What is the management for a 77-year-old male with impaired renal function, as indicated by elevated BUN, sodium, and creatinine levels, and a low eGFR?

Acute-on-Chronic Kidney Disease with Severe Hypernatremia and Hyperchloremia

This 77-year-old male has Stage 3b-4 chronic kidney disease (eGFR 31) with acute kidney injury superimposed, complicated by severe hypernatremic hyperchloremic dehydration (sodium 150, chloride 110) and pre-renal azotemia (BUN 35, creatinine 2.17, BUN:Cr ratio ~16:1), requiring immediate fluid resuscitation and urgent nephrology consultation. 1

Immediate Management Priorities

Assess Volume Status and Etiology

• Examine for signs of dehydration: dry mucous membranes, decreased skin turgor, orthostatic hypotension, tachycardia, and oliguria—these findings confirm hypovolemic hypernatremia requiring aggressive fluid replacement 2
• Review all medications immediately for nephrotoxins (NSAIDs, ACE inhibitors/ARBs, diuretics, aminoglycosides) and renally-dosed medications requiring adjustment at eGFR 31 3
• Obtain urinalysis with microscopy to differentiate pre-renal azotemia from intrinsic kidney disease, looking specifically for proteinuria, hematuria, or casts 4, 5
• Calculate fractional excretion of sodium (FENa) if not on diuretics—FENa <1% confirms pre-renal etiology, while >2% suggests acute tubular necrosis 3

Fluid Resuscitation Strategy

• Administer isotonic saline (0.9% NaCl) initially to restore intravascular volume and renal perfusion, as the hypernatremia with hyperchloremia suggests free water deficit from dehydration rather than sodium excess 2
• Correct sodium slowly at 0.5 mEq/L per hour (maximum 10-12 mEq/L per 24 hours) to avoid osmotic demyelination syndrome, particularly critical in elderly patients 4
• Monitor serum sodium, chloride, and creatinine every 4-6 hours during initial resuscitation to guide fluid therapy adjustments 2
• Transition to hypotonic fluids (0.45% saline or D5W) once hemodynamically stable and sodium begins declining, calculating free water deficit: 0.6 × body weight (kg) × [(serum Na/140) - 1] 4

Electrolyte and Metabolic Monitoring

• Check serum potassium, bicarbonate, calcium, phosphate, and magnesium immediately as electrolyte depletion commonly occurs with diuretic use and dehydration, particularly hypokalemia and hypochloremic alkalosis 2
• Assess for metabolic acidosis or alkalosis with arterial blood gas or venous CO2—metabolic alkalosis with hypochloremia suggests loop diuretic overuse, while acidosis at this eGFR suggests CKD progression 4, 3
• Monitor for hyperkalemia risk given eGFR 31, especially if ACE inhibitors or ARBs are being used—potassium >5.5 mEq/L requires immediate treatment 4

Nephrology Referral Criteria

Urgent Consultation Indicated

• Refer immediately to nephrology as eGFR 31 mL/min/1.73 m² represents Stage 3b-4 CKD, meeting criteria for specialist evaluation per KDIGO guidelines 1, 3
• The combination of elevated creatinine (2.17), low eGFR (31), and elevated BUN (35) with severe electrolyte abnormalities warrants urgent nephrology assessment to determine if this represents acute-on-chronic kidney disease requiring intervention 1
• Patients with eGFR <30 mL/min/1.73 m² have >10-20% annual risk of progression to end-stage renal disease, necessitating timely referral for dialysis access planning and transplant evaluation 1, 3

Diagnostic Workup Before Referral

• Obtain spot urine albumin-to-creatinine ratio (ACR) to assess for albuminuria—ACR >30 mg/g indicates kidney damage and increases cardiovascular risk 4
• Perform renal ultrasound to evaluate kidney size, echogenicity, and rule out obstruction (particularly important in elderly males with potential prostatic hypertrophy) 4, 5
• Send serologic studies if indicated: ANA, ANCA, complement levels, serum protein electrophoresis, and hepatitis serologies if history suggests glomerulonephritis or systemic disease 5

Medication Management

Nephrotoxin Avoidance

• Discontinue NSAIDs immediately if being used, as they reduce renal perfusion through prostaglandin inhibition and can precipitate acute kidney injury in CKD patients 3
• Hold ACE inhibitors/ARBs temporarily during acute illness and volume depletion, as they can cause acute deterioration in renal function and hyperkalemia, particularly when combined with diuretics 2
• Avoid radiocontrast agents unless absolutely necessary—if required, ensure adequate hydration and consider N-acetylcysteine prophylaxis, as patients with eGFR <30 are at high risk for contrast-induced nephropathy 2

Diuretic Management

• If patient is on loop diuretics (furosemide, torsemide), hold temporarily during acute dehydration phase until volume status restored, as continued diuresis will worsen hypernatremia and azotemia 2
• Reversible elevations of BUN occur with dehydration and should be avoided, particularly in patients with baseline renal insufficiency—BUN:creatinine ratio >20:1 suggests pre-renal component 2
• Monitor for signs of fluid/electrolyte imbalance when restarting diuretics: hyponatremia, hypochloremic alkalosis, hypokalemia, hypomagnesemia, hypocalcemia, manifesting as weakness, lethargy, muscle cramps, or arrhythmias 2

Medication Dose Adjustments

• Adjust all renally-cleared medications for eGFR 31, including antibiotics (fluoroquinolones, aminoglycosides, vancomycin), antivirals (acyclovir), and oral hypoglycemics (metformin contraindicated at eGFR <30) 3
• Avoid metformin as eGFR 31 approaches the contraindication threshold of <30 mL/min/1.73 m² due to lactic acidosis risk 4

Chronic Kidney Disease Management

Blood Pressure Control

• Target blood pressure <130/80 mmHg in CKD patients to slow progression, using ACE inhibitors or ARBs as first-line agents once volume status normalized and hyperkalemia excluded 4
• ACE inhibitors or ARBs are indicated if albuminuria present (ACR ≥30 mg/g), as they delay progression to macroalbuminuria and end-stage renal disease in both diabetic and non-diabetic CKD 4
• Monitor serum creatinine and potassium 1-2 weeks after initiating or titrating ACE inhibitors/ARBs—accept up to 30% increase in creatinine if stable, but discontinue if creatinine rises >30% or potassium >5.5 mEq/L 4

Cardiovascular Risk Reduction

• Initiate statin therapy as CKD itself is an independent cardiovascular risk factor—patients with eGFR <60 have 16% increased CVD mortality, and this patient's eGFR 31 confers even higher risk 4, 3
• Assess for diabetes and optimize glycemic control if present, targeting HbA1c <7-8% to prevent microvascular complications while avoiding hypoglycemia 4

Monitoring Schedule

• Check serum creatinine, eGFR, and electrolytes every 3-6 months at baseline eGFR 31, with more frequent monitoring (monthly) if rapid progression suspected or after medication changes 4, 3
• Assess for CKD complications: anemia (hemoglobin, iron studies), bone mineral disease (calcium, phosphate, PTH, vitamin D), and metabolic acidosis (serum bicarbonate) 3
• Screen for albuminuria annually with spot urine ACR to monitor disease progression and cardiovascular risk 4

Common Pitfalls to Avoid

• Do not attribute elevated creatinine solely to age—while GFR declines 1-2 mL/min/year after age 60, creatinine 2.17 with eGFR 31 represents significant kidney disease requiring evaluation 4
• Do not delay nephrology referral for "optimization"—eGFR 31 already meets criteria for specialist consultation, and acute deterioration with severe electrolyte abnormalities requires urgent assessment 1
• Do not overcorrect hypernatremia rapidly—correction >12 mEq/L per 24 hours risks osmotic demyelination syndrome, particularly in elderly patients and those with chronic hypernatremia 4
• Do not continue nephrotoxic medications during acute kidney injury—NSAIDs, aminoglycosides, and contrast agents can precipitate irreversible kidney damage in vulnerable patients 2, 3
• Do not assume stability—BUN 35 with creatinine 2.17 and severe hypernatremia indicate acute decompensation requiring immediate intervention, not outpatient management 1