Vascular Surgery Flashcards
When does atherosclerosis become a significant health concern?
5th to 6th decade of life
What is thought to cause atherosclerosis?
Damage to the innermost layer of an artery , deposits lipids, cholesterol, platelets, cellular debris and decreases BF and oxygen delivery
What surgical procedures can treat atherosclerosis?
Transluminal angioplasty Endarterectomy Thromnectomy Endovascular stenting Arterial bypass
What is the single most important factor in determining patient outcomes in patients with atherosclerosis?
Smoking
What three arteries branch off of the aortic arch?
Brachiocephalic
Left Common Carotid
Left Subclavian
What are the three layers of an artery?
Intima
Media
Adventitia
What is an aneurysm?
Dilation of all three layers of an artery that cause a decrease in diameter
When are most AAs found?
During diagnostic testing for other disorders
What symptoms are associated with a thoracic aortic aneurysms?
Hoarseness stretching RLN
Stridor compression of trachea
Dysphagia compression of esophagus
Dyspnea compression of the lungs
What is the law of leplace?
T = P x r Tension = transmural pressure x radius
Why does increasing the size of the aneurysm increase the chance of rupture?
The vessel radius and wall tension are directly proportional so as the aneurysm increases in size so does the tension on the vessel wall
What is thought to be the reason why the incidence of AAA have increased over the last five decades?
Improved detection of asymptomatic aneurysms
What is thought to be the primary cause of AAA?
Atherosclerosis from proteolytic degradation of the extracellular matrix proteins elastin and collagen
What criteria place a patient at high risk for a AAA?
Greater than 70 years old Diabetes Stroke Renal disease COPD/ emphysema/ dyspnea Hx MI, CHF, Angina
When is an open AAA indicated?
AAA greater than 5.5cm in diameter
Smaller AAA become symptomatic
AAA grows greater than 0.5cm in six months
What type of blood products should be available prior to AAA surgery?
4 units RBCs and have in the room prior to induction
What tool could be used as a sensitive indicator for cardiac function and ischemia?
TEE
When should a RSI be considered for a AAA procedure?
If the aneurysm is compressing abdominal contents up or if they have been bleeding into their abdomen
What type of fluid requirement do patients undergoing a AAA need?
High fluid requirements, due to large fluid shifts and high risk of bleeding
Do NOT over hydrate prior to cross clamping (avoid HTN)
When should heparin be given when bypass is indicated?
Prior to cross clamp
When should the ACT be checked after giving heparin?
Three minutes after heparin administration
What causes an increase in BP above the cross clamp?
Due to impedance of blood flow and systolic ventricular wall tension (after load)
Clamping in which location causes the largest increase in BP?
At or above the diaphragm, unless blood is shunted around the level of the clamp or vasodilators are used
What physiologic changes are seen above and below the level of the clamp on bypass?
HTN above the clamp
HoTN and ischemia below the clamp
Why hemodynamic changes occur when when the clamp is released?
Profound vasodilaton leading to HoTN, primarily due to reactive hyperemia and relative central hypovolemia
What drugs are used to vasodilate HTN above the clamp?
SNP
Nitroglycerine
What is the mechanism of action of SNP?
Non Selective
Releases cyanide and NO into the circulation, NO crosses the cellular membrane causing an increase in cGMP which inhibits Ca entry into the vascular smooth muscle
What is the mechanism of action of Nitroglycerine?
Acts on venous capacitance vessels and large coronary arteries
NO formed thought glutathione dependent pathway leading to vasodilation
What metabolic products are increased during an open AAA repair?
Mixed venous O2 saturation Epi and norepi Lactic acid Thromboxane A2 Cytokines/ inflammatory response
How are the kidneys affected by AAA repair?
Renal insufficiency and failure are not uncommon regardless of level of clamp
What is the most significant predictor of post op renal dysfunction in AAA repair?
Pre op renal function
What is the most effective renal protective mechanism in patients undergoing AAA repair?
Optimal systemic hemodynamics and maintenance of intravascular volume
What pharmacological interventions could potentially preserve renal blood flow in patients undergoing a AAA repair?
Mannitol
Dopamine
Statins
What factors determine the hemodynamic response to removal of cross clamp?
Level of clamp
Total clamp time
Use of diverting support
Intravascular volume
What should the provider do prior to removing the cross clamp in an open AAA procedure?
Assess and maximize intravascular volume
Reduce or discontinue vasodilators
Decrease volatile agent concentration (recall)
What agent should be given to combat heparin prior to emergence?
Protamine
What is the mechanism of action of Protamine?
Positively charged substance that neutralizes the negatively charged heparin
What can protamine cause pulmonary HTN?
Can cause release of thromboxane A2 and serotonin
What can be seen if protamine is given too quickly?
Histamine release causing facial flushing, tachycardia and HoTN
What population may develop an allergic reaction to protamine?
Allergic to fish or chronic exposure to NPH insulin
Why should the lower body be warmed during AAA?
May increase ischemic injury to tissues below the cross clamp due to increased metabolic demands
How are AAA repaired endovascularly?
A stent is placed in the aortic lumen with bilateral femoral arteries cannulated
Fluoroscopy used to position sheath at the site of the aneurysm
What type of anesthetic can be used for an EVAR?
Neuraxial anesthesia or GA
What size aneurysm is appropriate for EVAR?
Non ruptured aneurysm greater than 5cm but less than 24cm long
What are hemodynamic advantages of an EVAR compared to a open AAA repair?
Less hemodynamic instability and blood loss
What can occur with stent deployment in patients undergoing an EVAR?
HoTN and Bradycardia during deployment
What should the provider always be prepared to do when taking care of a patient undergoing an EVAR?
Be prepared to convert to an open procedure
What are the most common symptoms of a ruptured AAA?
Abdomina discomfort/back pain
Pulsatile abdominal mass
Decreased peripheral pulses
HoTN
What are the primary goals of treatment of a ruptured AAA?
CV resuscitation and hemodynamic stability
What is the greatest concern for a patient with a ruptured AAA?
Gaining control of the proximal aorta
How many units of blood should be brought to the OR for a patient with a ruptured AAA?
10-12 units of O negative blood
How should the provider induce a patient with a ruptured AAA?
Minimal anesthesia (ketamine, vec and no gas) for induction, use Midaz liberally Place lines after the patient is asleep
What drug should not be given to a ruptured AAA that would normally be given for repair cases?
Heparin, can induce DIC
What is thought to be the reason that patients survive a ruptured AAA?
Tamponade of the bleeding, when opened will code almost immediately
When does an aortic dissection occur?
With injury to the intima of the aorta, blood enters the media layer of the blood vessel via a tear in the intima
What classification systems are used to describe aortic dissections?
Crawford and DeBakey
What characteristics are used to classify an aortic aneurysm?
Size
Shape
Location
What layers of the arterial wall are involved in an aneurysm?
A true aneurysm involves all three layers of the arterial wall
What is considered a Crawford Type I aneurysm?
Descending thoracic and upper abdominal aorta
What is considered a Crawford Type II aneurysm?
Descending thoracic and most of abdominal aorta
What is considered a Crawford Type III aneurysm?
Lower thoracic and most of abdominal aorta
What is considered a Crawford Type IV aneurysm?
Most of all of abdominal aorta
What type of dissections are DeBakey I and II?
Proximal
What percentage of dissections are DeBakey I?
60%
What percentage of dissections are DeBakey II?
10-15%
What type of dissection is a DeBakey III?
Distal
What percentage of dissections are DeBakey III?
25-30%
What drug can help reduce blood loss in an ascending aortic dissection?
Aprotinin (Amicar)
What shout the ACT be with full heparinization?
Greater than 400
What is a Bentall procedure?
Often involves aortic valve replacement/repair and coronary reimplantation with ascending aortic surgery
What is done with a transverse aortic arch repair?
Performed with mediansternotomy and CPB Deep hypothermic (15degreesC) circulatory arrest
What should the provider do for a transverse aortic arch repair?
Pack head in ice Maintain flat EEG Methylprednisolone or dexamethasone Mannitol Phenytoin
Where does a descending thoracic aneurysm typically occur?
Occurs between left subclavian artery and aortic hiatus
What type of ventilation is required for a descending thoracic aneurysm repair?
One-lung ventilation R DLT or Bronchial blocker
Why should the provider place the arterial line of the right side with an aortic aneurysm repair?
Monitor blood flow to the innominate arteries and artery of adamkiewicz
What is the most devastating complication for a descending thoracic aneurysm repair?
Paraplegia
What are the components of intrinsic circulation to the spinal cord?
One anterior spinal artery (75% to 80% of blood flow, anterior cord)
Two posterior spinal arteries (20-25% blood flow, posterior cord)
What are the components of extrinsic circulation to the spinal cord?
Radicular and medullary arteries
What is another name for the great radicular artery or the arteria radicularis magna?
Artery of Adamkiewicz
Where does the artery of Adamkiewicz enter circulation?
Enters intravertebral foramen in thoracolumbar region
• T9-T12 (75%)
• T5-T8 (15%)
• L1-L2 (10%)
What is the importance of the artery of Adamkiewicz?
This artery is the main determinant of paraplegia because it provides most of the blood flow to the anterior spinal cords, or motor tracts of the spinal cord
Major source of blood flow to the lower 2/3 of the spinal cord
What patient populations are at highest risk for spinal cord ischemia?
Aortic dissection or rupture Extensive aneurysm size Prolonged aortic occlusion time Patient age CSF pressure Perioperative hypotension
What is the most important determinant of paraplegia and acute renal failure in aortic surgery?
Duration of aortic cross clamping
What is considered a safe cross clamp time with almost no paraplegia?
20-30minutes
What is considered the vulnerable time for paraplegia during cross clamping?
30-60 minutes of cross clamp time = 10-90% incidence of paraplegia, the likelihood of paraplegia increases with duration
How does administering Intrathecal papaverine help in protecting the spinal cord from ischemia?
- Dilates spinal arteries
* Oxygen free radical scavenger
How do we determine spinal cord perfusion pressure?
Spinal cord perfusion pressure (SCPP) = Mean aortic pressure - CSF pressure
What perfusion pressure are we concerned with causing paraplegia?
Distal perfusion pressure
How is CSF pressure affected by cross clamping?
Normally, CSF pressure increases during cross clamp while arterial pressure decreases distal to the cross clamp.
How can the perfusion pressure be manipulated during cross clamping?
Altering ABP and draining CSF through an intrathecal catheter
What is the primary cause of carotid occlusive disease?
Atherosclerosis
Where is the most common place to find carotid occlusive disease?
Carotid bifurcation
What determines the degree of cerebral injury in patients with carotid occlusive disease?
Cerebral collateral flow due to the integrity of the Circle of Willis, duration of hypoperfusion, cerebrovascular vasoreactivity, plague morphology
What are indications for a carotid endarterectomy?
TIA associated with ipsilateral severe carotid stenosis (>70%)
Severe ipsilateral stenosis with minor stroke
30-70% stenosis with ipsilateral symptoms
Asymptomatic but with significantly stenotic lesions
(>60%)
What are the end effects of carotid artery occlusion?
Ischemia and ultimately loss of cerebral blood flow autoregulation
Why is it important to have a fully awake patient at the end of a carotid endarterectomy?
To allow for comprehensive neurologic assessment
What is a major benefit of regional anesthesia for awake endarterectomies?
Allows continuous assessment of an awake patient
What dermatomes would need to be blocked for an awake endarterectomy?
Superficial and Deep cervical block C2-C4 dermatomes
What are major disadvantages to using regional for an awake endarterectomy?
Inability to use pharmacologic tx for cerebral protection
Patient panic and loss of cooperation
Inadequate airway access
Phrenic nerve paralysis leading to potential for respiratory compromise
LA toxicity with high volumes of LA or intravascular
injection
What are relative and absolute contraindications for regional anesthesia in patients undergoing an endarterectomy?
Absolute: – Patient refusal – Language barrier Relative: – Difficult anatomy – Sever COPD or diaphragmatic dysfunction
What is the most sensitive monitor of cerebral perfusion and ischemia during a CEA?
An awake patient
What do carotid sum pressures measure?
Assess extent of collateral flow
What does a carotid stump pressure less than 60mmHg suggest?
Hypoperfusion and need for shunt placement
What is a good range to keep SBP when cross clamping is released?
SBP be kept 140-160mmHg to ensure adequate but not excessive cerebral perfusion
What is a complication of CEA that can affect PaO2?
Blunted ventilatory response to hypoxemia by CAROTID CHEMORECEPTORS (primarily decreases in PaO2)*** - NOT CENTRAL
What is post op cerebral hyper perfusion syndrome?
Increase in cerebral BF with loss of autoregulation in reperfused brain leading to a h/a, seizures, focal neurologic signs, edema and hemorrhage
What population is at risk for cerebral hyper perfusion syndrome?
Patients with severe preop carotid stenosis and post-op HTN are at increased risk
When are symptoms associated with cerebral hyper perfusion syndrome following a CEA typically seen?
Typically occurs several days following CEA
What pathologies are known to cause respiratory compromise following a CEA?
Hematoma Bilateral RLN injury Deficient Carotid Body function Vocal cord paralysis Tension pneumo Stroke or loss of consciousness
