Continuing Education Activity

Acute ischemic stroke is a neurological emergency that prompts urgent evaluation and treatment to limit disability and mortality. This is a multidisciplinary team effort where different teams are involved at varying levels of care. This activity describes the interprofessional team's role in deciding the type of anesthesia, maintaining hemodynamic and metabolic parameters for best neurological outcomes.

Objectives:

• Describe the vascular pathophysiology of acute ischemic stroke.
• Review the importance of initiating the treatment early in order to limit disability.
• Summarize the anesthetic concerns of patients undergoing endovascular treatment (mechanical thrombectomy) and establish goals of care.
• Outline the importance of communication between interprofessional teams taking care of patients with acute ischemic stroke.

Introduction

Approximately 795000 people suffer from stroke annually in the US. By this estimate, one person gets a stroke every 40 seconds, and approximately one patient dies due to stroke every 4 minutes.[1]

Acute stroke can be classified as ischemic, hemorrhagic, subarachnoid, cerebral thrombosis, and spinal stroke.[2]

About 80 to 87% of all strokes are of ischemic origin. Ischemic stroke is further divided into five subtypes:[3][4][5]

1. Large-artery atherosclerosis
2. Cardioembolism
3. Small-vessel occlusion
4. Stroke of other determined etiology
5. Stroke of undetermined etiology

Risk factors of stroke can be divided into modifiable and non-modifiable. Modifiable factors are hypertension, diabetes, hyperlipidemia, tobacco use, alcohol and drug use, physical inactivity, atrial fibrillation. Non-modifiable factors are age, sex, race, genetics.

Anatomy and Physiology

Cerebral Circulation: Arterial System and Venous System

The arterial blood flow to the brain is through two major sources: the anterior source is provided by internal carotid arteries, and the posterior source originates in vertebral arteries. Internal carotid and vertebral arteries confluence at the circle of Willis, and from there, all the major cerebral arteries arise. Thus, arteries supplying brain tissue are the anterior cerebral artery, middle cerebral artery, anterior choroidal artery, posterior cerebral artery, anterior inferior cerebellar artery, posterior inferior cerebellar artery, basilar artery.

Cerebral venous system: superficial dural venous sinuses and deep cerebral veins.[6]

Acute Ischemic stroke (AIS) is caused by deficient blood and oxygen supply to the brain; hemorrhagic stroke is caused by bleeding or leaky blood vessels.

Pathophysiology

In ischemic stroke, acute occlusion of blood vessels is most commonly embolic, while rupture of atherosclerotic plaque is a less common cause.[7] This leads to a reduction in blood flow and cell death.

Approximately 10 to 15% of all strokes are hemorrhagic in nature (caused by ruptured blood vessels) and are associated with high mortality.

After an acute stroke, the area of ischemic brain tissue (core) is surrounded by reversibly damaged tissue called the penumbra.[8] This tissue is salvageable and is the focus of stroke treatment.[9]

Indications

Indications of endovascular therapy in acute ischemic stroke are patients who present late. They are out of the window for intravenous recombinant-type tissue plasminogen activator (IV rtPA) therapy, who have contraindications to IV rtPA therapy (e.g., recent surgery or coagulopathy), or who have failed IV rtPA therapy.[10]

Outcomes are favorable in patients who receive thrombectomy and standard medical care within 6 to 24 hours of the onset of symptoms.[11]

Equipment

For brain imaging, e.g., non-contrast computed tomography (NCCT), diffusion weight magnetic resonance imaging (DW-MRI)

Cerebral Angiography

• Airway equipment, endotracheal tubes, laryngoscopes, glide scopes
• Anesthesia machine
• Oxygen
• Anesthesia induction agents, propofol, etomidate, people with paralysis
• Vasoactive medications such as vasopressors and anti-hypertensive drugs
• Ultrasound machine for rapid vascular access/arterial line cannulation
• Arterial blood gas analyzer
• Glucometers

For Mechanical Thrombectomy

• Stent retriever
• Mechanical embolus removal in cerebral ischemia (MERCI) device
• The proximal balloon guide catheter
• A large-bore distal access catheter
• Cervical guide catheter

Standard American Society of Anesthesiology (ASA) monitors like, pulse oximeter, electrocardiogram, noninvasive and invasive blood pressure monitoring, temperature monitoring, end-tidal carbon dioxide monitor.

Personnel

Interprofessional care team, including emergency department personnel, neuro-interventionalists, anesthesiologists, neurologists, neurosurgeons, neurocritical care specialists, nurses, technicians.

Preparation

Mechanical thrombectomy is an emergent procedure. Therefore, neuro-angiography suite/operating room (OR) should be prepared well in advance for endovascular treatment of stroke to avoid any delay in anesthesia. An anesthesia machine should be checked and be ready to go. Airway equipment, monitoring devices, venous access kits, and drugs should be ready for starting and maintaining anesthesia.

Technique or Treatment

Hemorrhagic Stroke

Treatment modalities for hemorrhagic stroke mainly revolve around hypertension control and surgical evacuation of the hematoma.[12][13] The benefits of either of these interventions in improving the outcome of hemorrhagic stroke are uncertain. Studies comparing the effect of target systolic blood pressure of 110 to 139 mmHg vs. 140 to 179 mmHg did not show a reduction in mortality and morbidity in patients suffering from hemorrhagic stroke.[14] Early surgery for hematoma evacuation has some survival benefits.[15]

Acute Ischemic Stroke (AIS)

Brain tissue is lost rapidly after stroke, and hence, time is brain concept was introduced to emphasize the need for emergent evaluation and treatment to limit its progress.[16] Quantitative neurostereology and stroke neuroimaging show that for every minute of untreated large vessel stroke, the brain loses approximately 1.9 million neurons. Therefore, one of the significant anesthetic concerns is the preservation of the penumbra region. It lasts only a few hours on humans.[17] Every attempt should be made to avoid the delay of anesthesia.

There is an ongoing debate about the effectiveness of general anesthesia (GA) over conscious sedation and vice versa, as some studies have shown that GA is associated with a lower disability while others demonstrated worse outcomes with GA.[18][19][20][21]

Anastasian enumerated the advantages and disadvantages of GA and local anesthesia.[10] Advantages of GA are immobility, pain control, and airway protection, while disadvantages are more hemodynamic changes and time delay at the start of the procedure. Advantages of local anesthesia are superior hemodynamics and neurological evaluation, while the disadvantages are patient movement, pain, and agitation, loss of airway control.

American Heart Association/ American Stroke Association (AHA/ASA) guidelines recommend that the choice of anesthetic technique should be based on patient risk factors, clinical conditions, and technical performance of the procedure. They recommend that either method, i.e., GA or procedural sedation is reasonable until more data is available. Society for neuroscience in anesthesiology and critical care (SNACC) expert consensus statement also recommends that the choice of anesthesia should be tailored according to the patient’s clinical condition.[22][23]

Blood pressure, heart rate, electrocardiogram, oxygen saturation, end-tidal carbon dioxide concentration should be continuously monitored throughout the procedure. Invasive arterial blood pressure should be employed to monitor beat-to-beat pressure.[23]

Hypertension is present in about 80% of patients presenting with acute ischemic stroke.[24]

A U-shaped relationship exists between blood pressure and neurological outcome, with hypertension and hypotension, with both associated with poor outcomes. Data shows that the best neurological outcomes are observed at a systolic blood pressure of 150 mmHg (range between 140 to 179 mmHg).[25] Diastolic blood pressure should be maintained at < 105 mmHg.[23]

AHA/ASA guidelines recommend maintaining BP ≤180/105 mmHg during and for 24 hours after mechanical thrombectomy.

For patients presenting with hypertension in the setting of AIS, the overall clinical picture should be taken into account, e.g., patients with acute coronary syndrome, acute heart failure, aortic dissection, or post thrombolysis symptomatic intracerebral hemorrhage. In these cases, the initial lowering of BP should not be more than 15% of baseline.[22]

Different antihypertensive options to control BP as recommended by AHA/ASA are:

• Labetalol 10 to 20 mg IV over 1 to 2 min, may repeat one time; or
• Nicardipine 5 mg/h IV, titrate up by 2.5 mg/h every 5 to 15 min, maximum 15 mg/h;
• Clevidipine 1 to 2 mg/h IV, titrate by doubling the dose every 2 to 5 min until desired BP reached; maximum 21 mg/h
• Other agents (e.g., hydralazine, enalaprilat) may also be considered.

If BP is not controlled or diastolic BP >140 mm Hg, IV sodium nitroprusside can be considered.

Anesthesia should be planned in a way that avoids hypotension and acute fluctuations in blood pressure, as they are associated with loss of penumbra.[26]

Hypotension is associated with poor outcomes in the setting of acute ischemic stroke.[10] Systolic blood pressure of <140 mmHg is an independent predictor of poor neurologic outcome.

Hypotension and hypovolemia should be corrected to achieve hemodynamic stability and organ perfusion, and excessive volume expansion is not recommended as it may lead to hemodilution. If hypoglycemia is not a concern, non-glucose-containing fluids should be used.

Aspirin should be administered in patients with AIS within 24 to 48 hours after onset, but it should not be used as a substitute to the treatment by either thrombolysis or mechanical thrombectomy.

Supplemental oxygen should be used to maintain oxygen saturation >94%, or PaO2 > 60 mmHg.[27] All the measures should be taken to avoid hypoxia, hypercapnia, and hypocapnia.

Body temperature should be maintained in a range of 35 to 37 degrees centigrade. Causes of hyperthermia (temperature >38 degrees C) should be identified and treated. Antipyretic medications and cooling devices should be used to correct the temperature when needed.

Blood sugar should be closely monitored, and hypoglycemia (blood glucose <60 mg/dL) and hyperglycemia should be avoided. AHA/ASA recommends target blood sugar levels of 140 to 180 mg/dl range.[22] SNACC consensus statement recommends maintaining blood sugar levels between 70 to 140 mg/dl.[23]

Routine use of prophylactic antibiotics, antiseizure drugs, and flathead positioning has not been proven beneficial.

After the procedure, the patient should be transferred to the neuro-critical care unit for continued hemodynamic and neurological monitoring.

Complications

Potential complications are intracranial hemorrhage, vessel dissection, emboli to new vascular territories, vasospasm, stent dislocation/occlusion, extravasation.[28][29]

Clinical Significance

Avoidance of delay in anesthesia and hence treatment of acute ischemic stroke cannot be emphasized more. More delay causes more loss of penumbra and hence worse outcomes. Provision of hemodynamic stability is one of the most important anesthetic goals for patients undergoing mechanical thrombectomy for acute ischemic stroke.

Enhancing Healthcare Team Outcomes

Management of a patient with acute ischemic stroke requires a multidisciplinary effort, with multiple teams working at different levels and in coordination with each other. This requires efficient communication between teams. Code stroke should be initiated so that all teams are ready to deliver their responsibilities. For example, when the patient arrives in ED, physicians (ED physician, neurologist, anesthesiologist) should quickly assess the patient, stabilize them and send for a CT scan.

Meanwhile, nursing staff and technicians should be ready for the scan. If it is determined that the patient has an acute ischemic stroke and has no contraindications and is within the time frame of intravenous recombinant tissue plasminogen activator treatment, it should be administered. If not, then he should be taken to OR, avoiding any delay for mechanical thrombectomy.

The anesthesiologist should decide if he would require general anesthesia or conscious sedation depending on the clinical situation. Intraoperatively, care should be provided according to standard management protocols (AHA/ASA guidelines, SNACC recommendations), maintaining hemodynamic and metabolic parameters, providing adequate oxygenation and ventilation, all with an intent to salvage penumbra and limit neurological disability.

Nursing, Allied Health, and Interprofessional Team Interventions

Whenever a patient with suspected acute stroke symptoms presents, code stroke is called, and many different teams come into play. They work together and in succession to give the best care possible. With so many different persons working together, efficient communication becomes important.

Different teams may decide on doing interventions at different times during the hospital stay, such as ED physician/anesthesiologist may decide to intubate the patient if he thinks the patient’s consciousness is declining, a neurologist may decide on starting thrombolysis/thrombectomy and an interventional radiologist may help with mechanical thrombectomy. Also, the different teams may get involved to treat complications of stroke or its treatment. Good communication is valuable in all these scenarios.

Nursing, Allied Health, and Interprofessional Team Monitoring

Given the complexity of the procedure and co-morbidities associated with the patient, the importance of vigilant monitoring cannot be emphasized more. Neurologic parameters (consciousness, mental status), hemodynamic parameters (hypo/hypertension, cardiac rhythms, heart rate), metabolic parameters (blood sugar, renal function), and other clinical factors such as temperature should be continuously monitored. Effective communication should be established between the interprofessional team, and adequate interventions should be carried out in the best interest of the patients.