Acute Renal Failure

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 re re n a ld e c re ase d ren a l p erfu s ion

8 0 % o f ca ses

R e n a lin trin s ic ren a l d ise a se

1 0 % o f ca ses

P o s tre n a lo b s tru c tion

1 0%

A cu te R e n a l F a ilu re

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=50

Microscopic 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