A 65-year-old man presents with massive gastrointestinal bleeding. BP is 70/40 mmHg, HR 140/min, cold clammy extremities, and collapsed neck veins. Lactate is elevated. What is the primary pathophysiologic mechanism responsible for shock in this patient?
A
Reduced systemic vascular resistance due to cytokine release
B
Decreased preload causing reduced cardiac output
C
Primary myocardial pump failure with pulmonary congestion
D
Mechanical obstruction of venous return to the heart