Acute Renal Failure

John K. Amory MDAssociate Professor

Department of MedicineUniversity of Washington

Acute Renal Failure: Definition

● Rapid deterioration of renal function » (increase of creatinine of >0.5 mg/dl in <72hrs.)» “azotemia” (accumulation of nitrogenous wastes) » elevated BUN and Creatinine levels » decreased urine output (usually but not always)

● Oliguria: <400 ml urine output in 24 hours● Anuria: <100 ml urine output in 24 hours

Clinical Presentation of Acute Renal Failure

P r e r e n a ld e c r e a s e d r e n a l p e r f u s i o n

8 0 % o f c a s e s

R e n a li n t r i n s i c r e n a l d i s e a s e

1 0 % o f c a s e s

P o s t r e n a lo b s t r u c t i o n

1 0 %

A c u t e R e n a l F a i l u r e

Prerenal Azotemia

● Volume depletion: vomiting, diarrhea, decreased intake, diuretics, third-spacing

● Hypotension: sepsis, drugs, blood loss● Decreased cardiac output● Renal artery stenosis, embolism, or

thrombosis

Renal

● Vascular: Hypertension, Wegener’s, PAN

● Glomerular: Post-strep GN, Lupus, RPGN, Hepatitis related, IgA nephropathy,

● Tubular: Acute Tubular Necrosis (ATN) Medication toxicity, toxins

● Interstitial: Acute Interstitial Nephritis (AIN)

Intra-renal renal (e.g ) Acute Tubular Necrosis

● Ischemia ● Toxins (antibiotics, contrast), hemolysis,

rhabdomyolysis, heat stroke● Clinical course: initiation, maintenance, and

recovery “diuretic” phases● Clinical clues: Muddy brown, granular casts on

urinalysis

Postrenal● BPH

● Stones (usually unilateral with single kidney)

● Tumor (lymphoma, ovarian, prostate)

● Urethral stricture

● Neurologic (i.e. overflow incontinence)

Creatinine Clearance

● (Very!) Rough estimate (divide 100/Cr)● To Calculate Creatine Clearance

» (140 - age) x weight in kg (x 0.85 for women) 72 x serum creatinine

● Creatinine clearance of» < 50 adjust medications» < 25 refer to nephrology for pre-dialysis» < 10 most people need dialysis

Acute Renal Failure: Diagnostic Work-up

● Chem 7● Urine electrolytes● Urinalysis with

Microscopic analysis

● Renal ultrasound

● BUN/Cr ratio > 15-20● Na and CO2 may be high

● FeNa* = Cr S x NaU x 100 CrU x Na S

* < 1 prerenal, >1 renal● Urinary Na < 20 (very helpful) ● Urine Osms > 500

Other useful Tests

● 24 hour urine for protein and creatinine● urine eosinophils., UPEP● cholesterol, albumin, glucose● ANA panel, C-ANCA , SPEP, HIV, Hepatitis B/C,

ASO● Renal biopsy● Post-void residual or catheterization● PSA

Management Principles

● Establish urine output (fluids ± diuretics)● Remove nephrotoxins, dose-adjust medications ● Careful volume and electrolyte management (using

free daily weights, VS, I&Os, and labs)● Ca, Mg, P also useful● Provide nutrition (low K, low P)

Indications for Dialysis

● Volume overload with CHF● Pericarditis● Electrolyte abnormalities● Toxins which can be removed by dialysis● Life-threatening acidosis● Uncontrolled bleeding

Case #1● A 36 y.o. woman c/o n/v/sob x for 1

week. She had a bad sore throat one month ago. Creatinine is 4.5

● What is your differential?

● What tests should you order First?

Case #1 (cont.)

● Urine Na =30● Urine Cr=50● Serum Na=145● Renal ultrasound-

WNL● U/a

What is this? What is your differential and what do you do next?

Glomerulonephritis

● Post-strepGN● IgA nephropathy● SLE, PAN, Hep C,

HIV, Wegener’s, ● Goodpasture’s● HUS/TTP● MPGN, RPGN● Drugs● Tumors (leukemia,

lymphoma)

● ASO titer● Renal (or skin) biopsy● ANA/ANCA/serologies

● Anti-GBM antibodies● Smear/LDH● Renal Biopsy● Med history● CT scan

Post-streptococcal GN● Appears 6-14 days after pharyngeal or skin infection with

Gr A, beta-hemolytic strep; pathogenesis likely immune● Htn, edema, and pulmonary congestion are common;

nephrotic syndrome and oliguria are less common; ● UA shows dysmorphic RBCs and RBC casts ● 5% will progress to RPGN; most (70%) recover● ASO and “streptozyme,” CH50 and C3 decreased● Antibiotics are not helpful except for ?family members

Case #2

● A 55 y.o. man with type 2 diabetes for 15 years presents with decreased urine output for 4 days. Baseline Cr=1.6 with 1.3 grams of protein on his last 24 hour urine. Meds: lisinopril and insulin. He had a cardiac catheterization 1 week ago. BUN/Cr = 20/5.0, K=6.1, BP is 190/110. His JVP is 9 cm, he has bibasilar crackles, and 1+ edema.

● What is the differential for his renal failure and which is most likely?

● What tests would you order first?

Case #2 (continued)● Urinalysis shows:

» Una=50Microscopic analysis

reveals the following

What are these? And what They mean?What would they look like Under a polarizing microscope?

Contrast-Induced Renal Failure

● Risk is 40% for patient with diabetes ● Oliguria and other symptoms develop in 24 hrs● Prevention:● N-acetylcystine 600 mg po bid x 2d (1 before and day of)

» Give 0.45% NS IV 1 ml/kg/h 12 hrs before and after» Contrast nephropathy( defined as >0.5 mg/dl increase)- 21% of controls and 2% of N-acetylcysteine group

Tepel, NEJM, 2000.

Diabetic Nephropathy

● Approximately 50% of Type 1 patients and somewhat fewer Type 2 patients develop progressive proteinuria; initially patients have increased GFRs

● Test for microalbuminuria (30-300 mg/day) yearly at 5 years from dx for Type 1, begin at dx for Type 2

● ACE inhibitors, control of hypertension (and low protein diet) delay progression

Case #3

● A 40 y.o. IDU (IV heroin) is hospital day 7 for right-sided endocarditis treated with nafcillin and gentamicin. Your morning labs show creatinine of 4.0. His other meds are methadone 60 mg qd, and ibuprofen 600 tid for low back pain. He was dehydrated on admission (BUN 40/Cr 1.6) but now has good urine output and does not appear dehydrated on exam. UA shows 2+ protein.

Case # 3 continued

● Una is 60● Urinalysis reveals

the following:

What are these? WhatDo they imply? How is This situation treated?

ATN due to Aminoglycosides

● Related to trough levels of drug and duration; QD dosing decreases toxicity; tissue half-life >> serum half-life

● Co-factors: Age, renal disease, volume depletion, hypertension and other toxic drugs are risks (10-20% overall risk)

● Gradual onset, proteinuria, concentrating defects, nonoliguria, and reversibility are the rule

Case #4

● A 69 y.o. man has been unable to urinate for the last 24 hours. He was recently started on amitriptyline for insomnia. His abdomen is distended and diffusely tender. He feels a slight urge to urinate when you palpate his suprapubic area.

● What do you think is causing his problem?● What orders will you write?

Bladder Outlet Obstruction

● Commonly due to BPH or neurological disease● Onset may be gradual or sudden;

anticholinergic medications and narcotics pain medications may contribute

● Foley catheter insertion and renal US are diagnostic

● Post-obstructive diuresis may result in severe dehydration and hyponatremia

Case #6

● A 55 y.o. woman with pneumonia, started on cefuroxime in hospital. Now with creatinine of 2.3 (baseline 0.8 1 year ago) and UA shows 2+ WBCs.

● What is your differential?● What tests do you want to order?

● Una=50, FENA=1.5● Urinalysis reveals

the following:

What do you do now? Is there A special test which can helpYou in this circumstance?

Acute “Allergic” Interstitial Nephritis

● Most commonly caused by NSAIDs, antibiotics (e.g. penicillins, cephalosporins and others); or infectious diseases

● May present with fever, rash, joint pain and eosinophilia; or only renal dysfunction (anemia, Na wasting and increased uric acid common)

● UA with pyuria, granular casts, RBCs, urine eosinophils present in 75% (except NSAID);

● < 1.5 gm protein

Acute Renal Failure (redux)

● Increase in creatinine (rapid decrease GFR)

● Pre, intra and post renal causes● Three key tests:

» Urine electrolytes» Urinalysis with microscopic exam» Renal Ultrasound

● Disease specific Treatment