Contrast-induced acute kidney injury

Contrast-induced nephropathy (CIN) is the third most common cause of all hospital-acquired acute renal failure and accounts for approximately 10% of all cases. There is still an ongoing debate regarding its occurrence after the intravenous contrast administration because most of the cases occur after intra-arterial administration of contrast for angiographic procedures. Even though the incidence is 5% after intravenous contrast administration ⁵.

Definition

So far there are no standards to report the CIN, therefore, the definition used in the literature is variable.

The definition of contrast nephropathy relies on serial plasma creatinine concentrations. A baseline creatinine level should be obtained before the procedure. Estimated glomerular filtration rate (eGFR) has been used for the assessment of renal function before intravenous contrast injection. This is calculated from the patient's age, race, sex and serum creatinine level. Online calculators are also available to assist in easily calculating eGFR.

Post-contrast peak effect on creatinine occurs between 48 and 72 hours.  

• relative: 25% rise in creatinine over baseline
• absolute: rise of greater than 44μmol/L

Contrast-induced acute kidney injury (CI-AKI) has now also been described in which injury or damage to the kidney has taken place, but is sub-clinical in that no measurable reduction in renal filtration is apparent ⁴.

Risk stratification

Risk for most normal individuals with no risk factors is based on baseline renal function

• low: Cr <130μmol/L or CrCl >60ml/min
• medium: Cr 130-200μmol/L or CrCl 60-30ml/min
• high: Cr >200μmol/L or CrCl <30ml/min

For those using eGFR

• very low risk: >60 mL/min
• low risk: 45-59 mL/min
• moderate: 30-45 mL/min
• high risk: <30mls mL/min

High dose contrast

However, if they are going to have an investigation with more than 300ml of iodinated contrast or two studies less than 72 hours apart, their risk is elevated to the medium group irrespective of their baseline renal function.

Predisposing risk factors

Patients with risk factors are automatically elevated to higher risk groups

• diabetes mellitus, multiple myeloma, CHF, cirrhosis, nephrotic syndrome, sepsis
  • low: as above
  • medium: Cr 110-130μmol/L or CrCl <90ml/min
  • high: Cr 130-200μmol/L or CrCl <60ml/min
• renal transplant, dehydration or hypotension
  • low: not possible
  • medium: even if their renal function is normal
  • high: Cr 130-200μmol/L or CrCl 60-30ml/min

Treatment

The most important factor is adequate pre-hydration and assessment of renal function. Risk stratification helps to determine what the most appropriate preparation is

• low: oral fluids only
• medium
  • IV 0.9% N. Saline for 12 hours before and after the procedure
  • @ 48 hours: if the creatinine is 25% above baseline, a further check five days post-procedure should be taken
• high
  • IV 0.9% N. Saline for 12 hours before and after the procedure

  • N-acetylcysteine600mg orally bd (three days before the procedure and one afterwards)

  • check creatinine at baseline, 48 hours, five days and ten days