In an elderly patient with heart failure who presents with prerenal azotemia, what therapeutic measures would you undertake to protect their kidneys?
- submitted by Michael Bazylewicz
The problem with experts is that they do not know what they do not know. NNT.
This all depends on the volume status of the patient.
If the patient has a low effective arterial blood volume, then fluid boluses to promote better urine output is warranted.
If the patient is edematous, has elevated neck veins, an audible S3, and pulmonary edema on CXR, then I would give an inotrope to promote better perfusion of the kidney. Interventions could include digoxin, dopamine (B1), or dobutamine. Milrinone, a phosphodiesterase inhibitor, could be used because it is a positive inotrope and vasodilator.
I think the idea of diuresing the patient proves to be the most difficult to understand. In vivo, a descending limb of the starling curve has not been proven. Sarnoff showed that experiementally in frogs and dogs it could be illicited, but these experiments left the pericardium open and only after extremely large volumes did the descending limb of the starling curve reveal itself.
See Sarnoff's 1954 paper here and a figure depicting the descending limb here.
If you believe that the descending limb exists in physiologic conditions, then diuresing the patient to improve kidney function makes sense. However, if you believe that the starling curve plateaus, then diuresing or giving fluids won't make a difference in increasing or decreasing the cardiac output. In that case, only a positive inotrope, or in the case of diastolic dysfunction a lusitrope, would help.
Question: how would elevated central venous pressures affect renal venous pressures and subsequently glomerular efferent arteriole pressure? Would that decrease or increase perfusion pressure.
how often has dopamine or dobutamine been shown to affect mortality or outcome postively in these patients, since you are suggesting using these. Is it the standard of care to use these any more?
My short answer is no. they have not been proven to benefit patients ,and in fact they could potentiate mortality via causing arrythmias. diuresis in the acute setting is proven to be most useful for volume overloaded states and if pts. prove to be diuretic resistant, then short term HD or plasma ultrafiltration is the next step to attempt fluid removal.