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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
Pump rate in mL/h: volume divided by time in hours.
Drip rate in drops/min: volume × drop factor divided by time in minutes.
For time remaining: volume left divided by the rate.
Round as the question or the equipment requires.
2Practice problems
1.IV fluids & fluid balanceMedium
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).
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
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
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.