Pulse oximetry, a current in-use EMS monitoring tool with the aforementioned additional potential of helping to improve triage decisions, is an exciting, but not unreasonable prospect. Shock is a compensated state and ventilation perfusion mismatch (V/Q) causing hypoxemia is an accompaniment to the early stages after injury. V/Q mismatch may only be intermittently revealed by events such as administration of analgesic or sedation drugs, tasks such as tracheal intubation or pain on positioning during resuscitation and stabilization. Decreased SpO2 in combination with the multi-causative physiological response of tachycardia is proposed as the new triage tool. If the HR value obtained from SpO2 is artifact free, validation by matching with ECG HR would be unnecessary. This could be obtained by SpO2 pulsatile waveform analysis5
. ECG waveform analysis could add triage related information (HR variablility, R-R interval, respiratory rate) and confirm SpO2 HR6
. In addition other existing non-invasive monitors (transcutaneous CO2, hemoglobin concentration) could be built into a pulse oximeter probe .It is not surprising that NIBP was unhelpful, as blood pressure is notoriously inaccurate as a marker for shock due to compensatory mechanisms which maintain pressure despite the loss of 30% or more of circulating blood to hemorrhage. In addition, as shown by continuous VS data collection, NIBP is only an intermittent data point. In some instances NIBP was only measured every 15 minutes, so that it is unlikely to be a predictor of dynamic events occurring in the severely injured patient.
Because VS waveforms were recorded as continuous data (as they are normally displayed to the field care provider), documentation of life saving events (management of Airway, Breathing, Circulation) and interventions (tracheal intubation), was obtained automatically by the dynamic VS waveforms. It is clear from these preliminary data that analysis of trends and waveforms may reveal even greater predictions of severity of injury. QM measures such as duration of abnormal VS, conformity to EMS protocols (e.g. ventilation of intubated patients can be determined from data such as that in Fig1) frequency of measurement (e.g. NIBP), time of scene management and transport were recorded without any interruption of field provider care for the patient. For Trauma Registry and QM documentation purposes, the current standard is for the field care provider to report one NIBP, SpO2 and HR as VS for the Pre-Hospital phase, which are entered into the Trauma Registry. This study suggests that with only the processed HR and SpO2 record, we could identify patients with high risk for injuries within the ‘hidden body compartments’ as well as those with severe injury (ISS>= 15). As such, these signals, dynamically processed, could be a simple triage tool, directing the need for Trauma Center care and reducing errors in triage.
The scope of over triage is illustrated by studies in Minnesota, California and Maryland. In Minnesota among 9174 trauma patients having, in retrospect, at least one triage criterion indicating that their level of injury required trauma center care, 60% were transported to non-trauma centers. Of cases with injury severity scores of greater than 15 as well as one triage criterion, 77% were taken to trauma centers. In two large counties, 58% and 27% of trauma patients were under-triaged and taken to trauma centers7
In Orange County CA, there was a 74% increase in over-triage after revisions to the Injury Severity Scoring System for motor vehicle crashes between 1981–1988, when more than 30,000 trauma patients were transported8
. In a retrospective analysis in Maryland, of 1995 data among 32,950 trauma patient transports, 86% meeting injury triage criteria were appropriately transported to trauma centers, meeting mechanistic triage criteria (46%) and physiologic triage criteria (34%) 9
The process of integrating multiple inputs in the triage process is difficult to teach or automate. In the battlefield or civilian life threatening circumstances, successful triage depends on the experience of the care provider. Because the course of intra- abdominal bleeding and peritoneal irritation from blood (causing abdominal pain) takes a finite time to develop, with short helicopter transport times the signs and symptoms of intra abdominal bleeding may not be apparent and may not be noted by the pre-hospital provider. Automated, continuous monitoring of VS can potentially facilitate more rapid, accurate triage and better treatment 10
. The prime goal should be to develop decision support aids by using a commonly used device like the pulse oximeter capable of providing near real-time estimates of the level of injury early in the prehospital phase of trauma care.
For the patient with severe life-threatening abdominal or thoracic hemorrhage, the anatomic source of bleeding must be identified; this is the overarching principle of “The Golden Hour” of the Advanced Trauma Life Support (ATLS) course. The challenge for the pre-hospital care provider is to recognize the injured patient as early as possible, so that they can receive expedited diagnosis, early control of the source of bleeding and definitive trauma center care,. SpO2 and HR monitoring may be a promising real-time decision aid to enable this.