Practice exercise (made-up values, not clinical guidance). A man is 167 cm tall and weighs 88 kg. Find the actual weight as a percentage of the ideal body weight, %IBW, using the Devine formula (1 in = 2.54 cm). Round to the nearest whole number.
167 cm88 kgman
%IBW = %
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A critically ill man is 183 cm tall and weighs 115 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 500 mL bag runs by pump at 150 mL/h. At 07:30, 250 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
500 mL250 mL infused150 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: %IBW = 139 %
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.
Ideal body weight (Devine)
167 cm/2.54 = 65.75 in
IBW = 50 + 2.3·(65.75 − 60) = 63.22 kg
Percentage of ideal body weight
%IBW = 88/63.22·100 = 139.2 ≈ 139%
Answer
%IBW = 139%
2.Enteral & parenteral nutrition calculations
Answer: P = 155 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 = 115/1.83² = 34.34 kg/m²
Ideal body weight (Devine)
183 cm/2.54 = 72.05 in
IBW = 50 + 2.3·(72.05 − 60) = 77.71 kg
Protein goal
BMI 30 to under 40: 2 g per kg of ideal body weight.
P = 2·77.71 = 155.4 ≈ 155 g/day
Answer
P = 155 g/day
3.IV fluids & fluid balance
Answer: B = 640 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: 150 + 240 = 390 mL
ice chips: 200/2 = 100 mL
IV infusion: 125·8 = 1000 mL
IV antibiotic: 2·50 = 100 mL
total intake = 1590 mL
Total output
425 + 175 + 350 = 950 mL
Balance
B = 1590 − 950 = 640 mL
Answer
B = 640 mL
Positive: more fluid went in than came out.
4.IV fluids & fluid balance
Answer: t = 1.7 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
500 − 250 = 250 mL
Time
t = 250/150 = 1.667 ≈ 1.7 h
Answer
t = 1.7 h
That is about 1 h 40 min, so the bag runs out at about 09:10.