Saturday, July 26, 2008

Cardiorenal Syndrome

Any nephrology fellow running the Consult Service will rapidly realize that heart failure and renal failure often go hand in hand, earning the moniker "cardiorenal syndrome." The thought here is that decreased forward flow from pump failure results in renal hypoperfusion and a resultant decrease in the GFR.

The most joyous moments in the treatment of cardiorenal syndrome--and unfortunately this does not happen as often as we would like--are when a patient's creatinine starts decreasing WHILE the patient is getting diuresed.

How to explain this phenomenon of decreasing Cr with diuresis? One potential explanation would be that the patient is being brought onto a more favorable portion of the Frank-Starling curve (above) by fluid removal, thereby allowing increased cardiac output and increased renal perfusion.

However, according to many cardiologists (and according to the figure above), the Starling curve actually plateaus--there is no "downswing" with very high filling pressures. An alternative explanation for decreasing Cr during diuresis is that the high CVP during severe CHF results in a back-transduction of pressure through the glomerulus, thereby decreasing GFR. Reducing the CVP (e.g. with diuresis) would then result in an improved GFR.

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