AKI Flashcards
ARF definition
SEVERE AKI - implies need for dialysis
AKI Definition
ABRUPT decrease of kidney function
Diagnosis of AKI
Based on serum Cr used to calculate GFR OR decrease in patient’s urine output
Problem with using serum Cr for diagnosis
- In EARLY stages serum Cr may be low even though actual GFR is markedly reduced (not enough time)
- If patient is on dialysis there will be a false negative
Best criteria for diagnosing AKI
KDIGO
KDIGO diagnosis criteria
- Increase in serum Cr >0.3 mg/dL w/in 48 hours OR
- Increase in serum Cr >50% w/in 7 days OR
- Urine output <0.5 mL/kg/hour for > 6 hours
KDIGO Stage 1
- Increase in serum Cr >0.3 mg/dL OR
- Increase in serum Cr 1.5 to 1.9 times baseline OR
- Urine output <0.5 for 6 to 12 hours
KDIGO Stage 2
- Increase in serum Cr 2.0 to 2.9 times baseline OR
2. Urine output <0.5 for >12 hours
KDIGO Stage 3
- Increase in serum Cr >4.0 mg/dL OR
- Increase in serum Cr 3.0 times baseline OR
- ANURIA for > 12 hours OR
- Initiation of renal replacement therapy
Highest incidence of AKI
ICU - Develops in 60% of patients!
Classifications of AKI
Prerenal, Intrinsic renal, postrenal
Causes of prerenal AKI
Volume depletion Hypotension Edematous states Selective renal ischemia (bilateral renal artery stenosis) Drugs affecting GFR (NSAIDs, ACE-I)
Causes of intrinsic renal AKI
Acute tubular necrosis (ATN) caused by:
- Renal ischemia
- Sepsis
- Nephrotoxins
Types of nephrotoxins
Aminoglycosides IV CONTRAST* Heme pigments (rhabdo) Cisplatin HIV meds IVIG Mannitol
Risk factors for ATN from IV contrast
Preexisting renal disease Volume depletion Repeated doses of contrast Comorbid conditions: DM, CHF Age
Prevention of ATN by IV contrast
HYDRATION
Low osmolal agents at low doses
Avoid repetitive doses
Avoid nephrotoxic drugs for 48 hours after exposure
Causes of postrenal AKI
Obstruction
Most common cause of obstruction
Prostatic disease (hyperplasia or cancer) or metastatic cancer
Reduction in GFR in patients without intrinsic renal disease requires…
BILATERAL obstruction (or unilateral in one functioning kidney)
Nonoliguric
> 400 mL in 24 hours
Oliguric
<400 mL but >100 mL in 24 hours
Anuric
<100 mL in 24 hours
Workup of AKI
UA
Serum metabolic panel
U/S, CT, MRI, or biopsy (as indicated)
Core urine parameters in a UA
Heme Leukocyte esterase Nitrite Albumin pH Specific gravity Glucose
Pathognomonic cast of AKI
Muddy brown casts
Normal range for serum Cr
Male: 0.6 - 1.2 mg/dL
Female: 0.5 - 1.1 mg/dL
More accurate estimation of GFR
Modification of diet in renal disease (MDRD) - takes into account ethnicity and gender
Simplified measurement of GFR
Doubling of serum Cr is 1/2 GFR
Fractional excretion of sodium (FENa)
Percent of filtered sodium that is excreted in urine
FENa calculation
FENa = (Urine Na/Serum Na) / (Urine Cr/Serum Cr) x 100%
FENa <1%
Prerenal
FENa >2%
Intrinsic Renal
FENa between 1-2%
Either pre or intrinsic renal
When is FENa unreliable?
Pts on diuretics
CHRONIC renal failure
Imaging for AKI
Renal U/S
When to image AKI
Underlying cause is unknown
Assess for obstruction (postrenal)
Most common imaging finding with obstruction
Hydronephrosis
When to do a renal biopsy
No clear explanation of AKI AND
Disease is severe OR
Patient is declining FAST
Renal biopsy contraindications
Bleeding diathesis
Pyelonephritis
Renal tumor
Solitary native kidney
Mild AKI
Transient increase in serum Cr or fall in urine output without complications
Life-threatening complications of AKI
Volume imbalance Metabolic acidosis (pH <7.4) Hyperkalemia (>5.5 or rapidly increasing) Hypocalcemia Hyperphosphatemia Uremia (urine in blood) Altered mental status
Treating AKI with life threatening complications
Medical management of complications while waiting for HEMODIALYSIS (required for most patients)
First line management of AKI
Assess volume status and correct - correction may improve or even reverse AKI
Signs of volume depletion
Hx consistent with fluid loss (ie. diarrhea)
Hypotension
Tachycardia
Oliguria
What to do if signs of volume depletion
Administer IV fluids (crystalloid isotonic fluids preferred)
Fluid challenge helps identify…
PRERENAL failure. If patients don’t respond to fluids, it is unlikely to be a prerenal cause
Treating with IV fluids (how much?)
Begin with 1-3 L and reassess patient status
Complication of fluid overload
Pulmonary edema»_space; Respiratory failure (monitor I&O)
Treating volume overload
Diuretics (typically furosemide) - Temporary
Dialysis (most efficient method)
When administering diuretics
- Should not be prolonged therapy
2. Monitor UOP
If UOP does not increase with diuretics you should…
Diuretics should be STOPPED and alternative therapy (ie. dialysis) started
Causes of metabolic acidosis in AKI
- Excretion of acid and regeneration of bicarb is impaired with a low GFR
- Many causes of AKI produce acid (sepsis, trauma)
What can worsen metabolic acidosis?
Diarrhea (net loss of bicarb)
Treating metabolic acidosis
Dialysis OR
Bicarbonate administration
What treatment is preferred in a volume overloaded patient with metabolic acidosis?
Dialysis
When to use dialysis for metabolic acidosis
Severe oligo-anuric AKI who are volume OVERLOADED and have severe metabolic acidosis (pH <7.1)
Indication for treating acidosis with bicarb
- Acidosis is related to diarrhea
- No other reason for acute dialysis
- pH <7.1 and awaiting dialysis
- AKI due to RHABDOMYOLYSIS
S/Sx of Hyperkalemia
Very few until you DIE! May cause:
- Impaired neuromuscular function
- Arrhythmias
Treatment for hyperkalemia
Both medical therapy and dialysis
Main cause of hypocalcemia in AKI
Increase in serum phosphate from a reduced GFR
Treatment of hypocalcemia in an ASYMPTOMATIC patient
Correct the hyperphosphatemia
Accurate measurement of serum calcium
Ionized calcium
Treatment of hypocalcemia in a SYMPTOMATIC patient
IV calcium while waiting for DIALYSIS
Problem with IV calcium if hyperphosphatemic
Deposition of calcium phosphate into vasculature and organs
Symptoms of hypocalcemia
Paresthesias Tetany Confusion Seizures Trousseau's sign Chvostek's sign QT prolongation
Trousseau’s sign
Carpal spasm after occlusion of the brachial artery with BP cuff for 3 min
Chvostek’s sign
Contraction of the facial muscle in response to tapping the facial nerve anterior to the ear
Hyperphosphatemia value
> 6 mg/dL
Treatment of hyperphosphatemia
Dietary (oral) phosphate binders or dialysis
Phosphate binders used if calcium is LOW
Calcium acetate or calcium carbonate
Phosphate binders used if calcium is HIGH
Aluminum hydroxide or lanthanum carbonate
When to dialyze patients with hyperphosphatemia
> 12 mg/dL or patient cannot tolerate oral intake
Uremia is most common in…
CKD (not AKI)
When to treat uremia
Only if it is SEVERE
S/Sx of severe uremia
Pericarditis
Neuropathy
Unexplained decline in mental status
Treatment of severe uremia
Dialysis
AKI prognosis depends on
Cause of AKI
Presence/absence of pre-existing renal disease
AKI prognosis
Most patients recover renal function, but remain with some renal dysfunction
How do you know if renal function has recovered
UOP and Cr normalize
Patient’s who recover from AKI are at a high risk of…
CKD and ESRD
AKI during hospitalization is associated with…
High in-hospital and long-term mortality