Acute Renal Failure (acute kidney injury)

Question 1

Renal function

Answer 1

o Filtration, Reabsorption, Secretion, Excretion
o 21% cardiac output - 0.4% body weight
o Require adequate perfusion
o Functional unit = nephron
o Glomeruli -> ultrafiltrate -> tubules
o Tubules resorb/secrete solute, H2O
“ End product passed to collecting system
o 750ml-2L/day: homeostatically perfect urine

Question 2

acute renal failure of acute kidney injury

Answer 2

o Defined - precipitous decline in renal filtration function
o Characteristics:
“ Rise in serum creatinine from baseline
“ Decreased GFR
“ Alteration in urine output, concentration
“ Active urine sediment - casts
“ Changes in urine sodium concentration

Question 3

who gets acute renal failure and whos at risk

Answer 3

o Renal perfusion alterations
“ Hypotension (shock), hypovolemia (volume loss)
o Diabetics, HTN: early end-organ damage
o Kidney injury: drugs, contrast, trauma
o Rheumatologic/Collagen Vascular Dz: progression
o Intrinsic Kidney Disease
o Blood pressure will alter perfusion rates through the kidney

Question 4

kidney problems - markers

Answer 4

o UA micro and Chem Panel
“ First clues to presence of Dz
o Volume: definitions
“ Polyuria: >2500ml/24hrs
“ Oliguria: <500ml/24hrs
“ Anuria: <100ml/24hrs
o Concentration (specific gravity)
“ On dipstick/UA: 1.005-1.020
“ Sick kidneys don’t concentrate normally
o Urine sediment on micro
“ Active or bland? Casts or no casts?
o Serum Creatinine
“ Chem panel: 0.6-1.2mg/dl
“ Skeletal muscle, diet
“ Filtered and secreted, balanced amount in serum - normally
“ Increase = glomerular/tubular injury/Dz
“ Indicates Dz presence - not etiology of problem
“ Rises late: GFR already reduced by ~50%
“ Normal creatinine does not equal normal GFR
o Cbc contributes NOTHING to kidney function
o These are the first clues that kidney problems are present
o Dialysis patients are usually the people with anuria
o Small increases in creatinine are a big deal
o If you have a rise in creatinine on chem panel, you already have a GFR reduction of 50% because creatinine rises later on in the liver disfunction situation

Question 5

kidney function - markers

Answer 5

o	BUN: Blood Urea Nitrogen
"	Chem panel: 5-20mg/dl
"	Nitrogenous waste from cellular protein breakdown
"	Elevated in: dehydration renal dz, GI bleeding, etc
o	BUN to Creatinine Ratio
"	Helpful in determining etiology of AKI
o	Urine Microalbumin
"	Albumin to creatinine ratio
o	Glomerular Filtration Rate
"	GFR is estimated (120mL/min)
"	Calculations - not exact
"	Reduction implies renal Dz
"	Progression is marker in CKI
"	Increase = improvement
o	Cystatin C w/ creatinine
"	May be useful in early Dz
o	BUN to creatinine ratio is usually about 10:1 í that's normal
o	CKI í chronic kidney injury

Question 6

Azotemia and uremia

Answer 6

o Terms that describe degree of failure
o Azotemia
“ Retention of nitrogenous wastes
“ Inadequate renal filtration, decreased GFR
“ Increased creatinine, renal “insufficiency”
o Uremia
“ Severe azotemia, renal “failure”
“ Creatinine high, GFR very low
“ Clinical symptoms/consequences of renal failure

Question 7

Disease duration - key to ddx

Answer 7

o Acute - hours to days
o Rapidly progressing - weeks to months
o Chronic - progressive, months/years
“ May have acute insult on chronic failure
o Compare UA, creatinine from previous
“ No previous? Sx duration
o Hospitalized pt’s close monitoring - daily
“ Monitor events - hypotension, drugs, contrast
o You can have an acute hit to your renal function while having chronic kidney

Question 8

Causes of ARF/AKI

Answer 8

o Think - where in the system?
o Prerenal
o Intrarenal (Intrinsic)
o Postrenal
o How do you think about acute kidney injury í how do you characterize it
“ Is it prerenal, intrarental, or postrenal

Question 9

Prerenal causes of ARF/AKI

Answer 9

o	Think - hypoperfusion
o	Hypotension - low vascular resistance
"	Shock - all forms
"	Medication induced
o	Volume depletion - intravascular
"	Dehydration, blood loss (trauma, GI) 
"	"third spacing": burns, hypoalbuminemia
o	Decreased cardiac output
"	MI, CHF, arrhythmias, PE, etc..
o	Low blood pressure

Question 10

prerenal AKI

Answer 10

o Most common form - 50-80%
o Acute time course - creatinine elevated
o BUN to Creatinine Ratio =/>20/1
o Glomeruli, tubules are intact
o “Bland” sediment (no casts)
o Most prerenal AKI is reversible if treated promptly
“ GFR will return to near normal if reversed
o Acute prerenal on chronic renal failure

Question 11

Intrarenal/intrinsic causes

Answer 11

"	Structural injury/insult to kidney itself
o	Prerenal, postrenal causes excluded
"	Glomerular
"	Tubular
"	Vascular

Question 12

Intrarenal cause - clomerular

Answer 12

o AGN: Acute glomerulonephritis
“ Hx, UA, urine sediment key to DDx
“ Postinfectious, rheum, IgA nephropathy, hereditary Dz, DM, etc
“ BUN to Creatinine ratio also =>20/1
“ Focal or diffuse glomerular damage
“ Focal: mild AKI - dysmorphic RBC’s, red cell casts (nephritic), mild proteinuria
“ Diffuse: signif AKI - nephritic w/ heavy proteinuria (nephrotic), HTN, edema

Question 13

Intrarenal causes - tubular

Answer 13

o ATN - Acute tubular necrosis
“ Most common cause intrinsic AKI - 80%
“ Common in hospitalized pt’s
“ **Prerenal AKI not resolving with volume
“ BUN to Creatinine ratio <20/1 (10/1 common)
“ Increase in urine Na - >2%
“ Active sediment
“ “Muddy brown” granular & epithelial cell casts
“ Nephrotoxins: Abx, IV contrast, etc…
“ Ischemia: sepsis, rhabdomyolysis, burns, heat stroke, venomous bites
“ Most common kidney infection í prerenal
“ Most common intrarenal = acute tubular necrosis
o AIN - Acute interstitial nephritis
“ Drugs (NSAID’s, Abx), long list
“ Infections, autoimmune disorders
“ Fever, rash, eosinophilia
“ Active sediment - white cell casts
“ White, red cells, variable proteinuria
“ BUN to Creatinine ratio <20/1
“ Dx - renal biopsy but…consider temporal relation to drugs, stop the offender, monitor
“ Rash = vasculitis

Question 14

Intrarenal causes: vascular

Answer 14

o Large Vessel Dz:
“ Malignant HTN, renal artery occlusion, emboli
o Small Vessel Dz, Vasculitis common
“ Thrombocytopenia (HUS/TTP)
“ Hemolytic uremic syndrome (HUS)
“ Thrombotic thrombocytopenic purpura (TTP)
“ Scleroderma
o Malignant HTN í blood pressure that increases so rapidly that it causes acute end organ damage

Question 15

Postrenal causes

Answer 15

o	Think: obstruction of urine flow out
o	Anywhere, eminently reversible
o	Must obstruct both kidneys to cause ARF
"	Unless the pt has only one…
o	Prostatic Dz, malignancy - common
o	Stones, blood clots, crystals

Question 16

estimating GFR @ bedside

Answer 16

o Cockcroft-Gault: Creatinine Clearance (CrCl)
“ Best for CKD, may overestimate GFR (uses old creatinine assays)
“ ((140-Age) X (weight in kg)) / (serum creat X 72)
“ Normal: 90-140ml/min males; 80-125 females (X 0.85)
o MDRD equation: Modification of Diet in Renal Disease
“ More accurate than CrCl; best for CKD, not acute; commonly used
“ 175 x serum creat x age Add calc: (x .742(F)); (x 1.210(AA))
“ GFR >90 normal, GFR <60 abnormal

Question 17

estimating GFR

Answer 17

o CKD-EPI: Chronic Kidney Dz Epidemiology Collaboration
“ Better in mild Dz; better for risk prediction
“ Recently: better than CrCl or MDRD
“ GFR = 141 * min(SerumCreat/kappa, 1)alpha * max(SerumCreat/kappa, 1) -1.209 * 0.993Age * Sex * Race
“ Use a calculation app…
o Other methods:
o Serum Cystatin C
“ Alternative to creatinine-based calculations
“ Studies: best in conjunction with creatinine - not superior to others
o Pediatric GFR
“ Schwartz formula
o 24hr urine Creatinine Clearance

Question 18

Assessing tubular function

Answer 18

o	Tubular function assessed by solute concentration in urine over 24hrs. Especially Na
"	Sodium retention = prerenal
"	Sodium dumping = sick tubules
o	Urine osmolarity
o	Urine Na concentration
o	Fractional Excretion of Na - FENa

Question 19

Calculating FENa

Answer 19

” FENa = fractional excretion of sodium
“ Distinguishes ATN from Prerenal AKI
o Best in advanced AKI only
“ Urine Na X Plasma Creatinine/Plasma Na X Urine Creatinine X 100 (as %)
“ Prerenal, AGN <1%
“ ATN: usually high, =/>3%, AIN variable: 1-3%
“ Postrenal =/>1%

Question 20

Summary of AKI etiologies - prerenal

Answer 20

o	Prerenal
"	BUN/creatinine ratio 20/1 or greater
"	High urine specific gravity >1.020
"	Urine osmolality high >500
"	Urine Na <20
"	FENa <1% (kidney retaining Na)
"	Inactive/bland urine sediment
"	Oliguria

Question 21

Summary of intrarenal AKI

Answer 21

"	AGN
o	BUN/creatinine ratio >20/1
o	Specific gravity variable
o	Urine osmolality high >500
o	Urine Na <20
o	FENa <1%
o	Urine sediment active - RBC casts
o	Variable urine output
o	Similar to Prerenal - except the casts
o	ATN and AIN
"	BUN/creatinine ratio <20/1 (10/1)
"	Low urine specific gravity, brown urine
"	Urine osmolality <300
"	Urine Na >20
"	FENa usually high
"	Active sediment - Casts: WBC, fatty, muddy brown granular 
"	Oliguria/anuria

Question 22

Summary - postrenal

Answer 22

o	Variable amount and specific gravity
o	Hematuria common
o	BUN/creatinine ratio 10/1 or higher
o	FENa usually normal
o	Sediment usually normal - no casts

Question 23

Workup of AKI patient - hx

Answer 23

” Elicit Sx’s/Hx of pre-, post- or intrarenal
“ Volume loss: dizziness, syncope
“ Urinary abnormalities
“ Systemic - malaise, edema, weakness, n/v
“ Recent illness, new meds, travel, contrast or instrumentation

Question 24

Workup of AKI patient - PE

Answer 24

” Toxic or not? Vitals: fever, hypotension, tachy?
“ Skin - rash, pettechiae, excoriations
“ HEENT - dehydration
“ Lungs/heart
“ Abdomen - flank pain, bladder, prostate
“ Extremities - edema
“ Neurologic - weakness, reflexes

Question 25

Workup of AKI patient - labs

Answer 25

``` " Urine - dip, UA w/ micro, culture " Chem panel, CBC " Spot albumin to creatinine ratio " Urine microalbumin " Calculate CrCl, GFR " 24hr urine collection " Urine Na, urine creatinine, urine osmolarity " FENa ```

Question 26

Diagnostics and treatment of prerenal and intrarenal

Answer 26

``` o Prerenal " Correct volume status, hypotension " Correct source of problem " IV fluids, Abx for sepsis, etc… " Consider admission " Serial BUN/creatinine, urine volume " No need for acute diagnostic imaging " (except to investigate cause) o Measure ins and outs í urine volume vs. intake o Intrarenal " Pre- and postrenal causes eliminated " Consider admission " Remove/Tx the offender if present " Renal ultrasound first " CT scan of abdomen/pelvis " Referral to nephrologist for renal biopsy " Biopsy detects glomerulonephritis, interstitial nephritis, vasculitis ```

Question 27

Diagnostics - renal biopsy

Answer 27

o Indications " Glomerular hematuria with proteinuria " Nephrotic syndrome " Acute nephritic syndrome " Unexplained acute/subacute renal failure o Percutaneous procedure - bleeding common o Contraindications - prior bleeding Dz, hydronephrosis, severe HTN, infection

Question 28

diagnostics- postrenal

Answer 28

o Postrenal: identify cause of obstruction " Post-void residual useful - ultrasound " Catheter to relieve retention " Renal ultrasound to evaluate size, hydronephrosis, structural abnormalities " CT abd/pelvis w/o contrast for stones, with contrast for tumors " Urologist vs. nephrologist o Hydronephrosis is painful, not crying but in pain o Urologist take care of stuff past the kidneys o Nephrologists take care of kidneys

Question 29

when to admit/refer

Answer 29

o Admit new ARF if symptomatic or severe - new creatinine >2.0 above pt's baseline o Consult nephrologist early o Outpatient work-up if stable, subacute o Admit worsening chronic renal failure when symptomatic o Admit if prerenal on top of chronic renal fail

Question 30

Chronic renal failure

Answer 30

o Chronic Kidney Disease - CKD | o End-Stage Renal Disease - ESRD

Question 31

Overview of CKD

Answer 31

o Rarely reversible decline in kidney function - progressive, months to years o Initial injury or chronic insults o Often asymptomatic as kidneys compensate o Small kidneys - hallmark of CKD o Nephrons hypertrophy then become sclerotic o Nephrons are useless, they do not regenerate o Hallmark is small kidneys o You have about a million nephrons to begin with

Question 32

Staging of CKD

Answer 32

``` o National Kidney Foundation Dialysis Outcomes Quality Initiative (K/DOQI) o Structural or functional kidney abnormalities for >3 months " Includes abnormal UA, imaging, biopsy o OR: GFR <60 for >3 months " With or without evidence kidney damage o K/DOQI: o Stage 1 - GFR >90 - Tx comorbid Dz o Stage 2 - GFR 60-89 - follow progress o Stage 3 - GFR 30-59 - Tx complications o Stage 4 - 15-29 - prepare for dialysis o Stage 5 - <15/dialysis - transplant o Stage 1 is normal o Stage 3 is where you are in the non normal range ```

Question 33

Who gets CKD

Answer 33

o Diabetes - 30-40% o Hypertension - 25-30% o Glomerular Dz - 15-20% o Genetic renal Dz, other - the rest

Question 34

Labs for CKD

Answer 34

``` o Follow the usual suspects o BUN/creatinine - progressive increases " Compare with prior, track changes o Estimate GFR to stage pt o Monitor serum electrolytes - esp K+ o Imaging " Renal ultrasound - small kidneys " Plain x-rays - renal osteodystrophy " Subperiosteal resorption = hyperparathyroidism " Not used routinely for clinical staging ```

Question 35

Complications of CKD/ESRD

Answer 35

o Affects nearly all organ systems o Cannot predict when Sx's or complications will occur from Creatinine or GFR o Azotemia first o Frank uremia " Not a lab value or toxidrome " "Constellation" of symptoms o You cannot predict when (by creatinine or GFR) you will get symptoms o Constellation of symptoms = all the symptoms together

Question 36

complications of ESRD

Answer 36

o Hyperkalemia " Life threatening - K+ > 6.0 (get EKG) " GFR usually <10-20ml/min (<10%) " Pt usually oliguric " Causes: dialysis non-compliance a big cause " Dietary indiscretion " NSAID's, ACE Inhibitors, beta blockers " Trauma, acidosis o Anion gap metabolic acidosis " ESRD pt's chronically acidotic - events causing added acidosis are bad " Uremia = "U" in MUDPILES o Boards question: hyperkalemia is the feared complication of end stage renal disease o Hyperkalemia à K affects your heart à conduction disturbances o Renal failure patients (missed dialysis) à need to get a potassium right away " If potassium is high, next step is to get EKG immediately o People with end stage renal disease are chronically acidotic

Question 37

Cardiovascular sxs of CKD/ESRD

Answer 37

o Hypertension - common SBP>200, DBP>120 " Most common - 80-85% in CKD " Difficult to control, speeds path to ESRD " Directly related to Na and water retention " Diuretics, multi-drug antihypertensives " Diet, Na restriction, nephrologist o Accelerated atherosclerosis " Dyslipidemia common - statin tx OK " Risk of death from CAD > risk of eventually requiring dialysis " Independent risk for coronary artery Dz o Accelerated artherosclerosis = MIs at age 40! o Many people will die of a cardiac even before getting dialysis o Volume overload í pulmonary edema, CHF " Na and intravascular volume balance is maintained until GFR <10-15ml/min - then fluid overload " Left ventricular hypertrophy (LVH) and dilated cardiomyopathy (DCM) very common - HTN " Acute pulmonary edema = emergent dialysis " Tx w/ loop diuretics, ACEI's, ARB's " Be careful with IV hydration in renal failure pt! o You have to be very careful in hydrating a renal failure patient because they can't get rid of it! o You can cause pulmonary edema if you overload them with fluid o Pericardial effusion " Retention of uremic toxins, fluid overload " Fluid collects in pericardial sac, restricts ventricular filling " Don't forget infectious, neoplastic, autoimmune causes " Absolute indication for emergent dialysis " Cardiac tamponade can develop o You can get these effusions from infections, parasites, etc. o If you have an effusion but no tampenade physiology, then you get dialysis if you have time

Question 38

hematologic sxs of CKD/ESRD

Answer 38

o Anemia " Decreased erythrocyte production " Normochromic, normocytic - chronic " Common when GFR <30ml/min " Treat early: recombinant erythropoietin Epogen or Procrit IM o Coagulopathies " Platelet dysfunction " Platelet count OK but bleeding time prolonged " Treat if symptomatic or prior to surgery " Bleeding is indication for dialysis o Platelets are there, they just don't work very well

Question 39

GI sxs of CKD/ESRD

Answer 39

o Anorexia, nausea, vomiting " Dietary restrictions make goals difficult " Dehydration common, adds to fluid imbalance o GI bleeding common " Anemia and prolonged bleeding time complicate things

Question 40

neurologic sxs of CKD/ESRD

Answer 40

o Uremic encephalopathy " GFR 10-15ml/min " Accumulation of uremic toxins " Difficulty concentrating to lethargy, confusion, coma " Asterixis, hyperreflexia " Indication for emergent dialysis - reversible o Neuopathies " Very common, difficult to treat " Paresthesias - stocking/glove pattern " Restless leg syndrome " Motor involvement - lose DTR's, foot drop " Early dialysis may prevent progression o Asterixis í foot up and down and then keeps going

Question 41

mineral metabolism CKD

Answer 41

o Mineral/bone disorders of CKD " Hypocalcemia, hyperphosphatemia " High PTH - secondary hyperparathyroidism " àHigh bone turnover, renal osteodystrophy " Bone pain, spontaneous fractures " Monitor levels Ca, Phosphorus, PTH " Diet - low phosphorus (no eggs, coke) " Ca to bind phosphorus or binding agents " Vit D to suppress PTH, increase Ca

Question 42

Endocrine sxs in CKD

Answer 42

``` o Insulin and glucose tolerance issues " Hyper- or hypoglycemia o Thyroid disorders o Low estrogen and testosterone o Impotence and menstrual disorders o Complicated pregnancy - contraception ```

Question 43

dermatologic and miscellaneous sxs of CKD

Answer 43

``` o Dermatologic " Sallow appearance, pallor from anemia " Pruritis - difficult to treat " Uremic frost - severe, late, rareà o Miscellaneous " Immunocompromised state " Malnutrition " Susceptible to infection o Uremic frost í white frost around face and torso o Anyone with renal failure should be considered immunocompromised í very susceptible to infection ```

Question 44

Management of CKD

Answer 44

``` o Treat reversible causes o Involve nephrologist early in course o Renal-protective measures " Tight HTN, DM control " ACE inhibitors, ARB's to slow progression " Nutritionist: low Na, K, protein, phosphorous " Smoking/drug cessation o Identify and prepare pt for dialysis ```

Question 45

Dialysis

Answer 45

``` o Hemodialysis " Blood from body, thru A-V shunt " Semiperm membrane, dialysate " Blood returned to body " 3x/week, 3-4 hour process o Peritoneal dialysis " Dialysate into perioneal cavity, peritoneal membrane acts as dialyzer " At home, ambulatory, continuous o You WANT a thrill in a dialysis shunt ```

Question 46

indications for dialysis

Answer 46

``` o K/DOQI rec's (non-emergent) " Non-DM - GFR <10ml/min, Cr 8 " DM - GFR <15ml/min, Cr 6 o Emergent indications " Hyperkalemia (refractory) " Fluid overload (refractory to diuretics) " Pericardial effusion, coagulopathy (bleeding) " Severe metabolic acidosis " Neurologic Sx's of uremia " Encephalopathy, neuropathy, seizures o KNOW EMERGENT INDICATIONS ```

Question 47

Renal transplant

Answer 47

o Treatment of choice for ESRD o Successful = improved quality of life and reduced mortality risk compared to dialysis o Not all patients appropriate candidates o Refer to transplant program when dialysis is initiated (2-3 years wait)

Question 48

Summary of AKI, CKD

Answer 48

``` o AKI? Think - prerenal, intrarenal, postrenal " Know the characteristics of each o Know labs to order, calculations o Monitor patients at risk - DM, HTN o Follow hospitalized patients closely o Know, monitor complications of CKD o Know emergent indications for dialysis o Learn renal function and disease well enough to explain it to your patients ```