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 shiftjelly120 mLmilk200 mLsoup180 mLIV infusion125 mL/h × 12 hIV antibiotic1 × 100 mLurine475 mLurine250 mLurine250 mLurine225 mLwound drain60 mLvomit100 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.

jelly: 120 mLmilk: 200 mLsoup: 180 mLIV infusion: 125 mL/h × 12 hIV antibiotic: 1 × 100 mL
I = mL
2.IV fluids & fluid balanceHard
1000 mL50 mL/hstart 11:4518:15: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 11:45 and runs by pump at 50 mL/h. How many mL V are left in the bag at 18:15?

1000 mL50 mL/h11:45 → 18:15
V = mL
3.IV infusion ratesMedium
730 mLleft? mL/h4 h left

1000 mL was ordered over 6 hours. After 2 hours you find that 730 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?

1000 mL / 6 hafter 2 h: 730 mL
R = mL/h
4.IV infusion ratesHard
1 g500 mL? mL/h1 mg/min

A bag contains 1 g of a drug in 500 mL. The order is 1 mg per minute. At what rate R do you set the pump, in mL/h?

1 g/500 mL1 mg/min
R = mL/h

3Solutions

1.IV fluids & fluid balance

Answer: I = 2100 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: 120 + 200 + 180 = 500 mL
IV infusion: 125·12 = 1500 mL
IV antibiotic: 1·100 = 100 mL
I = 2100 mL

Answer

I = 2100 mL
2.IV fluids & fluid balance

Answer: V = 675 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

11:45 → 18:15 = 6.5 h

Volume infused

50·6.5 = 325 mL

Volume left

V = 1000 − 325 = 675 mL

Answer

V = 675 mL
3.IV infusion rates

Answer: R = 182.5 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

1000/6 = 166.7 mL/h

New rate

R = 730/4 = 182.5 mL/h

Answer

R = 182.5 mL/h

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

4.IV infusion rates

Answer: R = 30 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

1000 mg/500 mL = 2 mg/mL

Dose per hour

1·60 = 60 mg/h

Pump rate

R = 60/2 = 30 mL/h

Answer

R = 30 mL/h

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