Intravenous Therapy IV Calculation (Math)

Sasha A. Rarang, RN, MSN

Basic Infusion Time Formula

 Infusion Time = total volume to infuse ml/hr being infused

“How long

will it take for a particular amount of solution to be completed?” Ex: Calculate the infusion time for an IV solution of 500 ml D5W that is currently infusing at 50 ml/hr?

500 ml = 10 hrs 50 ml/hr OR by ratio 50 ml = 500 ml 1 hr x (cross multiply & solve for x) 50x = 500 x = 10 hrs

Basic Infusion Time Formula

   Time can also be expressed in hours & minutes Multiply the partial portion (after the decimal point) of the hour by 60 to obtain the time to the nearest minute Ex: 500 ml 75 ml/hr = 6.66 hr .66 x 60 min = 39.6 minutes or 40 minutes Therefore the TOTAL time is 6.66 hrs or 6 hrs & 40 minutes

Flow Rates

  Refers to an amount of solution over a period of time Can be expressed as gtt’s/min or ml’s/hr – For our purposes, whenever we discuss regulating an IV by the

roller clamp or by gravity

, we will use the flow rate of

gtt’s/min.

– When trying to figure out the flow rate using an

IV pump

or regulating the IV using a machine, we will use the flow rate of

cc’s/hr

Flow Rates

  Flow rate via gravity or by the roller clamp Refer to your handout “IV Calculation Worksheet”  Vital information needed: microdrip or macrodrip; drop factor

IV Drug Amounts

  D H “How much medication is the patient receiving?” “What is the flow rate to insure proper delivery of the amount of medication ordered?” x Q Ex: An IV of 1000 ml of D5W containing 40,000 U of Heparin is ordered to infuse at 30 ml/hr. Calculate the dosage of Heparin the pt is receiving (How many units/hr of Heparin) 30ml/hr x 40,000 u = 1200 u/hr 1000 ml OR by ratio 40,000 u =

x

u 1,000 ml 30 ml 1,000

x x

= 1200000 = 1200 u/hr (cross multiply & solve for

x

)

IV Drug Amounts

 Ex: Morphine Sulfate IV drip concentration 50 mg in 100 cc D5W. MD orders 2mg of Morphine per hour. What will the flow rate be to insure delivery of 2 mg/hr? ( How many cc’s per hr?) 2mg/hr 50 mg x 100 cc = 4 cc/hr Or by ratio 50 mg = 2 mg 100 cc

x

cc (cross multiply & solve for

x

) 50

x x

= 200 = 4 cc/hr