How does CHF cause AKI?

It is quite common to see accompanying acute kidney injury during a congestive heart failure exacerbation. 

WHY?

1. Renal hypo-perfusion secondary to poor cardiac output.
2. Renal venous congestion. Increased central venous pressure (CVP) is transmitted into the efferent arteriole, reducing the pressure gradient and subsequently the GFR.  
3. Neurohumoral mechanisms (i.e RAAS, ADH) which help acutely but are maladaptive in the long term on the kidneys’ GFR.

REFERENCES

1.  Marlies Ostermann, Heleen M. Oudemans-van Straaten and Lui G. Forni. Fluid overload and acute kidney injury: cause or consequence?. Critical Care 201519:443https://doi.org/10.1186/s13054-015-1163-7 
2. Han SW, Ryu KH. Renal Dysfunction in Acute Heart Failure. Korean Circulation Journal. 2011;41(10):565-574. doi:10.4070/kcj.2011.41.10.565.