery device is withdrawn and the endograft is deployed same anesthetic considerations should be observed, both in
within the aorta. After deployment, fluoroscopy and possibly the preoperative evaluation and in selection of monitoring

3. Anesthesia for Endovascular Aortic Stenting 43
for the procedure (Table 1). Furthermore, intervention for a incisions. With such a wide preparation and exposure,
descending thoracic aneurysm carries additional risks of temperature monitoring and maintenance is crucial.
mortality and morbidity, including the risk of ischemic spinal
cord injury. No data conclusively demonstrates that the
prevalence of spinal cord ischemic injury is less for en- ANESTHETIC TECHNIQUES
dovascular approaches than for open surgical repair.4 Different anesthetic techniques have been described for
Both procedures should be classified as high-risk surgery aortic stent graft placement including local anesthesia, re-
according to the American College of Cardiology/Amer- gional anesthesia, and general anesthesia (GA). With in-
ican Heart Association guidelines on preoperative cardiac creasing physician experience and the development of
evaluation.6 For such high-risk surgery, preoperative non- more sophisticated devices, regional anesthetics (including
invasive or invasive coronary interventions (PCI) are in- epidural, spinal-epidural, and spinal) and MAC using local
dicated if the patient has major or intermediate clinical anesthetics supplemented with sedation may be used.
predictors of cardiac risk. However, if the patient’s cardiac However, it is important to remember that in such en-
condition is stable, medical therapy should be seriously dovascular procedures, painful stimuli are concentrated at
considered over PCI, especially if the urgency of the op- specific moments, separated by intervals devoid of pain;
eration becomes an important factor. PCI invariably will thus, these moments of pain can be anticipated. Providing
cause postponement of surgery by two months to one year. a short-acting anesthetic by bolus is preferable to con-
These days, high-resolution multidetector computed to- tinuous infusion, as patient cooperation can be maintained
mographic coronary angiography is gaining wide accep- better. Remifentanil (0.03 mg/kg/minute) in 0.02 incre-
tance as an alternative for invasive coronary angiography, ments with midazolam is an appropriate method to pro-
sparing some of the complications related to invasive ca- vide effective analgesia for patients in whom deep sedation
theterization. Preliminary data provides promising scope is considered sufficient.11
for use of computed tomography preoperatively to evalu-
ate patients at risk for cardiac ischemia who are scheduled
for noncardiac surgery.7 In such endovascular procedures, painful
Perioperative b-blockade, ACE inhibitor, and statin ther-
apy are recommended to reduce the risk of cardiac morbidity stimuli are concentrated at specific moments,
and mortality, especially in patients scheduled for high-risk
surgery.8 b-Blockade, in particular, has been shown to reduce
separated by intervals devoid of pain; thus,
the risk of perioperative mortality while cessation of therapy
these moments of pain can be anticipated.
has been associated with an increase in short- and long-term
mortality.9 Similarly, perioperative use of ACE inhibitors,
although associated with greater need for vasoconstrictors, Choice of anesthetic technique is dependent on the
showed a significant reduction in major vascular complica- planned surgical interventions and the patient’s comorbid
tions, whereas cessation of therapy postoperatively seems to conditions. The need for extensive inguinal exploration
be related to fatal and nonfatal ischemic events (studied in and dissection or for the construction of a femoral artery to
recent coronary artery bypass graft patients).10 If therapy has femoral arterial conduit may favor either regional an-
not been initiated already, b-blockade, ACE inhibitor, and esthesia or GA. When thoracic stent placement analysis by
statin therapy should optimally be started between 30 days TEE is required, or a complex procedure is planned, or
and one week before surgery. conversion to open surgery is more likely, then GA should
Endovascular repair of aortic pathology carries a variable be considered. If surgical dissection is extended into the
risk of sudden conversion to a laparotomy or combined surgi- retroperitoneum, a higher level of regional anesthesia or
cal intervention (iliac artery exploration, arterial bypass at- GA will be necessary to provide adequate anesthesia. If the
tachment of critical vessels) and thus, appropriate anesthetic patient is undergoing local anesthesia with MAC or re-
monitoring should be considered. Large bore intravenous ca- gional anesthesia, adequate intravenous sedation is
theters should be placed for volume replacement and a right- necessary because of agitation associated with restlessness
sided arterial line. A central venous line and a pulmonary artery and pain from lying in one position for a prolonged period
catheter for volume monitoring may also be indicated, and of time. The disadvantage of high epidural anesthesia is
should be based on the institution’s perceived risk of conversion related to the difficulty in precisely controlling the anes-
to an open repair and the patient’s comorbidities. With an thetic level, and the concern for intercostal muscle weak-
average blood loss of approximately 500 mL and fluid re- ness with the need to support ventilation. For patients with
quirements of approximately 3,000 mL, invasive monitoring is severe coexisting diseases, a spinal/epidural technique or a
indicated in selected populations even when monitored an- continuous spinal anesthetic is likely to be a better option.
esthesia care (MAC) or regional anesthesia is used. The latter may offer hemodynamic stability and more ac-
Although there may be only two small incisions in the curate control of the anesthetic level.12
groin, the patient is usually prepared from the nipple line An unanswered question is whether the type of anesthesia
to the knees because of the possible need to extend the used for endovascular repair affects patient outcome.

4. 44 Drenger and Jain
Table 1. Perioperative Anesthetic Management for Endovascular Aortic Procedures
Identify Patient’s Comorbidities, with Emphasis on Neurologic, Cardiac, and Renal Conditions with Preoperative Optimization
Preoperative
Neurologic At risk for stroke or spinal cord ischemia Comprehensive neurologic evaluation
Consider with the surgeon the option of CSF drainage in high-risk
patients
Cardiac High risk according to ACC/AHA preoperative guidelines Follow ACC/AHA guidelines for workup (evaluation of coronary
vasculature, ventricular function)
Consider using coronary computed tomography angiography
when delay in operation is unwarranted
Perioperative b-blockade, ACE inhibitors, and statins are
recommended
Renal Risk for contrast-induced nephropathy Renal function tests and creatinine clearance
Consider postponement of surgery until recovery if renal function
deteriorated due to recent imaging test
Intraoperative
Hemodynamic Standard ASA monitors Continuous arterial blood pressure monitoring (preferably right
radial artery), large bore intravenous access
Be prepared for pharmacological intervention to slow heart rate
(adenosine, b-blockers)
Sudden major hemorrhage possible (visible or occult) Be prepared for significant blood loss
Neurologic Consider CSF drainage Intraoperative—Keep CSF pressure at 10 cmH2O
Postoperative—Keep CSF pressure at 15 cmH2O for 48 hours
Consider myogenic motor evoked potential monitoring Use intravenous anesthesia, avoid volatile anesthetics. N2O is
allowed
If very small dose of muscle relaxant is used, keep twitch height
greater than 80%
Periods of pain are defined according to intervention Consider ultra-short-acting opioids when needed
Cardiac TEE is essential in thoracic aorta endovascular stenting See Table 2
Renal Large dose of contrast material is used Adequate intravenous hydration with N-acetylcysteine and
bicarbonate
In renal dysfunction patients, consider use of low osmotic type dye
and limit dye load
Postoperative
Cardiac Patients are at high cardiac risk Use monitored bed for 24 hours; postoperative ECG
Expect cardiac morbidity (ischemia, congestive heart failure,
arrhythmias)
Neurologic Spinal cord ischemia is possible Maintain good hydration, and keep systolic blood pressure at
preoperative values
Perform neurologic examination
Keep CSF drainage for 48 hours
CSF ¼ cerebrospinal fluid; ECG ¼ echocardiography; TEE ¼ transesophageal echocardiography.
Although stent-graft insertion is minimally invasive com- 2,387 patients, Walschot et al.15 showed that GA was an
pared with the conventional procedure, the use of GA is independent risk factor for mortality after endovascular
traditionally preferred by the surgeons. Several studies repair. However, the EuroSTAR study14 demonstrated no
have demonstrated that GA was associated with increased advantage for any anesthetic technique regarding outcome
duration of surgery, intensive care unit admissions, in- or the incidence of intraoperative complications.
tensive care unit length of stay, and systemic complica-
tions. Verhoeven et al.13 in a study of 239 consecutive
patients and Ruppert et al.14 in a prospective multicenter
PROXIMAL GRAFT DEPLOYMENT
study of 5,557 patients (EuroSTAR) showed that older age Distal migration of the device occurring during proximal
and greater surgical complexity are the main reasons for endograft deployment may result in inadequate exclusion
the difference in patient outcomes with GA. Additional of the aneurysm sac with resultant endoleak. Device
studies reached opposite conclusions about the role of GA malposition caused by inadvertent migration may result in
in determining patient outcome. In a meta-analysis of either occlusion of major arterial branches or incomplete

5. Anesthesia for Endovascular Aortic Stenting 45
Table 2. TEE Examination in Thoracic Aortic Stenting
Aortic Aneurysm Identification
Preoperative Evaluation
Normal aortic diameters Aortic valve 23–26 mm
Ascending aorta/arch 29–36 mm
Descending aorta 17–26 mm
Transducer angle (degrees) Short axis aortic valve 40–60 degrees
Depth—6 cm from aortic valve/ Long axis aortic valve with proximal ascending aorta 90–120 degrees
antiflexion use color Doppler flow Short axis ascending aorta 0 degrees
Long axis aortic arch 0 degrees
Short axis aortic arch 90 degrees
Probe in stomach—withdraw slowly Short axis descending aorta 0 degrees
Long axis descending aorta 90 degrees
Aortic pathology Aortic aneurysm
Ascending aorta—fusiform aneurysm
Aortic arch—saccular aneurysm
Descending aorta—pseudoaneurysm
Aortic dissection—site of tear (entry)
Stanford type A—involves ascending aorta/aortic arch
Stanford type B—involves descending thoracic aorta
Intraoperative Evaluation
Before stent anchoring 1. Measurement of aortic dimensions
2. Aortic wall thickness diameter
3. Adequate wall length (landing zone) without aneurysm involvement below the subclavian artery
4. Visceral vessels identified
Aortic Dissection
1. Classification (Stanford type A and B)
2. Proximal site of entry
3. False and true lumen identification
4. Slow flow in the false lumen
5. Guide wire positioning
After stent anchoring 1. Incomplete stent-graft apposition
2. Adequate seal in healthy aorta; that is, parallel walls, consistent diameter, no luminal debris
3. Endoleaks
Type 1—incompetent seal at proximal or distal stent attachment
Type 2—leakage to aneurysmal sac from branch vessels
Type 3—Failure of anastomosis between stent components
Type 4—leakage through graft material
Limitations of TEE 1. Limited view to segment of ascending aorta, behind the right bronchus, parts of arch, and abdominal
segments beyond the celiac trunk
2. The need for general anesthesia
TEE ¼ transesophageal echocardiography.
exclusion of the aneurysm. Induced hypotension, by sodium TRANSESOPHAGEAL ECHOCARDIOGRAPHY
nitroprusside or nitroglycerin, during device deployment has MONITORING
been successfully used by some centers to assist in proximal
endovascular stent graft placement and may reduce the With the rapid evolution of TEE technology and with the
magnitude of migration. The risk of malposition may theo- esophagus being in close approximation to the aorta, TEE
retically be decreased further by ventricular quiescence, has become an excellent and safe tool for diagnosing pa-
which can be achieved by pharmacological induction of thology of the distal aortic arch, the descending thoracic
sinoatrial and atrioventricular nodal inhibition with high- aorta, and the proximal abdominal aorta (Table 2). TEE is
dose adenosine.16 an excellent tool with a high rate of accuracy in revealing

6. 46 Drenger and Jain
renovascular disease due to atherosclerosis and/or diabetes
mellitus. After successful exclusion of the aneurysm by the
stent graft, there will be aneurysm sac thrombosis with
subsequent hemolysis contributing to myoglobinuria. In
addition, myoglobinuria may occur in cases of ischemia
and reperfusion injury. All of these factors add to the risk
of renal complications. The incidence of renal complica-
tions after endovascular repair of an abdominal aortic
aneurysm can be as high as 10% compared with 25% in
open aortic surgery.21,22 Adequate hydration should be
ensured and urine output closely monitored during the
procedure. The intravenously injected contrast material
can induce diuresis, and can give a false sense of adequate
hydration and urine output if one relies solely on urine
output as a measure of volume status. Central venous
Figure. 1. Transesophageal echocardiography Doppler image of blood flow pressure monitoring may be a useful adjunct. Another
in the aortic arch and in the subclavian artery in 35-degree angle.
consequence of multiple angiograms is the increased ra-
diation exposure for all personnel involved. In one review
pericardial effusion, the presence of aortic regurgitation, of 47 cases over a year, the average fluoroscopy time was
the extent of a dissection, and the intimal tear location approximately 40 minutes per case.23 Lead aprons at-
(almost 100% of the time). It can provide instantaneous tenuate greater than 85% of the radiation dose and, if
views of the location of the guide wires (95%) and an es- keeping the appropriate distance, the average exposure of
timation of endograft sizing and location before deploy- an anesthesiologist was found to be 0 mSv over 6 months at
ment in relation to the normal and diseased thoracic one institution.24
aorta.4 TEE appears to have distinct advantages over peri- Blood loss can be steady and considerable, but hidden,
operative angiography as it provides exact vessel and lesion during endovascular repair of an abdominal aortic aneur-
sizing and localization, which is difficult to obtain during ysm. Most blood loss occurs as the introducer sheaths and
single plane angiography (Figure 1) (see Supplemental Di- stent grafts are passed into and out of the femoral arteries,
gital Content 2, http://links.lww.com/ASA/A109). In con- and may be hidden in the surgical drapes. The actual blood
trast to angiography, both endograft leakage and iatrogenic loss will depend on the amount of catheter manipulation and
dissections may easily be diagnosed by TEE. Although not duration of the procedure. A sudden, unexplained decrease
always possible, large intercostal arteries have been imaged, in blood pressure should alert the anesthesiologist to the
thus avoiding inadvertent obstruction by the aortic stent possibility of a vascular catastrophe such as rupture, per-
graft; however, consistent visualization of intercostal ar- foration, or avulsion of the aorta or a large artery. An aortic
teries may not be assured in all patients. After stent-graft rupture, recognized in a timely manner, may sometimes be
placement, exclusion of flow from the aorta into the aneur- amenable to treatment with intraluminal balloon tamponade
ysm, thrombosis of the false lumen, and the existence of re- and subsequent deployment of the device beyond the area of
sidual endoleaks can usually be confirmed using color rupture, but an emergent laparotomy is often necessary.
Doppler flow imaging.17,18 TEE can also become very decisive
in choosing the stent landing zone and in identifying
(B mode) incomplete obliteration of the false lumen that ne- A sudden, unexplained decrease in blood
cessitates additional balloon expansions of the stent (see Sup-
pressure should alert the anesthesiologist to
plemental Digital Content 3, http://links.lww.com/ASA/A110).
Initial thrombosis of the false lumen was noticed as ‘‘smoke’’ by the possibility of a vascular catastrophe such
the TEE.19 Intravascular ultrasound has been recommended in
endovascular repairs. It has no advantage over TEE; however, it as rupture, perforation, or avulsion of the
was found to be helpful in patients with complex anatomy and
abdominal extension of the dissection.20 aorta or a large artery.
INTRAOPERATIVE COMPLICATIONS AND
PATIENT OUTCOME SOMATOSENSORY AND MOTOR EVOKED
With multiple angiograms to position the prosthesis and to
POTENTIALS
check blood flow for endoleaks, approximately 250 to Today, the major risk from thoracic aortic repair procedures
300 mL of contrast will be administered during the comes from the central nervous system and not from the
procedure. Contrast-induced renal failure is a serious heart. Thus, monitoring the central nervous system and the
concern, particularly in those with chronic underlying spinal cord is advocated both in open surgery and in certain

7. Anesthesia for Endovascular Aortic Stenting 47
endovascular aortic procedures. It is indicated when a long SPINAL CORD ISCHEMIA
thoracic stent is planned, with previous aortic repair in
The reported incidence of neurologic injuries in the post-
which segmental arteries were probably not reimplanted,
operative period after endovascular thoracic aortic re-
when the stent placement involves critical level—T8-L1, and
construction is similar to that after open thoracic aortic
in the presence of dissection or rupture.
repair. Matsuda et al.29 reported an overall incidence of
Rapid loss of somatosensory evoked potentials (SSEPs)
paralysis of 3.7%; 6% when a large, distal thoracic section
occurs soon after aortic clamping, but may also be caused
of the aorta is covered by the endograft; and 12.5% when
by peripheral hypoperfusion, temperature changes, an-
the artery of Adamkiewicz is sacrificed.30 Open athero-
esthesia, and other factors. We found a consistent distinc-
sclerotic thoracic aneurysm repair carries an incidence of
tion between patients who received adequate distal bypass
paralysis of 2% to 8.3%.31,32 Intercostal arteries that
shunting and those who did not.25 Without distal bypass,
supply the anterior spinal cord may be sacrificed during
SSEP disappeared within 5 to 30 minutes of aortic cross-
reconstruction of the descending aorta, resulting in spinal
clamping, whereas with adequate distal perfusion, the
cord injury. The anterior spinal cord enjoys little if any
behavior of SSEP was commensurate with the clinical
reserve blood supply. The major collateral joining the
neurologic outcome. In recent years, transcranial motor
anterior spinal artery is the arteria radicularis magna of
evoked potentials (tcMEPs) have become the preferred
Adamkiewicz, which in most patients originates from an
method for clinical use during high aortic surgery. The
intercostal artery between the T8 and L1 level. If this cri-
pressure of time under which surgeons are trying to com-
tical branch is patent and emerges from the aneurysmal
plete the repair during aortic cross-clamping necessitates a
wall, a significant ischemic risk to the spinal cord might be
very fast response time for the expression of ischemic
anticipated if the vessel is excluded by the endoluminal
spinal changes in EP recordings. The tcMEP method was
stent. Additional supply to the distal cord comes from the
found to be highly sensitive in predicting neurologic out-
iliolumbar arteries and the lateral sacral arteries, branches
come, with a decrease in the myogenic signal amplitude
of the hypogastric arteries. Several reports demonstrated
within 2 to 5 minutes after the onset of spinal cord ische-
an increased incidence of poststent paralysis in patients
mia.26,27 Such short notice facilitated timely, fashioned
who had previously undergone operations on the abdom-
surgical and anesthetic interventions such as reattachment
inal aorta. It seems that during such operations, several
of intercostal arteries, relocation of the aortic clamp,
tributaries to the cord are sacrificed—a fact that becomes
management of distal aortic perfusion, induced hyperten-
crucial later, when additional endograft repair is needed.
sion, and cerebrospinal fluid (CSF) drainage. The ex-
Long-segment thoracic endovascular repair or con-
planation offered by van Dongen et al.26 and de Haan and
secutive endograft segments connected in a row also create
Kalkman27 for the faster myogenic response compared
a significant risk factor for spinal cord ischemia.33,34 Ap-
with SSEP recording is that synaptic transmission is much
plication of short endografts and avoiding the placement
more sensitive to ischemia compared with axonal trans-
of stent grafts between T8 and L2 is therefore re-
mission. The interneurons connecting the gray to white
commended to prevent spinal cord ischemia (see Supple-
matter are the first to be affected by ischemia. The energy
mental Digital Content 4, http://links.lww.com/ASA/
utilization of the axon to action potential propagation is
A111).
very low, resulting in late appearance of cell ischemia.
The successful use of CSF drainage during endovascular
In a series of 21 patients, Weigang et al.28 showed im-
aortic repair has been described anecdotally in several case
mediate, but short-term loss of tcMEPs after stent de-
reports of patients who underwent thoracic aortic aneur-
ployment in 3 of their patients (14%). The EPs recovered
ysm repair.35,36 Clinical symptoms of paralysis were re-
and no postoperative neurologic deficit was noticed, ex-
solved although the primary CSF pressure upon catheter
cept in one patient who suffered delayed onset paraplegia
insertion was not always high, and as several rescue pro-
after 21 days. The reaction to the loss of both tcMEPs and
cedures are used in parallel, the relative contribution of
SSEPs in this series was abrupt elevation of blood pressure
each method is not clear. The increase in CSF pressure after
with norepinephrine, reduction in central venous pressure
stent-graft deployment might be attributed to sympathetic
with nitroglycerin, and aspiration of CSF to reduce CSF
spinal stimulation or to the local acidosis-induced veno-
pressure to 10 cmH2O.
dilation that occurs in the presence of inadequate spinal
A critical disadvantage of tcMEPs is the high sensitivity
cord perfusion.37 CSF drainage should be continued for 48
to volatile anesthetics and muscle relaxants. Thus, when
to 72 hours, and strict control of hemodynamic status
EP monitoring is planned, intravenous anesthesia should
maintained to prevent hypotension.
be used with no volatile anesthetics. N2O can be used ex-
cept for patients in whom nerve conduction defects were
previously noted. If muscle twitch height is continuously CEREBROVASCULAR COMPLICATIONS OF CSF
monitored electronically, a small infusion dose of vecur-
DRAINAGE
onium (30 mg/kg/hour) to maintain 80% of the twitch
height can be performed without interfering with the Stroke after high aortic surgery is a devastating complica-
quality of EP monitoring26 (B.D., personal experience). tion and is usually thromboembolic in origin, which can

8. 48 Drenger and Jain
result in either an ischemic or a hemorrhagic presentation. 3. Prinssen M, Verhoeven ELG, Buth J, et al.: A randomized trial
Recently, after sporadic reports of intracranial hemorrhage comparing conventional and endovascular repair of abdominal aortic
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drainage was implicated as a possible explanation for the ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and
cerebral bleeding.38,39 Dardik et al.39 retrospectively re- management of patients with thoracic aortic disease. J Am Col
Cardiol 2010; 55:e27–129.
corded 8 of 230 patients (3.5%) who developed subdural 5. Criado FJ, Clark NS, Barnatan MF: Stent graft repair in the aortic
hematomas. In their multivariate analysis, they emphasized arch and descending thoracic aorta: A 4-year experience. J Vasc Surg
2002; 36:1121–8.
that the only significant factor correlating with the occur-
6. Fleisher LA, Beckman JA, Brown KA, et al.: ACC/AHA 2007
rence of subdural hematoma was large volume of CSF guidelines on perioperative cardiovascular evaluation and care for
drained. However, only one patient developed neurologic noncardiac surgery: A report of the American College of Cardiology/
symptoms while the spinal drainage catheter was still in American Heart Association Task Force on Practice Guidelines
developed in collaboration with the American Society of Echocardio-
place. Despite the conflicting data, the role of CSF drainage graphy, American Society of Nuclear Cardiology, Heart Rhythm
as a causative factor in subarachnoid, intracerebral, or sub- Society, Society of Cardiovascular Anesthesiologists, Society for
tentorial hemorrhage should be addressed. It has been at- Cardiovascular Angiography and Interventions, Society for Vascular
Medicine and Biology, and Society for Vascular Surgery. J Am Coll
tributed to a cerebral hypotension related traction effect, Cardiol 2007; 50:e159–e241.
which subsequently may trigger a tear of bridging veins and 7. Durst R, Bogot N, Gilon D, Drenger B: Potential role for coronary
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