Equivalency between the shock index and subtracting the systolic blood pressure from the heart rate: an observational cohort study

Yohei Kamikawa,Hiroyuki Hayashi

doi:10.1186/s12873-020-00383-2

Abstract

BackgroundAlthough the shock index is known to predict mortality and other severe outcomes, deriving it requires complex calculations. Subtracting the systolic blood pressure from the heart rate may produce a simple shock index that would be a clinically useful substitute for the shock index. In this study, we investigated whether the simple shock index was equivalent to the shock index.MethodsThis observational cohort study was conducted at 2 tertiary care hospitals. Patients who were transported by ambulance were recruited for this study and were excluded if they were aged < 15 years, had experienced prehospital cardiopulmonary arrest, or had undergone inter-hospital transfer. Pearson’s product-moment correlation coefficient and regression equation were calculated, and two one-sided tests were performed to examine their equivalency.ResultsAmong 5429 eligible patients, the correlation coefficient between the shock index and simple shock index was extremely high (0.917, 95% confidence interval 0.912 to 0.921, P < .001). The regression equation was estimated as sSI = 258.55 log SI. The two one-sided tests revealed a very strong equivalency between the shock index and the index estimated by the above equation using the simple shock index (mean difference was 0.004, 90% confidence interval 0.003 to 0.005).ConclusionThe simple shock index strongly correlated with the shock index.

Highlights

The shock index is known to predict mortality and other severe outcomes, deriving it requires complex calculations
Kamikawa and Hayashi BMC Emergency Medicine (2020) 20:87 risk of mortality [16], but it is sometimes difficult to quickly calculate whether the patient meets this cut-off when the value of the quotient is extremely close to 0.9 (e.g. When a patient has an heart rate (HR) of 103 beats per minute and systolic blood pressure (SBP) of 114 mmHg, the quotient is approximately 0.904 and it technically meets the cut-off but it is exceedingly difficult to calculate promptly without a calculator)
Characteristics of the study subjects There were 6687 patients who were transported to the two hospitals via ambulance during the study period; 1258 of these patients were excluded including 527 aged < 15 years, 136 who experienced prehospital cardiopulmonary arrest, and 595 who underwent inter-hospital transfer

Summary

Introduction

The shock index is known to predict mortality and other severe outcomes, deriving it requires complex calculations. Subtracting the systolic blood pressure from the heart rate may produce a simple shock index that would be a clinically useful substitute for the shock index. The shock index (SI) is an indicator of the severity of hypovolemic shock and is calculated by dividing the heart rate (HR) by systolic blood pressure (SBP) [1]. It serves to predict the mortality, need for blood transfusion, or necessity of intensive care unit admission. Having a confusing cut-off value, the SI needs to be interpreted from several variables to identify patients with a critical status but stable HR and SBP making it an impractical indicator that is rarely used in scoring systems assessing emergencies. If the calculation of the SI can be made simpler, it would lead to rapid progress in terms of the clinical research using SI

Methods

Results

Discussion

Conclusion