Tuesday, 6 March 2012

Diagnostic Cerebral Angiography

Catheter Angiography is still a gold standard for imaging cerebral vasculature.
Diagnostic angiography done as the first step during neuro interventional procedures.

Diagnosis of neurovascular disease like aneurysms, arteriovenous malformations, AV fistulas, Stenosis, Vasculopathy, Acute ischemic stroke etc.
Planning for neurointerventional procedures.
Intra-operative assistance with aneurysm surgery.
Follow-up imaging.

Preprocedure evaluation
General as well as detailed neurological exam.
History of iodinated contrast reactions.
The femoral pulse, as well as the dorsalis pedis and posterior tibialis pulses should be examined.
Routine blood, Serum Creatinine level and Coagulation parameters etc.

Contrast agents
Nonionic contrast agents are safer and less allergenic than ionic preparations.
Iohexol, a low osmolality, nonionic contrast agent, is relatively inexpensive and probably the most commonly used agent in cerebral angiography.
Diagnostic angiogram: Omnipaque®, 300 mg I mL−1
Neurointerventional procedure: Omnipaque®, 240 mg I mL−1
Patients with normal renal function can tolerate as much as 400–800 mL of Omnipaque®, 300 mg I mL−1 without adverse effects.

Midazolam 1–2 mg IV for sedation; lasts approximately 2 h
Fentanyl 25–50 mcg IV for analgesia; lasts 20–30 min
The use of sedation should be minimized, as over-sedation makes it hard to detect subtle neurological changes during the procedure.
Paradoxical agitation has been reported in up to 10.2% of patients,  particularly elderly patients and patients with a history of alcohol abuse or psychological problems. Flumazenil 0.2–0.3 mg IV can reverse this effect.

Femoral artery sheath 
Trans-femoral angiography can be done with or without a sheath.
Sheath allows for the rapid exchange of catheters and less potential for trauma to the arteriotomy site.
Lessen the frequency of intraprocedural bleeding at the puncture site.
Ease catheter manipulation.
Short sheath (10–13 cm arterial sheath) is used most commonly. Longer sheath (25 cm) is useful when ileofemoral artery tortuosity or atherosclerosis impair catheter navigation.
A 5-F sheath is slowly and continuously perfused with heparinized saline (2,000 U heparin per liter of saline) under arterial pressure.
Sheaths come in sizes 4 F up to 10 F or larger. The size refers to the inner diameter. The outer diameter is 1.5–2.0 F larger than the stated size.

Suggested guide wires and catheters
Hydrophilic wires.
The 0.035 in. angled Glidewire® (Terumo Medical, Somerset, NJ) is soft, flexible, and steerable.
The 0.038 in. angled Glidewire® (Terumo Medical, Somerset, NJ) is slightly stiffer than the 0.035 in., making it helpful when added wire support is needed.
Extra-stiff versions of these wires are available for even more support, but they should be used with extreme caution because of the tendency of the tip to dissect
5-F Angled Taper : all-purpose diagnostic catheter
4- or 5-F Vertebral : all-purpose diagnostic catheter, slightly stiffer than the Angled Taper but similar in shape
4 or 5 F Simmons 1 : Spinal angiography
4 or 5 F Simmons 2 or 3 : Left common carotid artery; bovine configuration; tortuous aortic arch; patient’s age >50
5 F CK-1 (aka HN-5) : Left common carotid or right vertebral artery
5 F H1 (aka Headhunter) : Right subclavian artery; right vertebral artery
4 or 5 F Newton : Tortuous anatomy, patients >65.

Catheter navigation
Diagnostic catheters should usually be advanced over a hydrophilic wire. The wire keeps the catheter tip from rubbing against the wall of the vessel and causing a dissection. The tip of the wire should be followed by direct fluoroscopic visualization. The catheter/wire assembly should never be advanced with <8–10 cm of wire extending from the tip, as a short length of leading wire can act as a spear and cause injury to the intima.

Roadmapping should be used when engaging the vertebrals and carotids.
Is essential during intracranial navigation.
A “false roadmap” can be used  which is a frame from an angiographic run is selected, then inverted so the vessels are turned white against a black background.
This technique conserves contrast and reduces radiation exposure.

Double flushing
Aspiration of the contents of the catheter with one 10 mL syringe of heparinized saline, followed by partial aspiration and irrigation with a second syringe of saline.
This clears clots and air bubbles from the catheter.
Should be done every time a wire is removed from the catheter, prior to the injection of contrast.
Continuous saline infusion
A three-way stopcock used to provide a continuous heparinized saline drip through the catheter, useful if there is any delay between injections of contrast, because it keeps the catheter lumen free of blood.
Careful double flushing is still required.

Hand injection
A 10 mL syringe containing contrast should be attached to the catheter, and the syringe should be snapped with the middle finger several times to release bubbles stuck to the inside surface. The syringe should be held in a vertical position, with the plunger directed upward, to allow bubbles to rise away from the catheter.
An adequate angiographic run can be done with a single injection of ~5 mL of contrast (70%) mixed with saline (30%).
The patient should be instructed to stop breathing and swallowing during the shoot.

Angiographic Images
Biplane angiography is the standard, allows for orthogonal images to be simultaneously obtained with a single contrast injection, limiting the time and amount of contrast needed.  Monoplanar  angiography if biplane equipment is not available.
Contrast and brightness of the image should be adjusted so that vessels are semitransparent; this can allow visualization of aneurysms, branches, or filling defect which may otherwise not be visible.
Standard views 

Femoral artery puncture
The groin area is prepped and draped.
The femoral pulse is palpated at the inguinal crease, and local anesthesia (2% lidocaine) is infiltrated, both by raising a wheal and injecting deeply toward the
Five-millimeter incision is made parallel to the inguinal crease with an 11-blade scalpel.
A Potts needle is advanced with the bevel facing upward. The needle is advanced at a 45° angle to the skin, pointing toward the patient’s opposite shoulder.
 A single wall puncture, can be done by looking for blood return from the hollow stylet of the Potts needle.
A two wall puncture is obtained by advancing the needle through and through both vessel walls, then removing the stylet, and slowly withdrawing the needle
until pulsitile blood return is obtained.
When bright red, pulsitile arterial blood is encountered, a J-wire is gently advanced through the needle for 8–10 cm.
The needle is then exchanged for a 5-F sheath.

Carotid artery catheterization
An angled diagnostic catheter is advanced over a hydrophilic wire over the aortic arch to a position proximal to the innominate artery.
The wire is then brought back into the catheter, and the catheter is gently pulled back, with the tip of the catheter facing superiorly, until the innominate artery is engaged.
The wire is then advanced superiorly in the right common carotid artery, followed by the catheter.
To engage the left common carotid artery, the catheter is gently and slowly pulled out of the innominate artery, with the wire inside the catheter and the tip facing to the patient’s left, until the catheter “clicks” into the left common carotid.
The wire is then advanced superiorly, followed by the catheter.
For older patients (>50 years), and those with a bovine arch configuration, the Simmons II catheter is helpful for accessing the left common carotid.  Catheterization of the internal carotid artery should be done under road-map guidance.
Turning the patient’s head away from the carotid being catheterized may allow the wire and/or catheter to enter the vessel more easily.
Once the common carotid is catheterized, turning the head away from the side being catheterized facilitates internal carotid catheterization, and turning toward the ipsilateral side facilitates external carotid catheterization.
When the wire or catheter does not advance easily into the vessel of interest, asking the patient to cough may sometimes bounce the catheter into position.

Vertebral artery catheterization
An angled diagnostic catheter is advanced over a hydrophilic wire and placed in the subclavian artery.
Intermittent “puffing” of contrast used for identification of the vertebral artery origin.
A road map is made and the wire is passed into the vertebral artery until the tip of the wire is in the upper third of the cervical portion of the vessel.
Placing the wire relatively high in the vertebral artery provides adequate purchase for advancement of the catheter, will help straighten out any kinks in the artery that may be present near the origin, and will also facilitate smooth passage of the catheter past the entrance of the of artery into the foramen tranversarium at C6.
The C6 foramen transversarium is where the vertebral artery makes a transition from free-floating to fixed, and is a region at risk for iatrogenic dissection if the catheter is allowed to scrape against the wall of the vessel.
The vertebral artery makes a right angle turn lafterally at C2, so be careful not to injure the vessel at that point.
After removal of the wire, and double flushing, an angiogram should be done with the tip of the catheter in view, to check for dissection of the vessel during
Uncommonly, the left vertebral artery arises directly from the aorta, which should be kept in mind when the origin of the vessel cannot be found on the left
subclavian artery.
When kinks or loops in the vessel prevent catheterization, tilting the head away from the vertebral artery being catheterized can help.

Femoral artery puncture site management
The manual compression is still gold standard method.
The sheath is removed while pressure is applied to the groin 1–2 cm superior to the skin incision for 15 min, usually 5 min of occlusive pressure, followed by 10 min of lesser pressure.
For patients on aspirin and/or clopidogrel, a longer time is required, usually 40 min.
At the end of the time period, pressure on the groin is slowly released and a pressure dressing is applied.

Post-angiogram orders
Bed rest with the accessed leg extended, head of bed _30°, for 5 h, then out of bed for 1 h.
Vital signs: Check on arrival in recovery room, then Q 6 h until discharge.
Check the puncture site and distal pulses upon arrival in recovery room, then Q 15 min × 4, Q 30 min × 2, then Q 1 h until discharge.
Call physician if Bleeding or hematoma develops at puncture site or Distal pulse is not palpable beyond the puncture site.
Extremity is blue or cold.
Check puncture site after ambulation.
Resume pre-angiogram diet.
Resume routine medications.

Neurological complications:
Commonly cerebral ischemic events due to thromboembolism or air emboli, vessel dissection.
Less common include transient cortical blindness, amnesia.
Overall rate of neurological complications is ~ 1.3%. Patients with atherosclerotic carotid disease have been reported to be at elevated risk of neurological complications.  Other risk factors include advanced age, long angiography procedure time, hypertension, diabetes, renal insufficiency.
Nonneurological complications:
Femoral artery puncture with groin and retroperitoneal hematoma, allergic reactions, femoral artery pseudoaneurysm, thromboembolism of the lower extremity, nephropaty and pulmonary embolism.

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