Practice exercise (made-up values, not clinical guidance). A man is 164 cm tall and weighs 85 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.
164 cm85 kgman
%IBW = %
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A child who weighs 15.5 kg receives 12.5% dextrose at 32 mL/h. Find the glucose infusion rate GIR in mg/kg/min. Round to two decimal places.
15.5 kg12.5%32 mL/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 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 120 mL/h. At 18:00, 300 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.
500 mL300 mL infused120 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: %IBW = 140 %
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)
164 cm/2.54 = 64.57 in
IBW = 50 + 2.3·(64.57 − 60) = 60.5 kg
Percentage of ideal body weight
%IBW = 85/60.5·100 = 140.5 ≈ 140%
Answer
%IBW = 140%
2.Enteral & parenteral nutrition calculations
Answer: GIR = 4.3 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 concentration
12.5% = 125 mg/mL
Dextrose per minute
125·32/60 = 66.67 mg/min
Per kilogram
GIR = 66.67/15.5 = 4.301 ≈ 4.3 mg/kg/min
Answer
GIR = 4.3 mg/kg/min
Shortcut: GIR = % dextrose × mL/h/(6 × kg).
3.IV fluids & fluid balance
Answer: B = 20 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: 180 + 120 = 300 mL
IV infusion: 60·12 = 720 mL
IV antibiotic: 2·50 = 100 mL
total intake = 1120 mL
Total output
200 + 475 + 425 = 1100 mL
Balance
B = 1120 − 1100 = 20 mL
Answer
B = 20 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 − 300 = 200 mL
Time
t = 200/120 = 1.667 ≈ 1.7 h
Answer
t = 1.7 h
That is about 1 h 40 min, so the bag runs out at about 19:40.