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 shiftwater300 mLjelly100 mLice chips200 mLIV infusion100 mL/h × 12 hIV antibiotic1 × 100 mLurine500 mLurine150 mLurine200 mLurine325 mLwound drain70 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. Count ice chips as half their volume.

water: 300 mLjelly: 100 mLice chips: 200 mLIV infusion: 100 mL/h × 12 hIV antibiotic: 1 × 100 mL
I = mL
2.IV fluids & fluid balanceHard
500 mL→ 150 mL/hstart 14:00ttotal​ = ? h120 mL/h × 2 h

Practice exercise (made-up values, not clinical guidance). A 500 mL infusion starts at 14:00 at 120 mL/h. After 2 hours the rate is changed to 150 mL/h and is not changed again. How many hours t after the start will the bag be empty? Round to one decimal place.

500 mL120 mL/h · 2 h150 mL/h
t = h
3.IV infusion ratesMedium
400 mLleft? mL/h7 h left

500 mL was ordered over 10 hours. After 3 hours you find that 400 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?

500 mL / 10 hafter 3 h: 400 mL
R = mL/h
4.IV infusion ratesHard
370 mLleft? mL/h2 h left

1500 mL was ordered over 10 hours. After 8 hours you find that 370 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?

1500 mL / 10 hafter 8 h: 370 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: I = 1800 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: 300 + 100 = 400 mL
ice chips: 200/2 = 100 mL
IV infusion: 100·12 = 1200 mL
IV antibiotic: 1·100 = 100 mL
I = 1800 mL

Answer

I = 1800 mL
2.IV fluids & fluid balance

Answer: t = 3.7 h

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.

First part

120·2 = 240 mL
500 − 240 = 260 mL left

Second part

260/150 = 1.733 h

Total time

t = 2 + 1.733 = 3.733 ≈ 3.7 h

Answer

t = 3.7 h

That is about 3 h 44 min, so the bag runs out at about 17:44.

3.IV infusion rates

Answer: R = 57.14 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

500/10 = 50 mL/h

New rate

R = 400/7 = 57.14 mL/h

Answer

R = 57.14 mL/h

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

4.IV infusion rates

Answer: Δ = 23.33 %

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

1500/10 = 150 mL/h

New rate

R = 370/2 = 185 mL/h

Percentage change

Δ = (185 − 150)/150·100% = 23.33%

Answer

Δ = 23.33%

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

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