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 shiftwater300 mLsoup180 mLtea150 mLIV infusion50 mL/h × 8 hIV antibiotic1 × 100 mLurine250 mLurine375 mLurine500 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).

water: 300 mLsoup: 180 mLtea: 150 mLIV infusion: 50 mL/h × 8 hIV antibiotic: 1 × 100 mLurine: 250 mLurine: 375 mLurine: 500 mL
B = mL
2.IV fluids & fluid balanceHard
1000 mL100 mL/hstart 12:1515:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 12:15 and runs by pump at 100 mL/h. How many mL V are left in the bag at 15:45?

1000 mL100 mL/h12:15 → 15:45
V = mL
3.IV infusion ratesMedium
1000 mL15 gtt/mL12 h? gtt/min

Infuse 1000 mL over 12 hours with a giving set of 15 gtt/mL. Find the drip rate R in drops per minute. Round to the nearest whole number.

1000 mL12 h15 gtt/mL
R = gtt/min
4.IV infusion ratesHard
300 mLleft? mL/h5 h left

500 mL was ordered over 10 hours. After 5 hours you find that 300 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?

500 mL / 10 hafter 5 h: 300 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: B = 5 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: 300 + 180 + 150 = 630 mL
IV infusion: 50·8 = 400 mL
IV antibiotic: 1·100 = 100 mL
total intake = 1130 mL

Total output

250 + 375 + 500 = 1125 mL

Balance

B = 1130 − 1125 = 5 mL

Answer

B = 5 mL

Positive: more fluid went in than came out.

2.IV fluids & fluid balance

Answer: V = 650 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

12:15 → 15:45 = 3.5 h

Volume infused

100·3.5 = 350 mL

Volume left

V = 1000 − 350 = 650 mL

Answer

V = 650 mL
3.IV infusion rates

Answer: R = 21 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.

Time in minutes

12·60 = 720 min

Drip rate

R = 1000·15/720 = 20.83 ≈ 21 gtt/min

Answer

R = 21 gtt/min

At the bedside you round to the nearest whole drop: 21 gtt/min.

4.IV infusion rates

Answer: Δ = 20 %

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

500/10 = 50 mL/h

New rate

R = 300/5 = 60 mL/h

Percentage change

Δ = (60 − 50)/50·100% = 20%

Answer

Δ = 20%

Many hospitals allow such an adjustment up to 25% without a new order; check local policy.

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