U of U PA School AKI

What is an AKI?

A decrease in renal function developing in minutes to a few days

What labs indicate AKI?

Creatinine rise of 0.3 mg/dl in 48 hours

Creatinine rise 1.5 times normal that is presumed to have occurred in last 7 days

How are AKI and oliguria related?

Oliguria impies severe AKI

-Anuric - <100ml output in 24 hours

-Oliguric - <400ml output in 24 hours

-Non-oliguric - >400ml output in 24 hours

What are the classfications of AKI?

Pre-renal AKI

Intrinsic renal AKI

Post renal AKI

What is a pre renal AKI?

Hypoperfusion of kidney leading to loss of filtration pressure in glomerulus

What is an intrinsic renal AKI?

Problem in glomerulus, tubules, or interstitium

What is a post renal AKI?

Obstruction in collecting system leading to back pressure

What are the most common causes of AKI?

Pre renal AKI

Acute tubular necrosis - Intrinsic renal AKI

What causes pre renal AKI? (5)

States of decreased effective arterial pressure

-Volume depletion

-Shock

-CHF

-Obstruction of major vessels/thrombosis

How do the kidneys react to pre renal AKI?

Renal tubules reabsorb as much as possible to preserve volume

How do urine studies present in pre renal AKI? (5)

Specific gravity >1.015

Urine sodium <20

Bun/Cr >20

FeNa <1%

Hyaline casts

What can cause intrinsic renal AKI? (6)

Intra renal vasoconstriction

-Hepatorenal syndrome

-Emboli

Glomerulonephritis (RPGN)

Acute tubular necrosis (ATN)

Intra tubular obstruction by crystals

Acute interstitial nephritis

What are the signs of RPGN? (4)

Rising creatinine

Hypertension

Oliguria

Hematuria

What will urine tests reveal for RPGN? (4)

Dipstick + for blood and protein

Urine protein:creatinine ratio elevated

24 hour protein elevated

Urine microscopy

-Glomerular hematuria - dysmorphic RBCs and RBC casts

How should a work up be done for suspected RPGN? (4)

ID underlying pathology

-ANA

-ANCA

-Anti GBM

-Complement levels

What is often used to treat RPGN?

Immunosuppressants

What are the types of ATN?

Ischemic ATN from prolonged pre renal states

Toxic ATN - intrinsic/extrinsic

What will urine results reveal in ATN? (5)

Specific gravity <1.015

Urine sodium >20

FeNa >1%

Bun:creatinine <20

Urine microscopy

-Muddy brown casts

What type of ATN is most common?

Ischemic ATN from prolonged pre renal states

What causes toxic ATN?

Toxin damaging tubules directly

What causes intrinsic ATN?

Pigments from hemoglobin/myoglobin

-Rhabdomyolysis

What causes extrinsic ATN? (5)

Contrast nephropathy

Drugs

-Amphotericin B

-Vancomycin

-Cisplatin

-Aminoglycosides

How does rhabdomyolysis cause intrinsic ATN?

Extensive muscle damage and release of myoglobulin form casts in tubules and cause intratubular damage

Myoglobin itself is toxic to epithelium

How is rhabdomyolysis diagnosed?

Elevated creatinine

BMP

Elevated CPK > 10,000

What BMP changes are associated with rhabdomyolysis?

Cell break down products

-Hyperkalemia

-Hyperphospathemia

-Hypocalcemia (from binding phosphorus)

What will urine results reveal for rhabdomyolysis?

Dipstick + for blood (from myoglobulin, no actual blood)

No RBCs on microscopy

How is rhabdomyolysis treated?

Vigorous hydration

Fasciotomy if compression syndromes

Dialysis if oliguria or life threatening electrolyte abnormalities

Why is calcium supplementation avoided in rhabdomyolysis?

Can cause precipitation of calcium-phosphorus in soft tissues of heart and kidneys

Can cause arrhythmias and renal failure

Only give if severely low

How does contrast cause AKI?

Iodinated contrast can cause renal vasoconstriction and oxidative damage

-Low, medium, and high osmolarity, high most likely to cause damage

How does the course of contrast nephropathy usually run?

Elevated creatinine peaking at days 7-10 then declining to baseline

It can precipitate ESRD in advanced CKD

Who is most at risk for contrast nephropathy? (4)

Pre existing CKD

DM

High volume of contrast

Intra arterial administration of contrast

What can be used to gauge the risk of contrast nephropathy?

Mehran score

How can contrast nephropathy be prevented?

ID high risk patients

-Hydrate with saline before and after contrast

What causes intra tubular obstruction by crystals?

Uric acid crystals from acute uric acid nephropathy

Drug-induced crystals

Phosphate nephropathy

What can cause acute uric acid nephropathy?

Tumor lysis syndrome

What drugs can induce intra tubular obstructions by crystals? (5)

Indinavir

Atazanavir

IV acyclovir

Sulfa drugs

Ethylene glycol

What causes phosphate nephropathy?

Deposit of calcium phosphate in tubules

Calcium supplementation for high serum phosphate

Fleets enema given in CKD

What characterizes acute interstitial nephritis?

Interstitial edema

Intense leukocyte infiltration into interstitium of kidney

What can cause acute interstitial nephritis?

Infections

Rheumatic diseases - sjorgens, lupus

Allergic (Drug induced allergic interstitial nephritis)

What is the most common cause of acute interstitial nephritis?

Allergic interstitial nephritis

What drugs are most implicated in allergic interstitial nephritis?

Antibiotics

NSAIDs

PPIs

How does allergic interstitial nephritis present?

GFR decreasing 7-10 days after exposure to a drug

Rarely - fever, rash, eosiniphilia

Urine - multiple WBCs/WBC casts but culture negative

-Sterile pyuria

How is allergic interstitial nephritis diagnosed?

Clinical

Consider patients with no apparent cause of AKI

Biopsy if exact diagnosis needed

What is the treatment for allergic interstitial nephritis?

Discontinue offending agents

Start steroids early

What causes post renal AKI? (4)

Strictures - ureteric or urethral

Obstructing stones

Enlarged prostate

Compressing extra renal masses

How is post renal AKI diagnosed?

Ultrasound of kidney or CT of abdomen/pelvis

-Shows hydronephrosis

When should a renal ultrasound be ordered?

All cases of AKI unless very apparent other cause

What are the consequences of AKI? (4)

Volume overload + hypertension

Hyperkalemia

Metabolic acidosis

Uremia

What are the principles for managing AKI? (6)

Optimize hemodynamics in pre renal AKI - if in doubt trial fluids

Discontinue offending drugs

ID glomerulonephritis and refer to nephrology

Control BP

Dose drugs based on current GFR

Assess indications for dialysis