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 mLsoup150 mLIV infusion50 mL/h × 8 hIV antibiotic1 × 50 mLurine425 mLurine350 mLurine375 mLwound drain30 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 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).

tea: 200 mLsoup: 150 mLIV infusion: 50 mL/h × 8 hIV antibiotic: 1 × 50 mLurine: 425 mLurine: 350 mLurine: 375 mLwound drain: 30 mLvomit: 200 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL100 mL/hstart 11:0015:30: ? mL

Practice exercise (made-up values, not clinical guidance). A 500 mL bag was started at 11:00 and runs by pump at 100 mL/h. How many mL V are left in the bag at 15:30?

500 mL100 mL/h11:00 → 15:30
V = mL
3.IV infusion ratesMedium
150 mLleft? mL/h3 h left

500 mL was ordered over 12 hours. After 9 hours you find that 150 mL is still in the bag, and the order must still finish on time. To what rate R in mL/h must the pump be reset?

500 mL / 12 hafter 9 h: 150 mL
R = mL/h
4.IV infusion ratesHard
500 mg100 mL15 mL/h? mg/h

A bag contains 500 mg of a drug in 100 mL and runs at 15 mL/h. How many milligrams per hour D does the patient receive?

500 mg/100 mL15 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: B = −580 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: 200 + 150 = 350 mL
IV infusion: 50·8 = 400 mL
IV antibiotic: 1·50 = 50 mL
total intake = 800 mL

Total output

425 + 350 + 375 + 30 + 200 = 1380 mL

Balance

B = 800 − 1380 = −580 mL

Answer

B = −580 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: V = 50 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

11:00 → 15:30 = 4.5 h

Volume infused

100·4.5 = 450 mL

Volume left

V = 500 − 450 = 50 mL

Answer

V = 50 mL
3.IV infusion rates

Answer: R = 50 mL/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.

Original rate

500/12 = 41.67 mL/h

New rate

R = 150/3 = 50 mL/h

Answer

R = 50 mL/h

Many hospitals allow such an adjustment up to 25% without a new order; check local policy.

4.IV infusion rates

Answer: D = 75 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

500/100 = 5 mg/mL

Dose rate

D = 5·15 = 75 mg/h

Answer

D = 75 mg/h

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