Here's how it works: the physician determines the appropriate dosage for the pain medication, choosing a dose and how frequently the dose can be given. A maximum dose per hour is also determined. The pain medication is placed on a pump very similar to a regular IV pump but with a trigger button. For example, the patient may have 1 mg of Morphine every 6 minutes, and a maximum of 6 mg of Morphine per hour.
When the patient is feeling the need for a dose of pain medication, they press the trigger button. If the patient has not exceeded the maximum dose, and (in this scenario) hasn't had a dose in the last six minutes, a dose of pain medication is given through their IV.
PCA pumps can also be connected to an epidural, but are most commonly given via IV.
