IV Fluids and Fluid Balance: 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

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

IV infusion rates

Pump rate
mL/h = volume (mL)/time (h)
Drip rate
drops/min = volume (mL) × drop factor / time (min)
Infusion time
time (h) = volume (mL)/rate (mL/h)

Method

  1. Pump rate in mL/h: volume divided by time in hours.
  2. Drip rate in drops/min: volume × drop factor divided by time in minutes.
  3. For time remaining: volume left divided by the rate.
  4. Round as the question or the equipment requires.

2Practice problems

1.IV fluids & fluid balanceMedium
IntakeOutput8-hour shiftsoup150 mLmilk100 mLice chips200 mLIV infusion125 mL/h × 8 hIV antibiotic1 × 50 mLurine275 mLurine175 mLurine200 mLurine375 mLwound drain50 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-hour shift. The patient weighs 74 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

74 kg8 hurine: 275 mLurine: 175 mLurine: 200 mLurine: 375 mLwound drain: 50 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
1000 mL100 mL/hstart 09:4517:15: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 09:45 and runs by pump at 100 mL/h. How many mL V are left in the bag at 17:15?

1000 mL100 mL/h09:45 → 17:15
V = mL
3.IV infusion ratesMedium
890 mLleft? mL/h5 h left

1500 mL was ordered over 10 hours. After 5 hours you find that 890 mL is still in the bag, and the order must still finish on time. To what rate R in mL/h must the pump be reset?

1500 mL / 10 hafter 5 h: 890 mL
R = mL/h
4.IV infusion ratesHard
4 g500 mL? mL/h3 mg/min

A bag contains 4 g of a drug in 500 mL. The order is 3 mg per minute. At what rate R do you set the pump, in mL/h?

4 g/500 mL3 mg/min
R = mL/h

3Solutions

1.IV fluids & fluid balance

Answer: U = 1.73 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

275 + 175 + 200 + 375 = 1025 mL

Per kilogram per hour

U = 1025/(74·8) = 1.731 ≈ 1.73 mL/kg/h

Answer

U = 1.73 mL/kg/h
2.IV fluids & fluid balance

Answer: V = 250 mL

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.

Elapsed time

09:45 → 17:15 = 7.5 h

Volume infused

100·7.5 = 750 mL

Volume left

V = 1000 − 750 = 250 mL

Answer

V = 250 mL
3.IV infusion rates

Answer: R = 178 mL/h

Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.

Original rate

1500/10 = 150 mL/h

New rate

R = 890/5 = 178 mL/h

Answer

R = 178 mL/h

Many hospitals allow such an adjustment up to 25% without a new order; check local policy.

4.IV infusion rates

Answer: R = 22.5 mL/h

Dose-based infusions: concentration = amount of drug in the bag/bag volume. Pump rate (mL/h) = dose per hour/concentration, and dose per hour = mL/h × concentration. Convert per-minute doses to per-hour (× 60) and keep the mass units the same (1 g = 1000 mg, 1 mg = 1000 mcg).

Concentration

4000 mg/500 mL = 8 mg/mL

Dose per hour

3·60 = 180 mg/h

Pump rate

R = 180/8 = 22.5 mL/h

Answer

R = 22.5 mL/h

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