Unit 8.2: IV Flow Rate and Infusion Calculations

• Topic 01

  Drops Per Minute Calculations

  45 questions
• Topic 02

  mL Per Hour Calculations

  45 questions
• Topic 03

  Infusion Completion Time

  45 questions
• Topic 04

  Syringe Driver Calculations

  78 questions

A few questions from this unit, with the answer and a full explanation. The complete bank is available when you start practising.

1. A nurse divides volume by rate and gets 6.024 hours. How many hours and minutes is this?

   • A
     6 hours 14 minutes
   • B
     6 hours 1 minute
     Correct answer
   • C
     6 hours 2 minutes
   • D
     6 hours 0 minutes
   Explanation

   Whole number = 6 hours. Decimal $0.024 \times 60 = 1.44 minutes, rounded to 1 minute. Answer: 6 hours 1 minute. The decimal is not minutes — it must be multiplied by \60. 0.024 \times 60 = 1.44,$ which rounds to 1 minute.

2. A syringe driver running at 0.7 mL/hr contains morphine sulphate 30 mg and midazolam 10 mg in a total volume of 17 mL. A nurse reviewing the patient at 6 hours calculates how much morphine and midazolam the patient has received. She then discovers the syringe driver had been accidentally set to 1.4 mL/hr for the first 3 hours before being corrected. How much morphine did the patient receive in the first 3 hours at the incorrect rate?

   • A
     About 7.4 mg of morphine (1.76 mg/mL $\times$ 1.4 mL/hr $\times$ 3 hr)
     Correct answer
   • B
     Approximately 4.2 mg of morphine (0.7 mL/hr $\times$ 2 mg/mL $\times$ 3 hr)
   • C
     Approximately 5.6 mg of morphine (0.7 mL/hr $\times$ 1.76 mg/mL $\times$ 3 hr $\times$ 1.5)
   • D
     Approximately 15 mg of morphine (30 mg $\div$ 2, since rate was doubled for half the time)
   Explanation

   Morphine concentration in the syringe = 30 mg divided by 17 mL = 1.76 mg/mL. At the incorrect rate of 1.4 mL/hr for 3 hours: volume delivered = 1.4 times 3 = 4.2 mL. Morphine dose = 4.2 times 1.76 = 7.4 mg (more precisely 7.39 mg). In just 3 hours the patient received close to a quarter of the intended 24 hour dose of 30 mg, because the driver was running at double the correct rate. An error of this kind must be identified immediately: it should prompt escalation and clinical assessment for signs of opioid toxicity, and must be reported as a clinical incident in line with local palliative care governance.

3. A syringe driver runs over 24 hours. A nurse is asked why a 24-hour rather than a 12-hour or 48-hour cycle is used. Which answer BEST explains the clinical rationale?

   • A
     A 24-hour cycle is used because subcutaneous drugs are only stable for 24 hours under most circumstances
   • B
     A 24-hour cycle ensures the nurse administers drugs twice daily, reducing the error rate
   • C
     A 48-hour cycle is standard in hospice settings; 24 hours is used only in acute hospitals
   • D
     A 24-hour cycle balances symptom control with practical preparation and checking, per NICE NG31
     Correct answer
   Explanation

   NICE NG31 recommends anticipatory subcutaneous drug prescriptions and continuous subcutaneous infusions for dying patients. A 24-hour cycle allows drug doses to be titrated daily based on symptoms, ensures regular two-nurse checks, and aligns with clinical reassessment intervals. Drug stability in a syringe varies by combination — most common palliative care combinations are stable for 24 hours, but this is checked against the Palliative Care Formulary for each combination.