Parenteral nutrition (PN) is used in a variety of patients to provide nutrition when the enteral route is unavailable or the patient cannot absorb nutrients. PN can be personalised to an individual’s specific requirements, though in many cases the use of standard composition bags provides adequate nutritional support. Whether individualised or standardised, a bag of PN is an extensive mixture of several dozen compounds that aim to provide nutrients directly into the blood in similar forms to digested dietary components.
Important considerations for determining how much PN is suitable for a patient are the amount of fluid it is acceptable to give the patient and the energy requirements of that patient on a given day.
These questions consider a patient on a hypothetical bag of standard PN with the formula in Table 1, in addition to a range of trace elements and phosphate. Please give all final answers to one decimal place.
Table 1. Hypothetical bag of standard PN
| Volume | Nitrogen | Total kcal | Sodium | Potassium | Calcium | Magnesium |
|---|---|---|---|---|---|---|
| 2000 ml | 16 g | 2000 kcal | 60 mmol | 60 mmol | 5 mmol | 5 mmol |
Protein content of PN is commonly listed as grams of nitrogen in the recipe, with 1 g of nitrogen equaling 6.25 g of protein.
QUESTION 1
If a 60 kg patient on ITU requires 1.3 g/kg/day of protein equivalents (Singer et al, 2019) from the bag of standard PN, what hourly infusion rate should they receive?
In addition to macronutrients that provide calories, PN also contains electrolytes and trace elements. Standard bags are tested for stability prior to being marketed, however, the stability of a bag cannot be guaranteed if other compounds are directly mixed with it. If a patient on a standard bag requires more of a specific component than the bag contains it may be possible to administer this to the patient by running an infusion down a separate line to the PN.
QUESTION 2
If this patient was at a severe deficit of potassium and required a total daily dose of 120 mmol of potassium, at what rate should you run a parallel infusion of 0.3% potassium chloride in 0.9% sodium chloride with the PN to meet their potassium requirements? 0.3% potassium chloride is equivalent to 40 mmol/litre.
QUESTION 3
In catering for the patient’s potassium requirements, what will be the total amount of sodium you administer to the patient in mmol/kg/day (0.9% sodium chloride contains 154 mmol/litre)?
Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clinical Nutrition. 2019;38(1):48-79. 10.1016/j.clnu.2018.08.037