Practice exercise (made-up values, not clinical guidance). Use the Devine formula to find the ideal body weight IBW of a woman who is 154 cm tall (1 in = 2.54 cm). Round to one decimal place.
154 cmwoman1 in = 2.54 cm
IBW = kg
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A critically ill man is 181 cm tall and weighs 153 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 50 mL/h. At 16:00, 50 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
500 mL50 mL infused50 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: IBW = 46.9 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
154 cm/2.54 = 60.63 in
Ideal body weight (Devine)
IBW = 45.5 + 2.3·(60.63 − 60) = 46.95 ≈ 46.9 kg
Answer
IBW = 46.9 kg
2.Enteral & parenteral nutrition calculations
Answer: P = 190 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 = 153/1.81² = 46.7 kg/m²
Ideal body weight (Devine)
181 cm/2.54 = 71.26 in
IBW = 50 + 2.3·(71.26 − 60) = 75.9 kg
Protein goal
BMI 40 or more: 2.5 g per kg of ideal body weight.
P = 2.5·75.9 = 189.7 ≈ 190 g/day
Answer
P = 190 g/day
3.IV fluids & fluid balance
Answer: B = 1125 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: 200 + 250 = 450 mL
IV infusion: 125·12 = 1500 mL
IV antibiotic: 1·50 = 50 mL
total intake = 2000 mL
Total output
325 + 300 + 150 + 100 = 875 mL
Balance
B = 2000 − 875 = 1125 mL
Answer
B = 1125 mL
Positive: more fluid went in than came out.
4.IV fluids & fluid balance
Answer: t = 9 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 − 50 = 450 mL
Time
t = 450/50 = 9 h
Answer
t = 9 h
That is about 9 h 00 min, so the bag runs out at about 01:00.