Clinical Nutrition: cram pack

Formula sheets, the key method steps for every topic and 4 practice problems, with full solutions at the back.

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1Formulas and methods

Enteral & parenteral nutrition calculations

Daily volume: mL = kcal / (kcal/mL)
Continuous feed: mL/h = daily volume / hours of feeding
Bolus feed: mL per feed = daily volume / number of feeds
Energy and protein delivered: kcal = mL × kcal/mL; g = L × g/L
Free water: mL = formula volume × water fraction
Ideal body weight (Devine): men 50 + 2.3 × (in − 60); women 45.5 + 2.3 × (in − 60); 1 in = 2.54 cm
Body mass index: BMI = kg/m²
Parenteral nutrition: dextrose 3.4 kcal/g, amino acids 4 kcal/g, lipid 20% 2.0 kcal/mL, 10% 1.1 kcal/mL
Nitrogen: g N = g protein / 6.25
Glucose infusion rate: GIR = mg/(kg·min) = % × mL/h / (6 × kg)

Method

Write down what is asked: a pump rate, a volume, kilocalories, grams of protein or water.
Turn energy into volume with mL = kcal/(kcal/mL), and volume into protein with litres × g/L.
Divide by the hours the feed actually runs for a rate, or by the number of feeds for a bolus.
For needs, multiply kcal/kg or g/kg by the weight the rule names; find the ideal body weight with Devine: 50 or 45.5 + 2.3 × (inches − 60).
For PN, find grams as % × mL/100, then use 3.4 kcal/g for dextrose, 4 kcal/g for amino acids and the stated kcal/mL for lipid.

IV fluids & fluid balance

Holliday–Segar per hour: 4 mL/kg (first 10 kg) + 2 mL/kg (next 10 kg) + 1 mL/kg (each kg above 20)
Holliday–Segar per day: 100 / 50 / 20 mL/kg for the same bands
Fluid balance: intake − output
Ice chips: count as half their volume
Urine output: mL/kg/h = mL / (kg × h)
Infusion time: time (h) = volume left (mL) / rate (mL/h)
Volume infused: mL = rate × time

2Practice problems

1.Enteral & parenteral nutrition calculationsMedium

Practice exercise (made-up values, not clinical guidance). Use the Devine formula to find the ideal body weight IBW of a man who is 174 cm tall (1 in = 2.54 cm). Round to one decimal place.

174 cmman1 in = 2.54 cm

IBW = kg

2.Enteral & parenteral nutrition calculationsHard

Practice exercise (made-up values, not clinical guidance). A child who weighs 7.5 kg receives 7.5% dextrose at 24 mL/h. Find the glucose infusion rate GIR in mg/kg/min. Round to two decimal places.

7.5 kg7.5%24 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 8-hour shift. The IV infusion ran at the rate shown for the whole shift. Find the total intake I in mL. Count ice chips as half their volume.

juice: 100 mLtea: 150 mLmilk: 240 mLice chips: 120 mLIV infusion: 60 mL/h × 8 hIV antibiotic: 1 × 50 mL

I = mL

4.IV fluids & fluid balanceHard

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 60 mL/h. At 14:30, 100 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL100 mL infused60 mL/h

t = h

3Solutions

1.Enteral & parenteral nutrition calculations

Answer: IBW = 69.6 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

174 cm/2.54 = 68.5 in

Ideal body weight (Devine)

IBW = 50 + 2.3·(68.5 − 60) = 69.56 ≈ 69.6 kg

Answer

IBW = 69.6 kg

2.Enteral & parenteral nutrition calculations

Answer: GIR = 4 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

7.5% = 75 mg/mL

Dextrose per minute

75·24/60 = 30 mg/min

Per kilogram

GIR = 30/7.5 = 4 mg/kg/min

Answer

GIR = 4 mg/kg/min

Shortcut: GIR = % dextrose × mL/h/(6 × kg).

3.IV fluids & fluid balance

Answer: I = 1080 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.

Add the intake

oral: 100 + 150 + 240 = 490 mL

ice chips: 120/2 = 60 mL

IV infusion: 60·8 = 480 mL

IV antibiotic: 1·50 = 50 mL

I = 1080 mL

Answer

I = 1080 mL

4.IV fluids & fluid balance

Answer: t = 6.7 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 − 100 = 400 mL

Time

t = 400/60 = 6.667 ≈ 6.7 h

Answer

t = 6.7 h

That is about 6 h 40 min, so the bag runs out at about 21:10.

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