Anesthesia for Vascular Surgery Flashcards
1
Q
What is atherosclerosis and when does it begin?
A
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
2
Q
What are some risk factors for atherosclerosis?
A
- elevated cholesterol/triglycerides
- smoking
- HTN
- diabetes
- obesity
- genetics
- sedentary lifestyle
- males
- elevated homocystine and C-reactive protein levels
3
Q
What are some surgical treatments for atherosclerosis?
A
- transluminal angioplasty
- endarterectomy
- thrombectomies
- endovascular stenting
- arterial bypass
4
Q
What 3 main comorbidites are you evaluating for preoperatively in someone with atherosclerosis?
A
- existing cardiac abnormalities
- coexisting pulmonary dysfunction
- renal dysfunction
5
Q
What is an aneurysm?
A
dilation of all three layers of an artery that causes a 50% increase in diameter compared to normal
6
Q
Where can aneurysms occur in the aorta?
A
anywhere
7
Q
What are some presenting symptoms of someone with a thoracic aortic aneurysm?
A
- 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
8
Q
What law explains the tension generated by an aneurysm?
A
law of laplace
T = P x r
9
Q
Who is at highest risk for an AAA?
A
elderly men (8%)
10
Q
What are other risk factors for AAA?
A
age
family hx
smoking
atherosclerosis
11
Q
What is the primary cause of AAA?
A
atherosclerosis, proteolytic degradation of the extracellular matrix proteins elastin and collagen
12
Q
What is the process that generates an AAA?
A
remodeling of the aortic wall from oxidative and biochemical wall stress
13
Q
What comorbidity do 60% of AAA patients have?
A
HTN
14
Q
What can increase the incidence of AAA by 8-fold?
A
smoking
15
Q
What age criteria indicates a high risk AAA repair?
A
> 70 years old
16
Q
What gender indicates a high risk AAA repair?
A
female
17
Q
What cardiac conditions indicate a high risk AAA repair?
A
hx of MI active angina myocardial disease Q waves on ECG ST changes ventricular ectopy HTN with LVH CHF
18
Q
What endocrine condition indicates a high risk AAA repair?
A
diabetes
19
Q
What neurologic condition indicates a high risk AAA repair?
A
stroke
20
Q
What renal condition indicates a high risk AAA repair?
A
chronic or acute renal disease
21
Q
What pulmonary conditions indicate a high risk AAA repair?
A
COPD
emphysema
dyspnea
previous pulmonary surgery
22
Q
At what aneurysm size is open repair done?
A
> 5.5 cm in diameter
23
Q
Where do most AAA repairs require cross clamping?
A
at the infrarenal level
24
Q
When do smaller AAA’s need open repair?
A
If they become symptomatic or expand >0.5 cm in 6 month period
25
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
26
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)
27
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
28
What type of anesthetic plan is appropriate for AAA repair?
high narcotic technique
29
What is important to avoid prior to cross-clamp for a AAA repair?
HTN, do not overhydrate prior to cross-clamp
30
What should be included in the maintenance phase of an AAA repair?
- volatile concentrations should be
31
Where should you maintain PCWP to ensure adequate fluid volume?
5-12 mmHg
32
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
33
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
34
What 2 vasodilators are commonly used with AAA repair?
SNP
| nitroglycerin
35
How does an open AAA repair affect your mixed venous O2 saturation?
increases mixed venous O2
36
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
37
How does an open AAA repair affect lactic acid production?
increases lactic acid which leads to metabolic acidosis
38
How does an open AAA repair affect thromboxane A2?
increases thromboxane A2 leading to decreased contractility and CO
39
How does an open AAA repair affect total body O2 consumption?
decreases total body O2 consumption
40
How does an open AAA repair affect total body CO2 production?
decreases total body CO2 production
41
How does an open AAA repair affect cytokines?
increases cytokines that trigger an inflammatory response and temperature, leukocytosis, tachycardia, and fluid sequestration
42
Are renal insufficiency and renal failure common after AAA repair?
Yes, regardless of level of clamp
43
How does infrarenal cross-clamping affect RBF and renal SVR?
causes a 38% decrease in RBF and 75% increase in renal SVR
44
What is the rate of mortality in patients that develop renal failure after aneurysm repair?
50-90%
45
What is the most significant indicator of post-op renal dysfunction?
preoperative renal function
46
Can SNS blockade with epidural at T6 or ACE inhibitors improve renal hemodynamics?
No
47
What is the most effective renal protection mechanism during a AAA repair?
Optimal systemic hemodynamics and maintenance of intravascular volume
48
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
```
49
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
50
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
51
What should you do prior to removal of the cross-clamp?
- assess and maximize intravascular volume
- reduce or discontinue vasodilators
- decrease volatile agent concentration
52
When should you administer Protamine?
prior to emergence and at the request of the surgeon
53
What are common side effects of Protamine?
hypotension, pulmonary vasoconstriction and pulmonary HTN from release of thromboxane A and serotonin
54
How does Protamine work?
positively charged substance that NEUTRALIZES the negatively charged heparin
55
What does rapid administration of Protamine cause?
histamine release causing flushing, tachycardia, and hypotension
56
Who may be at higher risk of having an allergy to Protamine?
patients with chronic exposure to NPH or who are allergic to fish
57
Should you warm the lower body during an emergent AAA repair?
NO, may increase ischemic injury to tissues below the cross-clamp due to increased metabolic demands
58
What are some benefits of endovascular AAA repair? TEVAR
- lower short-term mortality rates - no difference in AAA-related deaths at 1 year compared to open repair
- less hemodynamic instability and blood loss
59
What is an endovascular AAA repair?
deployment of graft stent in aortic lumen through the femoral artery, fluoroscopy used to position sheath at the site of the aneurysm
60
What kind of anesthetic technique can you use for an endovascular AAA repair?
neuraxial technique +/- GA or GA
61
Who are appropriate candidates for an endovascular AAA repair?
- non-ruptured aneurysm >5 cm
| - aneurysm
62
Is anticoagulation still necessary for an endovascular AAA repair?
Yes
63
What can happen during stent deployment during an endovascular AAA repair?
hypotension and bradycardia
64
What should you always be prepared for during an endovascular AAA repair?
conversion to open
65
What are potential complications from endovascular AAA repair?
- failed graft deployment
- microembolism
- migration/occlusion of major branch arteries
- aortic perforation/rupture/dissection
- hematoma formation
- endoleak
- stenosis/kink/thrombosis
- infection
- radiation exposure
- allergy to contrast due/associated renal insufficiency
- postimplant syndrome
66
What is the mortality rate for a ruptured AA?
94%
67
What are the most common symptoms for a ruptured AA?
- abdominal discomfort/back pain
- pulsatile abdominal mass
- decreased peripheral pulses
- hypotension
68
You have a patient in the ER with a ruptured AA, how would you proceed?
- immediate transport to OR, level 1
- very basic preop evaluation
- ensure placement of at least 1 functional PIV
- cardiovascular resuscitation and hemodynamic stability are primary goals
- greatest concern is gaining control of the proximal aorta!!
69
How much blood and what blood type should you have in the OR for a ruptured AA?
10-12 units O negative PRBCs
70
How should you do the induction for someone with a ruptured AA?
surgical team will prep while you are preparing for induction, use minimal anesthesia, use midazolam liberally and consider scopolamine
71
When would you place invasive lines for someone with a ruptured AA?
AFTER the patient is asleep and hemodynamically stable
72
What must you be adept in to manage a thoracoabdominal aortic surgery?
- one-lung ventilation
- extracorporeal circulatory support, including circ. arrest
- renal and spinal cord protection
- induced hypothermia
- invasive hemodynamic monitoring including TEE
- massive transfusion
- management of coagulopathy
73
How are thoracic aortic aneurysms classified?
Based on size, shape, and location
74
What is the primary cause of thoracic aortic aneurysms?
atherosclerotic disease (80%)
75
What are other causes for thoracic aortic aneurysms besides atherosclerotic disease?
chronic aortic dissection (17%)
| trauma or connective tissue disease (3%)
76
What is a type I thoracic aneurysm using the Crawford classification?
descending thoracic and upper abdominal aorta
77
What is a type II thoracic aneurysm using the Crawford classification?
descending thoracic and most of abdominal aorta
78
What is a type III thoracic aneurysm using the Crawford classification?
lower thoracic and most of abdominal aorta
79
What is a type IV thoracic aneurysm using the Crawford classification?
most of all of abdominal aorta
80
What is a dissection?
blood enters the media layer of the blood vessel via a tear in the intima
81
What symptoms may suggest a thoracic aortic dissection?
- pain in anterior chest, neck, or between shoulder blades
- may appear to be in shock although the systemic BP is elevated
- decreased or absent peripheral pulses
- acute mental status changes/stroke from occlusion of carotid artery
- pain may also be associated with MI due to compression of coronary arteries
- paraparesis or paraplegia of lower extremities due to impaired BF to the spinal cord
- GI and renal ischemia
82
Where are majority of the thoracic aneurysms?
ascending aorta (60%)
83
What is involved with an ascending thoracic aneurysm repair?
CPB and median sternotomy
84
What are major complications associated with an ascending thoracic aneurysms repair?
- aortic regurg.
- long aortic cross-clamp times
- large intraoperative blood loss
85
What drug can be used to help reduce blood loss during am ascending thoracic aneurysm repair?
aprotinin (Amicar)
86
What monitoring device is extremely useful during an ascending thoracic aneurysm repair?
TEE
87
What is a Bentall procedure?
repair of ascending thoracic aneurysm with replacement/repair of aortic valve and coronary reimplantation
88
Where is arterial monitoring done for an ascending thoracic aneurysm repair?
left radial artery
89
Will an ascending thoracic aneurysm repair require heparinization?
YES, ACT>400
90
What are anesthetic implications for a transverse aortic arch repair?
- median sternotomy and CPB
- deep hypothermia (15 degrees Celsius) with circulatory arrest
- pack head in ice
- maintain flat EEG
- methylprednisolone or dexamethasone
- mannitol
- phenytoin
- coagulopathies common
91
Where is a descending thoracic aneurysm?
between left subclavian artery and aortic hiatus (diaphragm)
92
Where is the incision for a descending thoracic aneurysm repair?
left thoracotomy - need one-lung ventilation R DLT or bronchial blocker
93
What are anesthetic implications for a descending thoracic aneurysm repair?
- left thoracotomy so one lung ventilation
- may use femoral bypass (partial CPB)
- arterial line on right side***
- high risk for significant blood loss
- have current T&C and have blood in room
94
What is the most devastating complication of descending thoracic aneurysm repairs?
poor perfusion of spinal cord causing paraplegia
95
What should you keep in mind during a descending thoracic aneurysm repair regarding immediate post-op care?
Will need to assess lower extremity movement ASAP so make sure patient fully reversed and watch amount of NDNMB given
96
What is the intrinsic circulation to the spinal cord?
- one anterior spinal artery (75-80% of blood flow to anterior cord)
- two posterior spinal arteries (20-25% blood flow to posterior cord)
97
What is the extrinsic circulation to the spinal cord?
Radicular and medullary arteries
98
What is the artery of adamkieweicz?
aka great radicular artery or the arteria radicularis magna, enters intravertebral foramen in thoracolumbar region and 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
99
At which thoracolumbar space do majority of arteries of adamkieweicz enter?
T9-T12 (75%)
T5-T8 (15%)
L1-L2 (10%)
100
Occlusion of what artery is the main determinant of paraplegia?
artery of adamkieweicz
101
Which patients are at highest risk of spinal cord ischemia?
- aortic dissection or rupture
- extensive aneurysm size
- prolonged aortic occlusion time
- patient age
- CSF pressure
- perioperative hypotension
102
What is the most important determinant of paraplegia and acute renal failure following aneurysm repair?
location and extent of the aneurysm notwithstanding, the duration of aortic crossclamping
103
About how much time during cross-clamping is there little change of spinal cord injury?
first 20-30 mins
104
After about how long during cross-clamp time is there increased risk for spinal cord injury?
aka "the vulnerable interval", 30-60 mins of cross-clamp time = ~10-90% incidence of paraplegia, the likelihood of paraplegia increases with duration
105
What are some strategies used to protect the spinal cord?
- monitoring of evoked potentials
- operative strategies
- CSF drainage
- mild to moderate hypothermia
- intrathecal papaverine (dilates spinal arteries and oxygen free radical scavenger)
- retrograde venous spinal cord perfusion
- neuroprotective pharmacolgoical intervention
106
What is the spinal cord perfusion pressure?
spinal cord perfusion pressure (SCPP) = mean aortic pressure - CSF pressure
107
At what distal perfusion pressure is there a higher association with paraplegia?
108
What normally happens to CSF pressure and arterial pressure during cross clamp?
CSF pressure increases while arterial pressure decreases distal to cross clamp
109
How can SC perfusion pressure be manipulated?
altering ABP and draining CSF through an intrathecal catheter
110
What is the primary cause of carotid occlusive disease?
atherosclerosis
111
Where are carotid artery occlusions usually found?
carotid bifurcation
112
What are clinical manifestations of carotid artery occlusions?
- stroke
- TIA
- monocular
- blindness (amaurosis fugax)
- asymptomatic bruit
113
What is the degree of cerebral injury with carotid artery occlusions dependent on?
cerebral collateral flow due to the integrity of the Circle of Willis, duration of hypoperfusion, cerebrovascular vasoreactivity, plaque morphology
114
What are indications for a carotid endarterectomy (CEA)?
- 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%)
115
What does carotid artery occlusion ultimately lead to?
ischemia and ultimately loss of cerebral blood flow autoregulation
116
What should a pre-op evaluation involve for someone having a carotid endarterectomy?
- cardiac function
- EKG, ECHO, TEE, previous cardiac surgeries, etc.
- pulmonary function
- previous surgical procedures involving neck
- vocal cord function/abnormalities
- pertinent labs - CBC, F&E, coags
117
What is involved with perioperative management of a CEA?
- maintain adequate cerebral and myocardial perfusion and oxygenation
- minimizing the stress response (avoid HTN & tachycardia, ensure adequate pain control)
- smooth induction and emergence
- avoid large swings in BP
- cerebral protective measures
- fully awake patient at the end of the procedure to allow for comprehensive neurologic assessment
118
What are benefits of regional anesthesia for a CEA?
- allows continuous assessment of an awake patient
- avoids use of expensive monitoring equipment
- reduces need for shunting
- less hemodynamic instability
- fewer medications needed for sedation/anesthesia
119
What regional block is used for a CEA and what dermatomes are blocked?
superficial and deep cervical block, C2-C4 dermatomes
120
What are potential disadvantages of regional anesthesia for CEA?
- 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
121
What are absolute contraindications for regional anesthesia for CEA?
- patient refusal
| - language barriers
122
What are relative contraindications for regional anesthesia for CEA?
- difficult anatomy
| - Severe COPD or diaphragmatic dysfunction
123
What is the most sensitive monitor of cerebral perfusion/ischemia during a CEA with regional anesthesia?
an awake patient!
124
When do you place an arterial line for a CEA?
prior to induction
125
How do you manage BP for a CEA?
treat hypotension
126
What monitors can be used during a CEA?
- EEG
- SSEPs
- carotid stump pressures
- transcranial doppler (TCD)
- cerebral oximetry
127
What is the purpose of using SSEPs during a CEA?
measures integrity of dorsal (sensory) portion of spinal cord and deep brain function
128
What is the purpose of monitoring carotid stump pressures during a CEA?
assess extent of collateral flow, pressures
129
Is there a correlation between EEG changes and stump pressures?
No
130
What is the purpose of transcranial doppler monitoring?
measures BF velocity of MCA, measures integrity of the cerebral hemispheres
131
What is the purpose of cerebral oximetry monitoring during a CEA?
assess cerebral regional O2 saturation, low positive predictive value
132
What should you do before the release of the cross-clamp during a CEA?
- ABP should be decreased to baseline level or slightly lower (within 20% of baseline value)
- most surgeons request SBP to be kept 140-160 mmHg to ensure adequate but not excessive cerebral perfusion
- DC phenylephrine and reduce volatile agent (if necessary) prior to unclamping
- be prepared to administer small boluses doses (20-40 mcg) of SNP or NTG
- surgeon may or may not ask to reverse heparin with protamine
133
What are post-op complications of CEA?
- denervation of ipsilateral carotid baroreceptor
- postoperative hoarseness, ipsilateral deviation of the tongue, and/or Horner's syndrome
- surgical retraction of RLN and hypoglossal nerves, respectively
- hematoma formation at surgical site may compromise ventilation--maintain normal BP
- postoperative cerebral hyperperfusion syndrome
134
What results from denervation of ipsilateral carotid baroreceptor as a complication from CEA?
HTN, blunted ventilatory response to hypoxemia by CAROTID CHEMORECEPTORS (primarily decreases in PaO2) --NOT CENTRAL
135
What is postoperative cerebral hyperperfusion syndrome?
Complicaiton from CEA:
- increase in cerebral BF with loss of autoregulation in reperfused brain leading to a h/a, seizures, focal neurologic signs, edema, hemorrhage
- typically occurs several days following CEA
- patients with severe preop carotid stenosis and postop HTN are at increased risk
136
What can cause acute respiratory compromise following CEA?
- hematoma
- bilateral RLN
- deficient carotid body functon
- vocal cord paralysis
- tension pneumo
- stroke or loss of consciousness
