Calculating Infusions

Medications can be prescribed in doses that must be administered continuously for a specified period of time. An infusion is administered at a flow rate that will give the required dosage per hour or minute for the patient. Clinical areas generally have standarised infusion strengths that are always used for specific medications, with the rate varied according to the prescribed dose for the patient. For example, a drug may be prescribed as 500 micrograms/kg/hour and infused using a solution of 500mg in 500ml sodium chloride. To administer the correct dose, the dose for the patientu2019s weight (dose x kg) must be calculated. This is done in steps:

Step 1

Calculate the millilitres//hour by working out what dose is contained in one millilitre of the infusion dosage. Ex.: 500ml/500mg = 1ml/mg

Step 2

Calculate the dosage per weight of the patient and convert this into milligrams. For example, a 45kg patient would be 45kg x 500 micrograms/kg = 22,500 micrograms. Converting into milligrams would be 22.5mg (22,500/1,000)

Step 3

1ml would administer 1mg of the drug, so 22.5ml would administer 22.5mg. The infusion rate would be set as 22.5ml/hour