Acute Kidney Injury- Dr. Alex Flashcards
What is acute kidney injury?
- Rapid deterioration in renal function resulting in the accumulation of nitrogenous waste (BUN-Azotemia)
- Inability of the kidney to regulate electrolyte, acid-base, and/or water homeostasis
What is the timeline for acute kidney injury?
Days to weeks in development (under 3 months)
What factors are not included in the definition of acute kidney injury?
- No specific level of BUN or K
- Clinical signs or symptoms
What is diagnosed by a change in serum creatinine of greater than 0.3mg/dL in days to weeks (under 3 months)?
Acute Kidney Injury (AKI)
What is diagnosed by a decrease in GFR (over 3 months duration)?
Chronic Kidney Disease (CKD)
What is an irreverisble loss of renal function that may or may not lead to End Stage Renal Disease (ESRD)?
Chronic Kidney Disease (CKD)
What is an irreversible renal failure of a magnitude that requires renal replacement therapy to survive (dialysis or kidney transplant)?
End Stage Renal Disease (ESRD)
-Creatinine clearance is under 10cc/min
What is azotemia?
Elevation of the BUN (blood urea nitrogen) level
What is BUN?
One of many nitrogen based molecules that accumulates in AKI and CKD and may lead to the development of uremia
What is uremia?
The clinical SE of excess accumulation of nitrogenous compounds (nausea, vomiting, confusion, anorexia)
Oliguria?
Under 500 cc of urine output in 24 hours
Non-Oliguric?
Greater than 500 cc of urine output in 24 hours
Anuric?
Under 100 cc of urine output in 24 hours
What is oliguric, non-oliguric, and anuric used to describe?
Types of AKI
What is used to assess renal function?
GFR
What is an indirect predictor of GFR?
Serum creatinine
What is used for measured GFR?
24 hour creatinine clearance
What 2 mathematical formulas are used for estimated GFR?
- Cockroft and Gault
2. MDRD
What is serum creatinine (2 things)?
- End product of muscle metabolism
2. Cyclic anhydride of creatine (nonenzymatic)
Where is creatine made and stored?
- Synthesized in the liver and stored in muscle (CPK)
- Also ingested orally and localized to muscle
What 2 ways is creatinine excreted renally?
- GFR- Filtration
2. Proximal tubular secretion
So, are creatine and creatinine the same thing?
NOPE…creatine is converted to creatinine (end product of muscle metabolism)
What is CPK?
Creatine phosphokinase (energy source for muscles) *Can raise serum creatinine level slightly
What pathway is used in the secretion of creatinine in the proximal tubule?
Organic cation secretory pathway
What % of urinary creatinine in healthy patients is from secretion?
15%
In patients with renal disease what is the % of urinary creatinine that is secreted and what is the relevance of this?
30-35% –> Overestimates true function since the blood level of creratinine will be lower than it really should be at any given GFR
What is a normal creatinine level relate to?
Muscle mass
What is normal creatinine for women?
Under 1.2 mg/dL (average is 0.95)
What is normal creatinine for men?
Under 1.5 mg/dL (average is 1.15)
What change in seru creatinine is needed to be confident that a real change in renal function has occurred?
0.3mg/dL
This is because the accuracy of the serum creatinine measurement is variable
What are the 3 cases where baseline creatinine is unusually very low (under 0.6mg/dL) and a rise of 0.3mg/DL will not increase the creatinine above the critical upper limit levels? (1.2 in woman and 1.5 in man)
- Cirrhosis: Minimal protein intake with severe malnutririon and liver failure with impaired creatine production
- Pregnancy: Volume expansion and an increase in GFR
- Extrenes of age/nutrition: Pediatric or elderly
In patients with cirrhosis, pregnancy, or extremes of age/nutrition, what is the serum creatinine where they can be in AKI?
1.1mg/dL
Is creatinine level an effective indicator of the degree of renal function?
NO, creatinine is a poor predictor of GFR
Is the change in serum creatinine with kidney failure linear?
No, it’s exponential
What must you use the range of normal values for serum creatinine as?
A relative guide
What must you use for each patient to determine what the normal range of creatinine for that patient should be?
- Clinical characteristics
2. Underlying medical disease state (not cause of kidney disease
4 tools for assessment of renal function?
- Serum creatinine
- Creatinine clearance
- Cockroft and Gault
- Iothalamate clearance
What assessment overestimates true kidney function by 15% in normal patients and by over 30% in patients with kidney failure?
24 hour creatinine clearance
Why does 24 hour creatinine clearance overestimate true kidney function?
- Creatinine is filtered but also secreted by tubules
- Accuracy of 24 hour urine collection isn’t proven (retained urine in bladder and timing errors of collection)
What is required for 24 hour creatinine clearance?
- Complete 24 hour urine collection
2. Simultaneous measurement of urine creatinine and serum creatinine
What is the clearance formula?
[(Urine concentration)*(Urine volume)]/Plasma concentraion
What is creatinine clearance always expressed in?
mL/min
How many minutes are in a day?
1440
What is normal creatinine clearance?
90-120mL/min
What is the most common mistake with calculating creatinine clearance?
Forgetting to include the minutes per day
What is the Cockroft and Gault Formula?
(140-age)weight (kg) / (72cr)
Multiply by 0.85 for women
Does the Cockroft and Gault formula require urine collection?
NO
What factors does the Cockroft and Gault formula take into consideration?
- Age
- Weight (muscle mass)
- Sex (muscle mass)
What is the MDRD formula?
186 * cr^-1.154 * age^-0.203
- 1.212 if black
- 0.742 if female
- More accurately predicts GFR
- Standard used by most laboratories
- From study…modification of diet in renal disease
Are all creatinine values the same?
NO…same creatinine level will mean different degrees of renal function based on
- Age
- Sex
- Weight
With the same creatinine value will renal function be better (higher GFR/creatinine clearance) in
- Men or women
- Young or old
Better in men v. women and young v. old
Quick and dirty of the urea cycle?
Amino Acids –> Ammonia (NH3) –> Liver –> Urea Cycle –> Urea –> Kidneys –> Excretion
What is blood urea nitrogen (BUN) directly related to?
Protein intake (AA)…byproduct of metabolism
What is the constant ratio of BUN to creatinine?
BUN/Cr = 10-15:1 * KNOW THIS*
Is BUN directly toxic to the body?
No…it reflects the simultaneous accumulation of other nitrogenous compounds that may result in the clinical sequaela of uremia
Is uremic syndrome due to the accumulation of urea?
Not directly
What is uremic syndrome?
A constellation of clinical findings resulting from the retention of toxic nitrogenous molecules in the setting of kidney injury (acute or chronic)
What are symptoms of uremic syndrome?
- Confusion/disorientation
- Nausea/vomiting
- Pericarditis (pericardial friction rub)
- Asterizes/Myoclonus (neurologic irritability)
- Seizures
When can you see an elevation of BUN (azotemia) with normal renal function?
- Corticosteroids
- GI Bleeding
- Catabolism
- Increased protein intake
Can the BUN be used independently as a marker for kidney function?
NO
What 3 questions must be asked with approach to the patient with renal injury?
- Is it real?
- Is it acute or chronic?
- If acute- Where is the lesion?
What 3 situations can give spurious elevations of serum creatinine with normal renal function?
- Interference with the creatinine assay
- Impaired tubular secretion of creatinine
- Increased creatinine production
What 2 circumstance (where other chromogens cause a false reading) can cause interference with the creatinine assay (Jaffe reaction- Calorimetric)
- Jaunidce: Bilirubin leads to a falsely lower level of creatinine measurement
- Diabetic Ketoacidosis: Ketones lead to a falsely higher level of creatinine
What 2 drugs result in impaired proximal tubular secretion?
- Trimethoprim- Bactrim (trimethoprim and sulfamethoxazole)
2. Cimetidine (Tagement)- H2 antagonist
What % increase in serum creatinine does trimethoprim cause?
15-35%
What % increase in serum creatinine does cimetidine cause?
20%
Is an increase in serum creatinine seen with proton pump inhibitors?
No
What can cause increased production of creatinine?
- Rhabdomyolysis
2. Increased intake (cooked meat/AA supplements)
What is rhabdomyolysis?
-Release of creatinine from damaged muscle membrane–> Conversion of creatine peripherally to creatinine
What are the etiologies for rhabdomyolysis?
- Trauma
- Statins (HMG CoA reductase inhibitors
- Seizures
* Check CPK levels in these patients
What are clinical clues for spurious elevations of serum creatinine with normal renal function?
- Normal level of BUN
- BUN/Cr ratio decrease under 10:1 (remember, normal was 10-15:1
- Normal urine output
- No obvious hemodynamic or toxic insult
What are 4 features of AKI?
- Renal size over 10cm *
- Normal echogenicity *
- Normal PTH level (absent osteodystrophy)
- Granular casts or bland sediment on urinalysis
What are 4 features of CKD?
- Renal size under 9cm
- Increased echnogenicity
- Elevated PTH level (renal osteodystropy)
- Waxy casts
What are 4 factors that don’t correlate with ARF or CRF?
- Calcium
- Phosphorous
- Anemia
- Acidosis
What is the purpose of a renal US?
Compare the echo texture of the kidneys to the liver
Are kidneys normally more or less echogenic than liver?
Kidneys are normall less echogenic than the liver due to the presence of glomeruli and tubules (the liver if more homogenous)
What is seen in a normal kidney US?
A clear differentiation is usually seen due to the difference in density of the tubules between the cortex and medulla of the kidneys (corticmedullary differentiation)
-10-12cm in length
What is seen on US in AKI?
- No change in echogenicity
- No loss of the corticomedullary differentiation
What is seen on US in CKD?
- Increased echogenicity of the kidneys (increased fibrosis of the cortex)
- Decreased size
- Loss of the corticomedullary differentiation
What is the first step in AKI workup?
Determine the site of the lesion
What are the 3 categories of AKI?
- Pre-renal: Inadequate perfusion of the kidney
- Renal: Specific damage to the kidney
- Post-renal: Obstruction to urinary flow with preserved perfusion
What are 4 potential causes of renal AKI?
- ATN
- Interstitial nephritis
- Glomerulonephritis
- Vascular
What are the etiologies of AKI in the hospital?
- ATN (48%)*
- Pre-renal azotemia (22%)
- Obstruction (11%)
- Acute on chronic (9%)
- Interstitial nephritis (5%)
- Glomerulonephritis (5%)
What are the etiologies of outpatient AKI?
- Pre-renal azotemia (66%)*
- Acute GN (14%)
- Obstructive uropathy (10%)
- Acute interstitial nephritis (10%)
What are the 3 categories of AKI?
- Pre-renal: Inadequate perfusion of the kidney
- Renal: Specific damage to the kidney
- Post-renal: Obstruction to urinary flow with preserved perfusion and lack of direct nephrotoxic damage
What is pre-renal azotemia?
A state of underperfusion of the kidneys
What is the normal response of the kidney to underperfusion?
- Expand intravascular volume
- Initiate renal autoregulation
How do the kidneys expand intravascular volume?
- They reabsorb sodium: 80% in proximal tubule, 20% in TALH, under 5% in DCT
- The reabsorb water: Collecting duct via ADH
What is MAP?
(Systolic-diastolic) * 1/3 + Diastolic
If BP is 120/80, what is MAP?
93
If BP drops to 80/50, what is MAP?
60
What is renal autoregulation?
The ability of the kidney to maintain adequate blood flow and GFR through a wide range of systemic blood pressures…a complex interaction of multiple enzyme and cytokine systems
What systems are involved in renal autoregulation?
- Renin-angiotensin
- Prostaglandin
- Neurohumoral
- Endothelial
What 2 things does hypovolemia induce?
- Activation of local myogenic response
2. Activation of carotid and cardiac baroreceptors
What does activation of carotid and cardiac baroreceptors lead to?
- Increased neurohumoral responses
- Norepinephrine
- Angiotensin II
- ADH
Where are filatration pores located?
In the basement membrane of the endothelial cell (In the glomerular capillary)
What is a podocyte?
Visceral epithelial cell (these contain foot processes)
In hypoperfusion does the intraglomerular pressure increase or decrease?
Decrease
In hypoperfusion, the kidneys will renal autoregulate to bring the intraglomerular pressure close to normal via what 2 mechanisms?
- Afferent arteriolar vasodilation
2. Efferent arteriolar constriction
What 3 substances cause afferent arteriolar vasodilation?
- PGE2/PGI2
- NO
- Dopamine
What substance causes efferent arteriolar constriction?
Angiotensin II
What is filtration fraction (FF)?
GFR/RBF