An 18-year-old man with hypovolemic shock receives saline infusion. What is the expected effect on cardiac output following this infusion?

• A. Decrease in cardiac output
• B. No change in cardiac output
• C. Increase in cardiac output
• D. Varies with age

Answer: (C)

In the context of hypovolemic shock, the body's ability to maintain adequate circulation to tissues is compromised due to reduced blood volume. Administering a saline infusion aims to restore this lost volume, effectively addressing the underlying cause of the shock.

Upon infusion of saline, blood volume is increased, leading to an improved venous return to the heart. This increased preload enhances the heart's ability to pump blood, reflected in an increase in cardiac output. The Frank-Starling mechanism explains this relationship, where increased volumes of blood filling the heart leads to more forceful contractions, thus enhancing stroke volume.

In scenarios involving hypovolemic shock, restoring blood volume through saline contributes to improved circulating blood volume and thus facilitates an increase in cardiac output. As a result, the correct answer indicates that an infusion of saline in this context would lead to an increase in cardiac output.