Reliability of the model MC-311 MDI chronolog

The Model MC-311 MDI Chronolog (Medtrac Technologies, Lakewood, Colo) is an electronic device for monitoring adherence to metered-dose inhalers (MDIs). It is a thermistor-actuated, microprocessor-equipped device that dispenses inhaled medication while recording the date and time of each canister activation.

We evaluated the reliability of the MC-311 MDI Chronolog to determine whether the model could accurately record and report the date, time, and number of MDI actuations.

Twenty-four of the MC-311 Chronologs were discharged at 8 hourly intervals across 8 days. Battery voltage was assessed before and after the experiment. The mouthpieces of 12 Chronologs were washed daily.

By using generous criteria for acceptable reliability, only 10 of 24 (42%) were rated as acceptable. None of these 10 Chronologs recorded 320 or greater actuations (mean +/- SD, 293.9 +/- 13.3; range, 266 to 308); all reliable Chronologs underestimated MDI activation. An additional 6 devices had an initial signature of erroneous recordings dating from device initialization. After removing this signature, the remaining data showed acceptable reliability. All the remaining Chronologs judged to be unacceptable showed time series patterns of seizures (ie, bursts of clustered, erroneous records). Seizures were distributed across trial days, were associated with washing, and preceded all 4 cases of battery failure. Damage to the thermistor is the likely cause of seizure-pattern failures.

In summary, because of a combination of a clear underreporting bias with frequent initialization and seizure-pattern failures, the Model MC-311 MDI Chronolog is not recommended for use in clinical care or research