Sraightening out the J-shaped curve: The relation between dialysis dose and mortality is dependent on total body water.
ASN 30th Annual Meeting, San Antonio
J Am Soc Nephrol (Sep) 8:279A 1997
The relationship between Kt/V and mortality tends to be J-shaped, with a slight increase found at high Kt/V levels in cross-sectional studies. Because the amount of dialysis given tends to be fixed, low Kt/V levels often mean a large patient (in whom survival will tend to be good), whereas high Kt/V levels may sometimes reflect a small cachectic patient with associated poor survival.
In this abstract, the authors find that if one looks at survival against not Kt/V but against K x t (computed by multiplying the URR-derived Kt/V by the anthropometrically estimated total body water), the J-shape is lost, and that there is a linear relation between K x t and survival.
Comment: This is an important observation. Consider, for example, a dialysis strategy based on Kt/V or URR. If one has a patient who initially weighs 100 kg, V = 60 liters, in whom a K x t of 72 liters is given to result in a Kt/V of 1.2. The patient falls ill and loses half of his body weight (reductio ad absurdum). To maintain a minimum Kt/V of 1.2, one could now cut the dialysis to a K x t of 36 liters, as V is now about 30 liters. Clearly this doesn't make sense. A more important and widespread implication may be, that perhaps it is not wise to restrict dialysis in smaller patients with low values for V (especially white females!, see authors' companion abstract. On the other hand, nature made us so GFR was indexed to body surface area, so maybe smaller patients should not require the same amount of dialysis as larger patients. These difficulties highlight the problems in interpreting cross-sectional studies of Kt/V, particularly when the reason why V is large or small has survival implications. (John T. Daugirdas, M.D., University of Illinois at Chicago)
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ASN 30th Annual Meeting, San Antonio
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