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 shiftjuice200 mLwater120 mLIV infusion60 mL/h × 12 hIV antibiotic1 × 100 mLurine275 mLurine350 mLurine200 mLurine250 mLwound drain110 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.

juice: 200 mLwater: 120 mLIV infusion: 60 mL/h × 12 hIV antibiotic: 1 × 100 mL
I = mL
2.IV fluids & fluid balanceHard
1000 mL100 mL/hstart 10:0012:30: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 10:00 and runs by pump at 100 mL/h. How many mL V are left in the bag at 12:30?

1000 mL100 mL/h10:00 → 12:30
V = mL
3.IV infusion ratesMedium
520 mLleft? mL/h3 h left

1500 mL was ordered over 10 hours. After 7 hours you find that 520 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 7 h: 520 mL
R = mL/h
4.IV infusion ratesHard
1000 mg500 mL15 mL/h? mg/h

A bag contains 1000 mg of a drug in 500 mL and runs at 15 mL/h. How many milligrams per hour D does the patient receive?

1000 mg/500 mL15 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: I = 1140 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 + 120 = 320 mL
IV infusion: 60·12 = 720 mL
IV antibiotic: 1·100 = 100 mL
I = 1140 mL

Answer

I = 1140 mL
2.IV fluids & fluid balance

Answer: V = 750 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

10:00 → 12:30 = 2.5 h

Volume infused

100·2.5 = 250 mL

Volume left

V = 1000 − 250 = 750 mL

Answer

V = 750 mL
3.IV infusion rates

Answer: R = 173.3 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 = 520/3 = 173.3 mL/h

Answer

R = 173.3 mL/h

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

4.IV infusion rates

Answer: D = 30 mg/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.

Concentration

1000/500 = 2 mg/mL

Dose rate

D = 2·15 = 30 mg/h

Answer

D = 30 mg/h

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