Patients with chronic kidney disease (CKD) with criteria for renal replacement therapy (RRT) including uremic syndrome, have a stable state of hyperosmolarity due to urea despite not being an osmotically inactive ion. Also, these patients have alterations in urea transporters in the central nervous system (CNS) conferring a risk of neurological involvement due to an abrupt decrease in serum urea causing manifestations of the post-dialytic syndrome.

Hemodialysis results in rapid removal of urea from the blood, much faster than the equilibrium rate between the brain and the bloodstream through the blood-brain barrier, resulting in an osmotic gradient that favors movement from water to the brain, causing cerebral edema, intracranial hypertension and dialysis-associated imbalance syndrome. Conventional hemodialysis (HD) uses diffusion and primarily decreases small solutes, while hemofiltration (HF) is based on convection that provides clearance mainly of medium-size molecules and small solutes with a slower rate of reduction.

Currently, there is little information about which is the safest modality in the first session of intermittent hemodialysis. Other than dialysis-associated imbalance syndrome, there is no evidence exploring the neurocognitive effects of the first hemodialysis session. Cognitive impairment is defined as a new deficit in two or more areas of cognitive function and its progression is associated with impaired kidney function. Most of the dysfunctions reported are in the domains of orientation, attention and executive functions. Therefore, the recognition of cognitive impairment can be done with tools such as the Minimental State Examination (MMSE) and the Montreal Cognitive Assessment (MOCA) test. Brain magnetic resonance imaging (MRI) can identify brain lesions such as 'silent' infarcts, microbleeds and white matter abnormalities in patients with CKD with and without RRT. Diffusion-weighted MRI before and after HD has shown brain edema in rats with dialysis-associated imbalance syndrome. In fact, there is evidence from brain MRI that before first HD session patients have interstitial cerebral edema, which worsens after the first HD treatment.

Because there is no clear evidence to support the choice of the modality in the first session and the prescription is still based on personal experiences and shared views. Therefore, we conducted a pilot study to determine the safest hemodialysis modality with the lowest risks and neurocognitive effects for patients with CKD and first HD treatment.

Inclusion Criteria:

• Age > 17 years
• Both gender
• CKD stage 5 with clinical or biochemical criteria to kidney replacement therapy initiation that includes:
• Urea nitrogen > 80 mg/dl
• Hyperkalemia
• Fluid overload
• Metabolic acidosis (ph < 7.2 and/or bicarbonate <12)

Exclusion Criteria:

• Visual disturbances
• Altered mental status at enrollment
• Hypothyroidism without optimal supplementation
• Advanced neoplasia
• Acute kidney injury