What is the management plan for an elderly male with hyponatremia, elevated BUN, severe chronic kidney disease, and secondary hyperparathyroidism?

Management of Elderly Male with Severe CKD, Hyponatremia, Azotemia, and Secondary Hyperparathyroidism

This patient with CKD G5 (GFR 16) requires urgent dialysis initiation for severe azotemia (BUN 63) and hyponatremia (Na 130), with concurrent management of mild secondary hyperparathyroidism (PTH 74) through phosphate control and vitamin D repletion before considering active vitamin D therapy.

Immediate Priority: Address Severe CKD and Metabolic Derangements

Dialysis Initiation

• Initiate hemodialysis urgently given GFR 16 mL/min/1.73m² (CKD G5) with symptomatic uremia (BUN 63 mg/dL) 1
• For hyponatremia correction during dialysis, use dialysate sodium concentration of 128 mEq/L (lowest permissible) with blood flow rate of 50 mL/min initially, targeting sodium correction of 1 mEq/L/hour to avoid osmotic demyelination syndrome 2
• Increase blood flow to 100 mL/min in subsequent sessions once sodium rises above 115 mEq/L, allowing 2 mEq/L/hour correction 2
• Target total sodium correction of no more than 18 mEq/L over 48 hours 2

Hyponatremia Management

• Do not correct sodium too rapidly - the severe hyponatremia (130 mEq/L) combined with uremia requires controlled dialysis as above 2
• Monitor neurological status closely during correction for signs of osmotic demyelination 2

Secondary Hyperparathyroidism Management (PTH 74 pg/mL)

Initial Assessment and Approach

• PTH of 74 pg/mL is only mildly elevated for CKD G5 - the target range for dialysis patients is 150-300 pg/mL (approximately 2-9 times upper normal limit) 3, 4
• Do NOT target normal PTH levels in this dialysis patient, as PTH <65 pg/mL causes adynamic bone disease with increased fracture risk 4, 5

Stepwise Management Algorithm

Step 1: Control Phosphate First (Measure immediately)

• Measure serum phosphorus and calcium within 1 week of dialysis initiation 3, 6
• Target serum phosphorus 3.5-5.5 mg/dL for CKD G5 4
• Initiate dietary phosphorus restriction to 800-1,000 mg/day while maintaining adequate protein intake of 1.0-1.2 g/kg/day 4
• Add calcium-based phosphate binders (calcium carbonate 1-2 g three times daily with meals) if phosphorus >4.6 mg/dL 3, 4
• Monitor phosphorus monthly after initiating therapy 4

Step 2: Assess Vitamin D Status

• Measure 25-hydroxyvitamin D levels at first encounter 3
• If 25(OH)D <30 ng/mL, supplement with ergocalciferol (vitamin D2) 50,000 IU monthly 3
• Critical: Do NOT use calcitriol or active vitamin D analogs for vitamin D deficiency 3
• Recheck 25(OH)D annually once replete 3

Step 3: Monitor and Reassess PTH

• Recheck PTH in 3 months after optimizing phosphate control and vitamin D repletion 4
• Given current PTH of 74 pg/mL is below target range for dialysis patients, active vitamin D therapy is not indicated at this time 3, 4
• If PTH rises above 300 pg/mL despite above measures, then consider active vitamin D sterols (calcitriol or paricalcitol) 3, 4

Step 4: Active Vitamin D Therapy (Only if PTH >300 pg/mL)

• Do not initiate active vitamin D until serum phosphorus <4.6 mg/dL - this is critical to avoid vascular calcification 4
• Start calcitriol or paricalcitol only after phosphate control achieved 3, 4
• Intermittent intravenous administration is more effective than oral for dialysis patients 4
• Monitor calcium and phosphorus monthly for first 3 months, then every 3 months 4
• If calcium rises above 10.2 mg/dL, discontinue all vitamin D therapy 3

Step 5: Calcimimetics (Only if PTH >300 pg/mL and Refractory)

• Consider cinacalcet 30 mg once daily if PTH remains >300 pg/mL despite optimized vitamin D therapy 6
• Ensure corrected serum calcium is at or above lower limit of normal before starting 6
• Monitor calcium within 1 week of initiation 6
• Titrate every 2-4 weeks through doses of 30,60,90,120,180 mg once daily 6

Critical Pitfalls to Avoid

• Never start active vitamin D (calcitriol/paricalcitol) with uncontrolled hyperphosphatemia - this dramatically worsens vascular calcification and increases calcium-phosphate product 4
• Never target normal PTH levels (<65 pg/mL) in dialysis patients - causes adynamic bone disease 4, 5
• Never correct hyponatremia faster than 1-2 mEq/L/hour during dialysis to prevent osmotic demyelination 2
• Never use calcitriol to treat vitamin D deficiency - use ergocalciferol instead 3

Monitoring Schedule Once Stable

• Serum calcium and phosphorus: monthly initially, then every 1-3 months 3
• PTH: every 3-6 months 3
• 25-hydroxyvitamin D: annually 3
• Alkaline phosphatase: every 3-6 months if PTH elevated 3