Interventional Radiology

·         Benzodiazepines are typically used to provide conscious sedation. Common benzodiazepines include midazolam, lorazepam, and diazepam. Flumazenil is used as a reversal agent for benzodiazepines. The effect of flumazenil is usually visible in 2 minutes, with peak effects at 10 minutes. The initial dose in adults may be as high as 1 mg.

·         Meperidine administered to a patient taking an MAO inhibitor can cause a variety of undesirable and potentially lethal side effects such as agitation; fever; and seizures progressing in some instances to coma, apnea, and death. The narcotic analgesic of choice for patients taking an MAO inhibitor is morphine.

·         A Cobra 1 catheter and a Cobra 2 catheter have the same general shape except that the radius of the secondary curve of the catheter is greater for the Cobra 2. A Cobra 3 catheter again has the same general "Cobra" shape, but the secondary curve is even greater still. The same nomenclature applies to Simmons catheters and others as well.

·         The Palmaz stent is the prototypical balloon-expandable stent. Such stents come packaged either individually or premounted on a balloon. When the balloon is inflated, the stent expands to the diameter of the balloon. As the stent expands, it changes very little in length. The relatively constant size and method of delivery/deployment of this type of stent makes for precise and predictable placement. Balloon-expandable stents are the stent of choice for treating renal artery stenosis. Because they are made of laser-cut stainless steel, these stents may cause significant artifact on magnetic resonance imaging examinations. Balloon-expandable stents may be permanently deformed by extrinsic compression and therefore should not be used in situations in which they could be subject to these forces.

There are two broad categories of self-expanding stents: those made from woven elgiloy wires and those laser-cut from nitinol tubes. Self-expanding stents exert a continuous outward force and resist deformation and therefore are preferable to balloon-expandable stents in regions potentially subject to external compressive forces. To ensure full expansion, self-expanding stents are dilated with a balloon of appropriate diameter after deployment.

·         Hoop strength is a measure of a stent's ability to avoid collapse and withstand the radial compressive forces of a vessel after dilatation.

Chronic outward radial force is the force a self-expanding stent exerts on a vessel as it tries to expand to its original diameter. The radial resistive force is the force a self-expanding stent exerts as it resists squeezing by a vessel.

·         Sometimes called a Balkin sheath, an up-and-over sheath is a U-shaped sheath. It is designed to facilitate interventions in which the arterial access is in one femoral artery and the lesion to be treated is in the contralateral extremity.

·         Trojan horse technique: Instead of pushing the stent across the lesion, the lesion is crossed with a sheath or guiding catheter. The balloon-mounted stent is advanced through the catheter or sheath to the desired location, and then the sheath or catheter is withdrawn to expose the stent in the proper location. In this way, complications related to stent slippage are minimized. This is just one example of how the technique is used. The term applies to the technique in general and can be used to deliver any device in this manner, not just a balloon-expandable stent.

·         Dr. Constantine Cope is one of the pioneers of interventional radiology and is credited with some of the field's most ingenious inventions. One of these is the Cope loop, which is a pigtail catheter with a locking mechanism to prevent accidental displacement.

·         A snare is a device that may be used to remove intravascular foreign bodies such as wires or coils. A snare consists of a wire with a nitinol loop at the end.

·         A Hickman catheter is a device used for chronic IV access, most commonly for chemotherapy or total parenteral nutrition. The line is available in single-, double-, or triple-lumen models. It is ideally placed in the internal jugular vein, with the exit site tunneled several centimeters away. The catheter has an antimicrobial cuff on its surface.

·         Filters are rarely placed in the SVC because the small clot burden in the upper extremities is rarely thought to lead to clinically significant PE. SVC filters are indicated in the unique setting of symptomatic PE that can be traced with a high degree of certainty to upper extremity clot.

·         Cope's law of vascular access: "You can't stick a vessel where it isn't." In essence, this law suggests that the puncture site should be chosen carefully. The puncture should not necessarily be where you think the artery might be, but instead, where it actually is as determined with palpation or ultrasound.

·         kissing balloon technique: This technique is most commonly used to perform angioplasty of the common iliac arteries. Often, stenoses of the proximal common iliac arteries are associated with large, eccentric, calcified plaques. Sequential-as opposed to simultaneous-angioplasty may displace the plaque and lead to compromise of the contralateral iliac artery. The kissing technique mitigates this risk through the use of simultaneous angioplasty. This requires bilateral retrograde femoral artery access. The kissing technique may be used for the dilation of complex bifurcation stenosis in other locations as well.

·         A simple way to help remember the collateral supply to supply the lower extremities in a patient with known aortic occlusion is to divide it into anterior, middle, and posterior pathways:

Anterior: subclavian artery through the internal mammary to the superior epigastric artery to the inferior epigastric artery and then into the external iliac artery

Middle: superior mesenteric to the inferior mesenteric artery via the arc of Riolan and the marginal artery of Drummond to the superior and inferior hemorrhoidal arteries to the internal iliac arteries and then to the external iliac arteries

Posterior: lumbar arteries to the internal iliac arteries via the retroperitoneal collaterals and then to the external iliac arteries by way of the iliolumbar and circumflex iliac arteries

·         Postembolization syndrome is an expected set of symptoms, including pain, fever, nausea, vomiting, and leukocytosis, that patients may experience after an embolization. The cause is likely secondary to organ ischemia/infarction. Prophylactic antibiotics to prevent superinfection of the ischemic tissue as well as pain control and antiemetic agents are helpful in treating postembolization syndrome. The syndrome is transient and should resolve within 3-5 days after the procedure.

·         Significant reconstitution of flow via collaterals can occur and cause recurrence of the lesion. For example, if only the proximal feeding vessel to a pseudoaneurysm is embolized, flow may then reverse in the outflow vessel and feed the pseudoaneurysm. Embolizing both sides of a pseudoaneurysm, aneurysm, or AV fistula is called "embolizing the front and back door of a lesion" and is also sometimes needed when embolizing bleeding vessels.

·         GENITOURINARY AND GASTROINTESTINAL INTERVENTIONAL RADIOLOGY

1.       Urosepsis is an indication for emergent PCN.

2.       A PCN tract should pass through the skin near the posterior axillary line, pass through the renal parenchyma in the relatively avascular plane denoted by Brödel's line, and enter the collecting system.

3.       Although ureteral stents successfully drain the collecting system into the bladder and cause passive dilation of the ureter, they are considered a temporary measure and are not necessarily curative.

4.       Patients with ascites should receive large-volume paracentesis before percutaneous gastrostomy.

5.       J tubes and G-J tubes are reserved for patients with known gastroesophageal reflux disease and/or documented aspiration.