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 shiftmilk200 mLsoup200 mLjuice150 mLice chips200 mLIV infusion75 mL/h × 8 hIV antibiotic1 × 50 mLurine350 mLurine150 mLurine500 mLurine500 mLwound drain90 mLvomit250 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 total intake I in mL. Count ice chips as half their volume.

milk: 200 mLsoup: 200 mLjuice: 150 mLice chips: 200 mLIV infusion: 75 mL/h × 8 hIV antibiotic: 1 × 50 mL
I = mL
2.IV fluids & fluid balanceHard
1000 mL120 mL/hstart 11:1514:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 11:15 and runs by pump at 120 mL/h. How many mL V are left in the bag at 14:45?

1000 mL120 mL/h11:15 → 14:45
V = mL
3.IV infusion ratesMedium
15 gtt/mL60 mL/h? gtt/min

An infusion is ordered at 60 mL/h, but no pump is available. It runs by gravity through a giving set of 15 gtt/mL. Find the drip rate R in drops per minute.

60 mL/h15 gtt/mL
R = gtt/min
4.IV infusion ratesHard
870 mLleft? mL/h4 h left

1000 mL was ordered over 6 hours. After 2 hours you find that 870 mL is still in the bag, and the order must still finish on time. By what percentage Δ must the original pump rate be increased?

1000 mL / 6 hafter 2 h: 870 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: I = 1300 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 + 200 + 150 = 550 mL
ice chips: 200/2 = 100 mL
IV infusion: 75·8 = 600 mL
IV antibiotic: 1·50 = 50 mL
I = 1300 mL

Answer

I = 1300 mL
2.IV fluids & fluid balance

Answer: V = 580 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

11:15 → 14:45 = 3.5 h

Volume infused

120·3.5 = 420 mL

Volume left

V = 1000 − 420 = 580 mL

Answer

V = 580 mL
3.IV infusion rates

Answer: R = 15 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

60/60 = 1 mL/min

Drip rate

R = 1·15 = 15 gtt/min

Answer

R = 15 gtt/min
4.IV infusion rates

Answer: Δ = 30.5 %

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

1000/6 = 166.7 mL/h

New rate

R = 870/4 = 217.5 mL/h

Percentage change

Δ = (217.5 − 166.7)/166.7·100% = 30.5%

Answer

Δ = 30.5%

This is more than a 25% increase: most hospitals require you to contact the prescriber instead of catching up, and to assess the patient for fluid overload.

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