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 shiftmilk200 mLjelly100 mLice chips200 mLIV infusion50 mL/h × 12 hIV antibiotic2 × 100 mLurine250 mLurine175 mLurine400 mLurine250 mLwound drain70 mLvomit100 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 fluid balance B = intake − output in mL (a negative answer means a net loss). Count ice chips as half their volume.

milk: 200 mLjelly: 100 mLice chips: 200 mLIV infusion: 50 mL/h × 12 hIV antibiotic: 2 × 100 mLurine: 250 mLurine: 175 mLurine: 400 mLurine: 250 mLwound drain: 70 mLvomit: 100 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL100 mL infused60 mL/h06:30t = ? h

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 60 mL/h. At 06:30, 100 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL100 mL infused60 mL/h
t = h
3.IV infusion ratesMedium
V = ?60 gtt/mL100 gtt/min6 h

A drip runs at 100 gtt/min through a set of 60 gtt/mL. How many millilitres V does the patient receive in 6 hours?

100 gtt/min60 gtt/mL6 h
V = mL
4.IV infusion ratesHard
400 mL60 gtt/mL32 gtt/mint = ? h

A drip runs at 32 gtt/min through a set of 60 gtt/mL. There are 400 mL left in the bag. How many hours t until it is empty?

32 gtt/min60 gtt/mL400 mL
t = h

3Solutions

1.IV fluids & fluid balance

Answer: B = −45 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 + 100 = 300 mL
ice chips: 200/2 = 100 mL
IV infusion: 50·12 = 600 mL
IV antibiotic: 2·100 = 200 mL
total intake = 1200 mL

Total output

250 + 175 + 400 + 250 + 70 + 100 = 1245 mL

Balance

B = 1200 − 1245 = −45 mL

Answer

B = −45 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: t = 6.7 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

500 − 100 = 400 mL

Time

t = 400/60 = 6.667 ≈ 6.7 h

Answer

t = 6.7 h

That is about 6 h 40 min, so the bag runs out at about 13:10.

3.IV infusion rates

Answer: V = 600 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

100·60/60 = 100 mL/h

Volume

V = 100·6 = 600 mL

Answer

V = 600 mL
4.IV infusion rates

Answer: t = 12.5 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.

Rate in mL/h

32·60/60 = 32 mL/h

Time left

t = 400/32 = 12.5 h

Answer

t = 12.5 h

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