Practice exercise (made-up values, not clinical guidance). A 51 kg patient has a fluid goal of 35 mL/kg/day and receives all fluid through a feeding tube. The formula is 76% free water and runs at 65 mL/h for 20 hours a day. The rest of the fluid is given as water flushes every 6 hours. What volume V is each flush? Round to the nearest whole number.
51 kg35 mL/kg/day76%65 mL/h · 20 hevery 6 h
V = mL
2.Enteral & parenteral nutrition calculationsHard
Practice exercise (made-up values, not clinical guidance). A critically ill woman is 164 cm tall and weighs 92 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 patient weighs 95 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 infusion starts at 13:00 at 75 mL/h. After 4 hours the rate is changed to 50 mL/h and is not changed again. How many hours t after the start will the bag be empty? Round to one decimal place.
500 mL75 mL/h · 4 h50 mL/h
t = h
3Solutions
1.Enteral & parenteral nutrition calculations
Answer: V = 199 mL
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.
Fluid goal
35·51 = 1785 mL/day
Free water from the formula
65·20 = 1300 mL
1300·0.76 = 988 mL
Water still needed
1785 − 988 = 797 mL/day
Volume per flush
24/6 = 4 flushes
V = 797/4 = 199.3 ≈ 199 mL
Answer
V = 199 mL
2.Enteral & parenteral nutrition calculations
Answer: P = 112 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 = 92/1.64² = 34.21 kg/m²
Ideal body weight (Devine)
164 cm/2.54 = 64.57 in
IBW = 45.5 + 2.3·(64.57 − 60) = 56 kg
Protein goal
BMI 30 to under 40: 2 g per kg of ideal body weight.
P = 2·56 = 112 g/day
Answer
P = 112 g/day
3.IV fluids & fluid balance
Answer: U = 0.83 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
150 + 300 + 500 = 950 mL
Per kilogram per hour
U = 950/(95·12) = 0.8333 ≈ 0.83 mL/kg/h
Answer
U = 0.83 mL/kg/h
4.IV fluids & fluid balance
Answer: t = 8 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.
First part
75·4 = 300 mL
500 − 300 = 200 mL left
Second part
200/50 = 4 h
Total time
t = 4 + 4 = 8 h
Answer
t = 8 h
That is about 8 h 00 min, so the bag runs out at about 21:00.