NAPLEX Question of the Week: The Totality of TPN

This week's question will test your TPN skills!
NAPLEX Question of the Week: The Totality of TPN

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SW is a 71-year-old woman who is in the ICU for sepsis with continued small bowel ischemia. This is day 8 of treatment while slowly being weaned off of Levophed. She currently has CRRT. The ICU physician approaches you about starting total parenteral nutrition (TPN) since she has had inadequate nutrition since admission. You take a look at SW’s chart.

PMH: HTN, Nursing home resident, CKD


Ht: 5’4 ft

Wt: 152 lbs

BP: 85/59 mmHg

Temp: 96.9 F

Glucose: 89 mg/dL

Scr: 3.2 mg/dL

Na: 145 mEq/L

Cl: 98 mEq/L

K: 4.0 mEq/L

Ca: 8.9 mg/dL

Mg: 1.8 mg/dL

Phosphorus: 3 mg/dL

Prealbumin: 8 mg/dL

Albumin: 2.7 g/dL


Medication List:

Levophed 0.1 mcg/kg/min IV

Normal Saline/D5W 1700 mL Q24h IV

Mitigo 1 mg IV q4-6h PRN

Vancomycin 1500 mg IV q12h

Piperacillin/tazobactam 4.5gm IV q6h

What are potential considerations for TPN for SW?

A. Starting SW on enteral nutrition over parenteral nutrition would be preferred.

B. Starting SW on TPN could put her at risk for refeeding syndrome, manifesting with hypokalemia and hypophosphatemia. 

C. When calculating requirements for TPN, 3.4 kcal/gm should be used for determining protein calorie requirements.

D. Basal insulin would be preferred to be administered within the TPN since it is generally administered continuously over 24 hours. 

Answer with Rationale

Total parenteral nutrition is a very important concept of critically ill patients. Having a general concept of assessing nutrition through lab levels and contraindications to certain types of nutrition is important in assessing the necessity of nutrition. Pharmacists at many institutions are relied upon heavily to either lead or contribute significantly to the development and compounding of TPNs. There are a number of important principles to discuss regarding TPNs. In addition, students taking the exam should be familiar with core calculation concepts that are needed to make a TPN. 

A. Incorrect. While the mantra "if the gut works, use it" is true, SW would be contraindicated for enteral nutrition because of her unresolved small bowel ischemia.

B. Correct. Refeeding syndrome is a significant concern for SW, especially considering the duration of reduced nutrition. Refeeding syndrome typically manifests with hypokalemia and hypophosphatemia due to consumption of these electrolytes as energy processes increase due to available nutrients. In some patients, the first day of TPN may be administered with half the normal calories on day 1 to try and decrease the risk. 

C. Incorrect. This would be the calculation factor for dextrose, not protein. Protein is 4 kcal/gm. 

D. Incorrect. While insulin is sometimes used within TPN, it should be regular insulin as this is the only one that is compatible within the compounded admixture. Basal insulin if used could only be used subcutaneously outside of the TPN. Insulin management can also occur "outside" of the TPN using either subcutaneous administration (standard insulin products) or a continuous infusion (regular insulin). 

Generic/Brand: Norepinephrine (Levophed), Normal Saline/D5W, Morphine (Mitigo), Vancomycin (Vancocin), Piperacillin/tazobactam (Zosyn)

Naplex Core Competencies Covered:

1.2 From laboratory findings

1.2 From medical records: chief complaint, medication history, medical history

1.5 Signs or symptoms of medical conditions

1.6 Risk factors of health and wellness

3.2 Therapeutic goals

3.5 Drug route of administration

3.6 Drug contraindications

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