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 mLsoup180 mLIV infusion125 mL/h × 8 hIV antibiotic1 × 100 mLurine375 mLurine475 mLurine150 mLwound drain60 mLvomit200 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-hour shift. The patient weighs 101 kg. Find the average urine output U in mL/kg/h. Round to two decimal places.

101 kg8 hurine: 375 mLurine: 475 mLurine: 150 mLwound drain: 60 mLvomit: 200 mL
U = mL/kg/h
2.IV fluids & fluid balanceHard
500 mL50 mL/hstart 11:1517:45: ? mL

Practice exercise (made-up values, not clinical guidance). A 500 mL bag was started at 11:15 and runs by pump at 50 mL/h. How many mL V are left in the bag at 17:45?

500 mL50 mL/h11:15 → 17:45
V = mL
3.IV infusion ratesMedium
V = ?60 gtt/mL30 gtt/min2 h

A drip runs at 30 gtt/min through a set of 60 gtt/mL. How many millilitres V does the patient receive in 2 hours?

30 gtt/min60 gtt/mL2 h
V = mL
4.IV infusion ratesHard
140 mLleft? mL/h2 h left

500 mL was ordered over 8 hours. After 6 hours you find that 140 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 / 8 hafter 6 h: 140 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: U = 1.24 mL/kg/h

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 urine

375 + 475 + 150 = 1000 mL

Per kilogram per hour

U = 1000/(101·8) = 1.238 ≈ 1.24 mL/kg/h

Answer

U = 1.24 mL/kg/h
2.IV fluids & fluid balance

Answer: V = 175 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 → 17:45 = 6.5 h

Volume infused

50·6.5 = 325 mL

Volume left

V = 500 − 325 = 175 mL

Answer

V = 175 mL
3.IV infusion rates

Answer: V = 60 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

30·60/60 = 30 mL/h

Volume

V = 30·2 = 60 mL

Answer

V = 60 mL
4.IV infusion rates

Answer: Δ = 12 %

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

500/8 = 62.5 mL/h

New rate

R = 140/2 = 70 mL/h

Percentage change

Δ = (70 − 62.5)/62.5·100% = 12%

Answer

Δ = 12%

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

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