During the study, the number of admissions in the three units varied among the study periods from 379 to 492, patient-days varied from 1,704 to 2,619, and medication orders varied from 10,070 to 15,025 (). The number of medication orders per admission remained relatively constant over the four periods, although the number of medication orders per patient-day was higher in the last two periods compared with the first two, reflecting shorter inpatient length of stay in later periods.
The main outcome, the non-missed-dose error rate per 1,000 patient-days, fell from 142 during baseline to 51.2 in period 1, then rose to 74.0 in period 2, and then fell again to 26.6 in period 3 (P < 0.0001, ). The largest differences were between the baseline and period 1 (a 64 percent drop), when POE was implemented, and between periods 2 and 3 (also a 64 percent drop), when the screens were changed to minimize the likelihood of potassium chloride errors ().
Medication Error and Event Rates, By Period
Figure 1 Event rates by period. Top, the non-missed-dose medication error rate per 1,000 patient-days, by period. This rate dropped 64 percent between baseline and period 1, then climbed 45 percent between periods 1 and 2, and finally fell 64 percent between (more ...)
In contrast, the missed-dose error rate climbed substantially over the study period (), almost doubling from 169 per admission in the baseline period, to 329 in period 3 (P < 0.0001).
The non-intercepted serious medication error rate (the combination of preventable ADEs and non-intercepted potential ADEs) fell over the four periods, from 7.6 per 1,000 patient-days in the baseline period to 7.3 per 1,000 patient-days in period 1 and to 1.7 and 1.1 in periods 2 and 3, respectively (, P = 0.0003). The rate of preventable ADEs was highest in period 1, at 5.7 events per 1,000 patient-days, although it fell in the following two periods.
An obvious concern was whether the increase in preventable ADEs in period 1 was due to POE. We therefore examined them more closely by evaluating the case descriptions, in particular to assess whether they were caused by POE. None appeared to have been caused by POE. Of the 15 preventable ADEs, 3 might have been prevented by changes made in period 2 or 3, while 12 would not; most of the 12 were due to use of multiple sedating drugs, not addressed by POE.
The rate of intercepted potential ADEs climbed substantially from baseline to periods 1 and 2; it rose from 15.8 per 1,000 patient-days at baseline to 31.3 in period 1 and 59.4 in period 2 (P = 0.15) before falling to 0.5 in period 3 (). These increases in errors were largely related to POE's initial structure for potassium chloride orders, which made it easy to order large doses of intravenous potassium without explicitly specifying that it be given in divided doses (i.e., not more than 20 milliequivalents at a time). Standard nursing practice is to give it in divided doses, and all of these errors were intercepted by nurses so that no patient was injured. These potassium ordering errors accounted for 77 of the 82 intercepted potential ADEs in period 1 and for 101 of the 106 in period 2. Once the potassium ordering screen was changed to include this stipulation, the rate of intercepted potential ADEs fell to 0.5 per 1,000 patient-days in period 3. Only one intercepted event was identified in period 3.
Examination of the severity of ADEs and potential ADEs across the periods () showed that in the baseline period all five errors associated with preventable ADEs were serious or life-threatening, and six of the eight errors associated with non-intercepted potential ADEs also fell within those categories. In periods 2 and 3 combined, there were only two such serious or life-threatening errors that were not intercepted.
Severity of Adverse Drug Events (ADEs) and Potential ADEs, by Period*
As expected, the non-missed-error rate was higher in the intensive care unit than in the general care units; it also fell more in the intensive care units than in the general care units (). In contrast, the missed-dose error rate did not display a consistent pattern in the intensive care unit, but in the general care units it rose substantially over the period of the study.
Medication Error Rate, By Unit Type Across Periods
Evaluation By Error Type
The results by type of error show that the rates for most subtypes fell over the course of the study (). Dose errors were the most frequent subtype, and these actually remained high in periods 1 and 2. However, most dose errors in periods 1 and 2 (86 and 89 percent, respectively) were potassium chloride ordering errors, and this rate fell substantially in period 3 after changes were made in potassium chloride ordering and usage practices. The next most common types of errors, frequency errors and route errors, both fell significantly between baseline and period 3 (P < 0.0001). Some of the rarer errors such as known allergy errors actually have the greatest potential for harm. There were ten known allergy errors in the first period, and only two in the following three periods combined (P < 0.0001). In period 1, approximately 50 orders per day hospital-wide were canceled because of a computer warning about drug allergies; in period 2, this number rose to 80 per day.
Non-missed-dose Medication Errors, By Type and Period
Analysis of Errors Missed in Period 3
We evaluated the errors still occurring in period 3 to see whether additional changes to POE could prevent similar errors in the future. Of the 50 errors in period 3, 48 could potentially be prevented with additional changes to POE. These changes fell into nine categories, but changes in two might prevent the majority. Eighteen errors were due to improper use of a “multiple routes” option, in which the physician could indicate more than one route for the medication, depending on the patient's condition (e.g., morphine sulfate IV/PO). These were considered errors if for one of the routes the dose would be inappropriate or if one route would not be feasible for the medication—for example, a drug that should not be given intravenously. The second large group (n = 13) of errors might be prevented with route restrictions for some oral medications, such as sustained-release preparations and gelatin capsules, which should not be ordered to be given by enterostomy.