RE4: Chapter 25: Anesthesia for Vascular Surgery Flashcards
What pharmacological therapy should be instituted in patients at high risk for myocardial ischemia and infarction days to weeks before surgery?
What range should the KR be kept?
B-blockers
HR should be between 50-60 bpm to decrease demand and increase supply
What are major risk factors associated with atherosclerotic lesions???
Hypercholesterolemia Elevated triglycerides levels Cigarette smoking HTN DM Obesity Genetic predisposition Sedentary lifestyle Sex (male > female) Impaired long-term glucose regulation Homocysteine C-reactive protein
What is the primary objective in patients with vascular disease?
Detection of myocardial ischemia
What do patients with HTN and/or angiopathology rely on to perfuse their vital organs?
Increased mean arterial pressures
Why is epidural opioids and local anesthetics in patients recovering from vascular surgery important postoperatively?
Pain can greatly enhance sympathetic nervous system stimulation
What are some risk factors associated with AAA?
Smoking Older age Gender (male > female) Family history CAD High cholesterol COPD Height (per 7cm interval) HTN Peripheral vascular occlusive disease Caucasian
Which risk factor is most highly correlated with AAA and how much does the incidence increase by?
Smoking
Incidence of AAA increases five-fold!
What size AAA is surgical intervention recommended for?
5.5cm or greater in diameter
<4cm have low risk of rupture, but risk dramatically increases for AAAs with a 5cm or greater diameter
What are contraindications to elective repair of AAA?
Intractable angina pectoris
Recent MI
Severe pulmonary dysfunction
Chronic renal insufficiency
What calculation measures the wall tension of an aneurysm?
Law of Laplace
T = P x r
(As the radius increases, the wall tension increases. Therefore, the larger the aneurysm, the more likely the risk of spontaneous rupture.)
What is the average growth per year of an AAA?
4mm/yr
What are the most important techniques used to enhance cardiac function during an AAA repair?
Preoperative fluidity loading and restoration of intravascular volume
What are the hallmark pharmacologic treatments for medical management of an AAA?
Beta blockers, statins, and aspirin
What monitors should be used for AAA?
ECG with lead II for detection of dysrhythmias and V5 for analysis of ischemic ST-segment changes Pulse ox Capnography Esophageal stethoscope Urinary catheter Invasive BP monitoring
What is the primary method of intraoperative cardiac assessment?
TEE
True or False. Wall motion abnormalities occur sooner than ECG changes during periods of reduced coronary blood flow.
TRUE
Where is the most common site for cross-clamping for AAA?
INFRARENAL - because most aneurysms appear below the level of the renal arteries
What happens to the BP above the clamp and below the clamp during the cross clamping of the aorta?
Hypertension ABOVE the cross-clamp
Hypotension BELOW the cross-clamp
What happens to the MAP and SVR with cross-clamping?
Increase
What happens to CO with cross clamping?
Decrease or remain unchanged
PAOP may increase or display no change as well
What may the increased wall stress from increased afterload with cross clamping contribute to?
Decreased global ventricular fxn and myocardial ischemia
What happens metabolically to the tissues distal to the cross-clamp?
Prone to developing hypoxia. In response to hypoxia, metabolites such as lactate accumulate.
What is released that may also contribute to cardiac instability during aortic cross-clamping?
What can be administered to pretreat this?
Arachidonic acid derivatives
Thromboxane A2 synthesis may be responsible for decreasing myocardial contractility and CO
ASA or ibuprofen
What can mesenteric traction cause during AAA?
What metabolite is associated with this?
Mesenteric traction syndrome - decreases in BP and SVR, tachycardia, increased CO, and facial flushing
6-ketoprostaglandin F1
What neuroendocrine response/mediators are release in response to surgical stress?
What do they cause?
Cytokines such as interleukin (IL)-1B, IL-6 and tumor necrosis factor as well as plasma catecholamines and cortisol.
They trigger an inflammatory response that results in increased body temp, leukocytosis, tachycardia, tachypnea and fluid sequestration.
What is one of the most significant predictors of postop renal dysfunction?
Preoperative evaluation of renal function!
What is associated with spinal cord damage with aortic occlusion?
Interruption of blood flow to the greater radicular artery (artery of Adamkiewicz) in the absense of collateral flow may cause paraplegia
What can identify spinal cord ischemia intraoperative?
SSEPs
What do SSEPs reflect and what does it NOT provide information about?
SSEPs reflect dorsal (sensory) spinal cord function and doesn’t provide information regarding the integrity of the anterior (motor) spinal cord.
What is capable of determining anterior (motor) cord function?
MEPs
What is attributed to the manipulation of the inferior mesenteric artery?
Ischemia of the colon b/c the inferior mesenteric artery is the primary blood supply to the left colon.
While the aorta is occluded, what metabolites are released d/t anaerobic metabolism?
What does this cause?
Metabolites such as lactate accumulate below the clamp inducing vasodilation and vasomotor paralysis.
As the cross clamp is released, SVR decreases and blood is sequestered into the previously dilated veins which decreases venous return. What does this cause?
Reactive hypermedia causes transient vasodilation secondary to presence of tissue hypoxia, release of adenine nucleotides and liberation of a vasodepressor substance that acts as a myocardial depressant and peripheral vasodilator. This causes DECREASED PRELOAD AND AFTERLOAD!!!
What is the hemodynamic instability that may ensue after the release of an aortic cross-clamp called?
What does this cause?
Declamping shock syndrome
Severe hypotension and reduction in CO
How can declamping shock syndrome be prevented?
Volume loading just before the clamp is released
What is paramount in providing circulatory stability before release of the aortic clamp?
Restoration of circulating volume
What are the consequences of the following with aortic declamping? MAP Contractility SVR CVP Preload CO PA pressures
Everything decreases except PA pressures
As the aorta is clamped more proximally, what happens to the LV afterload and what is more likely to occur?
Afterload increases and myocardial ischemia is more likely to occur
What surgical action results in less severe hypotension?
Partial release of the aortic cross-clamp over time
What are the two surgical approaches for an elective AAA reconstruction?
Advantages vs. Disadvantages
- Transperitoneal incision
Advantages: familiarity, exposure of infrarenal and iliac vessels, ability to inspect intraabdominal organs, rapid closure, and versatility
Disadvantages: increased fluid loss, prolonged ileus, postoperative incisional pain, and pulmonary complications - Retroperitoneal incision
Advantages: excellent exposure (esp. for juxtarenal and suprarenal aneurysms and in obese Pts), decreased fluid losses, less incisional pain and fewer postoperative pulmonary and intestinal complications
Disadvantages: unfamiliarity, poor right distal renal artery exposure, and inability to inspect the integrity of the abdominal contents
True or False. CAD exists in more than 50% of patients who require abdominal aortic reconstruction and is the single most significant risk factor influencing long-term survival.
True
Who should high concentrations of VAs not be used with during AAA and why?
Pts with moderate to severe decreased EF d/t depression of myocardium and hemodynamic instability caused by VAs
What are the benefits of epidurals used with AAA?
Decreased preload and afterload Preserved myocardial oxygenation Reduced stress response Excellent muscle relaxation Decreased incidence of postop thromboembolism Increased graft flow to lower extremities Decreased pulmonary complications Improved analgesia
What is an largely unfavorable result of epidurals?
HYPOTENSION during blood loss or declamping
What rate is crystalloid used for replacing basal and third space losses?
10mL/kg/hr
What ratio can blood loss be replaced by crystalloids?
3:1
What rate should UO be maintained intraoperatively?
1ml/kg/hr
What induction agent is most suitable for pts with limited cardiac reserve?
Etomidate
Slow induction with opioids and b-blockers can preserve hemodynamic stability
What is the difference between juxtarenal and suprarenal aortic aneurysms?
Juxtarenal aneurysms are located at the level of the renal artery, but spare the renal artery orifice. Whereas most proximal suprarenal aneurysms include at least one of the renal arteries and may involve visceral vessels.
When does renal failure occur more frequently, infrarenal or suprarenal aortic occlusion?
Suprarenal
What are some interventions that may minimize renal ischemia and dysfunction?
Maintaining adequate intravascular VoLTE and administrating osmotic and loop diuretics
True or False. Paraplegia is possible when the blood supply to the spinal cord is interrupted by aortic cross clamp at or below the level of the diaphragm.
FALSE. At or ABOVE the level of the diaphragm
What may be used as a means to increase spinal cord perfusion pressure?
Increasing MAP or decreasing CSF by placing a catheter in the subarachnoid space to drain CSF
What is imperative to maintain postoperatively in AAA pts?
Adequate BP, intravascular fluid volume, and myocardial oxygenation
What are common symptoms of ruptured AAA?
Abdominal discomfort or back pain
Hypotension
Pulsatile mass
What is the primary focus with a ruptured AAA?
Cardiovascular stability
What are aneurysms called that involve all three layers of the arterial wall?
What are the 3 layers called?
True aneurysm
- Tunica adventitia
- Tunica media
- Tunica intima
What are aneurysms called that solely involve the adventitia?
False aneurysms
What are aneurysms called that have spindle shape and result in the dilation of the aorta?
Fusiform aneurysm
What aneurysms are spherical dilations and generally are limited to only one segment of the vessel wall?
Saccular aneurysms
What is an aortic dissection the result of?
Spontaneous tear with the intima that permits the flow of blood through a false passage along the longitudinal axis of the aorta.
What are some symptoms of a thoracic aneurysm?
Pain, strider and cough due to compression of thoracic structures.
What types of aneurysms necessitates the use of CPB?
Resection of the ascending aorta and graft replacement
What does surgical resection of lesions in the transverse arch compromise?
What techniques help decrease this?
Cerebral perfusion
Profound hypothermia and circulatory arrest
What is the most common factor that contributes to the progression of the lesion of an aortic dissection?
HTN
Which type of lesions have the highest incidence of rupture and require immediate surgical intervention?
Type A - dissections that involves the ascending aorta
Which lesion may initially be managed medically with administration of arterial dilating and beta-blockers?
Type B - dissections that do not involve the ascending aorta
Aneurysms located where require CPB?
Ascending and transverse aorta
What should be carefully assessed preoperatively before a AA repair?
Renal function
Neuro function esp lower extremity function
Left RLN due to close proximity to aortic arch
What types of monitoring is recommended with thoracoabdominal aneurysms?
Arterial line and PAP with CPB!
(If aneurysm involves the thoracic region of the distal aortic arch, the RIGHT radial artery is preferred b/c of left subclavian arterial blood flow may be compromised with surgery.)
DLTs, lumbar intrathecal catheter to access CSF, SSEPs and MEPs
What is the most effective means of decreasing afterload during cross-clamp application?
Sodium nitroprusside
What may be given during aortic occlusion to decrease preload?
Nitroglycerin
Where does the artery of Adamkiewicz (greater radicular artery) originate from?
Intercostal branch b/w T8 and L2 and provides majority of blood flow to the ANTERIOR SPINAL ARTERY. This artery perfuses the VENTRAL aspect of the spinal cord, which is responsible for motor control.
What is vital to avoid spinal cord deficits?
Avoiding prolonged periods of hypotension
How can spinal cord perfusion be measured?
arterial BP - CSP pressure
What factors contribute to the development of neurological deficit with aortic cross clamping?
Level of aortic clamp application
Ischemic time
Embolization or thrombosis of a critical intercostal artery
Failure to revascularize intercostal arteries
Urgency of surgical intervention
What types of aneurysm can endovascular aortic aneurysm repair be performed on?
Descending thoracic aortic aneurysm and AAAs
What heparin dose is administered prior to catheter manipulation for endovascular aortic aneurysm repair?
50-100 units/kg
What are the goals for intraoperative management for EVAR?
Maintain hemodynamic stability
Provide analgesia and anxiolysis
Be prepared to convert to an open procedure
What is an Endoleak?
Which type is the most common?
persistent blood flow and pressure (endotension) between the endovascular graft and the aortic aneurysm
Most common are type II and 70% spontaneously close within the 1st month after implantation. Type II endoleaks are caused by collateral retrograde perfusion.
The increased risk of ________ associated with ___ provides the rationale for the use of carotid endarterectomy (CEAs)
Stroke associated with TIA
Carotid artery stenosis is the primary cause of approximately ____% of all strokes.
20%
Patients with carotid stenosis greater than ______%, have the greatest benefit from a CEA.
70%
What was found to the most significant factor for predicting postoperative stroke incidence?
Preoperative neurologic dysfunction
What syndrome occurs in 25% of patients with high grade carotid artery stenosis?
Amaurosis fugax or monocular blindness (caused by microthrombi that travel into the internal carotid and decreases the blood supply to optic nerve via ophthalmic artery)
How is cerebral perfusion pressure calculated?
CPP = MAP - ICP
**MAP plays the predominant role in determining CPP
At what MAPs does CPF remain constant?
Between 60 and 160mmHg
How does chronic systemic HTN affect CBF?
It shifts the curve to the right, therefore a higher than normal MAP may be required to ensure adequate cerebral perfusion
What is normal CBF?
50mL/100g/min
At what CBF rate is neural function generally maintained at?
> 25mL/100g/min
At what CBF does cellular death occur?
< 6mL/100g/min as evidenced by flattening seen on the an electroencephalogram
Why is normocapnia paramount?
Hypocapnia decreases and hypercapnia increases CBF
What is the most sensitive and specific measure of adequate cerebral blood flow?
An awake patient
What are the major objectives during carotid artery revascularization?
Maintain CBF and decrease cerebral ischemia
What is the gold standard in identifying neurologic deficits related to carotid artery cross-clamping?
Electroencephalographic monitoring
What on the EEG are indicative of neurologic dysfunction?
Loss of B-waves, loss of amplitude and emergence of slow wave activity.
What carotid stump pressure reflects neurologic hypoperfusion and a criterion for shunt placement?
< 40-50mmHg
Can a motor deficit occur despite a normal SSEP waveform?
Yes b/c SSEPs are only measuring the integrity of the dorsal or sensory portion of the spinal cord.
With cerebral oximetry, a reduction of critical oxygen saturation during clamping of greater than ___ or ____% if persistent for longer than ___ minutes indicates the potential for deficits.
20-25%
4 minutes
What measurements and intraoperative monitoring modalities are used to determine the need for shunt placement during CEAs?
Stump pressure and EEG
How is prevention of cerebral ischemia accomplished?
Increasing collateral flow (placement of intraluminal shunt) or decreasing cerebral metabolic requirements (pharmacological adjuncts)
What does the application of the intraluminal shunt pose the risk of?
Embolic complications and intimal dissections
Anesthetics except for which drug have cerebral protective properties.
Etomidate
The surgeon may request which two drugs to be administered before the carotid artery is cross-clamped for cerebral protection?
Propofol or Precedex
What is hypotension and hypertension related to with CEAs?
Hypotension - result of carotid sinus baroreceptor stimulation
Hypertension - surgical manipulation of the carotid sinus
What pharmacologic adjuncts should be used for BP control with CEAs?
(ALL patients should continue BP medications until the time of surgery!)
Short acting beta-blockers may stabilize BP during induction/emergence
Nitroglycerin and sodium nitroprusside should be available to treat HTN
What are the anesthetic goals specific to CEAs?
Maintain cerebral and myocardial perfusion and oxygenation
Minimize the stress response
Facilitate a smooth and rapid emergence
What regional technique can be used for CEA?
What is the advantage?
Superficial and deep cervical plexus block (CN II to IV)
Allows the ability to directly assess neurologic function in an awake patient.
What is the limiting factor for the use of a regional technique?
Patient acceptance
What are the advantages of GA with CEA?
Motionless surgical field
Inhalation agents provide hemodynamic stability and beneficial effects on cerebral circulation (provides a degree of protection against ischemia)
What is the degree of protection against ischemia that VAs provide called?
Anesthetic preconditioning
With carotid artery cross-clamping without shunting occurs, where should the MAPS be?
MAP values should approximate or be slightly above preoperative levels to ensure adequate cerebral perfusion through the contralateral carotid artery.
What is the most common postoperative problem with CEAs?
HTN
What systolic BP is associated with an increased incidence of TIA, stroke or MI?
SBP > 180mmHg
What is an uncommon, but very serious complication of a CEA?
Carotid artery hemorrhage
What are initial manifestations of carotid artery hemorrhage?
Upper airway obstruction - reintubation difficult or impossible b/c of tracheal deviation
RLN damage
Tension pneumothorax
Cerebral hyper perfusion syndrome (CHS)
What is cerebral hyper perfusion syndrome (CHS)?
Damage to the carotid body leading to blunting of the chemoreceptor reflex and O2 should be given. It results from increased blood flow to the brain as a result of loss of cerebral vascular autoregulation.
What are s/s of CHS?
Severe HA
Visual disturbances
Altered LOC
Seizures
What anesthetic technique is most often used with carotid artery angioplasty stenting (CAS)?
Local anesthesia at the femoral insertion site and minimal sedation
What is the heparin dose for CAS?
50 - 100unit/kg to maintain an ACT > 250 seconds
What can cause prolonged bradycardia and hypotension with balloon inflation in the internal carotid artery with CAS?
What drugs are commonly used to treat this?
Stimulation of the baroreceptor response
Robinal or atropine given prior to balloon inflation
What is the most common complication of CAS?
Stroke cause by thromboembolism
