In the latest review article in our Clinical Therapeutics series, a 20-year-old man with Marfan’s syndrome develops acute kidney injury after an aortic-valve replacement that was complicated by thoracic aortic dissection. Continuous renal-replacement therapy, rather than intermittent hemodialysis, is recommended because of hemodynamic instability.
Acute kidney injury is characterized by a sudden decrease in kidney function over a period of hours to days, resulting in accumulation of creatinine, urea, and other waste products. It may be associated with retention of sodium and water and the development of metabolic disturbances such as metabolic acidosis and hyperkalemia.
• How is acute kidney injury defined?
According to the Kidney Disease: Improving Global Outcomes (KDIGO) consensus guidelines, acute kidney injury is defined by an increase in the serum creatinine level of 0.3 mg per deciliter (26.5 micromoles per liter) or more within 48 hours; a serum creatinine level that has increased by at least 1.5 times the baseline value within the previous 7 days; or a urine volume of less than 0.5 ml per kilogram of body weight per hour for 6 hours.
• What is continuous renal-replacement therapy?
Continuous renal-replacement therapy includes a spectrum of dialysis methods developed in the 1980s specifically for the treatment of critically ill patients with acute kidney injury who could not undergo traditional intermittent hemodialysis because of hemodynamic instability or in whom intermittent hemodialysis could not control volume or metabolic derangements. The slower solute clearance and removal of fluid per unit of time with continuous renal-replacement therapy, as compared with intermittent hemodialysis, is thought to allow for better hemodynamic tolerance.
Morning Report Questions
Q: Is there a survival benefit with continuous renal-replacement therapy versus intermittent hemodialysis?
A: Randomized, controlled trials have not shown a survival benefit associated with continuous renal-replacement therapy instead of intermittent hemodialysis. Continuous renal-replacement therapy has advantages that may influence its use despite the lack of a demonstrated survival benefit. In a Cochrane meta-analysis, among patients who received continuous renal-replacement therapy, there was a trend toward less need for increased levels of pressors and significantly higher mean arterial pressures than among those who were not receiving continuous renal-replacement therapy. Removal of fluid with short sessions of intermittent hemodialysis can induce intradialytic hypotension, potentially increasing the risk of recurrent kidney injury.
Q: What adverse effects may be associated with renal-replacement therapy involving vascular access?
A: Complications of vascular access, including infection and vascular injury, are a common concern with continuous renal-replacement therapy. These complications are reported to occur in 5 to 19% of patients, depending on the access site selected. Arterial puncture, hematoma, hemothorax, and pneumothorax are the most common complications reported. Arteriovenous fistulas, aneurysms, thrombus formation, pericardial tamponade, and retroperitoneal hemorrhage have also been described.
During therapy, meticulous monitoring of machine performance and of the patient’s electrolytes and hemodynamics are required to prevent complications. Common problems include hypotension, arrhythmias, fluid-balance and electrolyte disturbances, nutrient losses, hypothermia, and bleeding complications from anticoagulation. Continuous renal-replacement therapy can result in clinically significant hypokalemia and hypophosphatemia, which may lead to severe complications if uncorrected.