Physiologic Mechanisms Underlying the Failure of the Shock Index as a Tool for Accurate Assessment of Patient Status during Progressive Simulated Hemorrhage
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
Pagination or Media Count:
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.
- Anatomy and Physiology
- Medicine and Medical Research