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Misprogramming PCA concentration leads to dosing errors

From the August 28, 2008 issue

Problem: ISMP has received a small but concerning number of reports of overdoses with patient controlled analgesia (PCA) due to pump programming errors. Although every aspect in the PCA process has the potential for an error, we are especially concerned about errors related to programming the concentration of the narcotic. Accidentally entering a higher than actual concentration of narcotic in the PCA pump results in the delivery of a lower PCA dose than prescribed. This can be significant in that the patient’s pain may not be controlled. If increased dosing (and thus increased rate of infusion) is prescribed to meet the patient’s needs, subsequent changes of the PCA syringe or bag for which the concentration is then reprogrammed correctly may result in the delivery of more drug than necessary, risking respiratory depression. At the same time, dosing errors due to inadvertently programming a lower than actual concentration of the narcotic into the PCA infusion pump result in the delivery of a higher PCA dose than prescribed—frequently 10 times more than intended. These are the more dangerous errors that have led to adverse drug events, including fatalities. See the sidebar on “inverse relationships” (at the end of this article).

While most organizations use a standard concentration for each PCA drug, occasionally morphine, HYDROmorphone, or fentaNYL concentrations will be customized for a patient who is opioid-tolerant. These concentrations are significantly higher than those typically used for opioid-naïve patients. The concentrated drug will allow less frequent syringe/bag changes.

Errors in initiating PCA infusions can occur at any point in the programming process. By using a limited number of standard concentrations, standardizing order forms, implementing smart PCA pumps with dose error reduction software (DERS), and requiring an independent double-check of the PCA programming, hospitals have put in place effective tools to help reduce PCA dosing errors. However, the risk of a PCA error increases significantly when there are atypical orders, non-standard concentrations, and doses that are unusually high compared to the “typical” PCA patient’s therapy.
In reports received by ISMP related to the concentration of PCA infusions, there have been several common findings: 

Lower than intended concentration programmed. A number of reports were associated with programmed concentrations that were significantly lower than the actual drug concentration. For example, a 60 mL syringe with a standard concentration of 1 mg/mL was inadvertently programmed as containing a 1 mg/60 mL concentration. This resulted in a programmed concentration that was 1/60th of the actual concentration, and a single patient request for a 1 mg dose delivered all 60 mgs (60 mL) of narcotic in the syringe. 

Significance of low concentration errors not always understood. Some smart PCA pumps with DERS can alert the nurse that the concentration is too low. These alerts can be soft, allowing them to be overridden, or hard, requiring the user to reprogram the pump. ISMP has evaluated concentration programming errors in patients where smart PCA pumps with DERS were used. In cases where a higher custom concentration was accidentally programmed using the more typical lower concentration, the pumps identified the error with a low concentration alert. However, the significance of the low concentration alerts may not have been appreciated as the soft alerts were sometimes overridden, with patients receiving overdoses of PCA medications. Since the primary emphasis on averting IV errors has been focused on doses that are too high and exceed the maximum limits, it appears that the “low concentration” soft alert may be interpreted incorrectly as being similar to “low dose” alerts that are frequently displayed as the doses of drugs are being titrated down prior to discontinuing the infusions. See the sidebar on “inverse relationships” (at the end of the article) for more about this common misperception. 

Confusing the concentration. For label clarity, we recommend that the PCA drug syringe/bag label include both the concentration expressed as the amount of drug/mL plus the total amount of drug in the final volume. However, this does not eliminate any possibility of confusion and misreading of the actual concentration, which could lead to a programming error. For example, in one case, a PCA pump equipped with DERS had two standard morphine concentrations (1mg/mL and 5 mg/mL) in the medical/ surgical drug library. A third custom concentration of __mg/__ mL was included in the library to accommodate non-standard concentrations. Although the PCA syringe contained 125 mg in 25 mL (the 5 mg/mL standard concentration), the custom concentration was selected and the concentration was programmed incorrectly as 5 mg/25 mL, or 1/25th the actual concentration. The soft “low concentration” alert was overridden, and the entire syringe was administered the first time the patient pressed the dose request button. Fortunately, the patient had a high tolerance for opioids, and no harm occurred. But in an opioid-naïve patient, the outcome could have been catastrophic.

Safe Practice Recommendations: Consider the following recommendations to help reduce the potential for concentration errors when programming PCA pumps:

Assess vulnerability to serious errors. Medication safety teams should review current practices around the use of custom concentrations. In particular, the team should assess vulnerability to programming errors related to concentration and the use of multiple standard concentrations and custom concentrations. The risk of serious adverse drug events due to these vulnerabilities should be communicated to all clinical staff, and the recommendations below and others that arise from the medication safety team assessment should be implemented and monitored for effectiveness.   

Limit concentrations. When possible, use a single, standard concentration for each PCA drug. If more than one concentration is deemed necessary by the Pharmacy and Therapeutics Committee, limit the number of standard concentrations to two at the most. Use of custom concentrations should be minimized, and when possible, restricted to selected patient care areas.

Distinguish custom concentrations. When a custom concentration is necessary, the container label should be very distinctive and should not look like the standard PCA syringe/bag label. Auxiliary labels (e.g., “High-Potency”) and a different color pharmacy label with specific instructions for programming the pump should be used for custom concentrations.

Clarify the label. ISMP usually recommends presenting the total drug concentration in the bag/syringe first, followed by the amount of drug per mL below this within the same background or border on the product label. But depending on the PCA pump vendor, the user may be prompted to enter the concentration in a mg/mL strength. In these cases, it would be safest to express the concentration with the amount of drug per mL listed first, and then the total amount of drug/total volume in the syringe/bag below this.

Match the MAR to the label. List the concentration on the medication administration record (MAR) the same way it is presented on the PCA label. This will help prevent confusion when comparing the actual product label to the verified order on the MAR.  

Employ an independent double-check. The narcotics used for PCA are high-alert medications; thus, an independent double-check of the product and pump programming should be considered. When replacing an empty syringe/bag, the empty container should be compared to the new container to verify that the concentration is the same.

Use bar-coding technology. Some infusion pumps incorporate bar-coding technology. Scanning the barcode on the PCA bag would help to ensure that the correct concentration is entered during the programming of PCA.

Use smart pumps. PCA pumps with DERS should be used whenever possible. Because the significance of a low concentration alert may not be fully appreciated, low concentration limits should always be set as hard limits. Clinical advisories should also be used to reinforce caution when using custom concentrations.

Pump vendors: standardize prompts. Among the various vendors of PCA pumps, a single way of entering the drug’s concentration should be standardized and used (e.g., per mL [5 mg/mL] or per total volume [125 mg/25 mL]) for all PCA pumps to promote consistency. 

Sidebar: Inverse relationships. Based on correspondence received in response to articles we’ve previously published about PCA pump programming errors, various healthcare practitioners have contacted ISMP suggesting that setting the pump at a higher concentration than the actual drug would result in an overdose, and setting the concentration at a lower concentration than the actual drug would result in an underdose. The opposite is true. Although counterintuitive, concentration and volume have an inverse relationship. More concentrated drugs require less volume to deliver a specified dose; less concentrated drugs require more volume to deliver a specified dose. With PCA, the concentration must be programmed into the pump so it can calculate the volume needed to deliver the prescribed dose. If the programmed concentration is lower than the actual concentration in the syringe/bag, the pump will deliver an overdose. If the programmed concentration is higher than the actual concentration in the syringe/bag, the pump will deliver an underdose. Take, for example, a patient who is supposed to receive 1 mg of morphine with each demand dose. If the concentration is programmed as 0.1 mg/mL, the pump calculates that 10 mL of solution must be administered to deliver each 1 mg dose. But if the actual concentration of morphine in the syringe/bag is 1 mg/mL, the pump will still deliver 10 mL, since the concentration was set at 0.1 mg/mL. Thus, the pump would deliver 10 mg (10 mL) of morphine, not the intended 1 mg dose. For more on this complex issue, visit: www.ismp.org/d/SpecialFollowUp.pdf.
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