nanari

I have a problem understanding lab data. My pt has ESRD with an increase potassium and decrease sodium level. I understand that sodium and potassium is inversely related. For those suffering with ESRD, little to no urinary output occurs, which means the body is retaining sodium and potassium . But because patients with renal failure is retaining volume (fluid overload), sodium is less concentrated thus the increase in potassium and the decrease in sodium. I can't entirely understand the sodium and potassium shift. I've been reading everywhere and it's not connecting.