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 shiftwater350 mLsoup250 mLjelly100 mLice chips240 mLIV infusion100 mL/h × 12 hIV antibiotic1 × 100 mLurine250 mLurine150 mLurine250 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 12-hour shift. The patient weighs 84 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

84 kg12 hurine: 250 mLurine: 150 mLurine: 250 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
1000 mL50 mL/hstart 09:0016:30: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 09:00 and runs by pump at 50 mL/h. How many mL V are left in the bag at 16:30?

1000 mL50 mL/h09:00 → 16:30
V = mL
3.IV infusion ratesMedium
V = ?15 gtt/mL25 gtt/min2 h

A drip runs at 25 gtt/min through a set of 15 gtt/mL. How many millilitres V does the patient receive in 2 hours?

25 gtt/min15 gtt/mL2 h
V = mL
4.IV infusion ratesHard
200 mg250 mL30 mL/h? mg/h

A bag contains 200 mg of a drug in 250 mL and runs at 30 mL/h. How many milligrams per hour D does the patient receive?

200 mg/250 mL30 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: U = 0.64 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

250 + 150 + 250 = 650 mL

Per kilogram per hour

U = 650/(84·12) = 0.6448 ≈ 0.64 mL/kg/h

Answer

U = 0.64 mL/kg/h
2.IV fluids & fluid balance

Answer: V = 625 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

09:00 → 16:30 = 7.5 h

Volume infused

50·7.5 = 375 mL

Volume left

V = 1000 − 375 = 625 mL

Answer

V = 625 mL
3.IV infusion rates

Answer: V = 200 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

25·60/15 = 100 mL/h

Volume

V = 100·2 = 200 mL

Answer

V = 200 mL
4.IV infusion rates

Answer: D = 24 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

200/250 = 0.8 mg/mL

Dose rate

D = 0.8·30 = 24 mg/h

Answer

D = 24 mg/h

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