Given that the MIMIC II Waveform and Clinical data are collected from different sources, they must be matched to a unique patient. The MIMIC II Waveform data included a unique identifier (the Case_ID), assigned automatically by the monitor, and fields for patient name (first and last name) and medical record number (MRN). The name and MRN fields were manually entered by nurses into the networked central station when a patient was admitted. Unfortunately in a some cases one or more identifier fields were not completed for admitted patients. Moreover, occasional human errors are likely to exist in the manually recorded name and MRNs. The clinical information system also includes a unique patient identifier for each ICU stay of a patient. The subject's clinical data also includes identifying information (such as a name and MRN) which was automatically input from the hospital-wide information system when a patient is admitted to a unit.
When waveform files included the patient's identifying information (name, and MRN), the physiologic data records (indexed by a Case_ID) were matched to the corresponding clinical information records. There were two stages to the merging process. The first stage included matching names and medical record numbers (when available and accurately recorded) from the waveform data records to those of the clinical data records. The second stage included comparing the similarity of the physiologic trends from the higher resolution monitoring data (approximately 1 sample per minute) with the nurse-validated vital sign trends in the clinical information system sampled on an hourly basis.
Briefly, determination of trend similarity included four stages:
- Determining a temporal overlap between the available trends that were present in the physiologic and clinical data.
- Identifying if unusual parameters had been recorded at the same time (e.g. cardiac output).
- Correlating median filtered, down-sampled heart rate and blood pressure numeric trends with heart rate and blood pressure trends in the clinical data.
- Visual inspection of a subset of files to verify the results.
However, it is possible that some of the matches may be incorrect. After manual review we believe we have caught most of the inconsistencies, but anomalies may still be present. For further details please see the MIMIC II User's Guide at the BRP website.