A miniature, portable wireless vital signs monitor (MWVSM), called Mini-medic™, could aid in the triage and diagnosis of trauma patients with and without traumatic brain injury (TBI). The MWVSM consists of two components, both of which are the approximate size and weight of a cellphone: one is a sensor that is placed either on the forehead or the fingertip of a patient, and the other is a monitor that receives a wireless signal transmitted up to 100 m carried by the medic.
The MWVSM was developed to capture whatever useful biological data is possible from small sensors placed on the forehead (or at a peripheral extremity site) of up to five casualties, then wirelessly transmit to small, cellphone-sized monitors carried by any first responder within range. To evaluate the MWVSM, it was hypothesized that changes in multiple parameters or derived variables monitored from the forehead (or extremity) of a severely injured patient correlate favorably with conventional vital-sign monitors, either before or after definitive treatment at a level 1 trauma center.
This study was comprised of 151 patients; an additional 23 pre-hospital patients were excluded because of missing or incomplete data. The majority of pre-hospital transports have finger sensors for logistic reasons, i.e. many patients are strapped to a backboard and the head strap is in the exact location for the MWVSM forehead sensor. The monitoring period varied from 60 minutes. Some sensors fall off during transport. In many cases, valid data are obtained for only a portion of the pre-hospital time.
Over a 20 to 40-minute pre-hospital monitoring period, the MWVSM heart rate sensor agrees with the heart rate measured by the conventional monitor, but the MWVSM SpO2 sensor does not. It should be emphasized that continuous digital data from MWVSM are averaged over the entire transport time for each patient and compared to the average of intermittent spot checks from the standard monitor obtained from the pre-hospital run reports. The data suggest that R-wave detection in the MWVSM more or less agrees with a standard monitor: it deviates 1-6 beats/min relative to a standard monitor. However, the MWVSM SpO2 detector is consistently 5-7% lower than the standard monitor.
These data show that the R-wave detection and pulse oximeter in the MWVSM finger probe are more accurate and follow changes better than those in the forehead probe in trauma patients. The results of this trial led to a redesign of the method for affixing the forehead sensor to the skin.
In summary, pre-hospital data showed there are major demographic differences in the characteristics of trauma patients and non-trauma patients. The MWVSM tracks heart rate within 1-6 beats/min, but the MWVSM SpO2 sensor consistently underestimates true SpO2, and this is almost entirely due to problems with the forehead sensor.
This work was done by Dr. Kenneth G. Proctor of the University of Miami for the Army Medical Research and Materiel Command. ARL-0168