Editing Acute renal failure (section)

== Approach to workup/investigation: ==

* Sudden onset post-op complete anuria is post-renal UNTIL PROVEN OTHERWISE
** Catheter kinks
** Surgical damage to urinary tract
** Probably needs an USS straight away if nothing obvious found
* Initial investigations:
** Dipstick/MCS/osmolarity
*** Marked proteinuria or microscopic haematuria with casts suggests a primary renal insult
*** Casts
**** ATN: pigmented coarse granular casts and renal tubular epithelial cells
**** Glomerulonephritis: proteinuria, haematuria, red cell casts
**** Pyelonephritis: White and red cell casts
** USS
*** As above - mandatory in anuric patient
*** The acutely injured kidney will be echo bright due to oedema, but normal size
*** CKD likely shows a small (<9cm) kidney with echo-bright parenchyma
** Bloods to consider
*** FBE/UEC/CMP
*** LFT (hepatorenal)
*** CK (rhabdomyolysis - dark brown urine that tests positive for myoglobin)
*** CRP
*** VBG/ABG (for lactate and overall physiology)

* Establish aetiology:
** Is it pre-renal? And do we need to restore volume?
** Differentiating prerenal from renal
*** Prerenal will be a/w dehydration - consider whether large losses are occurring elsewhere
*** BUN > 20
*** Brown urine? Myoglobinuria?
*** In ATN, expect low osmolar urine with high sodium and low urea/creatinine, because the concentrating ability is impaired. In pre-renal AKI, the concentrating ability is retained, so you tend to get high osmolarity and high urea/creatinine. See full table below.
** If prerenal - is it hypovolaemia or heart failure?
*** If hypovolaemic - give fluids
*** If heart failure - give diuretics
* Management:
** IDC?
** Avoid nephrotoxics - aminoglycosides, NSAIDs, ACE inhibitors, opioids, beta blockers
** Alter dose of renally excreted meds
** Careful fluid balance - restore perfusion as much as possible by first restoring euvolaemia, then an accurate maintenance fluid rate
** Check electrolytes - essentially check indications for dialysis
** Check for complications below
** Maintain sats >94%