The DDS is an acute neurologic complication of hemodialysis. Symptoms can range from mild (headache, nausea, vomiting, muscle cramps) to severe (altered mental status, seizure, coma and rarely death). These tend to occur during dialysis or shortly after. Minor symptoms can occur in chronic patients but the major forms manifest in previously undialyzed individuals.
Patients at risk for the syndrome include those with very high blood urea nitrogens (>130mg/dl), CKD (as opposed to AKI) and those with high urea clearance rates during their initial hemodialysis session.
DDS is thought to be caused by cerebral edema due to a lag in osmolar shifts between the blood and brain during dialysis, but changes in cerebral pH may also contribute. Preventative strategies include:
1) Low initial urea clearance
2) High initial dialysate sodium and glucose levels
3) Administering osmotically active substances
Clearance of urea can be lowed by slowing the blood and dialysate flow rates, reducing the time of the dialysis session and reducing the size of the dialyzer. An initial urea reduction ratio of 40% is what the Daugirdas Handbook recommends. Using a higher sodium or glucose dialysate allows movement of sodium and glucose into the serum raising serum osmolarity and attenuating the blood brain gradient. Giving mannitol has a similar effect.
In our patient, the initial BUN was in the 150 mg/dL range. Our urea reduction ratios where 30% and 40% on the first and second runs respectively with mannitol and a dialysate sodium of 145 mEq/L used on both. The seizure occurred twelve hours after the second dialysis session.
Further workup did not reveal any clear toxic, cerebrovascular or metabolic cause. I’m not sure what role dialysis played in the seizure but we did do our best to try and minimize the risk of DDS. A final pearl I picked up from the case on seizures post initial HD: the rapid correction of acidosis in undialyzed uremic patients can drop the ionized calcium concentration and precipitate seizures. Our patient’s ionized calcium was also normal.
Graham Abra, MD