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 shiftjuice100 mLsoup150 mLjelly100 mLIV infusion50 mL/h × 12 hIV antibiotic1 × 50 mLurine500 mLurine375 mLurine400 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 fluid balance B = intake − output in mL (a negative answer means a net loss).

juice: 100 mLsoup: 150 mLjelly: 100 mLIV infusion: 50 mL/h × 12 hIV antibiotic: 1 × 50 mLurine: 500 mLurine: 375 mLurine: 400 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL250 mL infused150 mL/h18:00t = ? h

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 150 mL/h. At 18:00, 250 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL250 mL infused150 mL/h
t = h
3.IV infusion ratesMedium
V = ?20 gtt/mL25 gtt/min3 h

A drip runs at 25 gtt/min through a set of 20 gtt/mL. How many millilitres V does the patient receive in 3 hours?

25 gtt/min20 gtt/mL3 h
V = mL
4.IV infusion ratesHard
100 mg250 mL12 mL/h? mcg/min

An infusion of 100 mg in 250 mL runs at 12 mL/h. How many micrograms per minute D does the patient receive?

100 mg/250 mL12 mL/h
D = mcg/min

3Solutions

1.IV fluids & fluid balance

Answer: B = −275 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.

Total intake

oral: 100 + 150 + 100 = 350 mL
IV infusion: 50·12 = 600 mL
IV antibiotic: 1·50 = 50 mL
total intake = 1000 mL

Total output

500 + 375 + 400 = 1275 mL

Balance

B = 1000 − 1275 = −275 mL

Answer

B = −275 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: t = 1.7 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.

Volume left

500 − 250 = 250 mL

Time

t = 250/150 = 1.667 ≈ 1.7 h

Answer

t = 1.7 h

That is about 1 h 40 min, so the bag runs out at about 19:40.

3.IV infusion rates

Answer: V = 225 mL

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

25·60/20 = 75 mL/h

Volume

V = 75·3 = 225 mL

Answer

V = 225 mL
4.IV infusion rates

Answer: D = 80 mcg/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

100000 mcg/250 mL = 400 mcg/mL

Dose per hour

12·400 = 4800 mcg/h

Dose per minute

D = 4800/60 = 80 mcg/min

Answer

D = 80 mcg/min

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