BCCCP: Phosphate and Trace Electrolyte Management

Question 1 of 10

1. Question

A 58-year-old, 70-kg woman is admitted to the ICU for management of status epilepticus. She is receiving a continuous insulin infusion for hyperglycemia and is on maintenance phenytoin 200 mg IV every 12 hours. Her vital signs are stable. Laboratory studies reveal: serum phosphate 0.4 mg/dL (normal 2.5–4.5 mg/dL), serum albumin 2.0 g/dL (normal 3.5–5.0 g/dL), serum potassium 3.4 mEq/L (normal 3.5–5.0 mEq/L), total phenytoin 9 μg/mL (therapeutic 10–20 μg/mL), and free phenytoin 2.4 μg/mL (therapeutic 1–2 μg/mL). Which of the following initial pharmacotherapy plans is MOST appropriate?

Administer IV potassium phosphate 40 mmol over 2 hours (≈0.6 mmol/kg) and decrease the phenytoin dose by 25% based on the elevated free level.
Administer IV sodium phosphate 20 mmol over 1 hour and increase the phenytoin dose by 25% to reach therapeutic total levels.
Administer IV potassium phosphate 20 mmol over 2 hours and maintain the current phenytoin dose, with serial monitoring of free levels.
Administer IV sodium phosphate 40 mmol over 4 hours and switch anticonvulsant therapy from phenytoin to levetiracetam.

Question 2 of 10

2. Question

A 58-year-old, 65 kg male with a history of severe malnutrition has been receiving total parenteral nutrition (TPN) for 4 days. His TPN prescription includes 30 mmol/day phosphate, 15 mEq/day magnesium, standard trace elements (chromium 10 µg, copper 1 mg, manganese 0.5 mg, selenium 60 µg, zinc 5 mg), and 20 mEq calcium. On day 3, he developed stage 1 acute kidney injury (serum creatinine rose from 0.8 to 1.3 mg/dL). Labs drawn today reveal: corrected serum calcium 7.2 mg/dL (baseline 8.8 mg/dL), potassium 5.1 mEq/L, phosphate 3.2 mg/dL, and magnesium 1.9 mg/dL. Which of the following monitoring parameters should the critical care pharmacist prioritize as MOST critical for detecting an acute toxicity in this patient?

Corrected serum calcium
Serum potassium
Serum phosphate
Serum magnesium

Question 3 of 10

3. Question

A 58-year-old man in the ICU, intubated, hemodynamically unstable on vasopressors, and NPO, is receiving prolonged parenteral nutrition via a central venous catheter. He is diagnosed with severe hypophosphatemia (serum phosphate 0.8 mg/dL). Considering the need for safe, rapid phosphate correction and appropriate trace element supplementation in this critically ill patient, which strategy optimizes efficacy and safety?

Initiate intravenous phosphate via a weight-based, rate-controlled infusion pump through the central venous catheter and include trace elements in the parenteral nutrition admixture delivered through the same central line.
Administer oral phosphate via nasogastric tube for gradual correction and infuse trace elements through a separate peripheral intravenous line.
Give intravenous phosphate as a rapid bolus through the central line and add trace elements to the parenteral nutrition admixture infused via a peripheral intravenous catheter.
Administer intravenous phosphate via a controlled infusion pump through a peripheral intravenous line and inject trace elements intramuscularly.

Question 4 of 10

4. Question

A 62-year-old critically ill male (weight 70 kg) is receiving mechanical ventilation in the ICU. Laboratory studies reveal a serum phosphate of 0.7 mg/dL (normal 2.5–4.5 mg/dL) and a serum potassium of 3.4 mEq/L (normal 3.5–5.0 mEq/L). He has proximal muscle weakness and shallow respirations. Which of the following is the most appropriate initial pharmacologic treatment for his hypophosphatemia?

Oral sodium phosphate solution 16 mmol phosphate three times daily
Intravenous potassium phosphate 15 mmol infused over 3 hours
Intravenous sodium phosphate 30 mmol infused over 6 hours
Sevelamer carbonate 800 mg orally with meals

Question 5 of 10

5. Question

A 68-year-old man (70 kg) with chronic alcohol use disorder and malnutrition is in the ICU with acute respiratory failure. He has been receiving parenteral nutrition at 20 kcal/kg/day for the past 24 hours. Vital signs are: BP 100/60 mmHg, HR 110/min, ventilator rate 16 breaths/min (assist-control mode, FiO2 0.40, PEEP 5 cm H2O), temperature 37 °C. He is tachypneic with shallow respirations. Arterial blood gas shows pH 7.30, PaCO2 55 mmHg, PaO2 60 mmHg. Laboratory values reveal serum phosphate 0.5 mg/dL (2.5–4.5), potassium 3.8 mEq/L, magnesium 1.9 mg/dL, creatinine 1.0 mg/dL. Which of the following is the MOST appropriate immediate management strategy?

Initiate intravenous phosphate replacement (20 mmol over 1 hour with continuous ECG monitoring) and continue mechanical ventilation.
Administer oral phosphate supplementation and recheck serum phosphate in 12 hours.
Increase the rate of parenteral nutrition to 25 kcal/kg/day and monitor daily phosphate levels.
Administer intravenous furosemide for presumed fluid overload and reassess electrolytes.

Question 6 of 10

6. Question

A 62-year-old man with chronic alcoholism and prolonged poor oral intake is admitted to the ICU for sepsis. His recent labs show mild hypophosphatemia (2.4 mg/dL) and borderline low thiamine. He is at high risk for refeeding syndrome. What is the best initial management step to prevent immediate metabolic complications when initiating enteral nutrition?

Administer prophylactic thiamine (200–300 mg IV daily) and phosphate supplementation prior to feeding; begin enteral nutrition at 10–20 kcal/kg/day with gradual caloric advancement.
Fully correct all electrolyte deficits (phosphate, potassium, magnesium) to normal levels before feeding, then advance calories rapidly to goal (25–30 kcal/kg/day).
Start enteral nutrition at 10–20 kcal/kg/day without prophylactic vitamin or electrolyte supplementation, monitoring electrolytes during advancement.
Administer prophylactic thiamine before feeding and initiate enteral nutrition at 5 kcal/kg/day, but defer phosphate supplementation until serum phosphate falls below 2 mg/dL.

Question 7 of 10

7. Question

A 65-year-old man with acute kidney injury is receiving continuous renal replacement therapy (CRRT) in the intensive care unit. During treatment, he develops severe hyperkalemia with a serum potassium level of 7.2 mEq/L. His ECG shows peaked T waves and a widened QRS complex. The hyperkalemia is suspected to be iatrogenic due to potassium-containing intravenous fluids administered during CRRT. Considering his current clinical status and laboratory findings, which of the following interventions should be prioritized FIRST to manage this complication?

Administer intravenous calcium gluconate.
Initiate regular insulin with dextrose infusion.
Discontinue potassium-containing infusions and adjust the CRRT dialysate potassium concentration to zero.
Administer nebulized albuterol (beta-2 agonist).

Question 8 of 10

8. Question

A 72-year-old female with advanced metastatic colon cancer and severe cachexia is admitted to the ICU on assist-control ventilation and low-dose norepinephrine for distributive shock. She has been NPO for 7 days due to intractable nausea and vomiting and presents with severe hypophosphatemia (0.8 mg/dL), hypokalemia, and hypomagnesemia. The ICU team is considering aggressive intravenous phosphate repletion and initiation of total parenteral nutrition (TPN). The family has not yet discussed the patient’s prognosis or goals of care. As the critical care pharmacist, what should you prioritize as the MOST crucial next step in her management?

Begin cautious intravenous phosphate repletion using a standardized protocol, with dose adjustments based on serial serum phosphate measurements.
Initiate a multidisciplinary discussion with the ICU team and the patient’s family to clarify prognosis and establish goals of care before starting aggressive electrolyte repletion or TPN.
Coordinate with the nutrition support team to initiate a hypocaloric (10 kcal/kg/day) TPN regimen with close electrolyte monitoring to reduce refeeding risk.
Recommend an early palliative care consultation to assist with advance care planning and symptom management.

Question 9 of 10

9. Question

A 58-year-old male patient in the intensive care unit is recovering from severe sepsis complicated by profound hypophosphatemia (initial serum phosphate 1.0 mg/dL). He has been receiving intravenous sodium phosphate at 0.32 mmol/kg every 6 hours for the past 72 hours. His serum phosphate has improved to 2.8 mg/dL (normal range 2.5–4.5 mg/dL), his vital signs are stable, and there are no signs of ongoing phosphate losses. Given this clinical improvement and laboratory trend, what is the MOST appropriate next step in managing his intravenous phosphate therapy?

Reduce the intravenous phosphate dose by 50% (to 0.16 mmol/kg every 6 hours) and recheck serum phosphate in 6 hours.
Reduce the intravenous phosphate dose by 25% (to 0.24 mmol/kg every 6 hours) and recheck serum phosphate in 8 hours.
Continue the current intravenous phosphate dose (0.32 mmol/kg every 6 hours) until serum phosphate remains normal for 24 hours, then begin tapering.
Transition to oral phosphate supplementation at 1,000 mg daily and recheck serum phosphate in 24 hours.

Question 10 of 10

10. Question

A 65-year-old, 60-kg man with alcoholic cirrhosis (BMI 18.5) is in the ICU for sepsis. He is now hemodynamically stable off vasopressors and tolerating nasogastric tube feeds of a standard polymeric formula at 20 mL/hour (80 kcal/hour), with a planned advancement of feeds by 10 mL/hour every 8 hours as tolerated. He has received thiamine 200 mg IV daily since admission and has been on stable IV phosphate replacement at 60 mmol/day plus IV trace elements. Current labs show serum phosphate 1.9 mg/dL, magnesium 1.5 mg/dL, and potassium 3.6 mEq/L. Given his high risk for refeeding syndrome, which of the following is the MOST appropriate plan for transitioning him from IV to enteral phosphate and trace element supplementation?

Gradually taper IV phosphate over 48–72 hours while initiating low-dose enteral phosphate modules (15 mmol/day) and trace element capsules concurrently, advancing doses as enteral feeds increase by 10 mL/hour every 8 hours, with daily electrolyte monitoring and continuation of thiamine 200 mg IV daily (ASPEN Grade A Recommendation).
Stop all IV phosphate and trace elements immediately and advance enteral feeds to goal rate (80 mL/hour) within 12 hours to meet full phosphate and trace element requirements enterally.
Continue IV phosphate and trace element supplementation at current doses until enteral feeds reach 40 mL/hour (160 kcal/hour), then convert abruptly to full-dose enteral phosphate and trace elements without taper.
Maintain IV phosphate at current rate and start enteral trace elements at low dose, delaying initiation of enteral phosphate modules until serum phosphate exceeds 2.5 mg/dL.

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