PREVENTION OF CONTRAST-INDUCED NEPHROPATHY

Geneva Coats R.N.

 

Contrast medium nephrotoxicity is a condition in which impairment in renal function (an increase in serum creatinine by more than 25% or 0.5 mg/dl) occurs within three days following the intravascular administration of a contrast medium (CM) in the absence of an alternative etiology. Contrast-induced nephropathy (CIN) involves toxic and hypoxic insults to the kidney. CIN has been linked to morbidity, mortality and prolonged length of stay.

 

Patients with normal kidney function and no risk factors have a very low incidence of CIN. There are several risk factors for CIN, however, which should be taken into consideration prior to deciding to order a contrast exam.

 

Risk factors include:

 

·        older age (with normal kidney function)

·        concomitant use of selected drugs:

      metformin

      non-steroidal anti-inflammatory drugs

      diuretics

      cisplatin

      cyclosporine

      aminoglycoside antibiotics

      beta blockers

      interleukin-2

      hydralazine

      amphotericin B

      tacrolimus

·        proteinuria (of any cause)

·        diabetes

·        heart failure

·        chronic renal insufficiency

·        hypotension

·        dehydration (BUN:Cr ratio >20:1)

·        hypovolemia

·        elevated creatinine level (>1.3)

·        low serum albumin level (<3.5)

·        multiple contrast exams within a 24-48 period of time

 

 

The vast majority of cases of CIN are reversible. However, there are no effective therapies for established CIN. Rare patient will require acute hemodialysis. Thus, physicians should focus on prevention. Avoiding contrast entirely for high-risk patients is the safest and simplest option. Consultation with the radiologist may reveal non-nephrotoxic alternatives such as ultrasound, magnetic resonance, and nuclear medicine studies. Non-contrast CT may also prove to be of value.

 

The decision to order a contrast study should always include:

 

ü      risk assessment

ü      avoidance of contrast in patients with one or more risk factors

ü      determination of medical necessity

ü      appropriate prophylaxis and monitoring if a contrast study is vital to diagnosis and treatment.

 

 

Benefits of diagnosing particular conditions such as cancer, abscesses, stenosis, vascular insults etc, must be weighed against the risks of contrast administration (allergic reactions and nephrotoxicity). When a contrast study will provide more benefit than risk, the patient should receive the exam, with appropriate intervention for prophylaxis and monitoring. The radiologist will utilize the smallest effective amount of low osmolar CM to further reduce risk.

 

Minimal baseline labs at CVMC include BUN and creatinine.  Creatinine levels of < or = 1.3 are considered normal. Borderline levels of 1.4-1.9 may normalize with hydration, while a level above 2.0 is considered severe renal insufficiency. A desirable BUN:Cr ratio is <20:1. If the ratio is >20:1, it is usually due to dehydration, although this may also be due to other causes, such as GI bleeding.

 

In patients with high risk factors, adequate hydration is the primary method to reduce risk of CIN. Volume depletion can be ameliorated with pre- and post- scan hydration. For at least four hours prior to the study, and preferably for twelve hours prior, fluid should be administered at a rate of at least 75-125 ml/hr. Fluid administration should continue for 12-24 hours post-exam. More cautious hydration may be indicated in cases of CHF and oliguric renal failure. 

Avoidance of concomitant administration of drugs listed above, especially diuretics, nsaids, and metformin. is also important.

Some studies have shown a benefit when hydration is accompanied by administration of N-acetylcysteine (600 mg bid one day before and the day of the contrast exam) or theophylline (various doses and schedules). Further studies are ongoing in this area.

             A followup BUN/creatinine level is advisable within 24-48 hrs.

Chronic renal dialysis patients are candidates for contrast exams if not at high risk for allergy or pulmonary edema.

In conclusion, when the benefit of a contrast exam outweighs the risk of nephropathy in a patient with several risk factors, complications can be mitigated through appropriate prophylaxis and careful monitoring.

 

Copyright Jan 2007. This article may not be reproduced or distributed in any form without the express written consent of the author.