PCA: The principles of Patient Controlled Analgesia

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Patient Controlled Analgesia (PCA) overcomes some of the problems encountered by traditional intramuscular therapy and continuous infusions. This mode of delivery enables  the patient to 'control' the administration of the drug. It may be more accurate to call it patient-assisted analgesia, as it is prescribed and limited by the doctor. The first demonstration of a PCA machine was in 1976 at the Welsh National School of Medicine [1]. This became the first commercially available PCA machine: 'The Cardiff Palliator'. Since this time there has been considerable development in the design of the infusion devices that are used for this purpose. The sophisticated advanced infusion devices enable the programming of a sequence of events within set parameters. In turn PCA evoids the variable absorption of intramuscular analgesia and the problems of frequent adjustments of infusion rate with intravenous infusions.

The concept of PCA allows on-demand repetitive dosing of small amounts of opioids by the patient, followed by a lockout period during which the machine will not allow any more doses of analgesic. The patient uses PCA to titrate their plasma concentration of opioids around the Minimum Effect Analgesic Concentration. Constant plasma levels of opioid and consistent analgesia are more easily attained with PCA than with the other modes of delivery. PCA is dynamic and flexible; it allows patients to have as little or as much opioid as they want. Advances in technology may mean more flexibility as bolus doses and background doses can be altered by patients recording their pain on a specially designed handset which is linked to a computer which can faciliate changes. PCA can accommodate the widely divergent analgesic requirements of different patients. The concept of PCA depends on the patients staying in 'the analgesic corridor' but there are many factors that may influence this. For instance, lack of education in using the device, fear and anxiety, myths and misconceptions associated with opioid use, mental incapacity and very young age can all be influential. Careful assessment in identifying patient suitability accompanied by good and continued education and support enhances the success of PCA.

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