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 shiftsoup250 mLmilk240 mLice chips120 mLIV infusion50 mL/h × 8 hIV antibiotic1 × 100 mLurine350 mLurine425 mLurine400 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 81 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

81 kg8 hurine: 350 mLurine: 425 mLurine: 400 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
1000 mL120 mL/hstart 08:1515:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 08:15 and runs by pump at 120 mL/h. How many mL V are left in the bag at 15:45?

1000 mL120 mL/h08:15 → 15:45
V = mL
3.IV infusion ratesMedium
1000 mL10 gtt/mL5 h? gtt/min

Infuse 1000 mL over 5 hours with a giving set of 10 gtt/mL. Find the drip rate R in drops per minute. Round to the nearest whole number.

1000 mL5 h10 gtt/mL
R = gtt/min
4.IV infusion ratesHard
500 mg500 mL20 gtt/mL30 mg/h? gtt/min

500 mg of a drug is diluted in 500 mL and given by gravity through a set of 20 gtt/mL. The order is 30 mg per hour. Find the drip rate R in drops per minute.

500 mg/500 mL30 mg/h20 gtt/mL
R = gtt/min

3Solutions

1.IV fluids & fluid balance

Answer: U = 1.81 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

350 + 425 + 400 = 1175 mL

Per kilogram per hour

U = 1175/(81·8) = 1.813 ≈ 1.81 mL/kg/h

Answer

U = 1.81 mL/kg/h
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

08:15 → 15:45 = 7.5 h

Volume infused

120·7.5 = 900 mL

Volume left

V = 1000 − 900 = 100 mL

Answer

V = 100 mL
3.IV infusion rates

Answer: R = 33 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

5·60 = 300 min

Drip rate

R = 1000·10/300 = 33.33 ≈ 33 gtt/min

Answer

R = 33 gtt/min

At the bedside you round to the nearest whole drop: 33 gtt/min.

4.IV infusion rates

Answer: R = 10 gtt/min

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

500/500 = 1 mg/mL

Volume per hour

30/1 = 30 mL/h

Drip rate

R = 30·20/60 = 10 gtt/min

Answer

R = 10 gtt/min

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