Chapter 60: Acute Kidney Injury

KEY CONCEPTS

• Three classification systems exist for staging severity of acute kidney injury (AKI): (a) Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Kidney Disease (RIFLE), (b) Acute Kidney Injury Network (AKIN), and (c) Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guidelines. All three classification systems are based on separate criteria for serum creatinine (S_cr) and urine output.

• AKI is a common complication in critically ill patients and is associated with high morbidity and mortality.

• AKI is typically categorized based on three types of injury: (a) prerenal—decreased renal blood flow, (b) intrinsic—structural damage within the kidney, and (c) postrenal—an obstruction within the urine collection system.

• Serum creatinine, urea, and urine output are commonly used markers of renal function in clinical practice. However, advances in AKI research have led to the development of multiple novel biomarkers that can be used for risk assessment, early detection, classification, and prognosis in AKI.

• Conventional formulas used to estimate glomerular filtration rate (eGFR) are not recommended in AKI patients. In addition, drug dose adjustment recommendations are typically based on pharmacokinetic studies conducted in CKD patients and may not be reflective of pharmacokinetic changes seen in AKI patients.

• The most effective prevention strategies for AKI include limiting exposure to nephrotoxic medications and optimizing the patient’s hemodynamic and fluid status. Incorporation of electronic health record alerts may increase early detection and decrease risk of AKI progression.

• Supportive management remains the primary approach to prevent or reduce complications associated with AKI or comorbid conditions. Supportive therapies include renal replacement therapy (RRT), nutritional support, avoidance of nephrotoxins, and blood pressure and fluid management.

• For patients with prolonged or severe AKI, RRT is the cornerstone of support along with aggressive fluid and electrolyte management.

• Drug dosing for AKI patients receiving continuous renal replacement therapy (CRRT) or prolonged RRT is poorly characterized. Dosing requirements of agents primarily eliminated by the kidney may require individualization and adjustment as renal function changes. Therapeutic drug monitoring should be utilized whenever possible for any agent with a narrow therapeutic index.

Patient Care Process for Acute Kidney Injury

Collect

• Patient characteristics (eg, age, sex, muscle mass)

• Chief complaint/reason for admission

• Patient medical history including other related comorbid conditions (eg, CKD, diabetes, HTN, cirrhosis)

• Current medication list

• Current or recent administration of nephrotoxins (eg, nonsteroidal anti-inflammatory drugs [NSAIDs], ACE-I/ARBs, contrast dyes, aminoglycosides, vancomycin)

• Blood pressure, heart rate, respiratory rate, weight

• Complete blood count and chemistry panel

• Changes in serum creatinine since last visit or admission (if available)

• Volume status (eg, fluid intake, urine output, patient weight)

• Hemodynamic status (eg, BP, MAP)

• Microbiology results (if available)

• Urinalysis results (eg, WBCs, RBCs, protein, granular casts, FE_Na)

• Acid-base status ...