Shock index is positively correlated with acute blood loss and negatively correlated with cardiac output in a canine hemorrhagic shock model

OBJECTIVE To determine whether shock index (SI) positively correlates with percentage blood loss and negatively correlates with cardiac output (CO) in a canine hemorrhagic shock model and whether SI and metabolic markers may be used as end point targets for resuscitation. ANIMALS 8 healthy Beagles. PROCEDURES Between September and December 2021, dogs underwent general anesthesia for experimental induction of hypotensive shock, with the total volume of blood removed, CO, heart rate, systolic blood pressure, base excess, blood pH, and concentrations of hemoglobin, lactate, ionized calcium recorded, and SI calculated at 4 time points (TPs): after anesthetic induction when the dog had been stable for 10 minutes (TP1), 10 minutes after the mean arterial pressure stabilized to a target of 40 mm Hg following jugular removal of up to 60% blood volume to induce hemorrhagic shock (TP2), 10 minutes after autotransfusion of 50% of the removed blood (TP3), and 10 minutes after autotransfusion of the remaining 50% of the removed blood (TP4). RESULTS Mean SI increased between TP1 (1.08 +/- 0.35) and TP2 (1.90 +/- 0.73) and did not return to the prehemorrhage values for TP3 or TP4. SI correlated positively with percentage blood loss (r = 0.583) and negatively with CO (r = -0.543). CLINICAL RELEVANCE An increase in SI may support diagnosis of hemorrhagic shock; however, SI cannot be used as the sole end point of resuscitation. Significant differences in blood pH, base excess, and lactate concentration suggested they may be useful markers of hemorrhagic shock and need for blood transfusion.