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 shiftjelly100 mLtea240 mLice chips240 mLIV infusion100 mL/h × 8 hIV antibiotic1 × 100 mLurine300 mLurine450 mLurine225 mLwound drain120 mL

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 total intake I in mL. Count ice chips as half their volume.

jelly: 100 mLtea: 240 mLice chips: 240 mLIV infusion: 100 mL/h × 8 hIV antibiotic: 1 × 100 mL
I = mL
2.IV fluids & fluid balanceHard
500 mL80 mL/hstart 06:0009:30: ? mL

Practice exercise (made-up values, not clinical guidance). A 500 mL bag was started at 06:00 and runs by pump at 80 mL/h. How many mL V are left in the bag at 09:30?

500 mL80 mL/h06:00 → 09:30
V = mL
3.IV infusion ratesMedium
V = ?15 gtt/mL50 gtt/min12 h

A drip runs at 50 gtt/min through a set of 15 gtt/mL. How many millilitres V does the patient receive in 12 hours?

50 gtt/min15 gtt/mL12 h
V = mL
4.IV infusion ratesHard
440 mLleft? mL/h3 h left

1000 mL was ordered over 8 hours. After 5 hours you find that 440 mL is still in the bag, and the order must still finish on time. By what percentage Δ must the original pump rate be increased?

1000 mL / 8 hafter 5 h: 440 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: I = 1360 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: 100 + 240 = 340 mL
ice chips: 240/2 = 120 mL
IV infusion: 100·8 = 800 mL
IV antibiotic: 1·100 = 100 mL
I = 1360 mL

Answer

I = 1360 mL
2.IV fluids & fluid balance

Answer: V = 220 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

06:00 → 09:30 = 3.5 h

Volume infused

80·3.5 = 280 mL

Volume left

V = 500 − 280 = 220 mL

Answer

V = 220 mL
3.IV infusion rates

Answer: V = 2400 mL

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.

Rate in mL/h

50·60/15 = 200 mL/h

Volume

V = 200·12 = 2400 mL

Answer

V = 2400 mL
4.IV infusion rates

Answer: Δ = 17.33 %

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

1000/8 = 125 mL/h

New rate

R = 440/3 = 146.7 mL/h

Percentage change

Δ = (146.7 − 125)/125·100% = 17.33%

Answer

Δ = 17.33%

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

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