Acute kidney injury

Abstract

Acute kidney injury is a serious condition, occurring in up to two-thirds of intensive care unit patients, and 8.8-55% of patients with acute cardiac conditions. Renal replacement therapy is used in about 5-10% of intensive care unit patients. The term cardiorenal syndrome refers to combined heart and kidney failure; three types of acute cardiorenal syndrome have been described: acute cardiorenal syndrome or cardiorenal syndrome type 1, acute renocardiac syndrome or cardiorenal syndrome type 3, and acute cardiorenal syndrome type 5 (cardiac and renal injury secondary to a third entity such as sepsis). Acute kidney injury replaced the previously used term ‘acute renal failure’ and comprises the entire spectrum of the disease, from small changes in function to the requirement of renal replacement therapy. Not only failure, but also minor and less severe decreases, in kidney function are of clinical significance both in the short and long-term. The most recent definition for acute kidney injury is proposed by the Kidney Disease: Improving Global Outcomes clinical practice guidelines workgroup. This definition is a modification of the RIFLE and AKIN definitions and staging criteria, and it stages patients according to changes in the urine output and serum creatinine (see Tables 68.1 and 68.2). Acute kidney injury is a heterogeneous syndrome with different and multiple aetiologies, often with several insults occurring in the same individual. The underlying processes include nephrotoxicity, and neurohormonal, haemodynamic, autoimmune, and inflammatory abnormalities. The most frequent cause for acute kidney injury in intensive cardiac care patients are low cardiac output with an impaired kidney perfusion (cardiogenic shock) and/or a marked increase in venous pressure (acute decompensated heart failure). Predictors for acute kidney injury in these patients include: baseline renal dysfunction, diabetes, anaemia, and hypertension, as well as the administration of high doses of diuretics. In the intensive cardiac care unit, attention must be paid to the prevention of acute kidney injury: monitoring of high-risk patients, prompt resuscitation, maintenance of an adequate mean arterial pressure, cardiac output, and intravascular volume (avoidance of both fluid overload and hypovolaemia), as well as the avoidance or protection against nephrotoxic agents. The treatment of acute kidney injury focuses on the treatment of the underlying aetiology, supportive care, and avoiding further injury from nephrotoxic agents. More specific therapies have not yet demonstrated efficacy. Renal replacement therapy is indicated in life-threatening changes in fluid, electrolyte, and acid-base balance, but there are also arguments for more early initiation.