Dialysis Disequilibrium Syndrome Revisited.

An aggressive dialysis in a grossly azotemic patient, especially one with severe metabolic acidosis, can lead to dialysis disequilibrium syndrome (DDS). Mild forms present as nausea, vomiting, restlessness, and headache. Severe manifestations include seizures, obtundation, coma, and even death. This clinical picture is caused by cerebral edema induced by one or more of the following mechanisms: "Reverse urea effect" - Dialysis removes urea faster from the blood than from the brain; consequently, water enters the brain. "Cerebrospinal fluid acidosis" - Correction of systemic acidosis engenders the condition due to a lowering of brain pH. "Idiogenic osmoles" - As a response to blood hyperosmolar state, osmoles are produced in the brain. As blood osmolality decreases under relatively quick dialysis, idiogenic osmoles tend to induce brain edema. Because the symptoms of DDS can be life-threatening, preventive measures in patients with severe uremia are important. The first strategy relies on raising blood osmolality by introducing solutes (osmoles) into the blood. The second approach, which is the most common, decreases the efficiency of the dialysis treatment by shortening the duration of a dialysis run to 25% - 30% of normal, by lowering dialyzer blood flow or dialysate flow rate, by using a less efficient dialyzer, or by a combination of these maneuvers. Dialysis frequency is increased instead. Anticonvulsant drugs are needed in cases where the preventive measures have not been used or have been unsuccessful.