What causes somnolence after dialysis with significant fluid removal and how is it managed?

From the Guidelines

Somnolence after dialysis with significant fluid removal is primarily caused by cerebral edema resulting from rapid shifts in plasma osmolality, and management should focus on prevention through slower, gentler dialysis sessions with gradual ultrafiltration rates. When large volumes of fluid are removed during dialysis, the blood becomes more concentrated, creating an osmotic gradient between the blood and brain tissue. This causes water to move into the brain, leading to cerebral edema and symptoms like drowsiness, confusion, and headache, collectively known as dialysis disequilibrium syndrome.

Key Considerations

• The patient's respiratory rate (RR) of 10 and pO2 of 132 on room air, with a pCO2 of 34, indicate that while the patient is not currently experiencing respiratory distress, close monitoring is necessary.
• The removal of 1L of fluid during dialysis may have contributed to the somnolence, suggesting that the rate of fluid removal may have been too rapid.
• Adjusting the dialysate sodium concentration can help minimize rapid osmotic shifts, as suggested by guidelines for hemodialysis adequacy 1.

Management Strategies

• Immediate interventions for somnolence include stopping ultrafiltration, administering hypertonic saline (3% NaCl at 1-2 mL/kg over 30 minutes), or mannitol (0.5-1 g/kg IV) to increase plasma osmolality.
• Oxygen therapy should be provided if needed, and vital signs closely monitored.
• For subsequent dialysis sessions, the prescription should be modified with reduced blood flow rates (250-300 mL/min), shorter session duration (2-3 hours initially), and limited fluid removal (no more than 2-3 L per session) 1.
• Dividing necessary fluid removal across additional sessions can also help prevent recurrence of symptoms.

Differential Diagnosis

• While dialysis disequilibrium syndrome is a primary concern, other causes of somnolence, such as dialysis encephalopathy, should be considered, especially if symptoms persist or worsen over time 1.
• However, the presentation of dialysis encephalopathy typically includes more severe and progressive neurological symptoms, and its diagnosis is supported by elevated plasma aluminum levels and distinctive EEG findings.

From the Research

Causes of Somnolence after Dialysis

• Somnolence after dialysis can be caused by Dialysis Disequilibrium Syndrome (DDS), a rare central nervous system complication that occurs in patients receiving hemodialysis 2, 3, 4, 5, 6.
• DDS is characterized by neurological symptoms caused by rapid removal of urea during hemodialysis, resulting in an osmotic gradient between the brain and the plasma 6.
• The rapid removal of fluid during dialysis, as seen in the patient's case with 1L removed, can contribute to the development of DDS 2, 3, 4.

Management of Somnolence after Dialysis

• Management of DDS involves supportive care, and in some cases, the administration of mannitol and 3% hypertonic saline 2.
• Adjusting the hemodialysis prescriptions, such as duration, blood flow rate, and target reduction of blood urea, can help prevent DDS 3.
• In severe cases, patients may require intensive care unit (ICU) management, as seen in a case report where a patient made a full recovery with supportive management in the ICU 4.

Clinical Features and Prevention

• Clinical features of DDS include headache, nausea, vomiting, muscle cramps, tremors, disturbed consciousness, and convulsions 6.
• Prevention of DDS involves careful monitoring of patients during hemodialysis, especially new patients who are at the greatest risk for developing DDS 4, 6.
• Recent advancements in cell biology implicate the role of urea disequilibrium as the pathophysiological mechanism responsible for DDS, highlighting the importance of careful management of urea removal during hemodialysis 6.