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 shiftjelly120 mLsoup150 mLIV infusion75 mL/h × 8 hIV antibiotic2 × 100 mLurine350 mLurine200 mLurine175 mLurine275 mLwound drain140 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-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).

jelly: 120 mLsoup: 150 mLIV infusion: 75 mL/h × 8 hIV antibiotic: 2 × 100 mLurine: 350 mLurine: 200 mLurine: 175 mLurine: 275 mLwound drain: 140 mL
B = mL
2.IV fluids & fluid balanceHard
1000 mL50 mL/hstart 07:4509:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 07:45 and runs by pump at 50 mL/h. How many mL V are left in the bag at 09:45?

1000 mL50 mL/h07:45 → 09:45
V = mL
3.IV infusion ratesMedium
250 mL15 gtt/mL2 h? gtt/min

Infuse 250 mL over 2 hours with a giving set of 15 gtt/mL. Find the drip rate R in drops per minute. Round to the nearest whole number.

250 mL2 h15 gtt/mL
R = gtt/min
4.IV infusion ratesHard
100 mg250 mL30 mL/h? mcg/min

An infusion of 100 mg in 250 mL runs at 30 mL/h. How many micrograms per minute D does the patient receive?

100 mg/250 mL30 mL/h
D = mcg/min

3Solutions

1.IV fluids & fluid balance

Answer: B = −70 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: 120 + 150 = 270 mL
IV infusion: 75·8 = 600 mL
IV antibiotic: 2·100 = 200 mL
total intake = 1070 mL

Total output

350 + 200 + 175 + 275 + 140 = 1140 mL

Balance

B = 1070 − 1140 = −70 mL

Answer

B = −70 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: V = 900 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

07:45 → 09:45 = 2 h

Volume infused

50·2 = 100 mL

Volume left

V = 1000 − 100 = 900 mL

Answer

V = 900 mL
3.IV infusion rates

Answer: R = 31 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

2·60 = 120 min

Drip rate

R = 250·15/120 = 31.25 ≈ 31 gtt/min

Answer

R = 31 gtt/min

At the bedside you round to the nearest whole drop: 31 gtt/min.

4.IV infusion rates

Answer: D = 200 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

30·400 = 12000 mcg/h

Dose per minute

D = 12000/60 = 200 mcg/min

Answer

D = 200 mcg/min

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