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.

New problemsBack to the course

In the print window, choose “Save as PDF” to keep a copy on your device.

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 shiftmilk100 mLjelly120 mLjuice120 mLIV infusion100 mL/h × 8 hIV antibiotic1 × 50 mLurine225 mLurine400 mLurine425 mLurine400 mLwound drain140 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).

milk: 100 mLjelly: 120 mLjuice: 120 mLIV infusion: 100 mL/h × 8 hIV antibiotic: 1 × 50 mLurine: 225 mLurine: 400 mLurine: 425 mLurine: 400 mLwound drain: 140 mLvomit: 200 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL→ 200 mL/hstart 18:30ttotal​ = ? h100 mL/h × 4 h

Practice exercise (made-up values, not clinical guidance). A 500 mL infusion starts at 18:30 at 100 mL/h. After 4 hours the rate is changed to 200 mL/h and is not changed again. How many hours t after the start will the bag be empty? Round to one decimal place.

500 mL100 mL/h · 4 h200 mL/h
t = h
3.IV infusion ratesMedium
60 gtt/mL90 mL/h? gtt/min

An infusion is ordered at 90 mL/h, but no pump is available. It runs by gravity through a giving set of 60 gtt/mL. Find the drip rate R in drops per minute.

90 mL/h60 gtt/mL
R = gtt/min
4.IV infusion ratesHard
390 mLleft? mL/h2 h left

1000 mL was ordered over 6 hours. After 4 hours you find that 390 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 4 h: 390 mL
Δ = %

3Solutions

1.IV fluids & fluid balance

Answer: B = −600 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: 100 + 120 + 120 = 340 mL
IV infusion: 100·8 = 800 mL
IV antibiotic: 1·50 = 50 mL
total intake = 1190 mL

Total output

225 + 400 + 425 + 400 + 140 + 200 = 1790 mL

Balance

B = 1190 − 1790 = −600 mL

Answer

B = −600 mL

Negative: the patient lost more fluid than went in.

2.IV fluids & fluid balance

Answer: t = 4.5 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

100·4 = 400 mL
500 − 400 = 100 mL left

Second part

100/200 = 0.5 h

Total time

t = 4 + 0.5 = 4.5 h

Answer

t = 4.5 h

That is about 4 h 30 min, so the bag runs out at about 23:00.

3.IV infusion rates

Answer: R = 90 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

90/60 = 1.5 mL/min

Drip rate

R = 1.5·60 = 90 gtt/min

Answer

R = 90 gtt/min

With a microdrip set (60 gtt/mL), gtt/min equals mL/h.

4.IV infusion rates

Answer: Δ = 17 %

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 = 390/2 = 195 mL/h

Percentage change

Δ = (195 − 166.7)/166.7·100% = 17%

Answer

Δ = 17%

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

ExamProblems · examproblems.com/courses/iv-fluids-and-fluid-balance