Two problem types in one place. IV flow rate asks what to set on the pump in mL/hr, including short infusions timed in minutes. Infusion time works backwards: given the volume and the rate, how long until the bag runs out, in hours and minutes.
Divide the total volume in mL by the infusion time in hours: 1,000 mL over 8 hours is 1,000 ÷ 8 = 125 mL/hr. If the time is in minutes, convert it first: 100 mL over 30 minutes is 100 ÷ 0.5 = 200 mL/hr. Infusion time is the reverse: volume ÷ rate.
Pumps are programmed in mL/hr, so there is no drop factor anywhere in these problems. If a question mentions gtt/mL, it is a gravity question; practice those on the drip rate page.
| Order | Setup | Answer |
|---|---|---|
| 1,000 mL over 8 hr | 1,000 ÷ 8 | 125 mL/hr |
| 500 mL over 6 hr | 500 ÷ 6 = 83.33 | 83.3 mL/hr |
| 100 mL over 30 min | 100 ÷ 30 × 60 | 200 mL/hr |
| 50 mL over 20 min | 50 ÷ 20 × 60 | 150 mL/hr |
Short infusions surprise people because the hourly rate is high. A 100 mL antibiotic over 30 minutes runs at 200 mL/hr. The pump is not giving 200 mL; it is running at the speed that would give 200 mL if it ran a full hour. It stops after 100.
| Situation | Setup | Answer |
|---|---|---|
| 1,000 mL at 125 mL/hr | 1,000 ÷ 125 = 8 | 8 hr 0 min |
| 750 mL at 90 mL/hr | 750 ÷ 90 = 8.333 hr; 0.333 × 60 = 20 | 8 hr 20 min |
| 250 mL at 40 mL/hr | 250 ÷ 40 = 6.25 hr; 0.25 × 60 = 15 | 6 hr 15 min |
The trap is the decimal. 6.25 hours is not 6 hours 25 minutes. The 0.25 is a quarter of an hour, so multiply it by 60 to get 15 minutes.
Some exams ask for the clock time the bag will finish. Add the infusion time to the start time on a 24-hour clock: a bag started at 0930 that runs 8 hr 20 min finishes at 1750. Check your answer against the pump, which shows volume to be infused and time remaining.
Most programs round mL/hr to the nearest tenth, because modern pumps accept decimals: 83.33 becomes 83.3. Some programs, and some older pumps, use whole numbers, so 83.33 becomes 83. Pick your rule in the rounding settings and the practice tool will mark you by it. Infusion times round to the nearest whole minute.
Divide the volume in mL by the time in hours. 1,000 mL over 8 hours is 125 mL/hr. For short infusions in minutes, divide by the minutes and multiply by 60: 100 mL over 30 minutes is 200 mL/hr.
Divide the volume by the rate to get hours, then turn the decimal part into minutes by multiplying it by 60. 750 mL at 90 mL/hr is 8.333 hours, which is 8 hours 20 minutes.
It depends on your program and the pump. Most round to the nearest tenth because pumps accept decimals; some use whole numbers. Use your program's rule. The practice tool lets you choose either.
Flow rate is mL/hr and is what you program on a pump. Drip rate is gtt/min and is what you count on gravity tubing, using the tubing's drop factor.