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What are Positive Contrast Agents?
These are liquids containing iodine or gadolinium that have greater attenuation than the patient's soft tissues.
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What is Negative Contrast?
This has lower attenuation than the pt's tissues; at present, carbon dioxide is the only available option.
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Concerning contrast, what do you do when imaging the more distal vessels and why?
Increase the volume of contrast
because when the blood flow is slow, it may take several seconds for the opacified blood to pass through the vessel (hence, a long contrast bolus is necesary).
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What type of contrast is recommended in high-risk patients?
Non-ionic contrast media
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Most diagnostic and therapeutic intervention is performed using what strength contrast?
300 strength (300 mg/mL iodine)
for selective hand injections and for non-vascular examinations, 300 strength contrast is diluted with saline to 'two-thirds' or 'half-strength'.
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What are the two forms of contrast reaction?
direct effects
idiosyncratic responses
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What are the more basic contrast direct effects?
heat
nausea
pain
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What organ systems can be affected by the Direct Effects of contrast?
Renal [CI-AKI]
Cardiac [arrhythmias or ischemia]
Hematological [clotting]
Neurological [most during carotid angiography and are related to angiographic technique...problems are rare and are usually in pts with abnormalities in the blood-brain barrier.]
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List minor idiosyncratic reactions to contrast (4).
metallic taste
sensation of heat
mild nausea
sneezing
(these do not require treatment)
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List intermediate idiosyncratic reactions to contrast (1).
urticaria
(not life-threatening, responds quickly to treatment)
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List severe idiosyncratic reactions to contrast (4).
circulatory collapse
arrhythmia
bronchospasm
dyspnoea
(may be life-threatening, require prompt therapy)
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Name the highest level (above severe) of idiosyncratic reactions to contrast and most common causes:
Death.
cardiac arrhythmia, pulmonary edema, respiratory arrest, or convulsions
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What conditions are associated with an increased risk of a severe idiosyncratic reaction?
Previous allergic reaction to iodine-containing contrast and shellfish allergy
Cardiac disease
Asthma
General allergic responses
Drugs: β-blockers, interleukin-2
Age>50 years
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If the severe idiosyncratic reaction to contrast of bronchospasm occurs, what are some options?
monitor pulse, BP, oxygen saturation and ECG
give 100% O2
Treat initially with β-agonist inhaler e.g. salbutamol
Give IV corticosteroids, e.g. 100mg hydrocortisone
intramuscular epinephrine: 0.3-0.5mL of 1:1000 solution
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If the severe idiosyncratic reaction to contrast of lanyngeal edema/angioneurotic edema occurs, what are some options?
Seek anesthetic assistance and monitor the pulse, BP, oxygen saturation and ECG
Give 100% O2 and watch oxygen saturation closely
Give Chlorphenamine 20mg by slow IV injection
Give Epinephrine intramuscularly (IM) 0.3-0.5mL of 1:1000 solution
Get an anesthetist to assess the airway. Tracheostomy may be required in very severe cases
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If the idiosyncratic reaction to contrast of severe hypotension occurs, what are some options?
Call for support
monitor pulse, BP, oxygen saturation, and ECG
Consider causes related to pt's underlying diagnosis, e.g. bleeding or MI
Rapid infusion of IV fluids is essential and several liters of fluid replacement may be necessary
Epinephrine IM 0.3-0.5mL or 1:1000 solution. In severe circulatory shut down, IV epinephrine may be required, given with extreme caution by slow IV injection.
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Concerning gadolinium contrast administration, which groups are most vulnerable to Nephrogenic systemic fibrosis (NSF)?
Patients with acute or chronic kidney disease
patients in the immediate postoperative period following liver transplant
Neonates and infants
Pregnant or breastfeeding women
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Carbon Dioxide angiography is exclusively performed as:
subtraction angiography (DSA)
additional software may be necessary to optimize the image
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Why is Carbon Dioxide most commonly used as a contrast agent?
History of severe reaction to iodinated contrast
Renoprotection
Where there is another advantage, such as the use of CO2 for wedged hepatic venography
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Due to a risk of cerebral toxicity with CO2, how should it never be used as a contrast agent?
intra-arterially above the diaphragm or intravenously in patients with right-to-left shunts
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What equipment is used to administer CO2 as a contrast agent?
basic angiography set
medical grade CO2 from a disposable cylinder
standard bacterial filter (from a blood-giving set)
high-pressure connector
three-way tap
lockable stopcock for each syringe
sixty-mL Luer lock syringes
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Why must pressurized CO2 never be connected directly to the patient?
this risks inadvertent injection of a large volume of gas that may cause a 'vapor lock'.
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What type of syringe should be used for CO2 contrast administration and why?
peripheral angiography typically requires a volume of around 50mL CO2 for each run, so use a 50mL Luer lock syringe.
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List the steps to correctly prepare fill syringes with CO2 for contrast.
Allow a syringe to fill from the system
Use the three-way tap to discard the contents three times to flush out any residual air in the system before finally filling
Shut the lockable stopcock and disconnect the syringe from the three-way tap
The syringe will now contain CO2 at slightly above atmospheric pressure
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What is the dose limit for CO2 administration as contrast?
There is no dose limit as long as injections are restricted to 100mL every two minutes
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If using CO2 as contrast and performing venography, why do you always fluoro over the pulmonary artery?
to look for gas trapping.
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When CO2 collects abovethe blood, it forms what? And what complications can this lead to?
forms a vapor lock
reduces the surface area for the gas to dissolve which can potentially lead to ischemia or thrombosis
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If gas trapping occurs (with the use of CO2), what can be done to alleviate?
turn or tilt the patient's head down so the gas can disperse
if necessary, the gas can be aspirated via a catheter
DO NOT ELEVATE THE PT'S HEAD!
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When using CO2, if gas column fragments, what can be done?
use image summation techniques to integrate several frames onto the same image
consider raising the leg as this improves filling of the distal vessels
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