TOPIC DISCUSSION: CONGESTIVE RENAL FAILURE

Concept of congestive renal failure is slowly emerging again in regards to congestive heart failure (CHF) related renal disease. The classic teaching was that renal failure in CHF is related to poor forward flow. That would make sense is the MAP is low and SBP is low and you are in a shock state. That constitutes on 5% of the CHF patients that present with cardiogenic shock. The rest are stable CHF with AKI or CKD. What is then the patho-physiology?

Well, as this article nicely puts it – it’s congestive renal failure.  It’s renal venous congestion. Studies have shown that CVP>24 are more likely to lead to AKI then CVP <8.  It’s not the SBP.  This renal venous congestion and HTN is likely from parenchymal congestion within the confines of the non distensible kidney capsule.  This would then raise the renal interstitial pressure and would lead to affect the entire capillaries and tubules leading to tissue hypoxia.  The effect on tubules and capillaries occurs most at venous pressure >15mm Hg. The best measure of this is intra-abdominal pressures done via bladder pressures.  Intra abdominal HTN might be the best marker for how bad the kidneys might be congested and about to have a renal tamponade( as Jai Radhakrishnan or a cardio-nephroligst would say it). 

Besides the above mechanisms, the active inflammatory mileau, endothelin release, reactive oxidative species release might also be contributing to AKI. 

In other words, CHF leads to venous congestion and decreased cardiac output, but the former plays  a bigger role in AKI then the later.  This below table helps summarize a quick and dirty way of looking at CHF and how to manage it in the setting of AKI based on low perfusion and or congestion at rest.

                                                                                Congestion At Rest

	No	Yes
No	Warm and Dry( good job)	Warm and Wet( most common – optimize diuretics and/or add other agents UF/tolvaptan)
Yes	Cold and Dry( r/o over diuresis)	Cold and Wet( Most dangerous and requiring LVAD/transplant)

Low Perfusion at Rest

image source: http://ahmedshokry.files.wordpress.com/2012/04/hf.jpg