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Commentary |
1 Department of Radiology, University of California Davis Medical Center, 4860 Y St., Ste. 3100, Sacramento, CA 95817.
Received January 2, 2008; accepted after revision January 3, 2008.
Acute life-threatening reactions, although very rare, can occur
unexpectedly in any patient, at any time
[1].
Keywords: angiography • contrast media • CT • excretory urography • iodine-based contrast media
Iodinated contrast media are among the most commonly prescribed medications in the history of modern medicine, with approximately 80 million doses administered in 2003 worldwide corresponding to approximately 8 million liters [2]. Because contrast media have no therapeutic effect, the ideal agents should provide optimal quality without substantial adverse effects. Before the advent of CT, excretory urography and angiography were the major indications for contrast media. In the pre-CT era, most radiologists were using 30-50 mL of high-osmolar contrast media with hand injection rates of less than 1 mL/s for urography. In contrast, the average contrast media dose for CT today is approximately 100-150 mL, with power injection rates in the neighborhood of 3-4 mL/s.
Over the 1980s and 1990s, the use of CT increased by 800%, and a continued increase in CT procedures of 122% has been projected for 2002-2008 [3]. It is estimated that more than 62 million CT examinations per year are currently performed in the United States, with well over 50% requiring contrast media [4]. Vascular indications have shown a growth rate of 235%; cardiac 145%; abdominal, pelvic, and thoracic, each 25%; and head and neck 7%. According to the Heart Disease and Stroke Statistics: 2005 Update of the American Heart Association, 1,463,000 inpatient cardiac catheterizations were performed in the United States in 2000 [5]. From 1979 to 2002, the number of cardiac catheterization procedures increased by 390%.
Although clinically significant acute reactions to contrast media after parenteral administration are uncommon, they continue to constitute a significant hazard to patients, a circumstance well known by most physicians. With the advent of nonionic, low-osmolality contrast media, the overall incidence of adverse reactions has significantly decreased. For example, the incidence of severe and very severe contrast reactions was noted to be 0.26% for ionic and 0.04% for nonionic contrast media in a study by Katayama et al. [6], indicating that the current agents are safer by a factor of six compared with ionic media. However, the increased use of contrast media on a daily basis has not decreased radiologists' exposure to patient risk and possibly increases patient vulnerability to a greater extent today than during the ionic contrast media era because CT is a procedure that generally no longer involves direct physician-patient contact as was the case for urography. Thus the classic, milestone centennial article by Witten et al. [1] is even more relevant today than it was when published 35 years ago.
Witten et al. [1] prospectively studied 32,964 consecutive outpatients at the Mayo Clinic who were referred to the department of diagnostic radiology for excretory urography during a 27-month period, gathering a tabulation of the presence or absence of "allergy," specific allergens if known, and clinical characteristics of previous hyper sensitivity responses, if known in the first phase of 9,934 patients. In the remaining 23,030 patients in the study, details of historical data relating to history of allergy or hypersensitivity were obtained before injection but tabulated only in those patients who developed acute reactions. Clinical char acteristics, severity, and treatment for analysis were recorded for any reactions that occurred in all patients.
A unique value of the Witten et al. [1] approach was that all patients were examined in a single radiologic facility under highly uniform conditions. The same type of ionic high-osmolar contrast medium was used and a routine IV test dose of approximately 1 mL of this agent was administered. The standard contrast medium dose was 30-50 mL in most patients. The response of these patients to the injection of the contrast medium was tabulated into categories of "no clinically significant response," "minor side effects," or "acute reactions." Overall, clinically in significant responses were encountered in 93.2% (30,713 patients), minor side effects in 5.1% (1,683 patients), and acute reactions in 1.72% (568 patients).
Of the 568 patients with acute reactions, 334 (59%) were classified as mild, 204 (36%) as moderate, and 30 (5%) as severe. These acute reactions were further identified as dermal, nasal or mucosal, cardiovascular, respiratory (asthma), and neurologic. Of the 24 cardiovascular reactions encountered, there were three types: syncope associated with transient hypotension in eight patients, hypo tension (shock) accompanied by a diffuse erythematous rash in 15, and cardiovascular collapse with cardiac arrest and death in one. Respiratory symptoms included bronchospasm or bronchial asthma in nine patients and episodes of laryngeal edema with signs of airway obstruction of mild to moderate severity in seven. Neurologic symptoms were seen in three patients; all of these were grand mal seizures not accompanied by other signs or symptoms.
Reactions that are classified as severe are those in which there is concern for the patient's life and intensive treatment is required. This type of reaction was encountered in 30 patients (one per 1,100 examinations). One of these proved fatal despite prompt and vigorous treatment. An extremely important observation was the distinction between episodes of severe hypotension by pulse rate: bradycardia (pulse 30-40 beats per minute) accompanied the hypotension in nine patients and tachycardia in six. This is critical because bradycardia would be treated with atropine (0.5-1.0 mg IV), whereas hypotension and tachycardia would be treated with epinephrine (1:10,000 dilution, 1 mL IV, slowly over 2-5 minutes). These severe reactions occurred either during the actual injection of contrast material or within 3-5 minutes after the injection. These events were preceded by nausea and vomiting, and the patients almost invariably lost consciousness.
Another major observation in the Witten et al. [1] investigation was an assessment of the value of a preliminary test dose. Nine subjects (1.6%) had a positive response in the form of an acute reaction to the test dose itself, two of these reactions were severe. In the remaining 559 patients (98.6%) with acute reactions, the test dose gave no hint that a reaction would occur. "Thus, the results in this study confirm the opinion of many authors: that the IV test dose is of no value in prediction of reaction; that it is potentially hazardous to the patient; and that its continued use cannot be justified on medical grounds" [1].
The association between the history of allergy and acute reactions was investigated. Reactions were 2.5 times (3.0% compared with 1.2%) more frequent in patients with a positive history of allergy. However, there was no increase in severity of reactions with a history of allergy. If the patient had a history of mild to moderate reaction to urographic contrast media, repeat reactions occurred in 20%. However, there was no evidence of increasing sensitivity with the repeated use of contrast media. Witten et al. [1] did not encounter any patients in whom a second, third, or even fourth reaction was more severe than the initial reaction with repeated contrast media examinations in the same subjects. Only four (13%) of the 30 severe reactions occurred among patients with a history of allergy, whereas 25% of patients overall claimed a history of allergy. This investigation's legacy was to provide seminal information regarding contrast media reaction pathophysiology, logistics and daily throughput (omission of the test dose), and treatment implications (epinephrine vs atropine).
The final and cogent recommendation by Witten et al. [1] reemphasizes the unpredictable nature of contrast media reactions: the need for staff members who are well trained in the recognition and treatment of contrast media reactions and the importance of having emergency equipment on hand and available for immediate use in every radiologic suite where contrast media are injected. Given that most CT is now performed without the immediate presence of radiologists and with the use of higher doses and injections using mechanical instrumentation, it is timely to reemphasize the value of this significant contribution to our daily clinical practice.
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