Intravenous infusion by gravity

Infusion devices

An infusion device is designed to accurately deliver measured amounts of fluid or drug via a number of routes (intravenous, subcutaneous or epidural) over a period of time. The infusion device is set at an appropriate rate to achieve the desired therapeutic response and prevent complications (Dougherty 2002, MHRA 2010b, MHRA 2011).

Gravity infusion devices

Gravity infusion devices depend entirely on gravity to deliver the infusion. The system consists of an administration set containing a drip chamber and a roller clamp to control the flow, which is usually measured by counting drops (Pickstone 1999). The indications for use are:

• delivery of fluids without additives

• administration of drugs or fluids where adverse effects are not anticipated and which do not need to be infused with absolute precision

• where the patient’s condition does not give cause for concern and no complication is predicted (Quinn 2008).

The flow rate is calculated using a formula that requires the following information: the volume to be infused; the number of hours the infusion is running over; and the drop rate of the administration set (which will differ depending on type of set). The number of drops per millilitre is dependent on the type of administration set used and the viscosity of the infusion fluid. Increased viscosity causes the size of the drop to increase. For example, crystalloid fluid administered via a solution set is delivered at the rate of 20 drops/mL; the rate of packed red cells given via a blood set will be calculated at 15 drops/mL (Quinn 2008).

The rate of administration of a continuous or intermittent infusion may be calculated from the following equation (Pickstone 1999):

In this equation, 60 is a factor for the conversion of the number of hours to the number of minutes.

(Royal Marsden 2015)