Ch 23 - Interventional radiology and endoscopy Flashcards

1
Q

Define interventional radiology

Define interventional endoscopy

A
  • Interventional radiology - use of contempory imaging modalities to gain access to different structures throughout the body or to deliver therapeutic materials
  • Interventional endoscopy uses endoscopes +/- fluoro to facilitate access to different structures, most commonly through natural orifices
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2
Q

What should OR tables be made of to facilitate fluoroscopy?

A

Carbon fibre or plexiglas

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3
Q

What form of fluoroscopy is recommended for vascular procedures?

A

Digital subtration angiography

Takes an initial non-contrast image and then subtracts this from all further images during a run

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4
Q

What type of scopes are recommended for urinary tract endoscopy in female and male dogs?

A
  • Female - 30degree rigid scope ranging from 1.9-6.5mm
  • Male - flexible endoscope 2.5-2.8mm diameter. Can also be used to gain ureteral access

Using a rigid scope has been describe into male dogs via percutaneous perineal access

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5
Q

When gaining vascular access, why is a cut down preferred for arterial vessels?

A

Permits ligation (standard) or repair (rarely) to prevent post-op haemorrhage

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6
Q

What are the two techniques for gaining vascular access?

A
  • Modified Seldinger technique - uses a simple needle (no stylet) with single wall puncture
  • Seldinger technique - An arterial needle with stylet is used, double wall puncture, stylet removed and needle is withdrawn until bevel is within lumen and blood flows

In both cases the guidewire is then placed and the needle removed

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7
Q

What is the typical needle and guide wire sizes used for vascular access in larger vessels?

A

18/19g needle and 0.038-0.035 inch guide wire

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8
Q

What are the benefits of introduced sheaths?

A
  • Allow safe, controlled, confluent dilation of the entry vessel, protection from luminal damage and haemorrhage
  • Convenient side ports for flushing or administering contrast
  • Check flow diaphragm to prevent back-bleeding
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9
Q

What is unique about the sizing of sheaths?

A

Named for their internal diameter (a 7Fr sheath will fit over a 7Fr dilator)

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10
Q

Name the following selective catheters

A
  • A - marker pigtail catheter (radiopaque markers, multiple fenestrations for rapid contrast injection)
  • B - Rim (reverse-curve) catheter (For accessing vessels at very acute angles)
  • C - Cobra-type catheter (gentle bend facilitating access into first-order arterial branches off the aorta or vena cava)
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11
Q

What are the two forms of balloon catheters used for interventional procedures?

A
  • Low-pressure occlusion balloons (temporary occlusion, redirect embolisation materials, flow-directed to facilitate access)
  • High-pressure balloon angioplasty catheters - filled with dilute contrast under pressure to dilate and efface strictures or stenoses
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12
Q

What are the three categories of stents?

A
  • Metallic vs non-metallic
  • Self-expanding vs balloon explandable
  • Covered vs uncovered
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13
Q

Name the following stents

A
  • A - stainless steel mesh SEMS
  • B - Nitinol mesh SEMS
  • C - Nitinol laser-cut SEMS
  • D - Silicon-covered nitinol mesh stent graft
  • E - Polyester covered mesh stent graft
  • F - BEMS compressed on percutaneous transluminla angioplasty balloon
  • G - BEMS after dilation

SEMS = self-explanding mesh stent, BEMS = balloon-expandable mesh stent

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14
Q

What are the various properties of mesh va woven/braided vs laser cut metallic stents

A
  • Mesh - Typically reconstrainable, have a variable degree of foreshortening
  • Woven - Not reconstrainable, minor foreshortening (rarely used, no significant advantage over mesh)
  • Laser cut - Shape memory nitinol (on reaching body temp, changes properties and resumes original diameter and length). Typically non-reconstrainable, minimal foreshortening. Most commonly used in urethra or vasculature but may have excessive rates of fracture within the trachea
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15
Q

What are the disadvantages of covered stents?

What are their main uses in vet med?

A

Disadvantages
- increased cost
- increased material
- increased migration rates
- larger delivery systems
- can cause occlusion of adjacent structures

Uses
- Recurrent strictures or malignancies that have frown through an uncovered stent

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16
Q

What are the disadvantages of BEMS?
What is their main use in vet med?

A

Disadvantages
- relatively short lengths available
- poor flexibility
- static response to compression (ie will not re-expand)

Mostly used for nasopharyngeal stenoses (short strictures surrounded by bone)

17
Q

What are the most common non-metallic stents?

A

Polyurethane compounds for use in the urinary tract such as ureteral stents - multifenestrated, double pig-tail catheters)

18
Q

List the classifications of embolics

List some uses of embolics

A

Classifications
- Mechanical or particulate
- Temporary/biodegradable or permanent
- Solid or liquid

Uses
- Reduce haemorrhage
- Occlude vascular anomalies
- Ablate neoplasms
- Improve local concentrations of chemotherapy

19
Q

Name the following mechanical embolic devices

A
  • A - Amplatz canine ductal occluder for PDA
  • B - Vascular plug (side on)
  • C - vascular plug (front on)
  • D - Thrombogenic coils in delivery system and deployed (center) with thrombogenic Dacron fibres
20
Q

What are the most common types of liquid embolics?
How do they work?

A
  • Polyvinyl alcohol particles and hydrogel microspheres
  • Form initial mechanical occlusion and then permanent fibrin ingrowth
21
Q

How does n-butyl cyanacrylate glue work as a liquid embolic?
What are its reported uses?
What can be added to it to enhance its efficacy/usability?

A
  • Action via vascular thrombosis and endothelial damage
  • Used for vascular AV fistulas, AV malformations and thoracic duct embolisation
  • Mixed with ethiodized oil (Lipiodol) to slow the rate of polymerisation and lend radiopacity
  • Powdered tantalum can also be used to slow polymerisation

Passes through capillary beds increasing the risj of non-target embolisation and is more difficult to control

22
Q

What is the most common temporary embolic?
What are its reported uses?

A
  • Gelatin sponge in powder, slurry or torpedo form
  • Lasts days to weeks and can be sued for trauma, gastric ulcers or in a coagulopathic patient
23
Q

What are the common lasers used in interventional radiology? What are their uses?

A
  • Diode laser - wavelength 980nm, absorbed well in water and haemoglobin giving good ablative and coagulation properties. Used for intramural ectopic ureters, persistent paramesonephric ducts remnants, nasal and laryngeal resections
  • Ho:YAG - wavelength 2100nm, absorbed in under 0.5mm of fluid making it very useful for endourologic applications such as lithotripsy
24
Q

Describe the process of extrocorporeal shockwave lithotripsy

A

External shockwaves are passes through a water bath or waterbag and the patients soft tissue, directed under fluoro onto the stone of interest. Shocked anywhere for 1000-3500 times at different energy levels causing implosion and powdering. Debris then moved into the bladder over 2-12 week period. Believed to be very safe and effective

25
Q

How can you prophylactically reduce contrast-induced nephropathy?

A
  • Aggressive hydration
  • Anti-oxidants
  • n-acetylcysteine (Renal vasodilator)