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 shifttea200 mLjelly120 mLIV infusion125 mL/h × 8 hIV antibiotic2 × 100 mLurine225 mLurine250 mLurine300 mLvomit200 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 52 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

52 kg8 hurine: 225 mLurine: 250 mLurine: 300 mLvomit: 200 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
500 mL→ 100 mL/hstart 08:30ttotal​ = ? h75 mL/h × 3 h

Practice exercise (made-up values, not clinical guidance). A 500 mL infusion starts at 08:30 at 75 mL/h. After 3 hours the rate is changed to 100 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 mL75 mL/h · 3 h100 mL/h
t = h
3.IV infusion ratesMedium
1500 mL10 gtt/mL12 h? gtt/min

Infuse 1500 mL over 12 hours with a giving set of 10 gtt/mL. Find the drip rate R in drops per minute. Round to the nearest whole number.

1500 mL12 h10 gtt/mL
R = gtt/min
4.IV infusion ratesHard
1 g500 mL? mL/h2 mg/min

A bag contains 1 g of a drug in 500 mL. The order is 2 mg per minute. At what rate R do you set the pump, in mL/h?

1 g/500 mL2 mg/min
R = mL/h

3Solutions

1.IV fluids & fluid balance

Answer: U = 1.86 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

225 + 250 + 300 = 775 mL

Per kilogram per hour

U = 775/(52·8) = 1.863 ≈ 1.86 mL/kg/h

Answer

U = 1.86 mL/kg/h
2.IV fluids & fluid balance

Answer: t = 5.8 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

75·3 = 225 mL
500 − 225 = 275 mL left

Second part

275/100 = 2.75 h

Total time

t = 3 + 2.75 = 5.75 ≈ 5.8 h

Answer

t = 5.8 h

That is about 5 h 45 min, so the bag runs out at about 14:15.

3.IV infusion rates

Answer: R = 21 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.

Time in minutes

12·60 = 720 min

Drip rate

R = 1500·10/720 = 20.83 ≈ 21 gtt/min

Answer

R = 21 gtt/min

At the bedside you round to the nearest whole drop: 21 gtt/min.

4.IV infusion rates

Answer: R = 60 mL/h

Dose-based infusions: concentration = amount of drug in the bag/bag volume. Pump rate (mL/h) = dose per hour/concentration, and dose per hour = mL/h × concentration. Convert per-minute doses to per-hour (× 60) and keep the mass units the same (1 g = 1000 mg, 1 mg = 1000 mcg).

Concentration

1000 mg/500 mL = 2 mg/mL

Dose per hour

2·60 = 120 mg/h

Pump rate

R = 120/2 = 60 mL/h

Answer

R = 60 mL/h

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