Practice exercise (made-up values, not clinical guidance). A man is 168 cm tall and weighs 100 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.
168 cm100 kgman
%IBW = %
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A 73 kg adult receives 1500 mL of parenteral nutrition containing 12.5% dextrose, infused over 24 hours. Find the glucose infusion rate GIR in mg/kg/min. Round to two decimal places.
73 kg1500 mLdextrose 12.5%24 h
GIR = mg/kg/min
3.IV fluids & fluid balanceMedium
Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 12-hour shift. The patient weighs 45 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.
Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 60 mL/h. At 08:30, 50 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
500 mL50 mL infused60 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: %IBW = 156 %
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)
168 cm/2.54 = 66.14 in
IBW = 50 + 2.3·(66.14 − 60) = 64.13 kg
Percentage of ideal body weight
%IBW = 100/64.13·100 = 155.9 ≈ 156%
Answer
%IBW = 156%
2.Enteral & parenteral nutrition calculations
Answer: GIR = 1.78 mg/kg/min
Parenteral nutrition: dextrose provides 3.4 kcal/g, amino acids 4 kcal/g and lipid emulsion the kcal/mL stated (2 kcal/mL for 20%, 1.1 kcal/mL for 10%). Grams = % × mL/100. Non-protein kcal (NPC) = dextrose + lipid kcal; nitrogen = protein/6.25. The glucose infusion rate (GIR) in mg/kg/min = dextrose mg/(kg × minutes). The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Dextrose in the bag
12.5·1500/100 = 187.5 g = 187 500 mg
Minutes of infusion
24·60 = 1440 min
Glucose infusion rate
GIR = 187 500/(73·1440) = 1.784 ≈ 1.78 mg/kg/min
Answer
GIR = 1.78 mg/kg/min
3.IV fluids & fluid balance
Answer: U = 2.41 mL/kg/h
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 urine
300 + 200 + 400 + 400 = 1300 mL
Per kilogram per hour
U = 1300/(45·12) = 2.407 ≈ 2.41 mL/kg/h
Answer
U = 2.41 mL/kg/h
4.IV fluids & fluid balance
Answer: t = 7.5 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 = 450/60 = 7.5 h
Answer
t = 7.5 h
That is about 7 h 30 min, so the bag runs out at about 16:00.