Hypovolemic shock in surgical patients is most commonly caused by hemorrhage due to blood loss during or after surgery. Surgical procedures often involve vascular injury or disruption, leading to significant bleeding. This blood loss reduces circulating blood volume, resulting in inadequate tissue perfusion and oxygen delivery. Prompt recognition and control of hemorrhage are critical to prevent progression to shock. Other causes like sepsis or burns may lead to shock but are less common in the immediate surgical setting. Effective management includes volume resuscitation and hemostasis to restore circulatory stability.

Reference: Schwartz's Principles of Surgery, 11th Edition.