C is the correct answer. Why?

Explanation

The shock index is the most reliable indicator in diagnosing occult shock and the need for transfusion. It is calculated using the following equation: shock index = heart rate/systolic blood pressure. A shock index greater than 0.7 suggests the presence of occult shock and the need for transfusion. Massive transfusion protocol is the administration of packed red blood cells, platelets, and fresh frozen plasma in a 1:1:1 ratio. The goal is to hemodynamically stabilize until definitive operative management can be achieved. Red blood cells are lost during massive hemorrhage, however, platelets and clotting factors are also lost, necessitating replenishment. There have been studies attempting to demonstrate the ideal ratio of packed red blood cells to platelets to fresh frozen plasma. Typically, the accepted ratio is 1:1:1. Fibrinogen is found in cryoprecipitate and is not typically included in the massive transfusion protocol. Complications of massive transfusion protocol include transfusion-related acute lung injury, hypothermia, dilutional coagulopathy, lactic acidosis, hyperkalemia, hypocalcemia, and hypomagnesemia. The latter two electrolyte abnormalities are due to high citrate concentrations present in blood products, which binds calcium and magnesium, leading to deficiency. As such, patients are often given calcium and magnesium supplementation during massive transfusion protocol.

Individual vital signs, such as the heart rate (A), respiratory rate (B) or systolic blood pressure (D), are less sensitive at detecting occult shock than the shock index.