Question

Safe dosage range: Lidocaine 1 to 4 mg/min Available: Lidocaine 2 g in 500 mL D5W The IV flow rates for the lowest and highest dosages are_and 1 and 16 ml/hr 30 and 120 ml/hr 15 and 60 ml/hr 3 and 20 ml/hr

Answer 1

Available concentration of Lidocaine = 2 gram in 500 mL D5W

= 2 x 1000 mg in 500 mL D5W

= 2000mg/500 mL D5W

= 4 mg/mL D5W.

Safe dosage range of Lidocaine = 1 to 4 mg/min.

For the lowest safe dosage,

Flow rate of Lidocaine must be = 1 mg per min

  = 60 mg per 60 min

= 60 mg/hr

The IV solution contains 4 mg Lidocaine in every 1 mL of the solution.

Therefore, amount of IV solution with 60 mg Lidocaine = 60 mg/4 mg per mL.

= 15 mL.

Thus, 15 mL of IV solution contains 60 mg Lidocaine. Since, at the very minimum, the patient should get 60 mg Lidocaine every hour, they must receive 15 mL of the IV solution every hour.

Therefore, at the lowest safe dosage, IV flow rate must be = 15 mL/hr.

Similarly for the highest safe dosage,

Flow rate of Lidocaine must be = 4 mg per min

  = 4 x 60 mg per 60 min

= 240 mg/hr

The IV solution contains 4 mg Lidocaine in every 1 mL of the solution.

Therefore, amount of IV solution with 240 mg Lidocaine = 240 mg/4 mg per mL.

= 60 mL.

Thus, 60 mL of IV solution contains 240 mg Lidocaine. Since, at the maximum, the patient should get 240 mg Lidocaine every hour, they must receive at most 60 mL of the IV solution every hour.

Therefore, at the highest safe dosage, IV flow rate must be = 60 mL/hr.

Therefore, the correct option is: 15 and 60 mL/hr.

The IV flow rates for lowest and highest dosage are 15 mL/hr and 60 mL/hr.

Thus, the following options are incorrect, because:

1 and 16 mL/hr.

1 mL/hr means 4 mg Lidocaine per hour as opposed to the 60 mg per hour minimum, and 16 mL/hr means 16 x 4 = 64 mg Lidocaine per hour as opposed to the 240 mg/hr maximum. These values are too low to be correct.

30 and 120 mL/hr.

30 mL/hr means 30 x 4 = 120 mg Lidocaine per hour as opposed to the 60 mg per hour minimum, and 120 mL/hr on the other hand means 120 x 4 = 480 mg Lidocaine per hour as opposed to the 240 mg/hr maximum. These values are too high to be correct.

3 and 20 mL/hr.

3 mL/hr means 3 x 4 = 12 mg Lidocaine per hour as opposed to the 60 mg per hour minimum, and 20 mL/hr on the other hand means 20 x 4 = 80 mg Lidocaine per hour as opposed to the 240 mg/hr maximum. These values are thus too low to be correct.