VASCULAR CHALLENGES
| INTESTINAL VASCULAR EMERGENCIES —Robert Maggisano, MD, Assistant Professor, Department of Surgery,
University of Toronto Faculty of Medicine, Toronto, ON
|
| Acute mesenteric ischemia (AMI): most common etiologies include embolus in superior mesenteric artery (≈50%
of cases) and nonocclusive mesenteric artery disease; patients often older, with chronic disease (eg, cardiovascular, renal);
thrombosis of superior mesenteric vessels responsible for <10% of cases; common pathway of death in patients
with variety of terminal diseases; overall incidence low; high morbidity and mortality (improved with early recognition
and aggressive treatment); progression—untreated AMI progresses to transmural bowel necrosis or infarction,
leading to gangrene or perforation; intervention—surgical resection required; revascularization recommended
|
| Classification of AMI: iatrogenic—eg, tumor resection may involve replacement of arterial structures;
traumatic—blunt and sharp injuries may cause AMI; diagnosis and treatment straightforward; nontraumatic—older
population with cardiovascular comorbidities (more difficult to treat); medically induced—toxic, life-sustaining
drugs may induce vascular insufficiency in mesenteric vascular bed
|
| Diagnosis: classic clinical triad of abdominal pain, bowel-emptying syndrome, and leukocytosis occurs infrequently;
leukocytosis often absent in older patients; abdominal pain frequently delayed; high index of suspicion important
for diagnosis
|
 | Laboratory studies: 75% of patients have occult blood, but no visible bleeding; most laboratory studies nonspecific
(better for ruling out other pathologies than for diagnosing intestinal ischemia)
|
| Imaging studies: magnetic resonance angiography (MRA)—good for diagnosing chronic, but not acute, mesenteric
ischemia; ultrasonography (US), duplex US, and radiography—sufficient for evaluating other causes of abdominal
discomfort, but not effective for diagnosing AMI; angiography—gold standard, but not always available; high
sensitivity and specificity; facilitates catheter placement and initiation of treatment (eg, lytic therapy, heparin, papaverine);
computed tomography angiography (CTA)—multiple slice CTA creates 3-D reconstructions; high sensitivity
and specificity
|
| Treatment: cardiovascular stabilization or resuscitation, as needed; initiation of antibiotics important to prevent sepsis
(caused by infiltration of bowel bacteria); appropriate pharmacologic treatment of comorbidities (eg, congestive heart
failure, atrial fibrillation); surgery—laparotomy; appropriate resection of segment of ischemic bowel; revascularization,
if possible; second-look surgery 24 to 48 hr after initial surgery
|
| Pathophysiology: occlusion occurs in visceral bed; at first, vasodilation occurs in region distal to occlusion (bowel resistant
to ischemia; patient asymptomatic); after 12 to 15 hr, intense vasoconstriction occurs (in attempt to maintain
pressure to vascular bed); animal models—introducing catheters to vascular bed and initiating vasodilation with papaverine
decreases mortality by 10% to 15%
|
| ENDOVASCULAR REPAIR OF THORACIC ANEURYSMS —Darren B. Schneider, MD, Assistant Professor of Surgery
and Radiology, Division of Vascular Surgery, University of California, San Francisco, School of Medicine
|
| Thoracic aortic aneurysm: annual incidence—≈10 cases per 10,000 patients; up to 70% of cases go undetected
(use of CT and magnetic resonance imaging [MRI] increases rate of detection); mortality—up to 70% of untreated
patients die within 5 yr; risk for rupture increases with size of aneurysm (5%-10% per yr for aneurysms ≥6 cm in diameter)
|
| Repair techniques: open-surgical repair—durable effective approach, but associated with high mortality (8%-20%),
especially in older patients; associated morbidities include neurologic sequelae (eg, stroke, paraplegia), cardiopulmonary
problems, and renal and visceral ischemia; case series looking only at reports of aneurysms isolated to thoracic aorta
(mostly elective cases) found mortality rates of 2% to 10% and incidence of paraplegia 2% to 4%; endovascular
repair—case series composed of patients with variety of pathologies and included patients with ruptures or dissections;
collective mortality rate 6.7%; incidence of paraplegia 2.7%
|
| Comparison of techniques: prospective multicenter industry-sponsored study compared endovascular stent-graft repair
to open-surgical repair of thoracic aneurysms; patients who did not meet anatomic criteria for stent grafting underwent
surgical repair (ie, some anatomic differences between study groups); results—endovascular approach associated
with reduced 30-day mortality and rate of cardiopulmonary complications; no significant difference in incidence
of stroke; rate of paraplegia reduced dramatically in endovascular group (findings call into question proposed etiology
of paraplegia); endovascular approach also associated with shorter stays in hospital (total decreased by ≈50%)
and intensive care unit (ICU); mortality—endovascular repair associated with lower aneurysm-related mortality, but
no difference in all-cause mortality at 2 yr
|
| Preparation: endovascular repair requires more planning; curved structure of thoracic aorta difficult to evaluate with
cross-sectional CT; high-resolution CTA critical for generating multiplanar reconstruction of aortic arch; accurate
measurements of diameter of aortic arch needed to determine size of graft and length of treatment area
|
| Challenges in endovascular repair: access—introduction of stent grafts often requires large sheath (diameter ≥9
mm); alternate approach needed for patients with small external iliac arteries; stent graft may be introduced directly to
common iliac artery through prosthetic conduit (attached to common iliac artery through incision in lower quadrant) to
bypass small-caliber vessels; coverage of great vessels—when repairing aneurysms involving or approaching distal
aortic arch, surgeon often must cover subclavian artery; sacrificing left subclavian artery sometimes necessary to position
stent graft appropriately; if patient has diseased (or absent) right vertebral artery or history of left internal mammary artery
to coronary bypass graft, bypass performed to maintain perfusion of left subclavian artery; implantation site—stability
of proximal implantation site affects outcome; branching aortic arch improves proximal placement when aneurysm encroaches
further up aortic arch; procedure more invasive, requiring sternotomy
|
| Acute type B aortic dissections: relatively common; treatable with endovascular approach; complications—aortic
rupture; visceral ischemia; neurologic sequelae; mortality—85% of deaths occur within first week after presentation;
treatment—surgery (generally reserved for complicated cases) associated with high mortality rate (\>30%); medical
therapy preferred for uncomplicated cases; chronic aneurysmal dilatation of dissected aorta common; data from international
registry shows lower overall mortality associated with medical therapy (≈13%) compared to surgical therapy
(≈30%); addition of percutaneous intervention improves outcome, compared to medical treatment alone
|
| Endovascular treatment of type B dissections: goals—place stent graft to exclude proximal entry tear; improve
perfusion of true lumen; if necessary, endovascular stenting of branch vessels or fenestration of septum increases perfusion;
meta-analysis of case series—high rate of technical success; low rates of neurologic complications and paraplegia;
30-day mortality 5%; 2-yr survival ≈80%; Investigation of Stent Grafts in Type B Aortic Dissection
(INSTEAD) trial—European multicenter randomized prospective trial (in progress) randomizing 136 patients with
uncomplicated type B dissections to medical therapy or endovascular repair; preliminary data suggest improved survival
associated with endovascular repair; speaker’s experience—endovascular repair in 34 patients (thoracic aortic
aneurysm or aortic dissection); no deaths; 2 cases of transient paraplegia; median postoperative hospital stay 4 days
|
| Future directions: endovascular repair of entire aorta, eg, treating thoracoabdominal aneurysms with multibranched
stent grafts, and performing branched repairs in aortic arch
|
| DVT/PE PROPHYLAXIS —Edward N. Libby, MD, Associate Professor of Medicine, Division of Hematology and Oncology,
University of New Mexico School of Medicine, Albuquerque
|
| Guidelines: American College of Chest Physicians (ACCP), 2004—recommendations about prevention and treatment
of thrombosis ranked by strength of evidence (available at www.chestjournal.org); patient safety—Agency
for Healthcare Research and Quality (AHCRQ) ranked 79 interventions based on strength of evidence; prophylaxis
for deep venous thrombosis (DVT) ranked highest; Surgical Care Improvement Project, which seeks to decrease
surgical complications by 25%, lists DVT prevention as target area; Sabiston Textbook of Surgery, 17th edition,
2004—follows ACCP guidelines
|
| Recommendations: look for personal or family history suggestive of hypercoagulable state; consider thrombophilia
panel (factor V Leiden and prothrombin gene mutations; antithrombin III [ATIII], proteins C and S, and antiphospholipid
antibody panel); risk-stratify patients based on age, surgical procedure, history of clots, cancer, obesity,
varicose veins, CHF, presence of deep intravenous lines, nephrotic syndrome, pregnancy, and estrogen use
|
| Sequential compression devices (SCDs): most common method of prophylaxis in surgery; efficacy—reduce incidence
of thrombosis by ≈60% after some surgeries; mechanism—unknown; effect on fibrinolytic activity not established
|
| Elastic stockings: reduce incidence of venous thromboembolism (VTE), but inferior to intermittent pneumatic compression
(IPC) devices; improperly fitted stockings may increase venous pressure and significantly increase risk for
VTE; no controlled trials looking at use for prolonged out-of-hospital prophylaxis; recommendations—only use in
combination with other modalities
|
| IPC devices: provide sequential pneumatic compression of leg or foot; proposed mechanism—pumps venous blood,
reducing stasis; may facilitate clearance of prothrombotic clotting factors; may increase plasminogen levels; safety
and efficacy—associated with decreased incidence of symptomatic VTE after hip arthroplasty, but only among
smaller thinner patients (BMI <25); excellent safety profile; minor complications include discomfort and possible
breakdown of skin; efficacy dependent on continuous use during nonambulatory periods (≥15 hr/day in one study);
potential to reduce ambulation (important to encourage patients to ambulate); recommendations—appropriate as
primary modality for prophylaxis in many settings; appropriate as adjunct modality for high-risk patients undergoing
general or urologic surgery, and for patients undergoing hip or knee replacement
|
| Heparin: unfractionated heparin (UFH), 5000 U given tid, reduces incidence of DVT; one study found bid administration
no more effective than placebo
|
| Prophylaxis of general surgery patients: low risk—minor surgery in young patients with no additional risk factors
associated with 2% risk for calf DVT, ≈0.5% risk for proximal DVT, and very low risk for clinical or fatal pulmonary
embolism (PE); no prophylaxis required; early and aggressive mobilization recommended; moderate risk—
surgery in patients 40 to 60 yr of age with no additional risk factors; minor surgery in patients with risk factors; risk for
calf DVT substantially increases; risk for proximal DVT 2% to 4%; risk for clinical PE ≈1%; risk for fatal PE <0.5%;
prophylaxis options include low-dose UFH (q12h or q8h), low molecular weight heparin (LMWH), compression devices,
or elastic stockings; high risk—surgery in older patients or those 40 to 60 yr of age with risk factors; risk for
DVT and PE increases; risk for fatal PE ≈1%; prophylaxis options include low-dose UFH (q8h), LMWH, or IPC devices;
highest risk—trauma patients; patients with cancer or prior DVT; hip or knee arthroplasty; patients at high risk
for DVT and PE; prophylaxis options include LMWH, fondaparinux, full-dose oral vitamin K antagonist (VKA), or
IPC plus another modality; standard of care—LMWH for patients with moderate or high risk
|
| Other issues: aspirin—ACCP recommends against use as sole prophylaxis for any surgical procedure; poor evidence
for use; other modalities superior; more studies needed; bleeding—LMWH associated with “acceptably low” risk for
clinically important bleeding and desirable risk-to-benefit ratio; exceptions include patients with renal insufficiency;
combining LMWH with other anticoagulants (including nonsteroidal anti-inflammatory drugs [NSAIDs]) increases
risk; hormone replacement therapy (HRT)—concern about perioperative use of HRT; recent studies suggest use
does not increase risk for postoperative VTE (even after hip or knee replacement), but caution warranted (consider
discontinuing in high-risk patients)
|
| LMWH options: enoxaparin most widely used in United States; good risk-to-benefit ratio and safety profile; dalteparin
and tinzaparin older, widely used in Canada and Europe; fondaparinux consists of small part of heparin molecule,
interacts with ATIII, and does not appear to cause heparin-induced thrombocytopenia (HIT)
|
| New drugs: ximelagatran—no longer available (associated with impaired liver function); dabigatran—oral thrombin
inhibitor in development; factor Xa inhibitors—fondaparinux and idraparinux (injectable); razaxaban and apixaban
(oral)
|
| Medicolegal aspects: involve patient in decision regarding thromboprophylaxis; obtain informed consent when possible
|
Educational Objectives
| The goal of this program is to provide the clinician with information about the prevention and management of several
vascular emergencies. After hearing and assimilating this program, the clinician will be better able to:
|
| 1. Diagnose and treat patients with acute mesenteric ischemia.
|
| 2. Summarize the advantages and disadvantages of endoscopic repair of thoracic aortic aneurysms.
|
| 3. Evaluate new and evolving applications for endoscopic repair of aortic injuries.
|
| 4. Risk-stratify surgical patients based on risk for thromboembolic events.
|
| 5. Choose appropriate prophylactic modalities for surgical patients to prevent postoperative venous thromboembolism.
|
Suggested Reading
Acosta-Merida MA et al: Identification of risk factors for perioperative mortality in acute mesenteric ischemia.
World J Surg 30:1579, 2006; Cherukapalli C et al: Aortic debranching for descending thoracic aortic aneurysm
repair by stent grafts. Am Surg 73:32, 2007; Gartenschlaeger S et al: Successful percutaneous transluminal angioplasty
and stenting in acute mesenteric ischemia. Cardiovasc Intervent Radiol, 2007 [Epub ahead of print]; Hiramoto
JS et al: A double-barrel stent-graft for endovascular repair of the aortic arch. J Endovasc Ther 13:72, 2006;
Khoynezhad A et al: Risk factors of neurologic deficit after thoracic aortic endografting. Ann Thorac Surg
83:S882, 2007; Leonardi MJ et al: A systematic review of deep venous thrombosis prophylaxis in cancer patients:
implications for improving quality. Ann Surg Oncol 14:929, 2007; Murray D et al: Access for endovascular aneurysm
repair. J Endovasc Ther 13:754, 2006; Patel HJ et al: Long-term results from a 12-year experience with endovascular
therapy for thoracic aortic disease. Ann Thorac Surg 82:2147, 2006; Schurink GW et al: Assessment of
spinal cord circulation and function in endovascular treatment of thoracic aortic aneurysms. Ann Thorac Surg
83:S877, 2007; Shih MC et al: CTA and MRA in mesenteric ischemia: part 2, normal findings and complications
after surgical and endovascular treatment. AJR Am J Roentgenol 188:462, 2007; Stewart D et al: A prospective
study of nurse and patient education on compliance with sequential compression devices. Am Surg 72:921, 2006;
Stone DH et al: Stent-graft versus open-surgical repair of the thoracic aorta: mid-term results. J Vasc Surg 44:1188,
2006; Summerfield DL: Decreasing the incidence of deep vein thrombosis through the use of prophylaxis. AORN
J 84:642, 2006; Testa L et al: Ximelagatran/melagatran against conventional anticoagulation: A meta-analysis
based on 22,639 patients. Int J Cardiol, 2007 [Epub ahead of print]; Zandrino F et al: Assessment of patients with
acute mesenteric ischemia: multislice computed tomography signs and clinical performance in a group of patients
with surgical correlation. Minerva Gastroenterol Dietol 52:317, 2006.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue,
the following has been disclosed: Dr. Schneider receives grant support from W.L. Gore & Associates and Cook, Inc.
Dr. Maggisano was recorded at Update in General Surgery, sponsored by the Department of Surgery, Faculty of
Medicine, University of Toronto, and held April 20-22, 2006, in Toronto, ON; Dr. Schneider was recorded at Postgraduate
Course in General Surgery, sponsored by the University of California, San Francisco, School of Medicine,
and held March 23-25, 2006, in San Francisco; Dr. Libby was recorded at Current Concepts in General Surgery and
Trauma Update, sponsored by the University of New Mexico Health Sciences Center, Department of Surgery and
Office of Continuing Medical Education, and held September 6-8, 2006, in Albuquerque. The Audio-Digest Foundation
thanks the speakers and the sponsors for their cooperation in the production of this program.
|
