Contrast nephropathy

In patients with impaired renal function, iodinated radiological contrast media may be nephrotoxic, possibly by causing renal vasoconstriction and by a direct toxic effect upon renal tubules. The effect is dose-dependent and therefore more commonly seen in procedures which require large amounts of contrast media such as angiography with or without angioplasty.

In many patients the effect is mild, transient, fully reversible and of no clinical significance. The risk and severity of contrast nephropathy is amplified by the presence of hypovolaemia and renal impairment, especially if due to diabetic nephropathy. Diabetes per se is not a risk factor.

Prevention involves minimization as far as possible of the dose of contrast employed and use of low-osmolality contrast medium. The only proven preventative measure is prevention of hypovolaemia before administration of contrast. Pre-hydration with intravenous saline is of proven benefit.

A popular regimen involves infusion of 1 litre of saline during the 12 hours before and 12 hours after contrast exposure. Care must be taken to avoid volume overload in susceptible patients.

Recent evidence that acetylcysteine may be of benefit in preventing worsening of pre-existing renal impairment following intravenous contrast requires confirmation.

When deterioration in renal function occurs after intra-arterial injection of contrast (for example, after coronary angiography) it may be difficult to differentiate the effects of contrast-induced damage from those of atheromatous embolization. The latter carries a worse prognosis.

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