Practice exercise (made-up values, not clinical guidance). Use the Devine formula to find the ideal body weight IBW of a man who is 175 cm tall (1 in = 2.54 cm). Round to one decimal place.
175 cmman1 in = 2.54 cm
IBW = kg
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A critically ill man is 185 cm tall and weighs 173 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 12-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).
Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 150 mL/h. At 19:30, 200 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
500 mL200 mL infused150 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: IBW = 70.5 kg
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.
Height in inches
175 cm/2.54 = 68.9 in
Ideal body weight (Devine)
IBW = 50 + 2.3·(68.9 − 60) = 70.46 ≈ 70.5 kg
Answer
IBW = 70.5 kg
2.Enteral & parenteral nutrition calculations
Answer: P = 199 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 = 173/1.85² = 50.55 kg/m²
Ideal body weight (Devine)
185 cm/2.54 = 72.83 in
IBW = 50 + 2.3·(72.83 − 60) = 79.52 kg
Protein goal
BMI 40 or more: 2.5 g per kg of ideal body weight.
P = 2.5·79.52 = 198.8 ≈ 199 g/day
Answer
P = 199 g/day
3.IV fluids & fluid balance
Answer: B = −335 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: 100 + 120 = 220 mL
IV infusion: 60·12 = 720 mL
IV antibiotic: 2·50 = 100 mL
total intake = 1040 mL
Total output
175 + 150 + 500 + 350 + 200 = 1375 mL
Balance
B = 1040 − 1375 = −335 mL
Answer
B = −335 mL
Negative: the patient lost more fluid than went in.
4.IV fluids & fluid balance
Answer: t = 2 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
500 − 200 = 300 mL
Time
t = 300/150 = 2 h
Answer
t = 2 h
That is about 2 h 00 min, so the bag runs out at about 21:30.