Contrast Media Part 2

• Kidney


  • Are paired organs behind the peritoneum
  • Consist of an outer cortex and inner medulla
  • Contain 1-2 million nephrons that filter blood and produce urine
• Glomerular filtration rate (GFR)


  Measure of kidney function; normal is ~120 mL/min
• Effective renal plasma flow (ERPF)


  Measure of kidney function; normal is ~500 mL/min
• Serum creatinine


  Byproduct of muscle metabolism used as an index of GFR
• Clearance


  The ability of the kidney to remove a substance from the blood
• Glomerular filtration rate (GFR)


  A method of estimating kidney function
• Effective renal plasma flow (ERPF)


  A method of estimating kidney function
• Inulin


  An ideal filtration marker because it is metabolically inert and cleared only by the kidney
• Hippuran clearance


  Used to measure ERPF
• Normal adult GFR is approximately 120 mL/min, and normal ERPF is approximately 500 mL/min
• Creatinine


  A byproduct of muscle protein metabolism generated by the body at a fairly steady rate and excreted entirely in the urine
• Creatinine is freely filtered by the glomerulus, but it is also secreted by the proximal tubule
• Creatinine generation is proportional to total muscle mass
• Muscle wasting is associated with reduced creatinine generation
• Renal failure


  The inability of the kidney to maintain homeostasis can result in the accumulation of nitrogenous wastes (or azotemia)
• Renal insufficiency


  Renal function is abnormal but capable of sustaining essential bodily function
• Types of renal failure

  • Anuric (absence of urine formation, <50 mL/24 hours)
  • Oliguric (diminished urine formation, <500 mL/24 hours)
  • Nonoliguric (normal urine formation, 500-6000 mL/24 hours)
  • Polyuric (>6000 mL/24 hours)
• Nephropathy


  Any condition or disease affecting the kidney
• Contrast-induced nephropathy (CIN)


  Acute impairment of renal function subsequent to the intravascular administration of contrast material
• CIN is defined as a reported rise in serum creatinine of more than 25% above baseline or an absolute rise of 0.5 mg/dL within 48 hours of receiving an iodinated contrast agent
• The serum creatinine level generally peaks at 4 to 5 days and then begins to return toward baseline within 7 to 10 days in CIN
• Patients with CIN are usually nonoliguric and CIN is usually reversible
• Urinalysis in CIN typically reveals coarse granular casts, renal tubular epithelial cells, and amorphous sediment. Proteinuria may be low grade. Hematuria is not a characteristic of CIN
• In the random population undergoing contrast-enhanced imaging, the incidence of CIN is low, generally thought to be between 1% and 6%
• Patients with diabetes mellitus and preexisting renal insufficiency represent a group with an extremely high risk of experiencing CIN
• There is a direct correlation between the volume of contrast administered and risk of CIN
• Dehydration before the imaging examination increases the risk of CIN
• Multiple myeloma has traditionally been regarded as a risk factor for CIN, but the risk is primarily related to the dehydration of the multiple myeloma patient
• High-osmolar contrast media (HOCM)

  Associated with a higher rate of nephrotoxicity than low-osmolar contrast media (LOCM)
• Hydration decreases the incidence of CIN
• CIN is dependent on the dose of contrast material used
• Medications like NSAIDs and dipyridamole are associated with the development of acute renal failure
• Metformin


  An oral medication given to non-insulin-dependent diabetics to lower blood sugar. It should be temporarily discontinued after any examination involving iodinated contrast and can be resumed after 2 days, assuming kidney function is normal
• The half-life of iodinated contrast media in patients with normal renal function is approximately 2 hours, but in patients with severe renal dysfunction it can be extended to more than 30 hours
• Thyroid storm


  A severe, life-threatening condition resulting when thyroid hormone reaches a dangerously high level, which can be precipitated by iodinated contrast media
• Iodinated contrast media can intensify thyroid toxicosis (excessive thyroid hormone) in patients with a history of hyperthyroidism
• Iodine deficiency is an important factor in the development of thyroid autonomy
• Potential pulmonary adverse effects of iodinated contrast agents include bronchospasm, pulmonary arterial hypertension, and pulmonary edema
• Patients with a history of pulmonary hypertension, bronchial asthma, or heart failure are at increased risk of pulmonary adverse effects from iodinated contrast agents
• The use of LOCM significantly reduces the risk of pulmonary effects from iodinated contrast agents