From the Guidelines
The correct answer is (a) 125 g protein/day for a patient receiving 1,800 cal/day in total parenteral nutrition (TPN). For patients on TPN, protein requirements are typically calculated as 15-20% of total caloric needs [ 1 ]. Using the middle of this range (17.5%), a patient receiving 1,800 calories would need approximately 315 calories from protein. Since protein provides 4 calories per gram, this translates to about 79 grams of protein. However, critically ill or metabolically stressed patients often require higher protein intake, typically 1.2-1.5 g/kg/day [ 1 ]. For an average 70 kg adult, this would mean 84-105 g of protein daily. Some guidelines suggest up to 1.5-2.0 g/kg/day for severely stressed patients, which could approach 125 g for a 70 kg individual [ 1 ]. The 125 g protein amount represents an appropriate upper-range protein provision that balances the need for adequate nitrogen for tissue repair while avoiding excessive protein that could lead to azotemia and increased metabolic waste.
Key Considerations
- Protein requirements for TPN patients are generally higher than for non-TPN patients due to increased metabolic stress [ 1 ].
- The ideal protein-to-calorie ratio for TPN is approximately 20% of total calories [ 1 ].
- Excessive protein intake can lead to metabolic complications, including renal stress and azotemia [ 1 ].
- Individual protein requirements may vary depending on factors such as body weight, age, and underlying medical conditions [ 1 ].
Protein Calculation
- 1,800 cal/day x 17.5% (protein percentage) = 315 calories from protein
- 315 calories / 4 calories/g protein = approximately 79 grams of protein
- However, considering the patient's potential metabolic stress and individual requirements, a higher protein intake of 125 g/day may be more appropriate [ 1 ].
From the Research
Protein Requirements for Total Parenteral Nutrition
To determine the protein requirements for a patient receiving 1,800 cal/day in total parenteral nutrition, we need to consider the available evidence.
- The study by 2 evaluated the protein and caloric requirements of patients receiving total parenteral nutrition (TPN) and found that increasing the amino acid concentration from 2.5 to 5% had no effect on the rate at which the body cell mass increased.
- However, the study does not provide a direct answer to the question of protein requirements for a patient receiving 1,800 cal/day in total parenteral nutrition.
- Another study by 3 applied total parenteral nutrition to 14 critically ill patients and administered nitrogen 0.350 +/- 0.004 g kg-1, as 10% crystalline L-aminoacids solution, but does not provide information on the total daily calorie intake.
- A study by 4 used medium-chain triglycerides in injured rats receiving total parenteral nutrition, but does not provide information on human protein requirements.
Calculation of Protein Requirements
- Assuming an average adult weight of 70 kg, the daily nitrogen intake of 0.350 +/- 0.004 g kg-1 would translate to approximately 24.5 g of nitrogen per day.
- Using the fact that 1 g of nitrogen is equivalent to approximately 6.25 g of protein, the daily protein intake would be approximately 153 g per day.
- However, this calculation is based on a single study and may not be generalizable to all patients receiving total parenteral nutrition.
Answer Choices
- Based on the available evidence, the closest answer choice would be (b) 150 g protein/day, but it is essential to note that this is an estimate and may not be accurate for all patients.
- The other answer choices (a) 125 g protein/day, (c) 200 g protein/day, (d) 250 g protein/day, and (e) 300 g protein/day are not supported by the available evidence.