28.1: Acute Kidney Injury I: Introduction

Introduction:

Acute Kidney Injury (AKI) describes a swift decrease in kidney function occurring over hours to days, characterized by the kidneys' failure to remove waste products from the bloodstream. This leads to dangerous complications like metabolic acidosis, fluid overload, and electrolyte imbalances, such as hyperkalemia, which can cause life-threatening arrhythmias. AKI is common in both hospital and outpatient settings, often triggered by dehydration, sepsis, or exposure to nephrotoxic drugs like NSAIDs and contrast agents​.

Definition:

Acute Kidney Injury (AKI) is identified by either an increase of 0.3 mg/dL or more in serum creatinine within 48 hours or a 1.5-fold rise in baseline creatinine over seven days. A reduced urine output, less than 0.5 mL/kg/hour for six hours, is also a key diagnostic marker​. Though potentially reversible, AKI has a high mortality rate, especially in hospitalized patients. Classification:

The RIFLE classification system is used to assess the severity of AKI and guide treatment. RIFLE stands for Risk, Injury, Failure, Loss, and End-Stage Kidney Disease (ESKD). It has three severity stages followed by two outcome stages​.

1. Risk:
   • It is characterized by a 1.5 times rise in serum creatinine levels or a 25% drop in glomerular filtration rate (GFR). Additionally, for six hours, urine output can decrease to less than 0.5 mL/kg/hour.
2. Injury:
   • This stage involves doubling serum creatinine or a 50% reduction in GFR. Urine output is often below 0.5 mL/kg/hour for 12 hours, with rising BUN and serum creatinine​.
3. Failure:
   • It is defined by a threefold rise in serum creatinine or a decrease in GFR of over 75%. Urine output may be less than 0.3 mL/kg/hour for 24 hours, or there may be no urine (anuria) for 12 hours​.

Outcome Stages:

1. Loss:
   • Refers to complete loss of kidney function for more than four weeks, often requiring renal replacement therapy (RRT)​.
2. End-Stage Kidney Disease (ESKD):
   • It occurs when kidney failure persists for more than three months, requiring long-term dialysis or kidney transplantation​.

AKI, if untreated, can lead to chronic kidney disease (CKD) or ESKD. Early detection using the RIFLE system is crucial to improving patient outcomes​.