Anesthesia for vascular surgery Flashcards
What are the risk factors of peripheral vascular disease?
-Advanced age
-smoking
-HTN
-Diabetes
-insulin resistance
-obesity
-family history/genetics
-physical inactivity
-male>female
-elevated c-reactive protein
-elevated lipoprotein
-elevated triglycerides
-hyperlipidemia
What is homocysteine?
protein in the blood; can make blood clot more easily than it should; comes from eating meat; may also be elevated if you do not have enough folate
In peripheral vascular disease and peripheral artery disease what may need to be elevated to perfuse their organs?
May rely on increased MAP to perfuse vital organs
-Increased range of coronary and cerebral autoregulation
Even short periods of what can lead to ischemia in these pts with PVD and PAD?
hypotension
-invasive BP monitoring is recommended for these cases
What are the major risk factors for an abdominal aortic aneurysm?
-Smoking** most highly correlated with AAA
-older age
-gender
what are some other risk factors for a AAA?
-Family Hx
-CAD- single most significant risk factor influencing long term survival
-Cholesterol
-COPD
-HTN
-2-6 times more common in men
-2-3 times more common in while males vs black males
(MIs are responsible for 40-70% of all fatalities that occur in aneurysm reconstruction)
How is AAA diagnosed?
Pulsatile abdominal mass- often missed in a routine physical exam
-CTA: imaging best of choice for AAA
CT, ultrasound and MRI are useful for determining size.
When is the risk of rupture low for AAA?
Less than 4cm in diameter
When is surgical intervention recommended for a AAA?
-5.5cm or greater
-4-5 cm with greater than 0.5cm enlargement in the last 6 months
-(growth more than 0.6-0.8 cm per year)
-Ruptured AAA
-pts who are symptomatic
How much do AAA approximately expand per year?
4 mm per year
Which law do the vessel dimensions correlate to?
Law of LaPlace
T= Px r
T= wall tension
p= transmural pressure
r= vessel radius
as the radius increases, the wall tension increases!
the larger the aneurysm, the higher the likelihood of spontaneous rupture.
Wall tension is directly proportional to: vessel radius and intraluminal pressure
Wall tension is inversely proportional to wall thickness
What are the contraindications to an elective AAA repair?
-Intractible angina pectoris
-Recent MI
-Severe pulmonary dysfunction
-Chronic renal insufficiency
What is the most frequent site for an AAA?
Infrarenal
-approx 5-15% involve the suprarenal area
Identify the statement that BEST describes perioperative considerations in the pt with an abdominal aortic aneurysm (select 2)
a.) surgical intervention is recommended when the diameter is >5.5cm
b.) risk of aneurysmal rupture is best described by poiseuille’s law
c.) it is more common in females
d.) back pain and hypotension suggest rupture
a.) surgical intervention is recommended when the diameter is >5.5cm
d.) back pain and hypotension suggest rupture
The law of LaPlace states that increased diameter increases wall tension. The greater the wall tension, the greater the risk of rupture. Surgery is indicated when aneurysmal diameter exceeds 5.5
Independent risk factors for AAA include cigarette smoking, gender (male>female), and advanced age. Acute onset of back pain and hypotension suggest rupture
What are the mechanisms for the development of AAA?
-Destruction of elastin and collagen (primary)
-inflammation
-endothelial dysfunction
-platelet activation
-atherosclerosis
What is the classic triad of symptoms for a AAA rupture?
-Hypotension
-Back pain
-pulsatile abdominal mass
(this triad is only present in 50% of pts)
what is the most common cause of post-op death?
MI
Why don’t all pts with an aortic aneurysm rupture exsanguinate immediately?
Most aneurysms rupture in the left retroperitoneum allowing for tamponade and clot formation
List the different AAA sites from most involved to least involved
Suprarenal AAA
Pararenal AAA
Juxtarenal AAA
Infrarenal AAA
How should you optimize a patient for adominal aortic reconstruction?
-optimize myocardial o2 supply and demand
-pre-op beta blockers and statins
-pre-op fluid loading (Large bore IV is a must)
-Type and cross pt- blood available in room
What monitors should be on the pt for AAA repair?
EKG:
- lead 2 for arrhythmia evaluation
-Lead V5 for detection of ischemic ST-segment changes
-a-line
-intra-op TEE (can guide fluid management, wall abnormalities, detect PE)
What monitors should be on the pt for AAA repair?
EKG:
- lead 2 for arrhythmia evaluation
-Lead V5 for detection of ischemic ST-segment changes
-a-line
-intra-op TEE (can guide fluid management, wall abnormalities, detect PE)
What hemodynamic changes are increased during cross clamping?
-Increase arterial BP above the clamp
-increased afterload which can lead to left ventricular myocardial wall tension and o2 demand
-increased MAP
-Increased SVR
- increased wall motion abnormalities and left ventricular wall tension
What will be decreased during cross clamping?
decreased arterial blood pressure below the clamp
metabolic changes: decreased total body carbon dioxide production
clamping starves distal tissues of o2, so these cells convert to anaerobic metabolism. The metabolic byproducts are washed into systemic circulation when clamp is released.
What is the most common site for cross-clamping?
Infra-renal
(most aneurysms appear below the level of the renal arteries)
What drug is good to give if the pts pressure is too high?
Nitro (d/t short half-life)
can also give:
- SNP
-Inhalation anesthetics
-milrinone
What are the metabolic alterations during aortic cross clamping?
-Hypoxic and ischemic environment distal to the clamp
-release of cytokines, prostaglanidns, nitric oxide, arachidonic acid
-anaerobic metabolism: build up of serum lactate
-acceleration of throboxane A-2 synthesis: leads to decrease in myocardial contractility/decrease CO
-Traction on mesentary- done for exposure to the aorta (may cause decrease in BP, SVR, tachycardia, increased CO, and facial flushing)
What is thought to be a main factor in cardiac instability and myocardial depression during cross-clamping?
Arachidonic acid
What does thromboxane A2 do?
produced by platelets during hemostasis Prothrombotic properties - stimulates activation of new platelets as well as increased platelet aggregation
Which clamping positions are associated with a higher risk for kidney injury?
Suprarenal and juxtarenal –> reduce renal blood flow by as much as 80%
intrarenal reduces renal blood flow by 40%
if the suprarenal cross clamp time is longer than 30 mins what does it increase the risk for?
Post-op renal failure
if the suprarenal cross clamp time is longer than 30 mins what does it increase the risk for?
Post-op renal failure
What nephrotoxic meds should be avoided when managing an AKI post-cross clamp?
NSAIDs
aminoglycosides antibiotics (gentamicin, neomycin)
are warm or cold crystalloids thought to have a renal protective effect?
cold fluids!
What provides 20% if the spinal cord blood flow?
two posterior and two posterolateral arteries
-supply dorsal (sensory) portion of the spinal cord.
What provides 80% of spinal cord blood flow?
one anterior spinal artery–> 80% of spinal cord blood flow
(supply anterior (motor) portion of spinal cord)
What controls the transverse blood flow to the spinal cord?
Greater radicular artery
AKA: artery of Adamkiewicz
What can cause paraplegia?
Interruption of blood flow to the greater radicular artery (artery of Adamkiewicz) in the absence of collateral blood flow.
Bowel and bladder dysfunction, flaccid extremities - motor affected if injured
Where does the artery of Adamkiewicz originate?
between spinal segments T8-T12 but can originate as low as L2
Incidence of neurologic complications increases as:
the cross clamp is positioned higher and more proximal to the heart
Methods to decrease the risk of spinal cord ischemia
-Cerebrospinal fluid drainage
-mild hypothermia
-maintenance of normotension (SBP >120) through second post-op day.
Risk is highest for motor spinal dysfunction
What is another type of injury that can occur with abdominal aortic resections?
Ischemic colon injury
-Attributed to the manipulation of the inferior mesenteric artery which supplies the main blood supply to the left colon. This vessel is often sacrificed during surgery. Blood flow to the descending and sigmoid colon rely on collateral vessels.
Which factors increase following cross-clamp removal during abdominal aortic aneurysm repair? (select 2)
a.) pulmonary vascular resistance
b.) venous return
c.) total body oxygen consumption
d.) coronary blood flow
a.) pulmonary vascular resistance
c.) total body oxygen consumption
When the aortic cross-clamp is released, ischemic tissue releases acid and vasoactive substances into the systemic circulation. This increases pulmonary vascular resistance and pulmonary artery pressure.
removal of the cross-clamp increases the size of the vascular tank and so venous return falls. hypotension reduces coronary blood flow.
What causes the transient vasodilation after cross clamp release?
-Tissue hypoxia
-release of adenine
-Leads to decreased preload and afterload
What is decreased during cross clamp release?
SVR
Venous return
Can give ca2+
restoration of circulating blood volume is paramount in providing circulatory stability before the release of the cross clamp.
What is decreased during cross clamp release?
SVR
Venous return
Can give ca2+
restoration of circulating blood volume is paramount in providing circulatory stability before the release of the cross clamp.
what influences the magnitude of circulatory instability during clamp release?
site and duration of clamping
-partial release of aortic clamp over time can decrease hypotensive response.
what influences the magnitude of circulatory instability during clamp release?
site and duration of clamping
-partial release of aortic clamp over time can decrease hypotensive response.
What is an EVAR? What are the benefits?
A minimally invasive approach of correcting an abdominal aortic aneurysm.
shorter operative times, lower rates of transfusion, shorter length of stay, reduced morbidity.
When does an endoleak occur?
when the original graft fails to prevent blood from entering the aortic sac. Sometimes endoleaks resolve spontaneously while others may require placement of a second graft or an open repair.
When does an endoleak occur?
when the original graft fails to prevent blood from entering the aortic sac. Sometimes endoleaks resolve spontaneously while others may require placement of a second graft or an open repair.
The pt’s physiologic response ot the aortic cross-clamp is related to what 3 factors?
1.) location of clamp placement (infrarenal most common)
2.) intravascular volume status
3.) cardiac reserve
Applying the aortic cross-clamp creates central hypervolemia by:
-reducing venous capacity
-shifting a greater proportion of the blood volume proximal to the clamp
-increasing venous return
removing the aortic cross-clamp creates central hypovolemia by:
- restoring venous capacity
-shifting a greater proportion of the blood to the lower body
-decreasing venous return
-creating a capillary leak that contributes to the loss of intravascular volume
Advantages of epidural anesthesia for open AAA repair:
-decreases preload and afterload
-preserves myocardial oxygenation
-decreases stress response
-decreases pulmonary complications
-post-op pain relief
Disadvantages of epidural anesthesia for open AAA repair:
-anticoagulation/possibility of epidural hematoma
-severe hypotension w blood loss or cross-clamp removal
Crawford classification
Normal
Crawford classification
class 1
distal to the left subclavian artery to the renal arteries
Crawford classification
class 2- can affect the kidneys the most - there is no blood flow to the renal arteries
distal to the left subclavian artery below the renal arteries
Crawford classification
class 3
from the 6th intercostal space to the renal arteries
Crawford classification
class 4
from the 13th intercostal space to the iliac bifurcation (entire abdominal aorta )
Crawford classification
class 5
below the 6th intercostal space to the renal arteries
Debakey Classification of acute aortic dissection
Type 1: originates in the ascending aorta and extends at least to the aortic arch and often in the descending aorta
Debakey Classification of acute aortic dissection
Type 2: originates in the ascending aorta; confined to this segment
Debakey Classification of acute aortic dissection
Type 3a and b: originates in the descending aorta, usually just distal to the left subclavian artery, and extends distally
Stanford classification of acute aortic dissection
Type A: dissections that involve the ascending aorta (with or without extension into the descending aorta)
Stanford classification of acute aortic dissection
Type B: dissections that do not involve the ascending aorta
Normal
What is Amaurosis Fugax?
Blindness in one eye= sign of impending stroke
Emboli travel from the internal carotid artery to the ophthalmic artery. This impairs perfusion of the optic nerve and causes retinal dysfunction.
It occurs in 25% of pts w high-grade carotid stenosis
