Microdrip tubing (sometimes called minidrip) comes in only one size: 60 gtt/mL. It is used for children and infants, or to infuse sensitive medications where precision in the flow rate is essential. Microdrip tubing is narrower and so produces smaller drops. (Note: 10 gtt/mL, for example, means 10 gtt = 1mL.) Macrodrip tubing comes in 3 sizes: 10 gtt/mL, 15 gtt/mL, and 20 gtt/mL. It is the tubing most commonly used for routine IV administration, such as infusion of IV fluids that do not contain sensitive medication. Macrodrip tubing is wider and so produces larger drops. IV tubing is pretty standard, and so there are two major categories of IV tubing: The size of a drop in an IV setup depends upon the width of the IV tubing: thinner tubing produces smaller drops and wider tubing produces larger ones. So, how do we measure the size of drops in an IV setup? IV Tubing Calibration In fact, any medications which are measured in drops always come with their own calibrated dropper, and the dropper from one medication cannot be used to dose another medication because the drops indicated on the labels are probably not going to be the same size. We can also convert between drops and milliliters, because both of these units measure volume, but we have to be careful, because drops come in many different sizes. We already know how to convert between hours and minutes because we know that 1 h = 60 min. We can convert between a flow rate measured in gtt/min and a flow rate measured in mL/h. Notice that both of these rates measure volume over time. For an IV setup on a volumetric pump or other electronic infusion device, we use the flow rate measured in mL/h because we can type this amount into the device manually without having to count drops in a drip chamber. For a manual IV setup, the flow rate is expressed in gtt/min, because we measure the rate by counting the number of drops which fall in the drip chamber each minute. In order to set up a IV, we need to know the flow rate the flow rate is the speed at which the fluid infuses into the patient, and it is expressed in volume over time. Lecture 7: IV Flow Rate and Infusion/Completion Times Calculating Flow Rates
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