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 shifttea150 mLsoup180 mLice chips100 mLIV infusion125 mL/h × 8 hIV antibiotic1 × 50 mLurine375 mLurine475 mLurine175 mLvomit150 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-hour shift. The patient weighs 104 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

104 kg8 hurine: 375 mLurine: 475 mLurine: 175 mLvomit: 150 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
500 mL→ 150 mL/hstart 09:00ttotal​ = ? h100 mL/h × 2 h

Practice exercise (made-up values, not clinical guidance). A 500 mL infusion starts at 09:00 at 100 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 mL100 mL/h · 2 h150 mL/h
t = h
3.IV infusion ratesMedium
20 gtt/mL120 mL/h? gtt/min

An infusion is ordered at 120 mL/h, but no pump is available. It runs by gravity through a giving set of 20 gtt/mL. Find the drip rate R in drops per minute.

120 mL/h20 gtt/mL
R = gtt/min
4.IV infusion ratesHard
750 mL60 gtt/mL42 gtt/mint = ? h

A drip runs at 42 gtt/min through a set of 60 gtt/mL. There are 750 mL left in the bag. How many hours t until it is empty? Round to one decimal place.

42 gtt/min60 gtt/mL750 mL
t = h

3Solutions

1.IV fluids & fluid balance

Answer: U = 1.23 mL/kg/h

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.

Total urine

375 + 475 + 175 = 1025 mL

Per kilogram per hour

U = 1025/(104·8) = 1.232 ≈ 1.23 mL/kg/h

Answer

U = 1.23 mL/kg/h
2.IV fluids & fluid balance

Answer: t = 4 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

100·2 = 200 mL
500 − 200 = 300 mL left

Second part

300/150 = 2 h

Total time

t = 2 + 2 = 4 h

Answer

t = 4 h

That is about 4 h 00 min, so the bag runs out at about 13:00.

3.IV infusion rates

Answer: R = 40 gtt/min

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.

Millilitres per minute

120/60 = 2 mL/min

Drip rate

R = 2·20 = 40 gtt/min

Answer

R = 40 gtt/min
4.IV infusion rates

Answer: t = 17.9 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.

Rate in mL/h

42·60/60 = 42 mL/h

Time left

t = 750/42 = 17.86 ≈ 17.9 h

Answer

t = 17.9 h

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