CMPP: Acute Kidney Injury

an abrupt decline in GFR

an increase in serum creatinine

* initially may have normal lab values and only a decreased urine output

in acute kidney injury, labs reveal...

decreased urine output

earliest finding in an acute kidney injury

hypovolemia

a normally functioning kidney interprets decreased GFR as...

GFR

the best overall laboratory indicator of kidney function is the...

Glomerular Filtration Rate (GFR)

estimates how much blood is filtered through the glomeruli each minute

creatinine clearance (inversely proportional to GFR)

what lab value is used to estimate the GFR?

completely filtered and neither reabsorbed or secreted

--> since it is testing filtration rate

the ideal substance to measure the GFR should be...

age, gender, and muscle mass

the "normal" serum creatinine level is affected by...

elderly, female, and/or have low muscle mass

what are some factors that can DECREASE GFR

50% decrease in renal function

a doubling of creatinine from baseline results in...

identifies acute kidney injury

stages of CKD

Contraindicates certain meds/IV contrast administration

requires adjustment of med doses/frequency

sensitivity/specificity issues based on age, gender, and muscle mass

significance of low GFR

inversely

BUN is typically _____ related to the GFR

increased; increases (>20:1)

in dehydration, there is significant _________ reabsorption, which does what to the BUN:creatinine ratio?

GI bleeding and high protein diets

BUN may be elevated due to...

liver disease and low protein diets

BUN may be decreased due to...

Azotemia

accumulation of nitrogenous waste products in the blood

Uremia

symptoms of multi-organ damage due to renal disease

drop in renal blood flow

pre-renal AKI is caused by...

direct kidney injury

renal AKI is caused by...

obstruction of the urine flow

post-renal AKI is caused by...

pre-renal

what is the most common form of kidney injury?

volume depletion (dehydration, hemorrhage)

decreased CO (CHF, MI, valvular heart disease)

systemic vasodilation (sepsis, anaphylaxis)

Afferent arteriolar vasoconstriction (NSAIDs, IV contrast)

Renal artery stenosis

reasons for decreased renal blood flow

ACEi/ARBs

--> preferentially vasodilate efferent arterioles

Aminoglycosides

Amphotericin B

IV radiocontrast agents

Prerenal AKI may be precipitated borderline volume-depleted states in what kind of situations?

volume depletion

a normal kidney interprets decreased GFR as...

Reabsorbing H2O by ADH

Reabsorbing Na/H2O via RAAS

how does the kidney compensate for decreased GFR?

high urine specific gravity

low urinary Na concentration

low fractional excretion of NA

Serum BUN:creatrinine ratio >20:1

decreased GFR results in what manifestations?

Fractional excretion of sodium

measures the fraction of the total amount of filtered Na (total Na entering Bowman's space) that is ultimately excreted in the urine

Excreted Na = filtered Na+secreted Na-reabsorbed Na

formula for FeNa

low % of urinary Na excretion (secondary to increased Na absorption)

low FeNa indicates...

volume depletion -- since kidney is reabsorbing Na (anything it can) to try and replete volume

--> kidneys are doing what they are supposed to be doing

what condition is associated with low FeNa if renal function is intact and why?

low urine specific gravity (urine is not appropriately concentrated to try and conserve fluid)

urine Na high (kidney is not appropriately reabsorbing Na+ to try and gain fluid)

FeNa high (see above)

*kidney is detecting low GFR but the kidneys are funky

what are some manifestations of renal AKI?

Obstructive (thrombotic, embolic, secondary to dissection

Microangiopathy (TTP, HUS, DIC, preeclampsia)

Malignant HTN

Transplant rejection

vascular causes of renal AKI

Acute immune complex-mediated glomerulonephritis

--> post-strep infxns (pharyngitis/impetigo)

--> SLE

Antibody mediated (Goodpasture's syndrome, Wegener's granulomatosis)

glomerular causes of renal AKI

Drug induced: Abx (beta-lactams, sulfa drugs, fluoroquinolones), NSAIDs, diuretics, PPIs

Pyelonephritis

SLE, leukemia, lymphoma

interstitial causes of renal AKI

acute tubular necrosis

what is the #1 cause of renal AKI?

drugs, abnormal pigments, or crystal formation

Nephrotoxin-induced ATN involves direct damage to the renal tubules secondary to...

secondary to ischemia or exposure to a nephrotoxin

-->pre-renal that goes unrecognized can turn into this

what causes acute tubular necrosis?

Drug induced (aminoglycosides, amphotericin B, chemotherapy, IB contrast, lithium)

Heme pigment -- rhabdo/intravascular hemoylsis

Crystals --

Ethylene glycol toxicity

what are some causes of ATN?

aminoglycosides, amphotericin B, chemotherapy, IB contrast, lithium

what drugs are indicated in causing ATN?

"muddy brown casts" visual on microscopic exam of the urine

what is commonly seen on UA for one with ATM?

Isothenuria

injured tubules are unable to maximally concentrate or dilute the urine; hallmark of ATN

respond to stressful situations

Isothenuria results in an inability of the kidneys to...

Urinary casts

cluster of urinary particles that forma mold in various areas of the renal tubular lumens; dehydration, stasis, and acidic urine favor the formation of these.

glomerulonephritis

red cell casts are classically seen in...

acute pelonephritis

white cell casts are classically seen in...

tubular image secondary to epithelial sloughing

epithelial cell casts indicate...

renal disease (nonspecific)

coarse/fine granular or waxy casts indicate...

healthy individuals -- acute dehydration

hyaline casts can be seen in...

Hepatorenal syndrome

occurs when AKI develops in patients with advanced liver disease

oliguria, increased creatinine & AKI

proteinuria

features of hepatorenal syndrome

the glomeruli

what needs to be damaged to cause proteinuria?

urethral caliculi

tumors

inadvertent legation during pelvic surgery

post-renal AKI can be caused by ureteral obstruction secondary to...

BPH #1 cause

Intraluminal blood clots

Prostate or bladder cancer

Drugs (antihistamines/decongestants, tricyclic antidepressants)

Neurogenic bladder

Cauda equina syndrome

Urethral structure, tumor

post-renal AKI can be caused by bladder obstruction secondary to...

increased, increased, decreased

conditions that lead to post-renal AKI can lead to ______ resistance, _______ intratubular pressure, and ultimately __________ GFR.

antihistamines/decongestants, tricyclic antidepressants

what medications are indicated in causing post-renal AKI?

foley catheter

-->suprapubic catheter if unable to insert a foley

what is the therapy of choice for post-renal AKI

ureteral stent -- hollow coiled tube inserted cystoscopically

what is the therapy of choice for a ureteral obstruction?

nephrostomy tube -- inserted directly in the kidney

how would you treat a pt with a ureteral obstruction that cannot get a ureteral stent placed?

reduced urine output

what finding is present in all cases of AKI?

low oral intake, vomiting, diarrhea, hemorrhage

what are some important historical factors for prerenal AKI?

only with generalized weakness, confusion, or anorexia

how may elderly people present with pre-renal AKI?

recent pharyngitis/skin infection (impetigo) -- glomerular

Nephrotoxic drug ingestion, recent exposure to IV contrast, recent trauma or unaccustomed exertion (rhabdo) -- ATN

what are some important historical factors for renal AKI?

lower abdominal pain/distension

inability to urinate

severe low back pain

associated neurologic symptoms

hx of BPH

antihistamines/decongestants, TCA use

what are some important historical factors for post-renal AKI?

CMP, CBC, UA with microscopy, bladder scan

how to begin the workup for AKI

WBC to evaluate for pyelonephritis

Blood smear to evaluate for hemolysis/schistocytes (TTP, HUS, vascular causes)

why do you get a CBC for AKI?

urine electrolytes (FeNa)

why do you get a UA with microscopy for AKI?

if suspected bladder neck/urethral obstruction

when would you get a bladder scan for AKI?

increased BUN/creatinine (creatinine more specific)

what lab findings are characteristic of AKI?

urea reabsorption increases (since kidneys are doing their job correctly) and BUN:creatinine > 20:1

what lab findings are characteristic of pre-renal AKI?

BUN:creatinine <20:1 (diseased kidneys cannot reabsorb urea)

what lab findings are characteristic of renal AKI?

glomerulonephritis, rhabdomyolysis

reddish-brown urine can indicate...

ethylene glycol poisoning (tubular cause)

Calcium oxalate crystals in the urine are characteristic of...

pros:

--> assesses size and quality of renal tissue

--> evaluates for dilatation of calyces and renal pelvis (hydronephrosis)

--> may detect mass/kidney stone

--> doppler evaluates renal blood flow

--> no ionizing radiation or contrast risks

--> can be done at bedside

what are some pros/cons of using U/S as a radiologic study for AKI?

pros:

--> provides more anatomic details

--> better at identifying post-renal causes

cons

--> cannot be done at bedside

--> significant IV contrast/radiation risks

what are some pros/cons of using CT as a radiologic study for AKI?

identify and treat underlying cause

always check patient's baseline creatinine

how to treat AKI (gen)

restore adequate perfusion

therapeutic options for pre-renal AKI

identify site od damage and treat the underlying disease

manage resultant fluid and electrolyte abnormalities

therapeutic options for renal AKI

relieve or bypass the urinary tract obstruction

therapeutic options for post-renal AKI

volume overload -- CHF/HTN

AKI can lead to retention of Na+/H2O, this can lead to...

serum Na+ (water follows the salt)

what lab value is usually normal in AKI?

hyperkalemia

AKI can lead to retention of K+, this can lead to...

metabolic acidosis (U in MUDPILES)

AKI can lead to retention of acids, this can lead to...

Azotemia/Uremia

AKI can lead to retention of nitrogenous wastes, this can lead to...

N/V, anorexia, altered mental status, seizures

Azotemia/Uremia can present as...

hyperphosphatemia and subsequent hypocalcemia

AKI can lead to retention of phosphate, this can lead to...

immunosuppression/infections

what is the leading cause of death in AKI?

anemia (low EPO)

platelet dysfunction (absolute number is normal)

what are some hematologic complications of AKI?

early restoration of renal blood flow

what is the most important prognostic indicator for AKI?