Acute Kidney Injury

Classifications of Kidney Failure

• Kidney failure: Partial or complete impairment of kidney function, leading to the inability to excrete metabolic waste products and water.

• Effects: Causes fluid, electrolyte, and acid-base imbalances impacting all body systems.

• Challenges: Requires adherence to diet therapy and treatment plans while managing changes in:

  • Lifestyle

  • Occupation

  • Family relationships

  • Self-image

Psychological Impact

• Emotional distress: Patients often experience withdrawal and depression due to:

  • Grieving loss of kidney function

  • Grieving loss of independence

Types of Kidney Failure

• Acute Kidney Injury (AKI): Rapid onset of kidney impairment.

• Chronic Kidney Disease (CKD): Gradual and progressive decline in kidney function.

Key Differences Between AKI and CKD (Table 51.1)

• Onset:

  • AKI: Sudden

  • CKD: Gradual, often over many years

• Most common causes:

  • AKI: Acute tubular necrosis

  • CKD: Diabetic nephropathy

• Diagnostic criteria:

  • AKI: Acute reduction in urine output and/or increased serum creatinine.

  • CKD: GFR <60 mL/min/1.73 m² for >3 months and/or kidney damage for >3 months.

• Reversibility:

  • AKI: Potentially reversible

  • CKD: Progressive and irreversible

• Main cause of death:

  • AKI: Infection

  • CKD: Cardiovascular disease (CVD)

Overview of Acute Kidney Injury (AKI)

• Definition: Describes a syndrome with a range from slight deterioration to severe kidney impairment.

• Characteristics:

  • Rapid loss of function with or without decreased urine output.

  • Increases in BUN, creatinine, and potassium.

  • Severity can range from slight to azotemia.

• Development: Can occur over hours or days, mainly affecting those with life-threatening issues.

• Common Causes: Severe, prolonged hypotension, hypovolemia, nephrotoxic exposure.

Causes of AKI

• Categorized as:

  • Prerenal causes: Factors reducing systemic circulation.

  • Intrarenal causes: Direct damage to kidney tissue.

  • Postrenal causes: Mechanical obstruction of urine outflow.

Prerenal Causes

• Definition: Factors leading to decreased renal blood flow.

• Characteristics: No damage to kidney tissue; reversible with treatment.

• Common causes:

  • Hypovolemia (e.g., dehydration, HF)

  • Decreased cardiac output (e.g., cardiogenic shock)

Intrarenal Causes

• Definition: Direct damage to kidney tissue impairing nephron function.

• Common causes:

  • Acute tubular necrosis (ATN)

  • Prolonged ischemia and nephrotoxins

  • Hemolysis and muscle injury

Postrenal Causes

• Definition: Obstruction of urine outflow impairs kidney function.

• Common causes:

  • Benign prostatic hyperplasia (BPH)

  • Prostate cancer

  • Stone formation and trauma

RIFLE Classification of AKI

• Stages:

  • Risk: GFR decrease by 25%, urine output <0.5 mL/kg/hr for 6 hr.

  • Injury: GFR decrease by 50%, urine output <0.5 mL/kg/hr for 12 hr.

  • Failure: GFR decrease by 75% or serum creatinine >4 mg/dL, urine output <0.3 mL/kg/hr.

  • Loss: Persistent acute kidney failure >4 weeks.

  • End-stage renal disease: Complete loss of function >3 months.

Clinical Manifestations during Oliguric Phase

• Common manifestations:

  • Urinary changes

  • Waste product accumulation

  • Fluid volume depletion

  • Metabolic acidosis

Additional Manifestations

• Electrolyte Imbalances:

  • Sodium imbalance

  • Potassium excess

• Neurological Issues: Fatigue, concentration difficulties, seizures due to waste accumulation.

Diuretic Phase of AKI

• Description: Daily urine output may reach 1-3 L.

• Characteristics: High volume due to osmotic diuresis; hypovolemia may occur from fluid loss.

• Duration: Lasts 1 to 3 weeks.

Recovery Phase of AKI

• Initiation: Begins with an increase in GFR and a decrease in BUN and creatinine.

• Duration: Initial improvements in the first 1-2 weeks; may take up to 12 months for stabilization.

• Considerations: Older adults less likely to recover completely; some may progress to CKD.

Diagnostic Tests for AKI

• History Assessment: Vital for diagnosing AKI causes, focusing on:

  • Prerenal: Dehydration and hypotension history.

  • Intrarenal: Exposure to nephrotoxins.

  • Postrenal: Urinary stream changes or stones.

Laboratory Tests

• Urinalysis: Detects sediment abnormalities, hematuria, and pyuria.

• Imaging: Ultrasound is frequently the first test; renal scans assess blood flow; CT scans visualize obstructions or lesions.

Main Goals of AKI Treatment

• Eliminate the cause.

• Manage signs and symptoms.

• Prevent complications:

  • Fluid management and diuretic therapy may be utilized.

Nutritional Considerations

• Calories: 30-35 kcal/kg to prevent catabolism.

• Protein: 0.8-1.0 g/kg/day; sodium restricted as needed.

• Potassium and phosphate: Monitored and restricted.

Monitoring and Management

• Daily assessments:

  • Weight, intake, output, vital signs, and urine output.

• Infection Prevention: Leading cause of death; careful monitoring and aseptic technique required.

• Fluid Balance: Managing hypervolemia or hypovolemia, especially during diuretic phase.

Recovery Considerations

• Recovery outcomes depend on the severity of injury, health status, and lifestyle factors.

• Educational focus: Patient education to prevent recurrence and emphasize the importance of follow-up care.

Risk Factors for AKI in Hospital Settings

• Key factors: Preexisting CKD, older age, trauma, major surgery, extensive burns, heart failure, sepsis.

• Nursing Role: Monitoring high-risk patients and educating on preventive measures.