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 shifttea240 mLsoup180 mLjuice150 mLIV infusion75 mL/h × 8 hIV antibiotic1 × 50 mLurine375 mLurine225 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 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).

tea: 240 mLsoup: 180 mLjuice: 150 mLIV infusion: 75 mL/h × 8 hIV antibiotic: 1 × 50 mLurine: 375 mLurine: 225 mLvomit: 200 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL80 mL/hstart 07:0008:30: ? mL

Practice exercise (made-up values, not clinical guidance). A 500 mL bag was started at 07:00 and runs by pump at 80 mL/h. How many mL V are left in the bag at 08:30?

500 mL80 mL/h07:00 → 08:30
V = mL
3.IV infusion ratesMedium
V = ?60 gtt/mL100 gtt/min4 h

A drip runs at 100 gtt/min through a set of 60 gtt/mL. How many millilitres V does the patient receive in 4 hours?

100 gtt/min60 gtt/mL4 h
V = mL
4.IV infusion ratesHard
500 mg250 mL8 mL/h? mg/h

A bag contains 500 mg of a drug in 250 mL and runs at 8 mL/h. How many milligrams per hour D does the patient receive?

500 mg/250 mL8 mL/h
D = mg/h

3Solutions

1.IV fluids & fluid balance

Answer: B = 420 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: 240 + 180 + 150 = 570 mL
IV infusion: 75·8 = 600 mL
IV antibiotic: 1·50 = 50 mL
total intake = 1220 mL

Total output

375 + 225 + 200 = 800 mL

Balance

B = 1220 − 800 = 420 mL

Answer

B = 420 mL

Positive: more fluid went in than came out.

2.IV fluids & fluid balance

Answer: V = 380 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

07:00 → 08:30 = 1.5 h

Volume infused

80·1.5 = 120 mL

Volume left

V = 500 − 120 = 380 mL

Answer

V = 380 mL
3.IV infusion rates

Answer: V = 400 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 = 100·4 = 400 mL

Answer

V = 400 mL
4.IV infusion rates

Answer: D = 16 mg/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.

Concentration

500/250 = 2 mg/mL

Dose rate

D = 2·8 = 16 mg/h

Answer

D = 16 mg/h

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