infusion
Meaning of infusion: Rate is the whole point, since spreading a dose across time changes how a substance is tolerated, not merely how long it takes.
Definition of infusion
An infusion is the delivery of fluid, medication, nutrients or blood products into the body gradually over a set period, most often into a vein. The rate is controlled deliberately rather than left to chance, usually by a pump, and the period can run from a few minutes to many hours depending on what is being given.
Why control the rate at all?
Giving the same total amount quickly or slowly does not produce the same result. A slow rate holds the concentration in the blood steadier, which matters for substances whose effect or toxicity tracks the peak level reached rather than the total dose. It gives the liver and kidneys time to keep pace with clearance. It dilutes irritant substances as they pass through the vein wall, reducing damage to the vein itself. And where a reaction is possible on first exposure, a slow start allows any response to appear before much has been delivered. Fluids given for dehydration or an electrolyte disturbance follow the same logic in reverse, since correcting a large deficit too fast can cause problems of its own.
How does an infusion differ from a bolus?
| Infusion | Bolus | |
|---|---|---|
| Delivery | Spread across a defined period | Given all at once |
| Level in the blood | Rises to a plateau and holds there | Peaks sharply, then falls away |
| What sets the rate | A pump or a counted drip rate | The syringe and the hand on it |
| Typical purpose | Holding an effect steady, giving irritant or reactive substances | Rapid effect, contrast for a scan, emergency medication |
The two are frequently combined. A bolus establishes the level quickly, and an infusion then maintains it, which is why an order may specify both for the same drug.
Where does an infusion go?
Most are intravenous, entering a small vein in the arm or, for irritant substances and long courses, a catheter threaded into a large vein near the heart. Other routes serve particular purposes. Subcutaneous infusion places fluid or medication in the tissue under the skin, from which it is absorbed slowly. An infusion can be directed into the artery feeding one organ so that the highest concentration reaches that organ while the rest of the body sees less. It can also be run into the abdominal cavity so that the fluid bathes the surfaces there. Chemotherapy, antibiotics, blood products, immune therapies and nutrition are all given this way, each over a duration set for the specific substance.
Also known as
Used in a sentence
The chemotherapy was given as an infusion over several hours in the outpatient clinic.
Good to know
An infusion delivers fluid or medication gradually over a controlled period, which distinguishes it from a bolus, a rapid single administration of the same substance.
Word origin
Where “infusion” comes from
From Latin infundere, meaning to pour into, formed from in-, meaning into, and fundere, meaning to pour.