Use of the Reverse Shock Index for Identifying High-risk Patients in a Five-level Triage System

Background: The ratio of systolic blood pressure (SBP) to heart rate (HR), called the reverse shock index (RSI), is used to evaluate the hemodynamic stability of trauma patients. To minimize undertriage in emergency departments (EDs), we evaluated whether RSI < 1 (i.e., SBP lower than HR) could be used as an additional variable to identify patients at high risk for more severe injury within a level category of the five-level Taiwan Triage and Acuity Scales (TTAS) system.

Methods: Data obtained from the Trauma Registry System, including triage level according to the TTAS system, were retrospectively reviewed for trauma admissions from January 2009 through December 2013 in a Level I trauma center. In our study, the primary outcomes were injury severity as measured using different scoring systems, including the Glasgow coma scale (GCS), abbreviated injury scale scores, and the injury severity score (ISS), and in-hospital mortality. The secondary outcomes were hospital and intensive care unit (ICU) length of stay (LOS).

Results: Of 10,814 trauma patients, 348 patients (3.2%) had RSI < 1, whereas 10,466 (96.8%) had RSI ≥ 1. Those with RSI < 1 had greater injury severity, a higher incidence of commonly associated injuries, lower GCS scores, greater deterioration of vital signs, and a higher incidence of procedures those with RSI ≥ 1. Patients with RSI < 1 also worse outcomes including hospital and ICU LOS, a greater frequency of ICU admission, and higher in-hospital mortality. Although the five-level TTAS system provides good prioritization of patients with major trauma, using the additional criterion of RSI < 1 could identify the patients at higher risk within the same triage level (I-III).

Discussion: The alert of a trauma patient's SBP being lower than his/her HR (RSI < 1) without the requirement of any additional equipment makes the concept of RSI particularly valuable in crowded EDs for identifying high-risk patients. RSI < 1 may serve as a principle trigger for action in the ED to alert trauma surgeons to the need for early intervention and timely preparation upon patient arrival particularly for those patients triaged in levels II and III of the TTAS system.

Conclusions: RSI < 1 upon arrival at an ED is an alarming sign of an associated worse outcome. Within the same triage level from level I to level III, patients with RSI < 1 had worse outcomes than those with RSI ≥ 1. The inclusion of RSI in the TTAS system may help to identify patients with more serious injuries who need an upgraded management level.