Anesthesia for Vascular Surgery

Question 1

What is the trongest predictor of postoperative renal dysfunction after vascular surgery?

Answer 1

The degree of preoperative renal insufficiency

Question 2

What is the leading cause of perioperative mortality at the time of vascular surgery?

Answer 2

Coronary artery disease

Question 3

Less than …% of patients who undergo vascular surgery have normal coronary arteries, and more than …% have advanced or severe CAD

Answer 3

10

50

Question 4

Unrecognized myocardial infarction (MI) (determined by …) and silent myocardial ischemia (determined by …) often occur in vascular surgery patients (…% and …%, respectively) and are associated with increased long-term mortality and adverse cardiac events.

Answer 4

wall motion abnormalities at rest in the absence of a history of MI

stress-induced wall motion abnormalities in the absence of angina

23

28

Question 5

When multiple recent studies about patients undergoing vascular surgery are pooled, the overall prevalence of perioperative MI and death is …, respectively. When outcomes are assessed over the long term (2 to 5 years), the prevalence of MI and death is …, respectively

Answer 5

4.9% and 2.4%

8.9% and 11.2%

Question 6

Describe the CARP trial

Answer 6

Coronary-artery revascularization before elective major vascular surgery. N Engl J Med. 2004

Patients were eligible for the study if they were scheduled for an elective vascular operation for either an expanding abdominal aortic aneurysm or severe symptoms of arterial occlusive disease involving the legs. The exclusion criteria were a need for urgent or emergency surgery, a severe coexisting illness, or prior revascularization without evidence of recurrent ischemia.

Of the 5859 patients screened in the CARP trial, 1190 underwent coronary angiography based on a combination of clinical risk factors and noninvasive stress imaging data. The incidence and severity of CAD on these angiograms were 43% of patients had one or more major coronary arteries with at least a 70% stenosis suitable for revascularization (and were randomized to either revascularization or no revascularization before vascular surgery).

Of the 510 patients who underwent randomization, 258 were assigned to a strategy of preoperative coronary-artery revascularization, and 252 to no revascularization.

The CARP trial showed that prophylactic revascularization (by CABG or PCI) was generally safe but did not improve long-term outcome after vascular surgery. Longterm mortality (2.7 years) was 22% in the revascularization group and 23% in the group whithout revascularization.

Question 7

The CARP trial results can be applied to most of the vascular surgery patients; however, they cannot be extrapolated to patients with … because these conditions excluded patients from study participation

Answer 7

unstable cardiac symptoms, left main coronary artery disease, aortic stenosis, or severe left ventricular dysfunction

Question 8

The lack of benefit of prophylactic coronary revascularization in the CARP and DECREASE-V trials is difficult to reconcile with the more favorable data from Hertzer and co-workers and other studies (Coronary Artery Surgery Study [CASS] and Bypass Angioplasty Revascularization Investigation [BARI]). What factors could explain this inconsistency?

Answer 8

Issues are involved that go beyond critical coronary lesions; perhaps the current understanding of the pathophysiology of perioperative MI is incomplete. For example, perioperative MI may be caused by culprit lesions (i.e., vulnerable plaques with high likelihood of thrombotic complications) often located in coronary vessels without critical stenosis. For this type of MI (atherothrombotic), perioperative strategies aimed at reducing potential triggers of coronary plaque destabilization and rupture may be more appropriate than those leading to coronary revascularization. Demand ischemia is likely the predominant cause of perioperative MI, which has been confirmed by a recent angiographic study

Question 9

Perioperative administration of … decrease risk for death in vascular surgery patients with renal impairment

Answer 9

β-adrenergic blocker and statin

Question 10

If a decision is made to initiate beta-blocker treatment in the perioperative period to reduce cardiac risk, the safest approach may be …

Answer 10

to initiate therapy with a small dose and titrate to effect over a 7- to 10-day period before the planned surgery

Question 11

Abdominal aortic aneurysms (AAAs) occur frequently in elderly men, with an incidence approaching …%.

… are established risk factors

Answer 11

8

Increasing age, smoking, family history of AAA, and atherosclerotic disease

Question 12

Current guidelines emphasize that it is not possible to recommend a single threshold diameter for operative intervention that can be generalized to all patients. Yet, elective repair should be undertaken in all patients with AAA … cm or larger in diameter.

Although some controversy exists regarding elective AAA repair when its diameter is in the …-cm range, the risk for rupture of a … cm aneurysm (per year) is equal to or greater than the risk for perioperative mortality, and thus surgical repair is indicated.

Answer 12

6

5.5-to 5.9

5.5-

Question 13

Surgical repair of AAA is often considered if small aneurysms become … or …

Answer 13

symptomatic

expand more than 0.5 cm in a 6-month period

Question 14

Unlike patients with aortic aneurysmal disease, patients undergo surgery for aortoiliac occlusive disease only if …

Answer 14

they are symptomatic

Question 15

… is the most common cause of renal artery stenosis. Occlusive lesions are located almost exclusively in the … of the renal artery and are usually an extension of …

… is an important, but less common, cause of renal artery stenosis and most frequently involves the … of the renal arteries

Answer 15

Atherosclerosis

proximal segment and orifice

aortic atherosclerosis

Fibromuscular dysplasia

distal two-thirds

Question 16

Stenosis at the origin of the celiac and mesenteric arteries occurs as a result of extension of aortic atherosclerosis. The … is by far the most commonly involved, followed by the …

Answer 16

inferior mesenteric artery

superior mesenteric artery and the celiac artery

Question 17

Describe the Hemodynamic Changes with Aortic Cross-Clamping

Answer 17

↑ Arterial blood pressure above the clamp
↓ Arterial blood pressure below the clamp
↑ Segmental wall motion abnormalities
↑ Left ventricular wall tension
↓ Ejection fraction
↓ Cardiac output†,‡
↓ Renal blood flow
↑ Pulmonary occlusion pressure
↑ Central venous pressure
↑ Coronary blood flow

†Cardiac output may increase with thoracic cross-clamping.
‡When ventilatory settings are unchanged from pre-clamp levels.

Question 18

Metabolic Changes with Aortic Cross-Clamping

Answer 18

↓ Total body oxygen consumption
↓ Total body carbon dioxide production
↑ Mixed venous oxygen saturation
↓ Total body oxygen extraction
↑ Epinephrine and norepinephrine
Respiratory alkalosis
Metabolic acidosis

Question 19

Describe Therapeutic Interventions for Afterload reduction, Preload reduction and Renal protection during Aortic Cross-Clamping

Answer 19

1) Afterload reduction
- Sodium nitroprusside
- Inhalational anesthetics
- Amrinone
- Shunts and aorta-to-femoral bypass

2) Preload reduction
- Nitroglycerin
- Controlled phlebotomy
- Atrial-to-femoral bypass

3) Renal protection
- Fluid administration
- Distal aortic perfusion techniques
- Selective renal artery perfusion
- Mannitol
- Drugs to augment renal perfusion

*** Other
Hypothermia
↓ Minute ventilation
Sodium bicarbonate

Question 20

Cross-clamping of the proximal descending thoracic aorta increases mean arterial, central venous, mean pulmonary arterial, pulmonary capillary wedge pressure and cardiac index by 35%, 56%, 43%, 90% and 29% respectively. Heart rate and left ventricular stroke work are not significantly changed

T or F

Answer 20

F

Cross-clamping of the proximal descending thoracic aorta increases mean arterial, central venous, mean pulmonary arterial, and pulmonary capillary wedge pressure by 35%, 56%, 43%, and 90%, respectively, and decreases the cardiac index by 29%. Heart rate and left ventricular stroke work are not significantly changed

Question 21

The marked increases in ventricular filling pressure (preload) reported with high aortic cross-clamping have been attributed to …

Answer 21

increased afterload and redistribution of blood volume, which is of prime importance during thoracic aortic cross-clamping. The splanchnic circulation, an important source of functional blood volume reserve, is central to this hypothesis. The splanchnic organs contain nearly 25% of the total blood volume, nearly two-thirds (>800 mL) of which can be autotransfused from the highly compliant venous vasculature into the systemic circulation within seconds. Primarily because of smaller splanchnic venous capacitance, blood volume is redistributed from vascular beds distal to the clamp to the relatively noncompliant vascular beds proximal to the clamp.
Thoracic aortic cross-clamping also results in significant increases in plasma epinephrine and norepinephrine, which may enhance venomotor tone both above and below the clamp. The splanchnic veins are highly sensitive to adrenergic stimulation. The major effect of catecholamines on the splanchnic capacitance vessels is venoconstriction, which actively forces out splanchnic blood, reduces splanchnic venous capacitance, and
increases venous return to the heart

Question 22

Describe the Anrep Effect

Answer 22

A sudden increase in afterload on the heart causes an increase in ventricular inotropy.

A sudden increase in aortic pressure, for example, causes a rapid increase in left ventricular end-diastolic volume. This leads to an initial increase in the contractile force of the ventricle through the Frank-Starling mechanism. If the increased afterload is maintained for 10–15 minutes, the force of contraction increases further, and in the intact heart, the end diastolic volume decreases. This delayed increase in ventricular contractile force represents an increase in inotropy. The functional significance of the Anrep effect is that the increased inotropy partially compensates for the increased end-systolic volume and decreased stroke volume caused by the increase in afterload. Without this mechanism, increases in afterload would cause greater reductions in stroke volume than what is normally observed.

The mechanisms responsible for the initial response and the delayed response appear to be different. The initial increase in contractile force (Frank-Starling mechanism) is due to increased troponin C sensitivity to calcium. The delayed response likely involves several mechanisms that promote increased release of calcium by the sarcoplasmic reticulum. Suggested mediators include the release of endothelin-1 and angiotensin II by cardiac cells in response to stretch.

Question 23

Cross-clamping of the thoracic aorta decreases total body O2 consumption by approximately …%. For reasons that are unclear, O2 consumption decreases in tissues above the clamp

Answer 23

50

Question 24

The cardiovascular response to infrarenal aortic cross-clamping is less significant than with high aortic cross-clamping. Although several clinical reports have noted no significant hemodynamic response to infrarenal cross-clamping, the hemodynamic response generally consists of … . Cardiac output is most consistently …

Answer 24

increases in arterial pressure (7% to 10%) and systemic vascular resistance (20% to 32%), with no significant change in heart rate

decreased by 9% to 33%.

Question 25

The preload changes with infrarenal aortic crossclamping may depend on the status of the coronary circulation. Patients with severe ischemic heart disease responded to infrarenal aortic cross-clamping with … central venous (35%) and pulmonary capillary (50%) pressure, whereas patients without CAD had … filling pressure

Answer 25

significantly increased

decreased

Question 26

Urine output is closely monitored and often augmented during aortic surgery. In this cases, intraoperative urine output predict postoperative renal function.

T or F

Answer 26

F

The adequacy of renal perfusion “cannot” be assumed by urine output. Although urine output is closely monitored and often augmented during aortic surgery, intraoperative urine output does not predict postoperative renal function.

Procedures requiring aortic cross-clamping above the renal arteries dramatically reduce renal blood flow. Experimental studies report an 83% to 90% reduction in renal blood flow during thoracic aortic cross-clamping.

Infrarenal aortic cross-clamping in humans is associated with a 75% increase in renal vascular resistance, a 38% decrease in renal blood flow, and a redistribution of intrarenal blood flow toward the renal cortex. These rather profound alterations in renal hemodynamics occurred despite no significant change in systemic hemodynamics, and they persisted after unclamping.

Question 27

The sustained deterioration in renal perfusion and function during and after infrarenal aortic cross-clamping has been attributed to renal vasoconstriction, but the specific pathophysiologic process remains unknown. Renal sympathetic blockade with epidural anesthesia to a T6 level prevent the severe impairment in renal perfusion and function that occurs during and after infrarenal aortic cross-clamping

T or F

Answer 27

F

The sustained deterioration in renal perfusion and function during and after infrarenal aortic cross-clamping has been attributed to renal vasoconstriction, but the specific pathophysiologic process remains unknown. Renal sympathetic blockade with epidural anesthesia to a T6 level DOES NOT prevent or modify the severe impairment in renal perfusion and function that occurs during and after infrarenal aortic cross-clamping

Question 28

… accounts for nearly all the renal dysfunction and failure after aortic reconstruction

In addition to aortic cross-clamping-induced reductions in renal blood flow, … all contribute to renal dysfunction

Answer 28

Acute tubular necrosis

ischemic reperfusion injury, intravascular volume depletion, embolization of atherosclerotic debris to the kidneys, and surgical trauma to the renal arteries

Question 29

Although not proved, pharmacologic “protection” before aortic cross-clamping is believed to be beneficial and is therefore given. The use of … to induce … before aortic cross-clamping is ubiquitous in clinical practice.

… improves renal cortical blood flow during infrarenal aortic cross-clamping and reduces ischemia-induced renal vascular endothelial cell edema and vascular congestion. Other mechanisms by which it may be beneficial include acting as a scavenger of free radicals, decreasing renin secretion, and increasing renal prostaglandin synthesis

Answer 29

mannitol 12.5 g/70 kg

osmotic diuresis

Mannitol

Question 30

Besides mannitol, what other medications … are used to protect the kidneys from aortic cross-clamp-induced injury?

Answer 30

Loop diuretics and low-dose dopamine (1 to 3 mcg/kg/min)

Question 31

Patients with impaired ventricular function requiring supraceliac aortic cross-clamping are the most challenging.

… is important to avoid abrupt and extreme stress on ‘the heart.

Afterload reduction, most commonly accomplished with the use of … (predominantly … dilators), is necessary to unload the heart and reduce ventricular wall tension.

A normal preload is equally important and involves …
… can be used because it increases venous capacity more than does sodium nitroprusside.

Answer 31

Controlled (i.e., slow clamp application) supraceliac aortic cross-clamping

sodium nitroprusside or clevidipine

arteriolar

careful IV fluid titration and vasodilator administration

Nitroglycerin

Question 32

In patients without evidence of left ventricular decompensation or myocardial ischemia during supraceliac aortic cross-clamping, a proximal aortic mean arterial pressure of up to … is acceptable

Answer 32

120 mm Hg

Question 33

The 1-year incidence of probable rupture in patients refusing or unfit for elective repair is … for aneurysms 5.5 to 5.9 cm, 6.0 to 6.9 cm, and 7.0 cm or greater, respectively

Answer 33

9.4%, 10.2%, and 32.5%

Question 34

Factors tha increase the Physiologic Changes with Aortic Unclamping

Answer 34

longer duration of cross-clamping and more proximal cross-clamping

Question 35

Hemodynamic Changes with Aortic Unclamping

Answer 35

↓ Myocardial contractility
↓ Arterial blood pressure
↑ Pulmonary artery pressure
↓ Central venous pressure
↓ Venous return
↓ Cardiac output

Question 36

Metabolic Changes with Aortic Unclamping

Answer 36

↑ Total body oxygen consumption
↑ Lactate
↓ Mixed venous oxygen saturation
↑ Prostaglandins
↑ Activated complement
↑ Myocardial-depressant factor(s)
↓ Temperature
Metabolic acidosis

Question 37

Possible Therapeutic Interventions to control Physiologic Changes with Aortic Unclamping

Answer 37

↓ Inhaled anesthetics
↓ Vasodilators
↑ Fluid administration
↑ Vasoconstrictor drugs
Reapply cross-clamp for severe hypotension
Consider mannitol
Consider sodium bicarbonate

Question 38

What is the most consistent hemodynamic response to aortic unclamping?

Answer 38

Hypotension

Question 39

What is the dominant mechanisms of the hypotension after aortic unclamping?

Answer 39

Reactive hyperemia in tissues and organs distal to the clamp and the resultant relative central hypovolemia

Question 40

During open aortic surgery, is the used of a combined anesthetic technique (epidural + general anesthesia) the best option? Explain

Answer 40

No it isn’t.

The duration and intensity of postoperative care after aortic surgery are critically dependent on the physiologic derangements incurred during the perioperative period (i.e., depression of consciousness, hypothermia, excessive intravascular fluids, incisional pain, ileus, and respiratory depression), as well as on the development of certain less common, but more severe postoperative complications (i.e., MI, pneumonia, sepsis, renal failure, and decreased tissue perfusion). Length of hospital stay may therefore be considered the outcome variable most directly proportional to an integrated final negative effect of all significant perioperative
morbidity (excluding in-hospital death) and the variable most likely
to be altered by the anesthetic or analgesic technique.
Randomized trials have not demonstrated any reduction in length of hospital stay after aortic surgery with the use of regional techniques.

Norris and colleagues14 reported the results of a randomized clinical trial
comparing alternative combinations of intraoperative anesthesia (i.e., general or combined epidural and general) and postoperative analgesia (i.e., IV patient-controlled analgesia [PCA] or epidural PCA) with respect to length of stay after abdominal aortic surgery. Although the overall length of stay was much shorter (median, 7.0 days) than that reported in other studies, they were not able to demonstrate a reduction in length of stay or direct medical costs based on anesthetic or analgesic technique. The overall incidence of postoperative complications in the trial was low and not different based on anesthetic or analgesic technique. Postoperative
pain was well controlled overall, with similar pain scores in both analgesic treatment groups. Thus, if perioperative care and pain relief are optimized, epidural anesthetic and analgesic techniques for aortic surgery offer no major advantage or disadvantage over general anesthesia and IV PCA.

Question 41

The lower part of the body should be warmed during the aorta crossclamp period to reduce the lower extremities vasoconstriction and hypoperfusion.

T or F

Answer 41

F

The lower part of the body should not be warmed during the crossclamp
period because doing so can increase injury to ischemic tissue distal to the cross-clamp by increasing metabolic demand

Question 42

Aneurysms of the thoracoabdominal aorta occur primarily because of atherosclerotic …

The remainder are caused by …

Answer 42

degenerative disease (80%) and chronic aortic dissection (17%)

either trauma or connective tissue diseases involving the aortic wall from conditions such as Marfan syndrome, cystic medial degeneration, Takayasu arteritis, or syphilitic aortitis

Question 43

Describe The Crawford classification of thoracoabdominal aortic aneurysms

Answer 43

• Type I: involve all or most of the descending thoracic aorta and the upper abdominal aorta;
• Type II: involve all or most of the descending thoracic aorta and all or most of the abdominal aorta;
• Type III aneurysms involve the lower portion of the descending thoracic aorta and most of the abdominal aorta;
• Type IV aneurysms involve all or most of the abdominal aorta, including the visceral segment.

Question 44

Patients with Crawford type … aneurysms are at greatest risk for paraplegia and renal failure from spinal cord and kidney ischemia during cross-clamping

Answer 44

II

Question 45

Describe The DeBakey classification of dissecting aneurysms of the aorta

Answer 45

• Type I: intimal tear in the ascending aorta with dissection extending down the entire aorta.
• Type II: intimal tear in the ascending aorta with dissection limited to the ascending aorta.

Type III: intimal tear in the proximal descending thoracic aorta (just distal to the left subclavian artery) with dissection either limited to the thoracic aorta (type IIIA) or extending distally to the abdominal aorta or aortoiliac bifurcation (type IIIB).

Question 46

Aortic dissection can be classified by duration, with those less than … classified as acute and those greater than … classified as chronic

Answer 46

2 weeks

2 weeks

Question 47

Acute aortic dissection involving … is a surgical emergency that requires immediate cardiac surgical repair.

Acute dissections involving … are most often treated conservatively (i.e., arterial blood pressure, heart rate, and pain control) because surgical repair has no proved benefit over medical or interventional treatment in
stable patients

Answer 47

the ascending aorta (DeBakey types I and II, Stanford type A)

the descending aorta (DeBakey type III, Stanford type B)

Question 48

Patients who undergo replacement of the entire thoracoabdominal aorta (Crawford extent type II) have the most frequent perioperative risk. Contemporary mortality rates reported from large institutions range from …%. Statewide and nationwide mortality rates may be considerably more frequent (∼…%). The perioperative mortality rate may significantly
underestimate the risk associated with TAA repair. In a large statewide series, the mortality with elective TAA repair was …% at 30 days and …% at 365 days

Answer 48

5% to 14

20

19

31

Question 49

Which system is the most common cause of complications after open thoracoabdominal aorta repair?

Answer 49

Pulmonary system

The incidence of postoperative pulmonary insufficiency approaches 50%,
with 8% to 14% of patients requiring tracheostomy

Question 50

Where should an arterial line be placed during and open thoracoabdominal aorta repair?

Answer 50

A right radial arterial catheter is used for aneurysms involving the proximal descending thoracic aorta because occasionally the cross-clamp is placed proximal to the left subclavian artery, thus occluding flow to the left upper extremity.

When distal aortic perfusion techniques are used,
arterial blood pressure distal to the cross-clamps can be monitored.
This can be accomplished with the placement of a right femoral
arterial catheter, or the surgical team can place a catheter directly
into the femoral artery or distal aorta

Question 51

Three general problems exist with SSEP monitoring when used during open thoracoabdominal aorta repair. Describe then.

Answer 51

1) Sensory monitoring is more likely to detect lateral and posterior sensory column ischemia and is a poor monitor for the anterior motor column. As a result, paraplegia can occur despite normal SSEP signals;

2) Inhaled anesthetics and hypothermia can significantly interfere with SSEP signals;

3) Ischemia affects peripheral nerves, and ischemia in the lower extremities delays conduction from the usual stimulation sites (e.g., posterior tibial nerve). To eliminate the peripheral nerves as a confounding factor, spinal stimulation via a lumbar epidural electrode can be used, which may be more specific for ischemic injury than peripheral monitoring alone

Question 52

During aortic cross-clamping, MEPs are monitored every minute. A
reduction in MEP amplitude to less than … of baseline is considered an indication of spinal chord injury (SCI) and requires corrective measures

Answer 52

25%