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 mLmilk100 mLwater250 mLice chips200 mLIV infusion75 mL/h × 12 hIV antibiotic2 × 100 mLurine300 mLurine175 mLurine200 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.

juice: 200 mLmilk: 100 mLwater: 250 mLice chips: 200 mLIV infusion: 75 mL/h × 12 hIV antibiotic: 2 × 100 mL
I = mL
2.IV fluids & fluid balanceHard
500 mL100 mL/hstart 06:4510:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 500 mL bag was started at 06:45 and runs by pump at 100 mL/h. How many mL V are left in the bag at 10:45?

500 mL100 mL/h06:45 → 10:45
V = mL
3.IV infusion ratesMedium
20 gtt/mL75 mL/h? gtt/min

An infusion is ordered at 75 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.

75 mL/h20 gtt/mL
R = gtt/min
4.IV infusion ratesHard
400 mg100 mL12 mL/h? mg/h

A bag contains 400 mg of a drug in 100 mL and runs at 12 mL/h. How many milligrams per hour D does the patient receive?

400 mg/100 mL12 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: I = 1750 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 + 100 + 250 = 550 mL
ice chips: 200/2 = 100 mL
IV infusion: 75·12 = 900 mL
IV antibiotic: 2·100 = 200 mL
I = 1750 mL

Answer

I = 1750 mL
2.IV fluids & fluid balance

Answer: V = 100 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

06:45 → 10:45 = 4 h

Volume infused

100·4 = 400 mL

Volume left

V = 500 − 400 = 100 mL

Answer

V = 100 mL
3.IV infusion rates

Answer: R = 25 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

75/60 = 1.25 mL/min

Drip rate

R = 1.25·20 = 25 gtt/min

Answer

R = 25 gtt/min
4.IV infusion rates

Answer: D = 48 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

400/100 = 4 mg/mL

Dose rate

D = 4·12 = 48 mg/h

Answer

D = 48 mg/h

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