Renal & Urinary Disorders
Key Takeaways
- Acute Kidney Injury is categorized as prerenal (renal hypoperfusion), intrarenal (direct parenchymal damage, e.g., acute tubular necrosis), or postrenal (urinary tract obstruction).
- Hyperkalemia is the most life-threatening electrolyte complication during the oliguric phase of acute kidney injury, presenting on the ECG as peaked T waves and requiring urgent stabilization with calcium gluconate.
- Chronic kidney disease is staged from 1 to 5 based on GFR; stage 5 (End-Stage Renal Disease) represents GFR less than 15 mL/min/1.73 m² and requires renal replacement therapy.
- Dietary restrictions in chronic kidney disease involve limiting sodium, potassium, and phosphorus intake; phosphate binders (e.g., calcium acetate) must be taken with meals to prevent bone disease.
- In elderly patients, urinary tract infections often present atypically with confusion, agitation, and mental status changes without fever or dysuria, and catheter-associated urinary tract infections must be prevented using strict insertion and maintenance bundles.
Renal & Urinary Disorders
Introduction to Renal and Urinary Nursing
The renal and urinary systems are critical for maintaining homeostatic balance, regulating fluid volume, managing acid-base and electrolyte concentration, and excreting metabolic waste products. In the DHA licensing assessment, renal nursing questions frequently test the nurse's ability to differentiate between types of acute kidney injury, manage the progressive complications of chronic kidney disease, and implement evidence-based practices to prevent and manage urinary tract infections (particularly catheter-associated infections). Understanding the physiological implications of renal impairment and the corresponding nursing priorities is essential for ensuring patient safety and optimal clinical outcomes.
Acute Kidney Injury (AKI)
Pathophysiology and Classification
Acute Kidney Injury (AKI) is defined as a sudden, rapid decline in kidney function, marked by an increase in serum creatinine, a decrease in glomerular filtration rate (GFR), and/or a reduction in urine output. Clinically, AKI is categorized based on the anatomical site of the insult:
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Prerenal AKI: Caused by conditions that impair renal blood flow and perfusion without causing direct damage to the renal parenchyma. This leads to decreased glomerular filtration.
- Causes: Hypovolemia (hemorrhage, dehydration, severe burns), decreased cardiac output (heart failure, myocardial infarction), systemic vasodilation (sepsis, anaphylaxis), or renal vasoconstriction.
- Diagnostic indicator: Fractional excretion of sodium (FE_Na) is typically < 1% because the renal tubules remain intact and reabsorb sodium to conserve volume. The BUN-to-creatinine ratio is often elevated (> 20:1).
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Intrarenal (Intrinsic) AKI: Results from direct damage to the kidney tissue (glomeruli, tubules, or interstitium), leading to impaired nephron function.
- Causes: Acute Tubular Necrosis (ATN) is the most common cause, often triggered by prolonged renal ischemia, nephrotoxic agents (contrast media, aminoglycosides, NSAIDs, amphotericin B), or rhabdomyolysis (myoglobin casts obstructing tubules).
- Diagnostic indicator: FE_Na is typically > 2% due to tubular damage preventing sodium reabsorption. The BUN-to-creatinine ratio remains normal or slightly decreased (10:1 to 15:1). Urine microscopy may reveal muddy brown granular casts.
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Postrenal AKI: Occurs due to mechanical obstruction of urine outflow anywhere from the renal pelvis to the urethra.
- Causes: Benign Prostatic Hyperplasia (BPH), bilateral renal calculi, urethral strictures, or tumors.
- Diagnostic indicator: Hydronephrosis on ultrasound.
| AKI Category | Primary Mechanism | Key Causes | Diagnostic Findings |
|---|---|---|---|
| Prerenal | Renal hypoperfusion | Dehydration, hemorrhage, shock, heart failure | FE_Na < 1%, BUN:Cr ratio > 20:1, high urine osmolality |
| Intrarenal | Direct parenchymal damage | Nephrotoxic drugs, contrast dye, prolonged ischemia | FE_Na > 2%, muddy brown casts, fixed urine specific gravity (1.010) |
| Postrenal | Urinary tract obstruction | BPH, renal calculi, prostate/bladder cancer | Hydronephrosis on ultrasound, fluctuating urine output |
Phases of AKI
- Oliguric Phase: Characterized by urine output < 400 mL/day. It typically begins within 1 to 7 days of the injury. Metabolic acidosis, hyperkalemia, hyponatremia, and fluid volume excess (edema, hypertension, pulmonary congestion) develop.
- Diuretic Phase: Gradual increase in daily urine output (typically 1 to 3 L/day, sometimes up to 5 L/day). The kidneys can excrete waste but cannot concentrate urine. Hypovolemia, dehydration, hyponatremia, and hypokalemia are primary clinical concerns.
- Recovery Phase: Glomerular filtration rate increases, and BUN and creatinine levels stabilize and return to baseline. This phase can take up to a year.
Nursing Management of AKI
- Fluid Balance: Perform strict hourly intake and output (I&O) measurements and daily weights (1 kg of weight gain matches approximately 1,000 mL of fluid retention).
- Electrolyte Monitoring: Hyperkalemia is the most life-threatening complication of the oliguric phase. Monitor for ECG changes (peaked T waves, prolonged PR interval, widened QRS). Administer emergency therapies as ordered: calcium gluconate (to stabilize cardiac membrane), insulin and dextrose (to shift potassium intracellularly), sodium polystyrene sulfonate or sodium zirconium cyclosilicate (to excrete potassium via GI tract), or prepare for emergent hemodialysis.
- Nephrotoxic Control: Ensure withholding or dosage modification of nephrotoxic medications.
Chronic Kidney Disease (CKD)
Chronic Kidney Disease (CKD) is characterized by gradual, irreversible loss of renal function lasting for 3 months or longer. It is classified into five stages based on GFR:
- Stage 1: Kidney damage with normal or increased GFR (>= 90 mL/min/1.73 m²)
- Stage 2: Mild reduction in GFR (60–89 mL/min/1.73 m²)
- Stage 3: Moderate reduction in GFR (3a: 45–59; 3b: 30–44 mL/min/1.73 m²)
- Stage 4: Severe reduction in GFR (15–29 mL/min/1.73 m²)
- Stage 5: Kidney failure / End-Stage Renal Disease (ESRD) (GFR < 15 mL/min/1.73 m² or requiring renal replacement therapy)
Multisystem Manifestations of CKD (Uremia)
- Cardiovascular: Hypertension (due to sodium/fluid retention and RAAS activation), fluid overload, heart failure, and uremic pericarditis.
- Hematologic: Anemia due to decreased renal production of erythropoietin.
- Metabolic/Electrolytes: Hyperkalemia, hyperphosphatemia, hypocalcemia (due to impaired activation of Vitamin D and reciprocal relationship with phosphorus), and metabolic acidosis (impaired hydrogen excretion and bicarbonate reabsorption).
- Musculoskeletal: CKD-Mineral and Bone Disorder (CKD-MBD). Chronic hypocalcemia stimulates the parathyroid glands to release PTH, causing calcium resorption from bones, leading to osteodystrophy and bone pain.
- Neurological: Uremic encephalopathy (confusion, asterixis) due to accumulation of nitrogenous waste.
Nursing Interventions and Patient Education in CKD
- Dietary Adjustments: Educate patients on restricting sodium (to control fluid retention and hypertension), potassium (to prevent arrhythmias), and phosphorus (to prevent bone disease). Limit protein intake in pre-dialysis patients to minimize nitrogenous waste, but increase protein once on dialysis to compensate for protein loss.
- Phosphate Binders: Administer calcium acetate or sevelamer with meals so they bind dietary phosphorus in the gut.
- Anemia Management: Administer recombinant erythropoietin (epoetin alfa) as ordered. Monitor hemoglobin and hematocrit. Crucial clinical point: Monitor blood pressure closely before administration, as epoetin alfa can cause severe hypertension.
Urinary Tract Infections (UTIs)
Urinary Tract Infections are infections of the urinary tract, most commonly caused by Gram-negative bacteria, particularly Escherichia coli.
Classification and Clinical Features
- Lower UTI (Cystitis/Urethritis): Characterized by localized symptoms including dysuria, urinary frequency, urgency, suprapubic pain, and hematuria. In elderly patients, atypical presentations such as acute confusion, agitation, or sudden decline in functional status are common and may occur in the absence of fever or dysuria.
- Upper UTI (Pyelonephritis): An infection of the renal pelvis and parenchyma. Symptoms include high fever, chills, flank pain, costovertebral angle (CVA) tenderness, nausea, vomiting, and systemic leukocytosis. Pyelonephritis carries a high risk of urosepsis.
Diagnostic Testing
- Urinalysis: Typically positive for leukocyte esterase (indicates white blood cells) and nitrites (indicates presence of nitrate-reducing bacteria like E. coli).
- Urine Culture and Sensitivity: The gold standard for identifying the causative organism and appropriate antibiotic therapy. Samples must be obtained via clean-catch midstream or sterile catheterization.
Prevention of Catheter-Associated Urinary Tract Infections (CAUTI)
In the acute care setting, CAUTIs represent a major patient safety concern. Nurses must strictly adhere to insertion and maintenance bundles:
- Insert indwelling catheters only for valid clinical indications (e.g., acute urinary retention, critical hourly output monitoring, open perineal wounds).
- Maintain a closed drainage system.
- Secure the catheter to the patient's thigh to prevent traction and urethral trauma.
- Keep the drainage bag below the level of the bladder at all times to prevent backflow of stagnant urine.
- Perform daily perineal and catheter care using mild soap and water (avoid antiseptic solutions).
- Remove the catheter at the earliest possible time.
A client with acute kidney injury (AKI) is in the oliguric phase. Which of the following electrolyte abnormalities and clinical findings should the nurse expect to monitor for?
A patient with chronic kidney disease (CKD) has a serum potassium level of 6.2 mEq/L. The nurse notes peaked T waves on the electrocardiogram (ECG). Which of the following prescriptions should the nurse prioritize to protect the cardiac membrane?
The nurse is caring for an older adult patient who was admitted with a sudden onset of confusion, agitation, and urinary incontinence. The patient does not have a fever or dysuria. Which action should the nurse take first?