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). A 55 kg patient needs 1.8 g of protein per kg a day. The tube feed contains 63 g of protein per litre and runs at 40 mL/h for 20 hours a day. A protein powder supplies 6 g of protein per scoop. How many scoops n a day are needed to cover the shortfall? Round up to a whole scoop.

55 kg1.8 g/kg/day63 g/L40 mL/h · 20 h6 g/scoop

n =

2.Enteral & parenteral nutrition calculationsHard

Practice exercise (made-up values, not clinical guidance). A critically ill woman is 166 cm tall and weighs 89 kg. The practice protocol gives 12 kcal/kg of actual body weight per day if the BMI is 30–50 kg/m², and 22 kcal/kg of ideal body weight (Devine) per day if the BMI is above 50 kg/m². Find the energy goal E in kcal/day. Round to the nearest whole number.

166 cm89 kgwomanBMI 30–50: 12 kcal/kg actualBMI > 50: 22 kcal/kg IBW

E = kcal/day

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 fluid balance B = intake − output in mL (a negative answer means a net loss).

milk: 240 mLjuice: 150 mLIV infusion: 100 mL/h × 8 hIV antibiotic: 2 × 100 mLurine: 200 mLurine: 225 mLurine: 200 mLwound drain: 150 mLvomit: 200 mL

B = mL

4.IV fluids & fluid balanceHard

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 50 mL/h. At 17:30, 300 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL300 mL infused50 mL/h

t = h

3Solutions

1.Enteral & parenteral nutrition calculations

Answer: n = 9

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.

Protein needed

1.8·55 = 99 g/day

Protein from the feed

40·20 = 800 mL = 0.8 L

0.8·63 = 50.4 g/day

Shortfall

ΔP = 99 − 50.4 = 48.6 g

Scoops

48.6/6 = 8.1 → n = 9

Answer

n = 9

2.Enteral & parenteral nutrition calculations

Answer: E = 1068 kcal/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). For BMI 30–50 the energy goal is 11–14 kcal/kg of actual body weight per day; above 50 it is 22–25 kcal/kg of ideal body weight per day. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Body mass index

BMI = 89/1.66² = 32.3 kg/m²

Energy goal

BMI 30–50: kcal per kg of actual body weight.

E = 12·89 = 1068 kcal/day

Answer

E = 1068 kcal/day

3.IV fluids & fluid balance

Answer: B = 415 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: 240 + 150 = 390 mL

IV infusion: 100·8 = 800 mL

IV antibiotic: 2·100 = 200 mL

total intake = 1390 mL

Total output

200 + 225 + 200 + 150 + 200 = 975 mL

Balance

B = 1390 − 975 = 415 mL

Answer

B = 415 mL

Positive: more fluid went in than came out.

4.IV fluids & fluid balance

Answer: t = 4 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 = 200/50 = 4 h

Answer

t = 4 h

That is about 4 h 00 min, so the bag runs out at about 21:30.

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