Tools of the Trade
Iodinated - default, often non-ionic, low-osmolality (e.g. Isovue) due to less side effects
Types - ionic is rarely used intravascularly due to higher rate of adverse reactions. Non-ionic agents are further divided into monomers like Isovue and Omnipaque and less viscous dimers like Visipaque.
Allergic-like reactions - not IgE mediated so can happen with first exposure or not happen for series of exposures and then happen again
Itching, urticaria (0.5%), dyspnea (0.04%), , severe reaction (<1:10,000), death (1:170,000)
Physiologic reactions, e.g., nausea/vomiting (1%), sneezing (0.2%), sialadenitis (<0.1%)
Transient cortical blindness (TCB): Rare possible direct toxicity. <0.1% risk generally but up to 0.3-1% for cerebral angiography particularly of posterior circulation. Can show increased T2/FLAIR signal in occipital cortex on MRI. Most resolve within a few days and all within a month.
Premedication - only data showing decrease of mild reactions but still used to try to prevent severe reactions (ACR protocol card for adults)
No convincing evidence than contrast affects renal long term renal function with GFR>30 or CKD. May be harmful with large contrast loads (e.g. >300 mL) with AKI, thyroid storm, dialysis with oliguria, or metformin with GFR<30
Studies suggest prehydration doesn’t hurt but probably doesn’t help. Timing of dialysis doesn’t matter.
Gadolinium - good alternative though less radio-opaque
Need to adjust fluoroscopy kVp for higher K-edge of gadolinium relative to iodine to improve contrast
No effect on renal function. Approved dose is 0.1-0.3 mL/kg but volumes of 40-60 mL have been used for years without known issue.
No risk of NSF with type II agents, thus can be used at any GFR, theoretical risk <0.07% chance even with ESRD
CO2 – good for injections below the diaphragm with no volume restraints or renal risk
Must prep carefully to not inject ambient air
Can cause air embolus and stroke if used above the diaphragm or veins in presence of PFO/ASD
Can be painful in the lower extremities
Angiography Rates
Rates are given in terms number of mL per second for a given amount of time, often shortened colloquially to “X for X.” This can be with or without an “X-ray delay,” delayed the start of filming to reduce radiation to only when the contrast is in the vessels of interest.
Shorter runs are sufficient for delineating vascular anatomy whereas longer runs are necessary to identify pathology such as tumors or bleeding.
Generally, the volume per second is roughly equal to the vessel diameter in mm. This will need to be increased for higher flow to opacify the vessel and decreased for lower flow to prevent reflux.
For cerebral angiography, meticulous care must be taken to avoid introducing air bubbles and thrombus formation on catheters, which can cause strokes. Many use double flush systems and heparinize to lessen the risk. Still permanent stroke can occur in up to 0.5% and TIA in 2% of patients undergoing cerebral angiography.
