Dosage Calculations Flow Rate

IV infusions are a mainstay in the nursing world, and so understanding how to use them to deliver an appropriate dose is essential. Because IV’s deliver a certain dose (mg) of liquid (ml) over time (t), we must take these three factors into consideration for this type of calculation. Consider this scenario: A client requires a 500mg dose of a medication given over a one hour infusion. The medication on hand is available in a 1000mg/1L solution. What would the appropriate flow rate be to deliver the correct amount of medication to the client? First, let’s review what we already know. We know that the infusion must last one hour, which equals sixty minutes. We also know that the client requires a 500mg dose, and that the drug on have comes is a 1000mg/1L formulation. Let’s figure out the volume of solution the client would need in order to get the correct dose by setting up a ratio: (dose available) / (volume available) = (dose desired) / volume desired) (1000mg) / (1 L) = (500mg) / (? L) First, we cross multiply the numerator and the denominator (500 x 1 = 500). Next, we divide by the remaining numerator (500 / 1000 = 0.5). We now know that the client requires 0.5 L to receive the correct dose, but let’s take this a step further and convert this answer to mL. 1 L = 1000 mL…. so that means 0.5 L = 500 mL Lastly, we need to figure out the amount of volume that needs to be delivered per minute in order for the full dose to be delivered in 1 hour. We do this by simply dividing the volume by the number of minutes in an hour (60). 500 mL / 60 min = 8.33 mL per minute. For simplicity, let’s round this to 8 mL per minute. And there’s our answer! For the client to receive 500mg of an IV solution over 1 hour using a formulation of 1000mg / 1L, we need to deliver approximately 8 mL per minute.

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