QUESTION 1
If a 60 kg patient on ITU requires 1.3 g/kg/day of protein equivalents from the bag of standard PN, what hourly infusion rate should they receive?
- 1.3 g/kg/day of protein x 60kg = 78g of protein
- Patient needs 78 g protein / 6.25 = 12.48 g of nitrogen per day
- 16 g of nitrogen in 2000 ml = 0.008 g/ml of nitrogen in PN
- 12.48 g per day needed / 0.008 g/ml = 1560 ml per day
- 1560 ml per day / 24 hours = 65 ml/hour.
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.
- PN will be running at 1560 ml/day
- PN has 60 mmol potassium in 2000 ml 60/2000 = 0.03 mmol/ml
- 0.03 mmol/ml x 1560 ml = 46.8 mmol potassium per day
- Total daily need is 120 mmol potassium per day
- 120 mmol – 46.8 mmol = 73.2 mmol from the parallel infusion (0.3% potassium chloride in 0.9% sodium chloride)
- 0.3% potassium chloride in 0.9% sodium chloride is 40 mmol/1000 ml = 0.04 mmol/ml
- 73.2 mmol / 0.04 mmol/ml = 1830 ml of 0.3% potassium chloride in 0.9% sodium chloride needed
- 1830 ml / 24 hours = 76.3 ml/hour of 0.3% potassium chloride in 0.9% sodium chloride needs to be run in addition to PN at the prescribed rate in order to deliver the correct daily dose of potassium.
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)?
- 0.9% sodium chloride contains 154 mmol/litre sodium
- 1830 ml = 1.830 litres
- 154 mmol /litre x 1.830 litres = 281.82 mmol / day from the parallel infusion
- PN contains 60 mmol / 2000 ml = 0.03 mmol/ml
- 0.03 mmol/ml x 1560 ml = 46.8 mmol/day from PN
- Total sodium = 281.82 + 46.8 = 328.62 mmol/day
- 328.62 mmol / 60 kg = 5.5 mmol/kg/day.