Rx Update: August 2003
Joan Murhammer, R.Ph., Mary Ross, R.Ph., M.B.A., Kevin Bebout,
R.Ph.
Peer Review Status: Internally Reviewed
Patient-controlled analgesia (PCA) has considerable potential to improve pain management for patients, allowing them to self-administer more frequent, but smaller doses of analgesia. When used as intended, PCA actually reduces the risk of over-sedation, which is an unintended consequence of the more traditional method of nurse-administered analgesia in larger, less frequent doses. In fact, with PCA, patients often develop a synergism with the device and can quickly learn how to manage their pain while avoiding undue mental clouding. However, errors can occur unless PCA is used appropriately. The following factors have been cited as contributing to errors.
PCA by proxy. Several safety features exist with PCA to make certain patients do not receive too much analgesia. These include a lockout interval that specifies the minimum amount of time between each dose, and a maximum allowable amount during a specified time interval. Another "built-in" safety feature that's often overlooked is that the device is intended for patient use. A sedated patient will not press the button to deliver more opiate, thus avoiding toxicity. However, family members and health professionals have administered doses for patients, by proxy, hoping to keep them comfortable. This well-intentioned effort has been reported to result in over-sedation, respiratory depression, and even death.
Improper patient selection. The benefits of PCA have led providers to extend its use to less-than-ideal candidates such as infants, young children, and confused elderly patients. This has facilitated the dangerous practice of PCA by proxy.
Inadequate monitoring. Even at therapeutic doses, opiates can suppress respiration, heart rate, and blood pressure, and patients may not be monitored frequently enough, especially during the first 24 hours of use and at night when nocturnal hypoxia can occur. There may also be too much reliance on pulse oximetry, which can offer a false sense of security since oxygen saturation is usually maintained even at low respiratory rates.
Inadequate patient education. Patients who have been taught to use the device during the immediate postoperative period have often been too groggy to fully understand its use, and they often report poor pain control during the first 12 hours after surgery.
Drug product mix-ups. Some of the opiates used for PCA have similar names and packaging, which has led to drug selection errors. Since opiates are typically in unit stock, these errors are rarely detected and, most often, they have led to significant overdoses; less often, they have led to undertreatment of pain or to an allergic response to the medication.
Practice-related problems. Mis-programming of the PCA pump is, by far, the most frequently reported practice-related issue. Other practice-related issues that have contributed to PCA errors include incorrect transcription of prescriptions into pharmacy computers or medication administration records, calculation errors when determining the patient's dose or rate of infusion, and IV admixture errors.
Device design flaws. Programming a PCA pump requires multiple steps, but the pump's design is often far from intuitive. Most programming errors have resulted because concentration settings for opiates such as morphine default to 0.1 mg/ml or 1 mg/ml, but a higher concentration may be used. Other design flaws that have facilitated programming errors include pumps that do not require users to review all settings before the infusion starts, pumps that require users to program the dose in ml (rather than mg), and free flow.
Inadequate staff training. Staff may not always receive adequate training in pump programming, or they may not retain their proficiency once trained if multiple pumps are in use, or if PCA therapy is encountered infrequently.
Prescription errors. The PCA order itself can be a source of error. Prescribers have made mistakes in converting an oral opiate dose to the IV route, prescribing a drug to which the patient is allergic, or selecting an opiate that is not appropriate for the patient (e.g., meperidine in patients with renal impairment).