EMCrit.org | Emergency Critical Care

“We are asking that you have a test to help us decide whether you have a serious condition causing your symptoms. The test requires giving you IV dye that could put stress on your kidneys. In a small number of patients, this stress can lead to major kidney damage, and needing dialysis. The risk is higher when there are signs of kidney weakness in blood tests or in someone with diabetes. There are several treatments that have been shown to reduce this risk, but the number of patients that benefit from them is small. The treatments are safe but may cause a 1- to 2-hour delay in doing the test and in making the diagnosis.” (Ann Emerg Med 2008;51(4))

Screening for Renal Failure

Screening Cr not necessary prior to CT, Screen for following risk factors instead, history of renal insufficiency, Diabetes Mellitus, on chemotherapy, Solitary Kidney. (“Are Screening Serum Cr Levels Necessary prior to Outpatient CT Examinations?”
Radiology 216:2, 2000.)

Based on evaluation of the receiver operating characteristic curve constructed in the derivation set, the sensitivity for renal insufficiency at BUN cut-offs of 15mg/dl and 20mg/dl was 99.5% and 96%, respectively. When this model was applied to the validation set, the sensitivity and specificity of a BUN cut-off of 15mg/dl were 99.7% and 56%, respectively (negative predictive value, 99.9%; negative likelihood ratio, 0.005). At a BUN cut-off of 20mg/dl, the sensitivity and specificity for renal insufficiency were 98% and 71%, respectively (negative predictive value, 99.4%; negative likelihood ratio, 0.03) (Am J Emerg Med 21(6):494, October 2003)

Seafood Allergies and Other Myths

The New EMedHome Clinical Pearl is: Radiocontrast, Iodine, and Seafood Allergies

Radiocontrast, Iodine, and Seafood Allergies

Asking if patients are allergic to shellfish or iodine has no relevance to radiocontrast allergies. Iodine cannot be an allergen - it is found throughout our bodies in thyroid hormones and amino acids and is added to most salt used in the US. Both fish and shellfish contain iodine, but it is not the source of people's allergies. The major allergens in shellfish are muscle proteins, tropomyosins (1,2).

Reactions to IV contrast are anaphylactoid, not allergic and therefore not anaphylactic (3). These reactions are not caused by IgE and thus require no pre-exposure. Nearly all life-threatening reactions to IV contrast occur immediately or within the first 20 min after contrast media injection (1).

Although prior allergic reaction to seafood, shellfish, or iodine-containing solutions would create IgE sensitized to those allergens, this sensitized IgE would play no role in a reaction to IV contrast media, since the reaction to contrast is not IgE mediated. For the same reason, a patient who had an adverse event after contrast injection is unlikely to experience a similar or more severe reaction if given contrast again - non-immune-mediated means no immune system memory. (1,3-5).

The risk of reactions to contrast media in patients with seafood allergy is similarly elevated (about a 3-fold relative risk) for persons with allergy to egg, milk or chocolate, indicating that a general atopic disposition, rather than an iodine-specific reactivity, accounts for the increased incidence of reactions in this sub-group. Thus, reactions to contrast media should not be construed as an indication of an IgE antibody-mediated iodine allergy (1,4).

Do not delay emergent studies for steroid premedication. Only lengthy 12 hour premedication protocols have shown any effect on reaction rates, and this small benefit was manifested primarily by decreasing minor reactions. No steroid protocol has shown a statistically significant improvement in severe adverse reaction rates (1).

References:
(1) Schabelman E, et al. The Relationship of Radiocontrast, Iodine, and Seafood Allergies: A Medical Myth Exposed J Emerg Med 2009 Dec 31. [Epub ahead of print].
(2) Leung PS, et al. Seafood allergy: tropomyosins and beyond J Microbiol Immunol Infect 1999;32:143–154.
(3) American College of Radiology. Manual on contrast media. Reston, VA: American College of Radiology; 2008.
(4) American Academy of Allergy Asthma and Immunology. The risk of severe allergic reactions from the use of potassium iodide for radiation emergencies. Milwaukee, WI: American Academy of Allergy Asthma and Immunology; 2004.
(5) Mishkin MM. Contrast media safety: what do we know and how do we know it? Am J Cardiol 1990;66:34F–36F.

Oral Contrast

NAC

ACETYLCYSTEINE AND CONTRAST AGENT-ASSOCIATED NEPHROTOXICITY
Click here to hear the Reviewer's comments via RealAudio
Briguori, C., et al, J Am Coll Card 40(2):298, July 17, 2002
did not do anything if >140 of contrast, 1.52-1.48 in aceytl 1.53-154 in non

ROLE OF N-ACETYLCYSTEINE IN THE PREVENTION OF RADIOCONTRAST-INDUCED NEPHROPATHY
Click here to hear the Reviewer's comments via RealAudio
Brophy, D.F., Ann Pharmacother 36:1466, September 2002

BACKGROUND: In hospitalized patients, development of radiocontrast-induced nephropathy (RIN) is associated with substantial morbidity and a more than five-fold increase in the risk of dying during the hospital stay. Risk factors for RIN include preexisting renal dysfunction, diabetes, chronic heart failure, dehydration, and the use of large contrast volumes and high-osmolar contrast. The pathophysiology of RIN is multifactorial, and oxygen-free radicals have been implicated as playing a potential role. Peri-procedural administration of hypotonic saline has been reported to be protective, but studies of other prophylactic strategies have yielded disappointing results. It is speculated that the antioxidant properties of N-acetylcysteine (NAC) may be protective.

METHODS: The author from Virginia Commonwealth University, discusses two randomized controlled trials (total 137 patients) of the effects of oral NAC (four 600mg doses) on the development of RIN in patients with chronic renal insufficiency, who also received hypotonic saline

RESULTS: In both trials, RIN was significantly more frequent in the control groups than in the NAC groups (21% vs. 2% and 45% vs 8%), and the effects of NAC were particularly notable in patients with baseline serum creatinine levels above 2.0 or 2.5mg/dl. Study limitations included small sample sizes, use of low-osmolar contrast, concomitant use of potentially protective calcium channel blockers, inclusion of some patients at relatively low risk and in one study, limitation of follow-up to 48 hours.

CONCLUSIONS Given the evidence suggesting a beneficial effect of NAC in preventing RIN, its relatively low cost, and its fairly innocuous adverse effect profile, the author feels that its use is appropriate in high-risk patients, but acknowledges the need for further trials.

28 references

Am J Card 92:1454, December 15, 2003

NAC prophylaxis was associated with a statistical reduction in the development of contrast nephropathy, defined as a creatinine increase exceeding 0.5mg/dl or 25% of baseline values at 48 hours (summary odds ratio 0.37, 95% confidence interval [CI] 0.16-0.84), with a number-need-to-treat of nine (95% CI 5- 33). The overall rate of contrast nephropathy was 13.3%, while the dialysis rate was 0.75% either with or without NAC.

CONCLUSIONS: Based on the impact of NAC prophylaxis on this surrogate marker, the authors suggest its routine use in stable patients undergoing elective imaging. 20 references (daniel.isenbarger@na.amedd.army.mil)

N-ACETYLCYSTEINE FOR RADIOCONTRAST-INDUCED NEPHROPATHY: POTENTIAL ROLE IN THE EMERGENCY DEPARTMENT?
Click here to hear the Reviewer's comments via MP3.
Chong, E., et al, Can J Emerg Med 6(4):253, July 2004

BACKGROUND: A need for urgent contrast-enhanced imaging in ED patients may preclude a careful assessment of the risk for radiocontrast-induced nephropathy (RIN) or adequate prophylactic hydration. It has been suggested that N-acetylcysteine, a potent vasodilator that enhances renal perfusion, prevents ischemia-reperfusion syndromes and may protect against the effects of circulating free radicals, might be an effective agent for RIN prophylaxis.

METHODS: The authors, from the University of British Columbia and Virtual Learning, Inc., in Toronto, conducted a systematic review of nine randomized, controlled studies (1,019 patients) of the effects of prophylactic N-acetylcysteine for the prevention of RIN.

RESULTS: Five of the nine trials reported a renoprotective effect of N- acetylcysteine prophylaxis, and four did not. However, seven of the nine trials involved prophylaxis prior to elective imaging, and only two could potentially be extrapolated to the ED setting. One reported that an aggressive regimen of IV N-acetylcysteine (150mg/kg given over 30 minutes prior to imaging followed by 50mg/kg/hr for four hours) in patients with stable chronic renal failure reduced the rate of contrast-induced renal dysfunction (4.9% vs. 20.5% in controls) at the expense of an increase in the rate of adverse effects. In the second trial, a 1200mg dose of oral N- acetylcysteine given one hour prior to, and three hours after, contrast administration was not renoprotective.

CONCLUSIONS: The authors feel that the available evidence does not support the use of N-acetylcysteine prophylaxis to protect against RIN in patients requiring urgent contrast- enhanced imaging. 20 references (zed@interchange.ubc.ca)

Sodium Bicarb

sodium bicarbonate 154mEq/L (3 ampules in 1 liter D5W)
3mL/kg/hr IV for 1 hour before contrast
1mL/kg/hr IV for 6 hours after contrast

Risk Score for CIN

Extravisation

ionic or concentrated contrast material can severe injuries, but the newer dilute non-ionic rarely causes problems

much greater chance of problems with metal butterfly needles as opposed to catheters.

Phlebitis can cause extravisation even whent he tip is in the vein, as larger catheters eventually weaken the vascular wall

EFFECT OF LOW DOSES OF IONISING RADIATION IN INFANCY ON COGNITIVE FUNCTION IN ADULTHOOD: SWEDISH POPULATION BASED COHORT
Click here to hear the Reviewer's comments via MP3.
Hall, P., et al, Br Med J 328:1, January 3, 2004

Radiographic Contrast