Disorders of the effective osmolality regulation are frequent in the cerebral affections that originate from trauma, vascular disease, imflamation or tumors. Hypo-osmolality and hyponatremia are presented in two different states: Inappropriate Vaseopressin Secretion Syndrome (IAHDS) and Cerebral Salt Wasting Syndrome (CSWS). Quick differential diagnose is important because the treatment of both syndromes is essentially different. Typical cause of hypernatremia is central diabetes insipidus (DI). The group of available calculated renal function parameters is applied in the differential diagnosis of these syndromes. They are creatinine clearance, excretion fraction of water and sodium, electrolyte clearance and electrolyte free water clearance. Investigation of ADH and natriuretic pepride could be even misleading. Pathophysiologic consequence of the state given by inappropriate elevation of one hormone can be the elevation of the second one.

The mentioned topic is documented with the four selected patients from the ICU. The syndromes were diagnosed using the computer program evaluating renal functions by means of 13 routinely monitored values and 12 output parameters.

Authors present brief clinical courses, biochemical results and calculated renal function parameters by one patient with the IADHS, by one with DI, by one with CSWS passing over to DI and by one with DI passing to IADHS. The importance of complex access to evaluation of renal functional parameters is stressed. These are influenced by actual therapy, eg by diuretics or osmotherapy.

Mentioned four cases are the example of the effective use of the currently investigated values in the diagnosis and monitoring of the effective osmolality disorders in cerebral affections.