A continuous infusion delivers a set amount of opioid every hour without the need for the patient to activate the system. Continuous infusions are not commonly used, as no documented benefits have been shown for most patients. Continuous infusions are not recommended in the opioid-na'ive or high-risk patient populations such as the elderly, concomitant use of other sedatives, those with obstructive sleep apnea, or morbid obesity. The use of continuous infusions increases the overall opioid consumption and has been identified as an independent risk factor for respiratory depression. Continuous infusions have not been shown to improve patient satisfaction or pain rating scores and they do not decrease the frequency of demand dose use.
It may appear to make sense to use a continuous infusion at night when the patient is theoretically sleeping and therefore unable to activate the PCA; however, studies have shown that nighttime basal infusions do not improve sleep or analgesia.
Continuous infusions may be needed in opioid-tolerant patients. If the patient cannot take their usual doses of opioid enterally, then a continuous infusion should be used. One way to achieve this is to determine an intravenous equivalent for the amount of opioid the patient takes in a day (taking into account incomplete cross-tolerance if switching to a different agent) and divide this amount by 24 h and administer this as the hourly continuous infusion rate.
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