Kidney

Introduction

Acute Kidney Injury (AKI), formerly referred to as acute renal failure, is a rapid decline in kidney function that develops within hours or days. This condition reduces the kidneys’ ability to remove waste products, regulate electrolytes, maintain fluid balance, and preserve acid-base equilibrium. Consequently, substances such as urea and creatinine accumulate in the bloodstream, while sodium, potassium, and fluid imbalances may develop.

AKI is frequently encountered in hospitalized patients, particularly those in intensive care units. The severity can vary from mild, reversible impairment to life-threatening kidney failure requiring dialysis. Prompt diagnosis and treatment are crucial because untreated AKI may result in severe complications such as pulmonary edema, hyperkalemia, metabolic acidosis, and multiple organ dysfunction.

The kidneys are essential for filtering blood, producing urine, controlling blood pressure, and stimulating red blood cell production. Therefore, sudden impairment of kidney function can negatively affect nearly every body system.

Pathophysiology of Acute Kidney Injury

AKI develops when there is a sudden decrease in the glomerular filtration rate (GFR), causing retention of waste products and disturbances in fluid and electrolyte regulation. AKI is divided into three primary categories according to its underlying mechanism:

Pre renal AKI

Pre renal AKI occurs when blood flow to the kidneys is reduced without direct kidney tissue damage. Decreased renal perfusion lowers filtration pressure.

Common causes include:

• Dehydration
• Hemorrhage
• Severe hypotension
• Heart failure
• Shock
• Sepsis

In response to reduced blood flow, the kidneys activate compensatory systems such as the renin-angiotensin-aldosterone system (RAAS) to retain sodium and water. Persistent hypoperfusion can eventually cause ischemic injury to renal tubules.

Intrinsic (Intra renal) AKI

Intrinsic AKI results from direct injury to kidney structures including tubules, glomeruli, interstitium, or blood vessels.

Frequent causes include:

• Acute tubular necrosis (ATN)
• Glomerulonephritis
• Acute interstitial nephritis
• Nephrotoxic medications
• Contrast-induced nephropathy

In ATN, toxins or ischemia damage tubular epithelial cells, leading to tubular obstruction, impaired filtration, and inflammation.

Post renal AKI

Post renal AKI develops due to obstruction of urine flow anywhere in the urinary tract.

Common causes include:

• Kidney stones
• Enlarged prostate
• Bladder tumors
• Urethral obstruction

Urinary blockage raises pressure inside the kidneys, decreasing glomerular filtration and potentially causing progressive kidney injury if not treated.

Causes of Acute Kidney Injury

Pre renal Causes

• Severe dehydration
• Vomiting and diarrhea
• Blood loss
• Burns
• Septic shock
• Heart failure
• Liver failure
• Excessive use of diuretics
• Low blood pressure

Intrinsic Renal Causes

• Acute tubular necrosis
• Glomerulonephritis
• Acute interstitial nephritis
• Vasculitis
• Hemolytic uremic syndrome
• Rhabdomyolysis
• Nephrotoxic drugs
• Imaging contrast dyes

Post renal Causes

• Kidney stones
• Benign prostatic hyperplasia
• Urinary tract obstruction
• Bladder cancer
• Blood clots in the urinary tract
• Neurogenic bladder

Risk Factors

Several conditions increase the likelihood of AKI, including:

• Advanced age
• Diabetes mellitus
• Hypertension
• Chronic kidney disease
• Severe infections
• Major surgical procedures
• ICU admission
• Use of nephrotoxic medications
• Dehydration
• Heart disease
• Liver disease

Signs and Symptoms

Early Manifestations

• Reduced urine output (oliguria)
• Fatigue
• Weakness
• Loss of appetite
• Nausea and vomiting
• Swelling in the legs and feet
• Mild confusion

Progressive Manifestations

• Shortness of breath caused by fluid overload
• Chest discomfort
• Severe hypertension
• Muscle cramps
• Persistent vomiting
• Generalized edema
• Drowsiness
• Altered mental state

Severe Complications

• Hyperkalemia leading to cardiac arrhythmias
• Pulmonary edema
• Metabolic acidosis
• Uremic encephalopathy
• Seizures
• Coma

Some individuals may initially show no symptoms, and AKI may only be identified through laboratory testing.

Diagnosis of Acute Kidney Injury

Medical History and Physical Examination

The physician evaluates:

• Fluid balance
• Medication use
• Toxin exposure
• Recent infections
• Surgical history
• Urine output

Physical findings may include dehydration, edema, hypotension, or signs of systemic illness.

Laboratory Tests

Kidney function test (KFT)

HbA1c (for diabetic patients)

CBC

ESR, CRP

LFT with viral markers

Electrolyte Assessment

Abnormal levels of potassium, sodium, calcium, phosphate, and bicarbonate may indicate renal dysfunction.

Urinalysis

Urine examination may reveal:

• Proteinuria
• Hematuria
• Urinary casts
• Infection
• Abnormal urine concentration

Imaging Studies

Ultrasound

Used to identify urinary obstruction, hydronephrosis, or structural abnormalities.

CT Scan

Helpful in detecting stones or masses.

Kidney Biopsy

Performed in selected patients when the exact cause of intrinsic kidney disease remains uncertain.

Staging of AKI

AKI is commonly staged according to KDIGO criteria using serum creatinine levels and urine output.

Stage 1

• Mild rise in creatinine
• Slight decrease in urine output

Stage 2

• Moderate increase in creatinine
• More noticeable reduction in urine production

Stage 3

• Severe renal dysfunction
• Markedly elevated creatinine
• Possible need for dialysis

Complications

Untreated or severe AKI may lead to:

• Hyperkalemia
• Pulmonary edema
• Hypertension
• Metabolic acidosis
• Fluid overload
• Uremia
• Cardiac arrhythmias
• Chronic kidney disease
• End-stage renal disease
• Multi-organ failure

Management of Acute Kidney Injury

Treat the Underlying Cause

Pre renal AKI

• Intravenous fluid administration
• Shock correction
• Blood transfusion when necessary
• Sepsis management with antibiotics.

Intrinsic AKI

• Discontinuation of nephrotoxic medications
• Treatment of infections
• Immunosuppressive therapy for Glomerulonephritis when indicated

Post renal AKI

• Relief of urinary obstruction
• Catheter insertion
• Surgical management
• Removal of stones

Fluid Management

Maintaining proper fluid balance is essential.

In dehydration:

• IV normal saline may be given.

In fluid overload:

• Fluid restriction
• Diuretics such as furosemide

Excessive hydration should be avoided because it may worsen pulmonary edema.

Electrolyte Management

Hyperkalemia Treatment

• Calcium gluconate
• Insulin with glucose
• Sodium bicarbonate
• Potassium-binding agents
• Dialysis in severe situations

Metabolic Acidosis

• Sodium bicarbonate therapy in selected patients

Medication Adjustment

Many medications require dose modification in AKI because impaired kidneys cannot effectively eliminate drugs.

Drugs to avoid include:

• NSAIDs
• Certain antibiotics
• Contrast agents
• Aminoglycosides

Renal Replacement Therapy (Dialysis)

Dialysis may be necessary in severe AKI when complications cannot be controlled medically.

Indications for Dialysis

• Severe Hyperkalemia
• Pulmonary edema
• Severe metabolic acidosis
• Uremic symptoms
• Persistent fluid overload

Diet Plan for AKI

Nutrition is important for recovery and complication prevention. Diet should be tailored according to:

• Severity of AKI
• Electrolyte levels
• Fluid balance
• Dialysis status

Dietary Goals

• Maintain adequate nutrition
• Prevent electrolyte disturbances
• Reduce kidney workload
• Avoid fluid overload

Recommended Foods

Low-Potassium Foods

• Apples
• Grapes
• Berries
• Cabbage
• Cauliflower
• White rice
• Pasta

Moderate Protein Sources

• Egg whites
• Skinless chicken
• Fish
• Tofu

Low-Sodium Foods

• Fresh vegetables
• Homemade meals
• Unsalted foods

Adequate Calorie Sources

• Rice
• Bread
• Healthy fats
• Low-potassium fruits

Foods to Avoid

High-Potassium Foods

• Bananas
• Oranges
• Potatoes
• Tomatoes
• Spinach
• Coconut water

High-Sodium Foods

• Processed foods
• Pickles
• Chips
• Fast food
• Canned soups

Excess Protein

High protein intake may increase nitrogen waste accumulation.

Excess Fluids

Patients with reduced urine output may require fluid restriction.

Prevention

Preventive measures include:

• Maintaining adequate hydration
• Avoiding unnecessary nephrotoxic medications
• Proper control of diabetes and hypertension
• Monitoring kidney function in hospitalized patients
• Prompt treatment of infections
• Limiting contrast dye exposure when possible
• Early detection of urinary obstruction

Prognosis

The prognosis of AKI depends on:

• The underlying cause
• Severity of injury
• Patient age
• Associated comorbidities
• Timeliness of treatment

Mild cases may completely recover with appropriate therapy, while severe AKI can progress to chronic kidney disease or permanent renal damage. Mortality is significantly higher among critically ill patients.

Conclusion

Acute Kidney Injury is a serious condition characterized by the rapid deterioration of kidney function. It may arise from decreased renal blood flow, direct kidney injury, or urinary tract obstruction. AKI can result in dangerous complications such as electrolyte imbalances, fluid overload, metabolic acidosis, and multi-organ failure.

Early recognition and prompt treatment are essential for improving outcomes and minimizing complications. Management focuses on correcting the underlying cause, maintaining fluid and electrolyte balance, avoiding nephrotoxic substances, and initiating dialysis when necessary.

Proper nutrition, hydration, and close medical monitoring are vital for recovery. Increased awareness, preventive strategies, and timely intervention can significantly reduce the burden of AKI and improve patient outcomes.