Anesthesiology

Interventional neuroradiology

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What the Anesthesiologist Should Know before the Operative Procedure

Understanding of the goals of different interventional neuroradiology (INR) treatments is essential in the planning of perioperative anesthetic management, especially the varying hemodynamic goals, such as appropriate management of systemic arterial pressure in the various disease states. It is important to secure backup equipment and personnel for emergency needs before starting the cases since INR suites are usually located outside of the main operating room area. Attention to distance and proper shielding is important for safety against radiation exposure.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Emergent: Timely intervention is critical in acute thromboembolic stroke. To reverse the neurologic deficits without additional risk of secondary hemorrhagic transformation, INR thrombolectomy and thrombolysis need to be performed as soon as possible. Outcome data have shown promising safety and clinical efficacy for INR interventions within 6 hours for the anterior circulation, and possible longer hours for mechanical thrombolectomy only or for the posterior circulation from the time of establishing the diagnosis.

Urgent: Early evaluation and treatment of a ruptured aneurysm reduce the risk of rebleeding and make the therapies safer for vasospasm caused by subarachnoid hemorrhage (SAH). Without intervention, risk of rebleeding from a ruptured cerebral aneurysm has been reported to be up to 40% accumulatively in the first month. The risk for morbidity and mortality is very high from re-ruptured aneurysms.

Elective: Most other procedures can be performed on an elective basis.

2. Preoperative evaluation

Most common medical conditions to evaluate for this procedure: Preoperative neurological symptoms and detailed neurological exams need to be documented. Patient's baseline blood pressure, cardiac function and cardiovascular reserve should be fully assessed. Blood pressure manipulation is commonly required in various diagnostic and treatment procedures in the endovascular approach.

Medically unstable conditions warranting further evaluation include: Unstable hemodynamics from acute myocardial infarction or arrhythmias, or life-threatening elevated intracranial pressure (ICP) from brain ischemia or hemorrhage. Further assessment, consultation and stabilization will be necessary before the patient can tolerate anesthesia and INR procedures.

Delaying surgery may be indicated if: Unstable medical conditions require immediate resuscitation.

3. What are the implications of co-existing disease on perioperative care?

b. Cardiovascular system

Perioperative evaluation

Acute/unstable conditions: Acute ischemic or hemorrhagic brain injuries from thromboembolism or rupture of vascular malformations can cause intracranial hypertension as well as neurogenic cardiac arrhythmias and dysfunction.

Baseline coronary artery disease (CAD) or cardiac dysfunction: Most commonly coexisting in patients with occlusive cerebral vascular diseases, but also relevant to patients with intracranial aneurysms, which often require manipulations of hemodynamics during ICU management, INR procedures, and postoperative care. The presence of symptomatic CAD is indicative of a high risk for stroke and affects survival after a stroke. Atrial fibrillation is the primary cardiac condition associated with cardiogenic embolism to the brain. Knowledge of baseline cardiovascular values and function reserves is important to ensure desirable INR treatment efficacy and patient safety.

Perioperative risk reduction strategies

Monitoring: Preinduction arterial line placement for patients requiring continuous tight blood pressure control perioperatively. Otherwise, a side port of the femoral artery introducer sheath can be used for intraoperative arterial line monitoring, keeping in mind that manipulation of endovascular catheters in and out of the sheath can interfere with the arterial line readings. Additional cardiac monitoring, such as CVP, may be indicated in patients with compromised cardiac function.

Goals

a. Apply standard management to optimize myocardial oxygen supply and demand ratio.

b. Provide mainly supportive management for patients with acute cardiovascular changes and proceed with INR procedures since prompt treatment is often critical for these cases unless unstable conditions need immediate resuscitation.

c. Achieve therapeutic goals of INR interventions without adding risks of brain ischemia or hemorrhage, or causing cardiac ischemia or dysfunction, when applying deliberate hypertension or deliberate hypotension.

c. Pulmonary

Acute/unstable conditions

Perioperative evaluation: SAH and acute ischemic stroke patients are at risk for pulmonary complications. Aspirational pneumonitis secondary to loss of functional airway reflexes may develop in patients with decreased consciousness level or seizures. Neurogenic pulmonary edema from catecholamine surges, or cardiogenic pulmonary edema from high afterload conditions and myocardial dysfunction, may also occur after SAH.

Perioperative risk reduction strategies: ETT intubation may be indicated to protect airway and to provide adequate oxygenation and ventilation. Hypertension should be avoided during laryngoscopy and ETT placement since untreated aneurysm remains at risk for rebleeding in SAH. The goal for mechanical ventilation is to maintain a normal pH and normocarbia. Hypoventilation may cause cerebral vasodilatation and accentuate elevated ICP, while hyperventilation may cause vasoconstriction and increase risk for cerebral ischemia. Time-limited hyperventilation may be applied as an emergency maneuver to decrease dangerously elevated ICP.

COPD: Standard perioperative care.

Reactive airway disease (Asthma): Standard perioperative care.

d. Renal:

Perioperative evaluation

Past medical history review and laboratory tests should include the assessment of pre-existing renal diseases. Patients with renal dysfunction are at high risk for contrast-induced nephropathy (CIN). Serum creatinine is a traditional marker for renal function. In CIN, the serum creatinine often starts to rise after the procedure, with the peak occurring in 48-72 hours and returning to normal within 2 weeks.

Perioperative risk reduction strategies

There is an established correlation between the osmolarity of contrast media and nephrotoxicity. Nonionic contrast, with less likelihood of causing CIN, should be a better choice in patients with preexisting renal dysfunction. Perioperative administration of N-acetylcysteine has shown benefits of renal protection in high risk patients. Fluid management goal is to keep the patients at normovolemia. Nephrotoxic medications should be avoided.

e. Neurologic:

It is essential for anesthetic planning and management for the anesthesiologist to have good understanding of the symptoms and time course of the present cerebral vascular disease, as well as pertinent neurological physiology and pathology.

Acute issues: Cerebral ischemia, edema and elevation of ICP could be a serious concern in cases of acute thromboembolic stroke and intracranial hemorrhage from ruptured aneurysm or arteriovenous malformation (AVM). Patient's preoperative neurological status should be carefully assessed and monitored. Details of any existing and evolving deficits need to be fully documented. Patient's blood pressure should be maintained accordingly to provide adequate cerebral perfusion.

Chronic disease: Some patients' prior neurological deficits (even with a full recovery previously) may reappear temporarily after the use of sedative medications or after emergence from general anesthesia, although the underlying mechanism remains to be fully elucidated. This phenomenon may interfere with the assessment of neurological status during the procedure in the sedated patients, or in the postoperative period.

f. Endocrine:

Hyperglycemia has been associated with poor outcomes in patients with neurological injuries, while hypoglycemia can be equally dangerous and life-threatening. Glucose should be closely monitored and maintained in the normal range in patients with diabetes mellitus. Diabetes mellitus patients are at high risk of CIN. Their renal function need to be closely monitored perioperatively.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

N/A

4. What are the patient's medications and how should they be managed in the perioperative period?

N/A

a. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Metformin: Contrast media can cause nephropathy that may delay the excretion of metformin from the body. High level of metformin accumulation can lead to dangerous lactic acidosis.

In type 2 diabetes mellitus patients:

Normal preoperative renal function - hold the drug on the day of INR procedure until 48 hours postoperatively and when the patient's renal function is confirmed at normal level.

Preexisting renal insufficiency - hold the drug 48 hours before and after the INR procedures.

b. What should be recommended with regard to continuation of medications taken chronically?

Cardiac: Beta-blockers and calcium channel blockers should be continued perioperatively.

Pulmonary: Continue daily medications for chronic pulmonary conditions.

Neurologic: Continue current medications.

Antiplatelet: Antiplatelet agents are commonly used in occlusive cerebrovascular disease management and for prophylactic treatment or rescue of thromboembolic complications in INR procedures, and are almost universally employed when stenting is performed for either occlusive or aneurismal disease. Stents are intrinsically thrombogenic. Patients need to receive the loading doses of antiplatelets, if they are not yet on the regimen, before the stents are placed.

Psychiatric: Continue current medications.

c. How To modify care for patients with known allergies -

For patients with known reactions to contrast media, preoperative treatment of steroids and antihistamines are recommended. For patients at risk for heparin-induced thrombocytopenia (HIT), direct thrombin inhibitors, including lepirudin or bivalirudin, may be used. Argatroban, predominantly metabolized in the liver, may be preferred in patients with renal dysfunction because of the renal elimination of lepirudin and its derivative bivalirudin.

d. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

N/A

e. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

N/A

f. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

Documented: avoid all trigger agents such as succinylcholine and inhalational agents:

  1. Proposed general anesthetic plan:

  2. Ensure MH cart available: [- MH protocol]

  3. Family history or risk factors for MH:

Local anesthetics/muscle relaxants

5. What laboratory tests should be obtained and has everything been reviewed?

Hemoglobin levels: INR procedures usually cause minimum blood loss. However, femoral vascular access carries a small but important risk of occult retroperitoneal hemorrhage that may be catastrophic. Unexplained decrease in hematocrit might be the first and only warning before hemodynamic instability develops. In patients with concerns of cerebral ischemia or vasospasm after SAH, it is recommended to keep hematocrit levels close to 30% to balance cerebral oxygen delivery and optimal blood rheology.

Electrolytes: Hyponatremia from cerebral salt wasting syndrome may be associated with change in mental status, and should be gradually corrected.

Coagulation panel: Heparin is commonly used to prevent thromboembolic complications in INR. Activated clotting time (ACT) needs to be checked at baseline before giving the bolus dose of heparin and monitored hourly during the procedure to verify the prolongation of ACT to two to three times of baseline. In rare cases, if a patient is refractory to attempts to achieve the anticoagulation, switching between bovine and porcine heparin may be considered.

Other tests: Renal function test should be checked to identify any pre-existing renal dysfunction.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

The choice of intravenuos sedation with monitored anesthesia care versus general anesthesia often depends on the local experience and preference of physicians involved, including the endovascular interventionalist and the anesthesiologist. General anesthesia is usually used in INR procedures that are complex or of long duration, and is required in patients who have decreased level of consciousness, have difficulty following commands or are at risk for aspiration. There has been a recently pointed debate on choice of anesthetic techniques for INR procedures in acute thromboembolic stroke. Future prospective randomized controlled clinical trials are needed to evaluate different types of anesthesia for the safety and clinical efficacy of INR endovascular procedures.

a. Regional anesthesia:

Not an option

b. General Anesthesia

Benefits

i. Protects the airway and controls ventilation.

ii. Useful for patients with an altered mental status.

iii. Tolerance of supine position in a prolonged case.

iv. Ensures immobilization of the patient.

v. Improves image quality.

Drawbacks: Neurological check cannot be accomplished during the procedure.

Other issues: Risk of unwanted hemodynamic changes during induction and emergence from general anesthesia

Airway concerns: There is increased risk of partial airway obstruction and risk of aspiration in patients with decreased level of consciousness, such as in acute thomboembolic stroke or hemorrhagic stroke from ruptured vascular malformations.

c. Monitored Anesthesia Care

Benefits: Facilitates frequent neurologic assessment and rapid recovery from anesthetics.

Drawbacks: Unsecured airway in patients who may have altered mental status. Oversedation may further cause upper airway obstruction and compromised gas exchange, or cause change of mental status which may be difficult to differentiate from worsening of cerebral ischemia, such as in the initial acute phase of stroke when the disease evolves rapidly.

Other Issues: It may be difficult for patients to lay supine and still for prolonged time, especially in patients with joint arthritis and chronic back pain. Discomfort may be associated with injection of contrast media, or distention and traction on the cerebral arteries.

6. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

No antibiotics required.

What do I need to know about the surgical technique to optimize my anesthetic care?

Vascular malformations

1. Embolization for aneurysms, AVMs, dural arteriovenous fistulas (AVFs), carotid caverous fistulas: These treatment procedures may last many hours. General anesthesia is usually required to ensure patient immobility, which is important for optimal image acquisition. Risk for parent vessel occlusion, thromboembolism, or vascular rupture.

(1) Aneurysms: Need preoperative antiplatelet treatment in unruptured aneurysms using stent-assisted coiling. Risk for aneurismal rupture and acute SAH at all times.

(2) AVMs: Usually as an adjunct to surgery or radiotherapy. The goal is to obliterate as much of the nidus as possible, by embolization of lesional fistulas or feeding arteries. Risk of acute hemorrhage from direct damage to vascular structures or from occlusion of venous outflow, pulmonary embolism from the embolic agents, and adverse reaction to the embolic agents.

(3) Dural AVFs: These are acquired arteriovenous shunt into dural veins or a dural venous sinus in the wall of a dura. Dural AVFs become high risk for spontaneous hemorrhage when their venous drainage is routed through intracranial instead of extracranial pathways. Intracranial venous hypertension, like increased ICP, may diminish the net cerebral perfusion pressure and its presence should inform appropriate management of systemic arterial pressure.

2. Angioplasty treatment of vasospasm from SAH: Balloon mechanical dilation or intra-arterial injection of pharmacological vasodilators. Patients are often critically ill with challenging comorbidities, complications from SAH and medical treatment of vasospasm. Intra-arterially administrated vasodilators may cause systemic effect of bradycardia and hypotension. Procedure risk of arterial dissection or rupture, thromboembolism, and/or reperfusion hemorrhage.

3. Ethanol sclerotherapy of brain or craniofacial venous malformations: have the potential to drain into intracranial veins or sinuses. Injection of 95% ethanol may cause brain or airway swelling. Ethanol intoxication may be evident after emergence from general anesthesia. Recirculation of ethanol can sometimes cause profound arterial hemoglobin desaturation. Airway control is required.

Occlusive cerebral vascular diseases

Patients often have other challenging cardiovascular comorbidities.

1. Balloon angioplasty and stenting for vascular stenosis: Carotid body stimulation can cause severe bradycardia or asystole. Procedure risk includes vessel occlusion, perforation, dissection, spasm, thromboembolism, occlusion of adjacent vessels, transient ischemic episodes, stroke, and postoperative brain hemorrhage or swelling.

2. Thrombolysis and thrombobectomy of acute thromboembolic stroke: Acute emergency treatment. Time from onset of symptoms to INR treatment is critical to good neurological outcome and to reduce risk of hemorrhagic transformation.

Other diagnostic and therapeutic procedures

1. Carotid occlusion for giant aneurysm: Risk of cerebral ischemia—may need to augment collateral blood supply.

2. Arterial embolization prior to tumor resection: Risk of cerebral ischemia.

3. Embolization for epistaxis: Airway control.

4. Intra-arterial chemotherapy of head and neck tumors: Risk of airway swelling and intracranial hypertension.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Deliberate hypotension

Indicated in carotid occlusion for the test of cerebrovascular reserve, and in embolization of arteriovenous or venous malformations for slowing the blood flow after injection of embolic agents. The choice of hypotensive agents, including increasing depth of anesthesia, beta-blockers and short-acting vasodilators (nitroglycerin or nipride), is often based on goals for blood pressure reduction, the patient's medical condition and the practitioner experience. The patient's hemodynamic and neurological stability should be maintained while lowering blood pressure to serve procedure needs.

Deliberate hypertension

Indicated in acute arterial occlusion or vasospasm. The goal is to augment collateral blood flow to the ischemic area by increasing systemic blood pressure. Systemic pressure is usually raised 30% to 40% above baseline to achieve resolution of ischemic symptoms or imaging evidence of improved perfusion. Phenylephrine is usually the first-line choice of drug, but given the high prevalence of post-SAH myocardial injury, inotropes may be appropriate. Signs of myocardial ischemia and cerebral hemorrhage need to be monitored.

Deliberate hypercapnia

Indicated sometimes in embolization of extracranial vascualr malformations. Hypercapnia can promote high venous outflow from cerebral venous system and help minimize the risk of embolic agents inadvertently moving into the intracranial compartment. It can be achieved by adding CO2 to the inhaled gas, or through controlled hypoventlation.

Intracranial catastrophes

The anesthesiologist's primary responsibility is to preserve gas exchange and secure the airway if necessary. Meanwhile, if suspicious of any adverse event, rapidly communicate with the INR team to distinguish the nature of the event.

1. Hemorrhagic: Immediate cessation of heparin plus reversal with protamine 1 mg/100 units of heparin given; check ACT. Be mindful of potential complications of protamine, including hypotension, anaphylactoid reaction with pulmonary hypertension. The pulmonary hypertension could be life-threatening and usually responds well to epinephrine. Patient may need to undergo an immediate CT scan for evaluation of intracranial hemorrhage.

2. Occlusive: Deliberate hypertension to augment collateral flow to maintain perfusion in territories distal to the occlusion site; may consider intra-arterial thrombolysis or thrombectomy.

3. Sudden loss of consciousness: First to differentiate the cause to be iatrogenic (oversedation), cerebral ischemia, hemorrhage, or seizures; then manage problems accordingly.

Cardiac complications

1. Severe bradycardia or asystole: Manipulations near the carotid body may induce reflex bradycardia. Transcutaneous pacing pads can be placed preoperatively for high-risk procedures. Intravenous atropine or epinephrine should be ready. Communicate with the team immediately at the first sign of a problem since stopping the manipulation is often effective for the heart rate to return to normal.

2. Hypotension: Severe systemic hypotension may occur after intra-arterial injection of vasodilators in vasospasm treatment. Good team communication, well-planned injection dosages and intervals, close monitoring and support of systemic pressure are essential.

Airway swelling

In ethanol sclerotherapy and certain tumor embolization procedures, always make sure there is enough air leak before ETT extubation.

a. Neurologic: *** Type Here.

N/A

b. If the patient is intubated, are there any special criteria for extubation?

Exubate the patient when airway can be maintained and ventilation is adequate.

c. Postoperative management

What analgesic modalities can I implement?

INR procedures usually do not cause much postoperative pain. Avoid long-acting sedatives to facilitate frequent neurologic assessments.

What level bed acuity is appropriate?

Patients should be transferred to critical care or stepdown units for continuous hemodynamic monitoring and control, and for frequent neurologic assessments in the immediate postoperative period after the endovascular treatment.

What are common postoperative complications, and ways to prevent and treat them?

Normal perfusion pressure breakthrough causing cerebral hemorrhage or edema

May occur in angioplasty or stent placement cases when normal systemic perfusion pressure is restored to a chronically hypotensive vascular bed and overwhelms the autoregulatory capacity. Hypertension should be prevented in the case of adequate collateral perfusion pressure. Blood pressure should be controlled in low normal range to prevent normal pressure perfusion breakthrough, or hyperperfusion edema. Beta-blockers, with minimum effects on cerebral vessels, can be used to control blood pressure.

Thromboembolic complications

May occur with any intracranial catheter navigation, especially with endovascular placement of stents or coils. Antiplatelet agents are often continued after the procedures. Heparinization may need to continue in some coiling cases in the immediate postoperative period.

Intracranial hemorrhage

It is crucial to keep in mind that anti-thromboembolic agents also increase the risk of bleeding. The combination of heparin and antiplatelets, especially, can synergistically predispose to hemorrhage. The effect of antiplatelets is difficult to monitor and can only be reversed by platelet transfusion. Specific clotting factors, such as recombinant factor VIIa, may be indicated in life-threatening hemorrhage uncontrolled by standard transfusion, including the empirical treatment using platelet transfusion.

What's the Evidence?

Lee, CZ, Litt, L, Hashimoto, T, Young, WL. "Physiologic monitoring and anesthesia considerations in acute ischemic stroke". J Vasc Interv Radiol. vol. 15. 2004. pp. S13-19.

Varma, MK, Price, K, Jayakrishnan, V, Manickam, B, Kessell, G. "Anaesthetic considerations for interventional neuroradiology". Br J Anaesth. vol. 99. 2007. pp. 75-85.

Young, WL, Dowd, CF, Cottrell, JE, Young, WL. "Cottrell and Young's Neuroanesthesia". Mosby Elsevier. 2010. pp. 247-63.

Meyers, PM, Heyer, EJ. "Stroke: sedation and anesthesia during endovascular stroke therapy". Nat Rev Neurol. vol. 6. 2010. pp. 474-5.

Anastasian, ZH, Strozyk, D, Meyers, PM, Wang, S, Berman, MF. "Radiation exposure of the anesthesiologist in the neurointerventional suite". Anesthesiology. vol. 114. 2011. pp. 512-20.

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