Practice exercise (made-up values, not clinical guidance). A 70 kg patient needs 1.2 g of protein per kg a day. The tube feed contains 40 g of protein per litre and runs at 45 mL/h for 18 hours a day. How many grams of extra protein ΔP a day are still needed? Round to one decimal place.
70 kg1.2 g/kg/day40 g/L45 mL/h · 18 h
ΔP = g/day
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A critically ill man is 166 cm tall and weighs 120 kg. The practice protocol gives 2 g of protein per kg of ideal body weight (Devine) per day if the BMI is 30 to under 40 kg/m², and 2.5 g/kg of ideal body weight per day if the BMI is 40 kg/m² or more. Find the protein goal P in g/day. Round to the nearest whole number.
Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-hour shift. The IV infusion ran at the rate shown for the whole shift. Find the fluid balance B = intake − output in mL (a negative answer means a net loss). Count ice chips as half their volume.
Practice exercise (made-up values, not clinical guidance). A 1000 mL bag runs by pump at 150 mL/h. At 19:30, 450 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
1000 mL450 mL infused150 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: ΔP = 51.6 g/day
Needs and free water: energy needs are often estimated as kcal/kg/day × weight and protein needs as g/kg/day × weight. A formula is only partly water, so its free water = volume × water fraction; water flushes make up the rest of the daily fluid goal. Ideal body weight (Devine): IBW = 50 kg + 2.3 kg for every inch over 5 feet (60 in) for men, and 45.5 kg + 2.3 kg per inch over 60 in for women; 1 in = 2.54 cm. The formula is meant for adults at least 152.4 cm (5 ft) tall. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Protein needed
1.2·70 = 84 g/day
Protein from the feed
45·18 = 810 mL = 0.81 L
0.81·40 = 32.4 g/day
Shortfall
ΔP = 84 − 32.4 = 51.6 g/day
Answer
ΔP = 51.6 g/day
2.Enteral & parenteral nutrition calculations
Answer: P = 156 g/day
Ideal body weight (Devine): IBW = 50 kg + 2.3 kg for every inch over 5 feet (60 in) for men, and 45.5 kg + 2.3 kg per inch over 60 in for women; 1 in = 2.54 cm. The formula is meant for adults at least 152.4 cm (5 ft) tall. Obesity in critical illness (ASPEN/SCCM 2016): BMI = weight/height² (kg/m²). The protein goal is 2 g/kg of ideal body weight per day for BMI 30–40 and up to 2.5 g/kg of ideal body weight per day for BMI 40 and above. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Body mass index
BMI = 120/1.66² = 43.55 kg/m²
Ideal body weight (Devine)
166 cm/2.54 = 65.35 in
IBW = 50 + 2.3·(65.35 − 60) = 62.31 kg
Protein goal
BMI 40 or more: 2.5 g per kg of ideal body weight.
P = 2.5·62.31 = 155.8 ≈ 156 g/day
Answer
P = 156 g/day
3.IV fluids & fluid balance
Answer: B = 225 mL
Intake and output: intake counts everything that goes in (oral fluids, IV infusions, IV medications and flushes, tube feeds); ice chips count as half their volume. Output counts urine, drains, vomit and other losses. Balance = total intake − total output; a negative balance is a net loss. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Total intake
oral: 120 + 200 + 150 = 470 mL
ice chips: 100/2 = 50 mL
IV infusion: 125·8 = 1000 mL
IV antibiotic: 2·100 = 200 mL
total intake = 1720 mL
Total output
250 + 475 + 450 + 250 + 70 = 1495 mL
Balance
B = 1720 − 1495 = 225 mL
Answer
B = 225 mL
Positive: more fluid went in than came out.
4.IV fluids & fluid balance
Answer: t = 3.7 h
Infusion time: time (h) = volume to infuse (mL)/rate (mL/h); use the volume still left in the bag, not the bag size. Volume infused = rate × time. Convert decimal hours to hours and minutes with the fraction × 60 (0.5 h = 30 min, not 50 min). The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Volume left
1000 − 450 = 550 mL
Time
t = 550/150 = 3.667 ≈ 3.7 h
Answer
t = 3.7 h
That is about 3 h 40 min, so the bag runs out at about 23:10.