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 mLwater200 mLIV infusion125 mL/h × 12 hIV antibiotic1 × 50 mLurine200 mLurine275 mLurine325 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 fluid balance B = intake − output in mL (a negative answer means a net loss).

milk: 200 mLwater: 200 mLIV infusion: 125 mL/h × 12 hIV antibiotic: 1 × 50 mLurine: 200 mLurine: 275 mLurine: 325 mLwound drain: 150 mL
B = mL
2.IV fluids & fluid balanceHard
1000 mL→ 75 mL/hstart 12:30ttotal​ = ? h120 mL/h × 3 h

Practice exercise (made-up values, not clinical guidance). A 1000 mL infusion starts at 12:30 at 120 mL/h. After 3 hours the rate is changed to 75 mL/h and is not changed again. How many hours t after the start will the bag be empty? Round to one decimal place.

1000 mL120 mL/h · 3 h75 mL/h
t = h
3.IV infusion ratesMedium
V = ?60 gtt/mL40 gtt/min2 h

A drip runs at 40 gtt/min through a set of 60 gtt/mL. How many millilitres V does the patient receive in 2 hours?

40 gtt/min60 gtt/mL2 h
V = mL
4.IV infusion ratesHard
2 g250 mL? mL/h2 mg/min

A bag contains 2 g of a drug in 250 mL. The order is 2 mg per minute. At what rate R do you set the pump, in mL/h?

2 g/250 mL2 mg/min
R = mL/h

3Solutions

1.IV fluids & fluid balance

Answer: B = 1000 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 + 200 = 400 mL
IV infusion: 125·12 = 1500 mL
IV antibiotic: 1·50 = 50 mL
total intake = 1950 mL

Total output

200 + 275 + 325 + 150 = 950 mL

Balance

B = 1950 − 950 = 1000 mL

Answer

B = 1000 mL

Positive: more fluid went in than came out.

2.IV fluids & fluid balance

Answer: t = 11.5 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.

First part

120·3 = 360 mL
1000 − 360 = 640 mL left

Second part

640/75 = 8.533 h

Total time

t = 3 + 8.533 = 11.53 ≈ 11.5 h

Answer

t = 11.5 h

That is about 11 h 32 min, so the bag runs out at about 00:02.

3.IV infusion rates

Answer: V = 80 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

40·60/60 = 40 mL/h

Volume

V = 40·2 = 80 mL

Answer

V = 80 mL
4.IV infusion rates

Answer: R = 15 mL/h

Dose-based infusions: concentration = amount of drug in the bag/bag volume. Pump rate (mL/h) = dose per hour/concentration, and dose per hour = mL/h × concentration. Convert per-minute doses to per-hour (× 60) and keep the mass units the same (1 g = 1000 mg, 1 mg = 1000 mcg).

Concentration

2000 mg/250 mL = 8 mg/mL

Dose per hour

2·60 = 120 mg/h

Pump rate

R = 120/8 = 15 mL/h

Answer

R = 15 mL/h

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