What is the role of radiocontrast agents in the administration of therapeutic injections for pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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Answer

Answer

Radiographic contrast agents aid in the localization of anatomical structures. Iodine atoms within these agents provide greater x-ray attenuation compared with human tissues, including bone. Osmolality describes a measure of the numbers of particles in a specific solution. The hyperosmolality of contrast agents relates directly to their toxicity. Second-generation radiocontrast agents have more physiologic properties, are labeled nonionic, and are more commonly used for spinal injections. The 2 most commonly used radiocontrast agents are iopamidol (Isovue-M) and iohexol (Omnipaque). Both are absorbed rapidly into the bloodstream from intrathecal, epidural, and paraspinal tissue injections.

Plasma levels are measurable within an hour after injection. The mean half-life is 12 hours and 80-90% is excreted via the kidneys within 24 hours with minimal excretion via fecal route. Adverse reactions may be chemotoxic, osmolar-related, or allergic. Also, 90% of adverse effects occur within 15 minutes of exposure.

If an allergic reaction is suspected, patients should be observed for up to 60 minutes. The primary concern when using contrast media is unintentional intrathecal injection. For this reason, the above-mentioned water-soluble contrast media are recommended: iohexol (Omnipaque) or iopamidol (Isovue). Radiologic contrast media are not licensed for intrathecal use, but these 2 specific radiocontrast agents have not been reported to cause adhesive arachnoiditis and exhibit a low risk of seizures and neurotoxicity.

Patients at greater risk for an adverse reaction to radiocontrast media include those with a history of a previous adverse reaction, especially allergy. Any question regarding an allergic reaction can be avoided by giving oral prednisone 20-50 mg, ranitidine 50 mg, and diphenhydramine 25-50 mg orally 12-24 hours prior to exposure by injection. An additional 25 mg of diphenhydramine can be given by IV immediately before contrast injection. Further caution is required when administrating radiocontrast to patients with asthma; allergy/atopy; cardiac disease with decompensation, unstable arrhythmia, or recent MI; renal failure/nephropathy; feeble individuals with general debility (especially infants or the elderly); and patients with dehydration, metabolic disorders, or hematologic disorders.

Adverse reactions vary from chemotoxic reactions (such as thyrotoxicosis or nephrotoxicity) hyperosmolar responses, or more typical allergic responses characterized by vasomotor responses, cutaneous reactions, bronchospasm, cardiovascular effects (hypotension), or anaphylactoid reactions.


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