Anesthesia for Vascular Surgery Flashcards
What is atherosclerosis and when does it begin?
Slow progressive disease that may begin in childhood but doesn’t become a concern until the 5th or 6th decade, involves deposition of lipids, cholesterol, platelets, cellular debris, decreased BF and O2 delivery, primarily affects medium-sized and large arteries
What are some risk factors for atherosclerosis?
- elevated cholesterol/triglycerides
- smoking
- HTN
- diabetes
- obesity
- genetics
- sedentary lifestyle
- males
- elevated homocystine and C-reactive protein levels
What are some surgical treatments for atherosclerosis?
- transluminal angioplasty
- endarterectomy
- thrombectomies
- endovascular stenting
- arterial bypass
What 3 main comorbidites are you evaluating for preoperatively in someone with atherosclerosis?
- existing cardiac abnormalities
- coexisting pulmonary dysfunction
- renal dysfunction
What is an aneurysm?
dilation of all three layers of an artery that causes a 50% increase in diameter compared to normal
Where can aneurysms occur in the aorta?
anywhere
What are some presenting symptoms of someone with a thoracic aortic aneurysm?
- hoarseness due to stretch of the left RLN
- stridor due to compression of the trachea
- dysphagia due to compression of the esophagus
- dyspnea due to compression of the lungs
What law explains the tension generated by an aneurysm?
law of laplace
T = P x r
Who is at highest risk for an AAA?
elderly men (8%)
What are other risk factors for AAA?
age
family hx
smoking
atherosclerosis
What is the primary cause of AAA?
atherosclerosis, proteolytic degradation of the extracellular matrix proteins elastin and collagen
What is the process that generates an AAA?
remodeling of the aortic wall from oxidative and biochemical wall stress
What comorbidity do 60% of AAA patients have?
HTN
What can increase the incidence of AAA by 8-fold?
smoking
What age criteria indicates a high risk AAA repair?
> 70 years old
What gender indicates a high risk AAA repair?
female
What cardiac conditions indicate a high risk AAA repair?
hx of MI active angina myocardial disease Q waves on ECG ST changes ventricular ectopy HTN with LVH CHF
What endocrine condition indicates a high risk AAA repair?
diabetes
What neurologic condition indicates a high risk AAA repair?
stroke
What renal condition indicates a high risk AAA repair?
chronic or acute renal disease
What pulmonary conditions indicate a high risk AAA repair?
COPD
emphysema
dyspnea
previous pulmonary surgery
At what aneurysm size is open repair done?
> 5.5 cm in diameter
Where do most AAA repairs require cross clamping?
at the infrarenal level
When do smaller AAA’s need open repair?
If they become symptomatic or expand >0.5 cm in 6 month period
What is involved in the preoperative preparation of someone having an AAA repair?
- thorough assessment of functional cardiac status
- full set of labs
- 4 units PRBC and have in the room prior to induction
- +/- PFTs
- 2 large bore PIVs or central line
- A-line
- +/- epidural depending on coagulation status
- adequate anxiolysis
What intraoperative monitoring should you do for a AAA repair?
- 5 lead ECG
- urinary catheter
- radial A-line
- +/- central line (placed in OR prior to induction)
- +/- pulmonary catheter
- TEE (sensitive monitor for cardiac function and ischemia)
How should an induction be done for an AAA repair?
smooth, slow, and controlled with vasoactive gtts in line prior to induction and multiple syringes with “uppers” and “downers” readily available
What type of anesthetic plan is appropriate for AAA repair?
high narcotic technique
What is important to avoid prior to cross-clamp for a AAA repair?
HTN, do not overhydrate prior to cross-clamp
What should be included in the maintenance phase of an AAA repair?
- volatile concentrations should be
Where should you maintain PCWP to ensure adequate fluid volume?
5-12 mmHg
What is the pathophysiology of aortic cross-clamping dependent on?
- level of the cross-clamp
- status of the IV
- degree of the periaortic collateralization
- blood volume and distribution
- activation of the SNS
- anesthetic agents and techniques
Cross clamping above what anatomic structure causes the greatest increase in ABP unless blood is shunted around the level of the clamp or vasodilators are used?
diaphragm
What 2 vasodilators are commonly used with AAA repair?
SNP
nitroglycerin
How does an open AAA repair affect your mixed venous O2 saturation?
increases mixed venous O2
How does an open AAA repair affect epi and norepi release and what are the subsequent effects?
increased epi and norepi release which causes increased HR and myocardial O2 demand
How does an open AAA repair affect lactic acid production?
increases lactic acid which leads to metabolic acidosis
How does an open AAA repair affect thromboxane A2?
increases thromboxane A2 leading to decreased contractility and CO
How does an open AAA repair affect total body O2 consumption?
decreases total body O2 consumption
How does an open AAA repair affect total body CO2 production?
decreases total body CO2 production
How does an open AAA repair affect cytokines?
increases cytokines that trigger an inflammatory response and temperature, leukocytosis, tachycardia, and fluid sequestration
Are renal insufficiency and renal failure common after AAA repair?
Yes, regardless of level of clamp
How does infrarenal cross-clamping affect RBF and renal SVR?
causes a 38% decrease in RBF and 75% increase in renal SVR
What is the rate of mortality in patients that develop renal failure after aneurysm repair?
50-90%
What is the most significant indicator of post-op renal dysfunction?
preoperative renal function
Can SNS blockade with epidural at T6 or ACE inhibitors improve renal hemodynamics?
No
What is the most effective renal protection mechanism during a AAA repair?
Optimal systemic hemodynamics and maintenance of intravascular volume
What are drugs that you can use for renal protection during an AAA repair?
Mannitol (0.25-0.5 mg/kg) Loop diuretics Low-dose dopamine (1-3 mcg/kg/min) Fenoldopam (0.05-0.1 mcg/kg/min) Statins
What does the hemodynamic response during removal of the cross-clamp dependent on?
- level of clamp
- total clamp time
- use of diverting support
- intravascular volume
What is the most common response following removal of the cross-clamp?
hypotension primarily due to reactive hyperemia (transient increase in organ BF) and relative central hypovolemia
What should you do prior to removal of the cross-clamp?
- assess and maximize intravascular volume
- reduce or discontinue vasodilators
- decrease volatile agent concentration
When should you administer Protamine?
prior to emergence and at the request of the surgeon
What are common side effects of Protamine?
hypotension, pulmonary vasoconstriction and pulmonary HTN from release of thromboxane A and serotonin
How does Protamine work?
positively charged substance that NEUTRALIZES the negatively charged heparin