In a low flux dialyzer, a rise in transmembrane pressure during hemodialysis indicates:

• A. Air Embolism
• B. Filter Leak
• C. Clotting in the extracorporeal circuit
• D. Improved clearance

Answer: (C)

A rise in transmembrane pressure means the resistance across the dialyzer membrane is increasing. In a low flux dialyzer, this happens most commonly when clotting forms in the extracorporeal circuit, especially within the hollow fibers. Clots obstruct the blood flow path, so more pressure is required to push blood through the membrane, driving TMP upward. This is a warning sign that the filter is beginning to malfunction due to clotting and needs attention (e.g., circuit assessment, potential anticoagulation adjustment, or filter change). Air embolism would cause different clinical signs and is not defined by a gradual TMP rise; a filter leak tends to alter pressures differently and may cause loss of containment rather than a progressive TMP increase; improved clearance would not manifest as a rising TMP.