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Acute Kidney Injury After Cardiac Angiography and
Exposure to Iodinated Contrast Media
Panupong Lisawat, MD; Neil Ybanez, MD; and Richard J. Solomon, MD A 75-year-old female patient with a history of chronic The diagnosis of ST-segment elevation myocardial infarction kidney disease stage IV, type 2 diabetes mellitus, hyperten- prompted the initiation of an emergent cardiac catheteriza- sion and dyslipidemia presented to an outside hospital with a tion. She underwent revascularization with drug-eluting stents. 3-day history of substernal chest pain that radiated to her jaw During the procedure, 100 ml of low osmolar contrast (Isovue and the left side of her back. An electrocardiogram showed 370, Bracco Diagnostics Inc., Princeton, NJ) was used. She was a slight ST elevation in the anterior leads, so she was subse- stable post-procedure. A nephrology consult was requested to quently transferred to our hospital. Before transfer, she re- help manage a potential contrast-induced acute kidney injury.
ceived ticagrelor, aspirin and heparin.
Post catheterization, the patient appeared to be slightly Her medications before the transfer included losartan, hy- volume overloaded with bibasilar rales and bilateral 2+ lower drochlorothiazide, simvastatin, acetylsalicylic acid and insu- extremity edema. She received 1 dose of intravenous furose- lin. On admission to our hospital, she was awake and alert, mide post-procedure and produced more than 1 L of urine with a blood pressure of 160/77, a heart rate of 82, and an output. The patient was otherwise stable hemodynamically, oxygen saturation of 97% on room air.
with a minimal supplemental oxygen requirement. Losartan She was found to have a serum creatinine of 1.96 (baseline and hydrochlorothiazide were held.
1.9–2.5 over the past year) that correlated with an eGFR of Eighteen hours after percutaneous coronary intervention 25 ml/min. Her sodium and potassium concentrations were (PCI), her serum creatinine was 2.24 mg/dl; it had increased to 138 mEq/l and 4.2 mEq/l respectively. Her troponin I was 1.6. 3.34mg/dl at 42 hours. Her urine output decreased from 2900 ml in the first day of admission to 300 ml in the next day.
Furosemide 40 mg oral 2 times daily was started on day 2 From Fletcher Allen Health Care, Burlington, VT. Address for correspondence:
of admission, but the patient had no increase in urine output. Richard Solomon, MD, Director, Division of Nephrology, Fletcher Allen Health Care, Burlington, VT, 05401. Email: [email protected]. Disclosures:
Dr. Solomon is a consultant/advisor to Bracco Diagnostics, Inc., PLC Med, Inc., and
Her serum creatinine peaked at 65 hours post-PCI at 3.36 mg/ MDSci Inc. He receives honoraria from Guerbet and research grants from REATA dl (Figure 1). Clinically, the patient was hemodynamically stable. Pharmaceuticals, Novartis, MDSci, Inc., and Medtronic.
The patient was discharged on the same day on a low-sodium diet. A follow-up serum creatinine 4 days later was 2.56 mg/dl.
Discussion
Consequences of CIAKI
This patient represents a classic example of acute kidney inju- CIAKI is a specific form of injury to the kidney. Evidence ry that occurred after cardiac angiography and exposure to iodin- that acute kidney injury of any etiology leads to an acceler- ated contrast media. Contrast media are water-soluble organic ated loss of kidney function is just beginning to be appreci-molecules that contain iodine and are excreted almost entirely by ated.6 Both small prospective studies7 and retrospective analyses the kidneys, with a half-life measured in a few hours. of large databases8 indicate that patients who develop CIAKI First described in 1954, what we now call contrast-induced progress to worse kidney function over the ensuing years com- acute kidney injury (CIAKI) is defined by a change in serum pared to those without CIAKI. creatinine that follows a characteristic course (see Figure 1).1 In the short-term, CIAKI increases hospital length of stay, Creatinine begins to rise usually within 24 hours of exposure in-hospital mortality and overall cardiovascular mortality over and peaks on day 3 or 4 before slowly returning to or close to the following 5 years.9 Are these adverse events caused by the the baseline value over the next 7–10 days. Other explanations CIAKI, or are patients who develop CIAKI already destined for a change in creatinine must first be excluded.
for worse outcomes because of their comorbid conditions and The threshold increase required for a definition of CIAKI the burdens of risk factors? The answer to this question is of varies in the literature from a relative increase of 25% to an abso- great importance and the subject of ongoing study.
lute increase of 0.5 mg/dL. These definitions produce different
incidences of CIAKI in the same population, making it difficult Prevention of CIAKI
to compare studies on prevention. Among patients undergoing
Because the administration of contrast is predictable and cardiac angiography, the incidence of CIAKI is ~5% but can the consequences of CIAKI are significant, efforts to prevent increase to more than 50% in some high-risk patients. In pa- this form of kidney injury are indicated. Knowledge of the tients undergoing contrast-enhanced computed tomography ex- pathophysiology of CIAKI has led to a number of strategies. ams, the incidence even in patients with chronic kidney disease The first step is identifying which patients are most likely appears less often and depends on the setting (inpatient versus to suffer CIAKI. Patients with decreased kidney function be-outpatient) and whether severe renal dysfunction is present.2 fore contrast exposure are at higher risk because each remaining The Acute Kidney Injury Network (AKIN) group has pro- nephron must excrete a greater load of the contrast, thus in- posed a new definition of acute kidney injury as an absolute creasing the potential for toxicity. Any condition that compro-0.3 mg/dL increase in creatinine within a 48-hour period, or a mises renal blood flow at baseline will further increase the risk. decrease in urine output to less than 0.5 mg/kg/h and sustained For example, patients with congestive heart failure, volume for at least 6 hours despite corrective measures.3 This defini- depletion, current NSAID use and a limited ability to gener- tion is just beginning to gain acceptance in the cardiology and ate nitric oxide (such as patients with diabetes) are all at some radiology literature. increased risk. Patients with hemodynamic instability at the time of angiography — particularly those requiring supportive Pathophysiology
measures, such as the use of pressors or an intra-aortic balloon Contrast media are nephrotoxic to the kidneys through at pump — are at increased risk. Finally, the more contrast agent least two mechanisms. First, all contrast media decrease blood used, the greater the CIAKI risk. A scoring system to calculate flow to the kidney, particularly in the medullary portion of the not only the incidence of CIAKI but also the need for renal kidney. Studies of isolated descending vasa recta, the main ves- replacement therapy has been in use for a number of years.10 sels supplying oxygen to the tubules in the medulla, indicate Once a high-risk patient has been identified, the next that contrast media cause vasoconstriction mediated by the step is to minimize the modifiable risk factors. Volume-de-generation of reactive oxygen species and a decrease in avail- pleting agents (diuretics) and NSAIDs should be held and ability of nitric oxide.4 This causes an ischemic injury in this intravenous fluid administered. Although some controver-portion of the kidney. Additional mechanisms of injury occur sies exist regarding the type, amount, and duration of IV through direct toxicity to the cells lining the renal tubules. This fluid, most recommendations include normal saline at 1 ml/injury also generates reactive oxygen species and proapoptotic kg/h for 4–6 hours before and 12 hours after cardiac an-stimuli, leading to loss of cell viability.5 giography. The amount can be increased to 3 ml/kg as a The contrast effects on vasa recta and tubule cells result in a de- bolus for urgent/emergency cases, and modified to 1.5 ml/ crease in glomerular filtration rate (GFR) and, thus, a rise in creati- kg bolus in the presence of the symptoms of congestive heart nine. The toxicity of contrast is not directly on the glomerulus, and failure. The use of IV fluid has now been incorporated into the decrease in filtration is a response to the downstream damage the latest guideline from the American Heart Association/to the tubule through a process called tubuloglomerular feedback American College of Cardiology (AHA/ACC).11 However, (TGF). Although the change in GFR occurs early in the course of despite the use of IV fluid, the incidence of CIAKI in high-CIAKI, it takes days for enough creatinine to be retained in the risk patients remains ~10%.
body to reach the threshold for a diagnosis of CIAKI. Newer in- The central pathophysiologic role of ischemia and the jury markers analogous to a renal troponin, such as NGAL, KIM- generation of reactive oxygen species have led to the use 1, and IL-18, will hopefully permit earlier diagnosis of this injury.
of antioxidant therapy as a strategy to prevent CIAKI. N-acetylcysteine (NAC) is a scavenger of reactive oxygen medium is used, every effort should be make to minimize species and a precursor of glutathione, a natural antioxidant. the amount of contrast administered.
Although initial studies suggested a preventive effect,12 sub-sequent prospective randomized trials and summary meta- analyses13 have diminished enthusiasm for this approach. As CIAKI reflects injury to the kidney and risk for cardiovascu- with any therapy, dose becomes critical, and a soon-to-begin lar events, mortality, subsequent progression of chronic kidney trial will use a high dose administered for a longer duration disease, and the need for dialysis. Patients at greatest risk can be (NCT01467466).
identified in advance, and most institutions take steps to mini- The use of isotonic sodium bicarbonate as the IV infu- mize the risk, such as using isotonic fluid administration and sion fluid instead of sodium chloride was proposed based antioxidants, and minimizing use of contrast. Specific protocols
up the importance of acid pH in the generation of some to risk stratify and treat patients undergoing contrast administra-
reactive oxygen species. Because urine is generally acidic, tion have been shown to improve patient outcomes.23,24 New and
administration of sodium bicarbonate to alkalinize the urine novel approaches to prevention continue to be investigated.
was initially found to reduce the incidence of CIAKI.14 As
with NAC, subsequent studies have reported mixed results, References
although meta-analyses15 still suggest a benefit. One mul-
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24. Marenzi G, Lauri G, Campodonico J, et al. Comparison of two hemofiltration proto- 21. Aspelin P, Aubry P, Fransson SG, et al; Nephrotoxicity in High-Risk Patients Study cols for prevention of contrast-induced nephropathy in high-risk patients. Am J Med. of Iso-Osmolar and Low-Osmolar Non-Ionic Contrast Media Study Investigators. All rights reserved. Reproduction in whole or in part prohibited.

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