Question 1 · Hard
A red-cell unit of 280 mL is running at 20 drops/min through a blood giving set that delivers 15 drops/mL. If the rate is unchanged, how long will the unit take to finish, and is it within the safe limit?
- A1 hour 45 minutes, within the 4-hour limit
- B3 hours 30 minutes, within the 4-hour limit
- C4 hours 40 minutes, beyond the 4-hour limit
- D2 hours 20 minutes, within the 4-hour limit
Show answerHide answer
Answer: B · 3 hours 30 minutes, within the 4-hour limit
Time (min) = volume (mL) x drop factor / drops per minute. Here 280 x 15 / 20 = 4,200 / 20 = 210 minutes, which is 3 hours 30 minutes. A red-cell unit must be completed within 4 hours of leaving the refrigerator, so this rate is acceptable if the unit was started promptly. Using the wrong drop factor is the commonest error in this calculation.
- A: 1 hour 45 minutes halves the correct time by a slip in the arithmetic.
- C: 4 hours 40 minutes comes from using a 20 drops/mL factor.
- D: 2 hours 20 minutes comes from using a 10 drops/mL factor.