An underocclusive pump head will cause which issue?

• A. Hemorrhage
• B. Thrombosis
• C. Ischemia
• D. Hemolysis

Answer: (D)

The key idea is how the level of occlusion in a roller pump head influences the mechanical forces on blood. When the tubing isn’t fully occluded, the compression between rollers is uneven or incomplete, creating zones of irregular, high-shear flow as the tubing is repeatedly squeezed and released. Red blood cells are delicate and can be damaged by those abrupt, repetitive stresses; this mechanical trauma ruptures their membranes, leading to hemolysis. Inadequate occlusion thus translates into increased shear forces that injure cells as they pass through the pump. Other problems like hemorrhage or ischemia come from different issues in the circuit or systemic factors, while thrombosis tends to relate to flow stagnation or activation of coagulation pathways rather than the direct shearing of cells from incomplete occlusion.