[Urine concentration during the oligoanuric phase of acute kidney failure]

Multiorgan dysfunction syndrome: how water might contribute to its progression

Multiorgan dysfunction syndrome (MODS) is one of the most frequent conditions encountered in intensive-care medicine. MODS is defined as total or partial loss of two or more organs with vital functions. The development of acute renal failure (ARF) in MODS leads to an additional aggravation with considerably higher hospital mortality than in other ICU patients with MODS. Whereas dissolved substances involved in the regulation of regional blood flow, endothelial cell injury, microvascular permeability, oxygenation, and nutrition of cells are at the focus of interest in MODS, hardly any scientific attention is paid to their main solvent water. An impaired renal water excretion and an increased metabolic water volume requiring excretion interfere with diffusive and convective oxygen transport through the different fluid compartments. It will be shown first that the ratio of U(osm)/ P(osm) appears to be a reliable tool to assess overhydration in ARF. Secondly, the limits of urinary output in response to water intake will be considered. Furthermore, the metabolic water formation by an enhanced degradation of endogenous protein and fat will be discussed. Finally, the daily caloric intake is questioned with respect to energy expenditure and metabolic water formation.

[Tubular response to antidiuretic plasma activity in the transplanted kidney (author's transl)]

Reabsorption of osmotically free water (TmcH2O) was studied in 10 patients after renal transplantation. A rising or constant free water reabsorption was observed under hydropenia and increasing tubular solute load. These findings suggest that in the transplanted kidney the functioning nephrons respond in a normal way to plasma ADH-activity. The excretion of plasma-hypotonic urine reflects decreased antidiuretic activity as in overhydration rather than tubular unresponsiveness to ADH. The excretion of plasma-hypertonic urine indicates tubular reabsorption of osmotically free water due to ADH, and this in general rules out overhydration. Daily estimation of urinary and plasma osmolality will be useful in judging the actual state of hydration after renal transplantation.