Nephrology - Acute Kidney Injury

Nephrology [ACUTE KIDNEY INJURY] Approach to Renal Failure Renal failure, or acute kidney injury, often presents with only an elevated creatinine or decreased urinary output. Because the kidneys are redundant, unless the GFR gets very low the kidneys generally maintain near normal function. That is, until electrolytes get out of control the patient will be asymptomatic. It’s usually on routine labs that it’s encountered. It’s important to differentiate between pre, post, and intra-renal failure. The list of potential diagnoses is epic so it becomes prudent to develop a system. Prerenal is the result of !perfusion - whether it be from !cardiac output, 3rd spacing of fluid, or ! vessel diameter. In this case, the kidneys think they’re dehydrated and hold onto salt and urine. Thus, the urinalysis will show a low urine sodium (UNa 20 UNa < 10 FENa < 1%

R/O PostRenal sonogram

Give IVF or Diuresis Hydroureter

PostRenal

Hydronephrosis Stent or Remove Obstruction

for pre and post renal Intrarenal

PreRenal

U/A

Diagnosis Variable

Bx

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Nephrology [ACUTE KIDNEY INJURY]

Intrarenal Once honed to Intrarenal, the damage can be thought of in 3 distinct regions:

Urinalysis Findings Pre-Renal Post-Renal

1)! Tubules (Acute Tubular Necrosis) Acute Tubular Necrosis is caused by either ischemic damage or toxin exposure. The tubules necrose, die, and slough off. They form the shape of the tubules and present as muddy brown casts. They’ll go through three phases: the prodrome where creatinine rises but urine output remains the same, an oliguric phase where creatinine rises and urine output plummets (caution fluid overload), and a Polyuric phase where the patient pees a lot. Through this time they need supportive care. a.!

Contrast Induced ATN If a patient has pre-existing renal damage or is at increased risk, and they NEED contrast, give vigorous hydration, prophylactic N-Acetyl-Cysteine, and Stop ACE/ARBs and Diuretics prior to contrast. Dialysis is ineffective at preventing contrast induced nephropathy.

Intra-Renal ATN Allergic Nephritis Pyelonephritis Myoglobin Nephritis Glomerulonephritis Gout

BUN/CR >2 0, UNa < 10; FENa < 1% Urinary Retention Hydronephrosis /ureter BUN/CR 20; FENa> 1%! Muddy Brown Casts Eosinophilia

IVF if dry Diuresis if wet Alleviate Obstruction: Catheter, Stent, Surgery

WBC Casts Blood, Ø RBC

Abx NaHCO3, IVF

RBC Casts

Disease Dependent

Uric Acid Crystals

Treat the Gout!

Supportive Care Remove Drug

2)! Interstitium (Acute Interstitial Nephritis) AIN is essentially an allergic reaction with invasion of white cells. Drugs, Infections, and Deposition Disease can cause it. The urine will present with immune cells: white blood cells, white cell casts (pyelonephritis), or eosinophils. Removal of the offending agent is crucial. That means either treat the infection or stop the drug. Steroids are often ineffective. 3)! Glomerulus (Glomerulonephritis) A patient with RBC casts on urinalysis is indicative of glomerulonephritis. There are a crap-ton of diseases that can cause it. The way to tell them apart is with a biopsy - something not often done. Learning the typical histories should be enough (memorize the chart to the right). What becomes important is to rule out Nephrotic Syndrome (>3.5g/24hr urine, Edema, and Hyperlipidemia) with a U/A Spot Test or 24-hr urine. This isn’t step 1 stuff so don’t worry about spending time memorizing biopsies, stains, or complement levels.

Acute Indications for Dialysis The decision to dialyze is NOT based on the Creatinine! Transplant is another definitive option. The decision to dialyze is based on the severity of the condition and the presence of one of the AEIOU mnemonic.

Glomerulonephritis IgA Nephropathy Post-Streptococcal Lupus Wegener’s Goodpasture Churg-Strauss Henoch-Schonlein

History Post-Viral Post Pharyngitis / Impetigo ANA, dsDNA, Sxs Sinus, Lung, Kidney Hemoptysis + Hematuria Asthma + Hematuria Post-Viral (IgA) and systemic vasculitis

Blood Test ASO titer !dsDNA ANCA Anti-GM

Indications for Dialysis: A E I O U

Acidosis Electrolytes (Na/K) Ingestion (Toxins) Overload (CHF, Edema) Uremia (Pericarditis)

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