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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 12-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). Count ice chips as half their volume.
Practice exercise (made-up values, not clinical guidance). A 1000 mL bag was started at 08:15 and runs by pump at 150 mL/h. How many mL V are left in the bag at 12:15?
1000 mL150 mL/h08:15 → 12:15
V = mL
3.IV infusion ratesMedium
Infuse 1000 mL over 10 hours with a giving set of 60 gtt/mL. Find the drip rate R in drops per minute.
1000 mL10 h60 gtt/mL
R = gtt/min
4.IV infusion ratesHard
A drip runs at 40 gtt/min through a set of 15 gtt/mL. There are 600 mL left in the bag. How many hours t until it is empty? Round to one decimal place.
40 gtt/min15 gtt/mL600 mL
t = h
3Solutions
1.IV fluids & fluid balance
Answer: B = 20 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: 150 + 200 + 180 = 530 mL
ice chips: 240/2 = 120 mL
IV infusion: 60·12 = 720 mL
IV antibiotic: 2·100 = 200 mL
total intake = 1570 mL
Total output
450 + 350 + 400 + 100 + 250 = 1550 mL
Balance
B = 1570 − 1550 = 20 mL
Answer
B = 20 mL
Positive: more fluid went in than came out.
2.IV fluids & fluid balance
Answer: V = 400 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
08:15 → 12:15 = 4 h
Volume infused
150·4 = 600 mL
Volume left
V = 1000 − 600 = 400 mL
Answer
V = 400 mL
3.IV infusion rates
Answer: R = 100 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
10·60 = 600 min
Drip rate
R = 1000·60/600 = 100 gtt/min
Answer
R = 100 gtt/min
4.IV infusion rates
Answer: t = 3.8 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.