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
IntakeOutput12-hour shifttea200 mLsoup200 mLwater250 mLIV infusion80 mL/h × 12 hIV antibiotic2 × 50 mLurine350 mLurine200 mLurine150 mLwound drain80 mL

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 total intake I in mL.

tea: 200 mLsoup: 200 mLwater: 250 mLIV infusion: 80 mL/h × 12 hIV antibiotic: 2 × 50 mL
I = mL
2.IV fluids & fluid balanceHard
1000 mL50 mL/hstart 06:4513:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 06:45 and runs by pump at 50 mL/h. How many mL V are left in the bag at 13:45?

1000 mL50 mL/h06:45 → 13:45
V = mL
3.IV infusion ratesMedium
1280 mLleft? mL/h9 h left

1500 mL was ordered over 12 hours. After 3 hours you find that 1280 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 / 12 hafter 3 h: 1280 mL
R = mL/h
4.IV infusion ratesHard
50 mg250 mL12 mL/h? mcg/min

An infusion of 50 mg in 250 mL runs at 12 mL/h. How many micrograms per minute D does the patient receive?

50 mg/250 mL12 mL/h
D = mcg/min

3Solutions

1.IV fluids & fluid balance

Answer: I = 1710 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: 200 + 200 + 250 = 650 mL
IV infusion: 80·12 = 960 mL
IV antibiotic: 2·50 = 100 mL
I = 1710 mL

Answer

I = 1710 mL
2.IV fluids & fluid balance

Answer: V = 650 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

06:45 → 13:45 = 7 h

Volume infused

50·7 = 350 mL

Volume left

V = 1000 − 350 = 650 mL

Answer

V = 650 mL
3.IV infusion rates

Answer: R = 142.2 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

1500/12 = 125 mL/h

New rate

R = 1280/9 = 142.2 mL/h

Answer

R = 142.2 mL/h

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

4.IV infusion rates

Answer: D = 40 mcg/min

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

50000 mcg/250 mL = 200 mcg/mL

Dose per hour

12·200 = 2400 mcg/h

Dose per minute

D = 2400/60 = 40 mcg/min

Answer

D = 40 mcg/min

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