IV Fluid Orders

When an IV is administered, the nurse has two important intravenous calculations: flow rate and infusion time. IV knowledge is not just limited to the nursing profession. Hospital pharmacies and long-term care pharmacies play an important role with the setting up and maintenance of IV pumps.

IV Flow Rate

The flow rate is the volume of fluid a patient receives over a period of time. The flow rate is measured by milliliters per minute (mL/min) or drops per minute (gtts/min).

Suppose you receive an order to set up an IV administration pump. The pump needs to run a saline IV 1,000mL for six hours. How many milliliters per minute should this pump run?

Set up a proportion of what you are given versus what you need. Since you are finding milliliters per minute, you must first convert the six hours to minutes to properly set up your proportion.

60 * 6 = 360 minutes

360x = 1,000

x = 2.78mL/min

We calculated that the pump will be set to run the saline IV at 2.78mL/min. Keeping with this example, let’s now find the gtts/min. Whenever the question specifically asks for drops per minute, you will be given a drop factor. The drop factor is the amount of drops per volume of 1mL solution. Drop factors vary because solutions’ weights vary.

In this scenario, the drop factor is 15 gtts. Simply multiply the drop factor by the mL/mins that we previously calculated to get the gtts/min.

15 * 2.78 = 41.7gtts/min

Infusion Time

Intravenous calculations include infusion time. Infusion time is important for a pharmacy to know how many IV bags to compound. If too many bags are made, then medication is wasted and might also cost the pharmacy money for returned medications due to pharmacy error. Once these bags are compounded, they are good for a limited time (48 hours at best for low-risk compounds) so they cannot just be held indefinitely for the next patient. Any returned bags need to be properly disposed. On the other hand, too few bags made can be detrimental to the patient’s health!

Let’s continue with the above example. With a 2.78mL/min, we can calculate that the patient will receive 166.8mL/hour. With a 1,000mL bag, we conclude that one bag will last the patient a little under six hours (5.995 hours without rounding).

2.78 * 60 = 166.8mL/hr

1,000 / 166.8 = 5.995 hours

This works out well since the patient is prescribed the saline IV for only six hours, the pharmacy would only need to send one bag. If the hospital decides to keep the patient on it for a 24-hour period, how many bags would the pharmacy send?

Divide 24 hours by the number of hours that one bag takes. In this case, with one bag lasting approximately six hours, the pharmacy would need to send four bags to cover a 24-hour period.