Physiologic Mechanisms Underlying the Failure of the Shock Index as a Tool for Accurate Assessment of Patient Status during Progressive Simulated Hemorrhage
Abstract
Shock index (SI), the ratio of heart rate (HR) to systolic arterial pressure (SAP), is a metric often used to diagnose patients at risk of impending cardiovascular instability and hemorrhagic shock. We hypothesized that if SI reflected impending cardiovascular instability and shock in an individual, then: (1) elevations in SI and HR would be greater in individuals with low tolerance (LT) to progressive lower-body negative-pressure (LBNP) compared with individuals with high tolerance (HT), and (2) LT would be associated with greater vagal withdrawal of the baroreflex sensitivity (BRS) compared with HT. A total of 187 healthy subjects (HT, 125; LT, 62) underwent exposure to LBNP until a SAP of less than 80 mm Hg (instability) was achieved. HR and SAP were used to calculate SI, and BRS was determined from spontaneous fluctuations in R-R interval and diastolic arterial pressure. Maximal cardiac vagal withdrawal was calculated as the difference between BRS at baseline and BRS at 100% LBNP tolerance. The low sensitivity of the SI observed in LT individuals is associated with a lower capacity to withdraw cardiac vagal activity and can lead to an undertriage of those patients most likely to develop early hemorrhagic shock.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2013
- Accession Number
- ADA615149
Entities
People
- Carmen Hinojosa-Laborde
- Christina Van Sickle
- Kristin Schafer
- Victor A Convertino
Organizations
- United States Army Institute of Surgical Research