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 shiftmilk240 mLwater120 mLIV infusion60 mL/h × 8 hIV antibiotic2 × 50 mLurine250 mLurine350 mLurine300 mLvomit150 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).

milk: 240 mLwater: 120 mLIV infusion: 60 mL/h × 8 hIV antibiotic: 2 × 50 mLurine: 250 mLurine: 350 mLurine: 300 mLvomit: 150 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL250 mL infused100 mL/h13:30t = ? h

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 100 mL/h. At 13:30, 250 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL250 mL infused100 mL/h
t = h
3.IV infusion ratesMedium
10 gtt/mL150 mL/h? gtt/min

An infusion is ordered at 150 mL/h, but no pump is available. It runs by gravity through a giving set of 10 gtt/mL. Find the drip rate R in drops per minute.

150 mL/h10 gtt/mL
R = gtt/min
4.IV infusion ratesHard
500 mg250 mL10 mL/h? mg/h

A bag contains 500 mg of a drug in 250 mL and runs at 10 mL/h. How many milligrams per hour D does the patient receive?

500 mg/250 mL10 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: B = −110 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: 240 + 120 = 360 mL
IV infusion: 60·8 = 480 mL
IV antibiotic: 2·50 = 100 mL
total intake = 940 mL

Total output

250 + 350 + 300 + 150 = 1050 mL

Balance

B = 940 − 1050 = −110 mL

Answer

B = −110 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: t = 2.5 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 = 250/100 = 2.5 h

Answer

t = 2.5 h

That is about 2 h 30 min, so the bag runs out at about 16:00.

3.IV infusion rates

Answer: R = 25 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

150/60 = 2.5 mL/min

Drip rate

R = 2.5·10 = 25 gtt/min

Answer

R = 25 gtt/min
4.IV infusion rates

Answer: D = 20 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

500/250 = 2 mg/mL

Dose rate

D = 2·10 = 20 mg/h

Answer

D = 20 mg/h

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