Acute Renal Failure

Internal Medicine Lecture Series

August 10, 2005

Julia Faller, D.O.

Objectives

Define acute renal failure (ARF) Describe the pathophysiology of ARF Outline appropriate testing to diagnose the

cause of ARF Recommendations for treating ARF Case presentation

Acute Renal Failure

An abrupt or rapid decline in renal function. Recognized by a rise in BUN or serum

creatinine concentrations. With or without a decline in urine output. Often transient and completely reversible.

Pathophysiology

ARF may occur in 3 clinical settings

1. An adaptive response to severe volume hypotension.

2. In response to cytotoxic insults to the kidney.

3. With obstruction to the passage of urine.

Classifying ARF

ARF is classified as oliguric or nonoliguric. Oliguria is defined as a daily urine volume of

less than 400 mL/d. Anuria is defined as a urine output of less

than 50 mL/d If anuria is abrupt in onset, it is suggestive of

obstruction.

Frequency of ARF

Approximately 1% of patients admitted to hospitals have ARF at the time of admission.

The estimated incidence rate of ARF is 2-5% during hospitalization.

Approximately 95% of consultations with nephrologists are related to ARF.

Morbidity and Mortality

The mortality rate estimates vary from 25-90%.

The mortality rate is 40-50% in general and 70-80% in intensive care settings

History and Physical

Hypotension Volume contraction Congestive heart failure Nephrotoxic drug ingestion History of trauma or unaccustomed exertion Blood loss or transfusions

History and Physical

Evidence of connective tissue disorders Exposure to toxic substances such as ethyl

alcohol or ethylene glycol Exposure to mercury vapors, lead, or other

heavy metals, which can be encountered in welders and miners

Causes of ARF

1. Prerenal 40-80%

2. Intrarenal 50%

3. Postrenal 5-10%

Prerenal

Hypotension CHF Hypovolemia from renal losses Hypovolemia from extrarenal losses Vasoconstriction

Intrarenal

Vascular causes Interstitial nephritis Glomerular factors

Postrenal

Bladder outlet obstruction due to prostatic hypertrophy

Uretheral stictures

Lab studies

BUN and creatinine CBC with peripheral smear Urinalysis Urine Electrolytes

BUN and Creatinine

BUN values that increase disproportionately larger than those of creatinine suggest prerenal azotemia

The ratio of BUN to creatinine greater than 20:1 suggest volume contraction.

CBC and peripheral smear

Results can increase differential diagnosis to include TTP, multiple myeloma, DIC

Urinalysis

Granular muddy-brown casts—ATN Reddish brown colour—acute glomerular nephritis,

presence of myoglobin or HgB Eosinophils—UTI’s, glomerulonephritis, acute

embolic disease, drug-induced interstitial nephritis RBC casts—glomerular disease WBC—pyelonephritis, or acute interstitial nephritis

Urine Electrolytes

Fractional excretion of sodium (FENa). With decreased GFR, the kidney will reabsorb salt and

water avidly if there is no intrinsic tubular dysfunction. Thus, patients with prerenal failure should have a low fractional excretion percent of sodium (< 1%).

FENa = (UNa/PNa) / (UCr/PCr) X 100 Oliguric states are more accurately assessed with this

formula than nonoliguric states because the kidneys do not avidly reabsorb water and sodium in nonoliguric states.

Imaging studies

Ultrasound Doppler scans Nuclear scans

Renal biopsy

Treatment

Balancing volume status and correcting biochemical abnormalities.

All nephrotoxic agents must be discontinued or used with extreme caution.

All medications cleared by renal excretion should be discontinued or their doses should be adjusted appropriately.

Treatment

Correct acidosis with bicarbonate administration

Correct hyperkalemia by decreasing the intake of potassium, delaying the absorption of potassium, using potassium-binding resins, controlling intracellular shifts, and instituting dialysis if necessary

Correct hematologic abnormalities

Case presentation

Pt is a 47 y/o WM who presented to MCH ER via ambulance after he was found by counselors at stairways falling and complaining of dizziness. Pt states unsteadiness has been going on for the past week with associated nausea, vomiting, and change in urine stream. Pt states he cannot hold any food down. He denies fevers/chills or diarrhea, CP, SOB. Pt has psych history. Pt had previously normal renal function.

Medications

Lithium ER 450 mg bid Promethazine 25 mg q 6hour prn Topamax 150 po bid Wellbutrin SR 150mg 2 in am 1 in pm Clonidine 0.1 mg bid Lamictal 25 mg 2 hs Lisinopril/HCTZ 20/25 qd Glipizide XL 5 qd Lipitor 40 mg qd Diltiazem 240 mg qd Paroxetine 20mg qd

Past Medical History

HTN Type II Diabetes Psychiatric history Hypercholesterolemia

LABS in ER

BUN 81 Creat 10.5 Potassium 3.1 Albumin 1.7 Myoglobin 442 UA yellow, hyaline casts Lithium 3.00 (0.60-1.20)

Admission

Pt was admitted to ICU and was hydrated aggressively

Nephrology consult was obtained U/S was significant for R hydronephrosis Pt was started on dopamine drip in the ER CT chest with contrast was done in ER Urine output was good and responded nicely to

fluids

Lab studies

Second set on day of admission

Creat 8.8

Bun 74 Day one

BUN 63

Creat 6.4

Day four

BUN 13 Creat 1.1 Patient discharged to home.

Questions or Comments