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 shiftjuice200 mLmilk240 mLice chips100 mLIV infusion100 mL/h × 12 hIV antibiotic2 × 50 mLurine475 mLurine150 mLurine375 mLwound drain150 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 total intake I in mL. Count ice chips as half their volume.

juice: 200 mLmilk: 240 mLice chips: 100 mLIV infusion: 100 mL/h × 12 hIV antibiotic: 2 × 50 mL
I = mL
2.IV fluids & fluid balanceHard
1000 mL450 mL infused150 mL/h15:30t = ? h

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag runs by pump at 150 mL/h. At 15:30, 450 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

1000 mL450 mL infused150 mL/h
t = h
3.IV infusion ratesMedium
60 gtt/mL30 mL/h? gtt/min

An infusion is ordered at 30 mL/h, but no pump is available. It runs by gravity through a giving set of 60 gtt/mL. Find the drip rate R in drops per minute.

30 mL/h60 gtt/mL
R = gtt/min
4.IV infusion ratesHard
1000 mg500 mL30 mL/h? mg/h

A bag contains 1000 mg of a drug in 500 mL and runs at 30 mL/h. How many milligrams per hour D does the patient receive?

1000 mg/500 mL30 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: I = 1790 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.

Add the intake

oral: 200 + 240 = 440 mL
ice chips: 100/2 = 50 mL
IV infusion: 100·12 = 1200 mL
IV antibiotic: 2·50 = 100 mL
I = 1790 mL

Answer

I = 1790 mL
2.IV fluids & fluid balance

Answer: t = 3.7 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

1000 − 450 = 550 mL

Time

t = 550/150 = 3.667 ≈ 3.7 h

Answer

t = 3.7 h

That is about 3 h 40 min, so the bag runs out at about 19:10.

3.IV infusion rates

Answer: R = 30 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.

Millilitres per minute

30/60 = 0.5 mL/min

Drip rate

R = 0.5·60 = 30 gtt/min

Answer

R = 30 gtt/min

With a microdrip set (60 gtt/mL), gtt/min equals mL/h.

4.IV infusion rates

Answer: D = 60 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

1000/500 = 2 mg/mL

Dose rate

D = 2·30 = 60 mg/h

Answer

D = 60 mg/h

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