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Flashcards in Acute Kidney Injury- Dr. Alex Deck (257)
1

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

2

What is the timeline for acute kidney injury?

Days to weeks in development (under 3 months)

3

What factors are not included in the definition of acute kidney injury?

-No specific level of BUN or K
-Clinical signs or symptoms

4

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)

5

What is diagnosed by a decrease in GFR (over 3 months duration)?

Chronic Kidney Disease (CKD)

6

What is an irreverisble loss of renal function that may or may not lead to End Stage Renal Disease (ESRD)?

Chronic Kidney Disease (CKD)

7

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

8

What is azotemia?

Elevation of the BUN (blood urea nitrogen) level

9

What is BUN?

One of many nitrogen based molecules that accumulates in AKI and CKD and may lead to the development of uremia

10

What is uremia?

The clinical SE of excess accumulation of nitrogenous compounds (nausea, vomiting, confusion, anorexia)

11

Oliguria?

Under 500 cc of urine output in 24 hours

12

Non-Oliguric?

Greater than 500 cc of urine output in 24 hours

13

Anuric?

Under 100 cc of urine output in 24 hours

14

What is oliguric, non-oliguric, and anuric used to describe?

Types of AKI

15

What is used to assess renal function?

GFR

16

What is an indirect predictor of GFR?

Serum creatinine

17

What is used for measured GFR?

24 hour creatinine clearance

18

What 2 mathematical formulas are used for estimated GFR?

1. Cockroft and Gault
2. MDRD

19

What is serum creatinine (2 things)?

1. End product of muscle metabolism
2. Cyclic anhydride of creatine (nonenzymatic)

20

Where is creatine made and stored?

-Synthesized in the liver and stored in muscle (CPK)
-Also ingested orally and localized to muscle

21

What 2 ways is creatinine excreted renally?

1. GFR- Filtration
2. Proximal tubular secretion

22

So, are creatine and creatinine the same thing?

NOPE...creatine is converted to creatinine (end product of muscle metabolism)

23

What is CPK?

Creatine phosphokinase (energy source for muscles)
*Can raise serum creatinine level slightly

24

What pathway is used in the secretion of creatinine in the proximal tubule?

Organic cation secretory pathway

25

What % of urinary creatinine in healthy patients is from secretion?

15%

26

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

27

What is a normal creatinine level relate to?

Muscle mass

28

What is normal creatinine for women?

Under 1.2 mg/dL (average is 0.95)

29

What is normal creatinine for men?

Under 1.5 mg/dL (average is 1.15)

30

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)

31

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)

1. Cirrhosis: Minimal protein intake with severe malnutririon and liver failure with impaired creatine production
2. Pregnancy: Volume expansion and an increase in GFR
3. Extrenes of age/nutrition: Pediatric or elderly

32

In patients with cirrhosis, pregnancy, or extremes of age/nutrition, what is the serum creatinine where they can be in AKI?

1.1mg/dL

33

Is creatinine level an effective indicator of the degree of renal function?

NO, creatinine is a poor predictor of GFR

34

Is the change in serum creatinine with kidney failure linear?

No, it's exponential

35

What must you use the range of normal values for serum creatinine as?

A relative guide

36

What must you use for each patient to determine what the normal range of creatinine for that patient should be?

1. Clinical characteristics
2. Underlying medical disease state (not cause of kidney disease

37

4 tools for assessment of renal function?

1. Serum creatinine
2. Creatinine clearance
3. Cockroft and Gault
4. Iothalamate clearance

38

What assessment overestimates true kidney function by 15% in normal patients and by over 30% in patients with kidney failure?

24 hour creatinine clearance

39

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)

40

What is required for 24 hour creatinine clearance?

1. Complete 24 hour urine collection
2. Simultaneous measurement of urine creatinine and serum creatinine

41

What is the clearance formula?

[(Urine concentration)*(Urine volume)]/Plasma concentraion

42

What is creatinine clearance always expressed in?

mL/min

43

How many minutes are in a day?

1440

44

What is normal creatinine clearance?

90-120mL/min

45

What is the most common mistake with calculating creatinine clearance?

Forgetting to include the minutes per day

46

What is the Cockroft and Gault Formula?

(140-age)*weight (kg) / (72*cr)
Multiply by 0.85 for women

47

Does the Cockroft and Gault formula require urine collection?

NO

48

What factors does the Cockroft and Gault formula take into consideration?

1. Age
2. Weight (muscle mass)
3. Sex (muscle mass)

49

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

50

Are all creatinine values the same?

NO...same creatinine level will mean different degrees of renal function based on
-Age
-Sex
-Weight

51

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

52

Quick and dirty of the urea cycle?

Amino Acids --> Ammonia (NH3) --> Liver --> Urea Cycle --> Urea --> Kidneys --> Excretion

53

What is blood urea nitrogen (BUN) directly related to?

Protein intake (AA)...byproduct of metabolism

54

What is the constant ratio of BUN to creatinine?

BUN/Cr = 10-15:1 *** KNOW THIS***

55

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

56

Is uremic syndrome due to the accumulation of urea?

Not directly

57

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)

58

What are symptoms of uremic syndrome?

1. Confusion/disorientation
2. Nausea/vomiting
3. Pericarditis (pericardial friction rub)
4. Asterizes/Myoclonus (neurologic irritability)
5. Seizures

59

When can you see an elevation of BUN (azotemia) with normal renal function?

1. Corticosteroids
2. GI Bleeding
3. Catabolism
4. Increased protein intake

60

Can the BUN be used independently as a marker for kidney function?

NO

61

What 3 questions must be asked with approach to the patient with renal injury?

1. Is it real?
2. Is it acute or chronic?
3. If acute- Where is the lesion?

62

What 3 situations can give spurious elevations of serum creatinine with normal renal function?

1. Interference with the creatinine assay
2. Impaired tubular secretion of creatinine
3. Increased creatinine production

63

What 2 circumstance (where other chromogens cause a false reading) can cause interference with the creatinine assay (Jaffe reaction- Calorimetric)

1. Jaunidce: Bilirubin leads to a falsely lower level of creatinine measurement
2. Diabetic Ketoacidosis: Ketones lead to a falsely higher level of creatinine

64

What 2 drugs result in impaired proximal tubular secretion?

1. Trimethoprim- Bactrim (trimethoprim and sulfamethoxazole)
2. Cimetidine (Tagement)- H2 antagonist

65

What % increase in serum creatinine does trimethoprim cause?

15-35%

66

What % increase in serum creatinine does cimetidine cause?

20%

67

Is an increase in serum creatinine seen with proton pump inhibitors?

No

68

What can cause increased production of creatinine?

1. Rhabdomyolysis
2. Increased intake (cooked meat/AA supplements)

69

What is rhabdomyolysis?

-Release of creatinine from damaged muscle membrane--> Conversion of creatine peripherally to creatinine

70

What are the etiologies for rhabdomyolysis?

1. Trauma
2. Statins (HMG CoA reductase inhibitors
3. Seizures
*Check CPK levels in these patients

71

What are clinical clues for spurious elevations of serum creatinine with normal renal function?

1. Normal level of BUN
2. BUN/Cr ratio decrease under 10:1 (remember, normal was 10-15:1
3. Normal urine output
4. No obvious hemodynamic or toxic insult

72

What are 4 features of AKI?

1. Renal size over 10cm *
2. Normal echogenicity *
3. Normal PTH level (absent osteodystrophy)
4. Granular casts or bland sediment on urinalysis

73

What are 4 features of CKD?

1. Renal size under 9cm
2. Increased echnogenicity
3. Elevated PTH level (renal osteodystropy)
4. Waxy casts

74

What are 4 factors that don't correlate with ARF or CRF?

1. Calcium
2. Phosphorous
3. Anemia
4. Acidosis

75

What is the purpose of a renal US?

Compare the echo texture of the kidneys to the liver

76

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)

77

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

78

What is seen on US in AKI?

-No change in echogenicity
-No loss of the corticomedullary differentiation

79

What is seen on US in CKD?

-Increased echogenicity of the kidneys (increased fibrosis of the cortex)
-Decreased size
-Loss of the corticomedullary differentiation

80

What is the first step in AKI workup?

Determine the site of the lesion

81

What are the 3 categories of AKI?

1. Pre-renal: Inadequate perfusion of the kidney
2. Renal: Specific damage to the kidney
3. Post-renal: Obstruction to urinary flow with preserved perfusion

82

What are 4 potential causes of renal AKI?

1. ATN
2. Interstitial nephritis
3. Glomerulonephritis
4.Vascular

83

What are the etiologies of AKI in the hospital?

1. ATN (48%)*
2. Pre-renal azotemia (22%)
3. Obstruction (11%)
4. Acute on chronic (9%)
5. Interstitial nephritis (5%)
6. Glomerulonephritis (5%)

84

What are the etiologies of outpatient AKI?

1. Pre-renal azotemia (66%)*
2. Acute GN (14%)
3. Obstructive uropathy (10%)
4. Acute interstitial nephritis (10%)

85

What are the 3 categories of AKI?

1. Pre-renal: Inadequate perfusion of the kidney
2. Renal: Specific damage to the kidney
3. Post-renal: Obstruction to urinary flow with preserved perfusion and lack of direct nephrotoxic damage

86

What is pre-renal azotemia?

A state of underperfusion of the kidneys

87

What is the normal response of the kidney to underperfusion?

-Expand intravascular volume
-Initiate renal autoregulation

88

How do the kidneys expand intravascular volume?

1. They reabsorb sodium: 80% in proximal tubule, 20% in TALH, under 5% in DCT
2. The reabsorb water: Collecting duct via ADH

89

What is MAP?

(Systolic-diastolic) * 1/3 + Diastolic

90

If BP is 120/80, what is MAP?

93

91

If BP drops to 80/50, what is MAP?

60

92

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

93

What systems are involved in renal autoregulation?

1. Renin-angiotensin
2. Prostaglandin
3. Neurohumoral
4. Endothelial

94

What 2 things does hypovolemia induce?

1. Activation of local myogenic response
2. Activation of carotid and cardiac baroreceptors

95

What does activation of carotid and cardiac baroreceptors lead to?

1. Increased neurohumoral responses
2. Norepinephrine
3. Angiotensin II
4. ADH

96

Where are filatration pores located?

In the basement membrane of the endothelial cell (In the glomerular capillary)

97

What is a podocyte?

Visceral epithelial cell (these contain foot processes)

98

In hypoperfusion does the intraglomerular pressure increase or decrease?

Decrease

99

In hypoperfusion, the kidneys will renal autoregulate to bring the intraglomerular pressure close to normal via what 2 mechanisms?

1. Afferent arteriolar vasodilation
2. Efferent arteriolar constriction

100

What 3 substances cause afferent arteriolar vasodilation?

1. PGE2/PGI2
2. NO
3. Dopamine

101

What substance causes efferent arteriolar constriction?

Angiotensin II

102

What is filtration fraction (FF)?

GFR/RBF

103

What is FF in normal perfusion?

0.20

104

What is RBF, GFR, and FF in hypoperfusion?

RBF and GFR are decreased equally, so FF is still 0.20

105

What is RBF, GFR, and FF in autoregulation?

RBF is increased, GFR is super increased, and FF is greater than 0.20

106

What is a big player in renal autoregulation?

The juxtaglomerular apparatus

107

What are the 3 components of the JGA?

1. DCT: Macula densa
2. Afferent arteriole: Juxtaglomerular cells
3. Lacis cells: Extraglomerular mesangial cells

108

What is the cascade from prostaglandins released by the macula densa cells in the DCT?

Prostaglandins --> Renin (from the juxtaglomerular cells in the afferent arteriole) --> Angiotensin I --> Angiotensin II --> Aldosterone (adrenal gland)

109

What are 4 causes of pre-renal azotemia decreased effective circulating volume

1. Absolute volume depletion
2. Relative volume depletion
3. Impaired cardiac output
4. Impaired renal autoregulation

110

What are 5 categories of pre-renal azotemia absolute volume depletion?

1. GI: Diarrhea and vomiting
2. Hemorrhage
3. Sweating
4. Renal: Diuresis (osmotic or diuretics) and salt-wasting
5. Burns

111

What is pre-renal azotemia relative volume depletion?

3rd spacing (interstitial space)
-1st space is intravascular and 2nd space is intracellular

112

What 3 conditions lead to 3rd spacing (interstitial space) in pre-renal azotemia?

1. Hypoalbuminemia: Nephrotic syndrome, liver disease, malnutrition
2. Pancreatitis
3. Sepsis

113

What are the cardiac/pulmonary dysfunctions leading to relative volume depletion in pre-renal azotemia?

1. Cardiomyopathy
2. Valvular disease
3. Myocardial infarction
4. Tamponade
5. Pulmonary HTN
6. Renal artery stenosis

114

What conditions cause low CO states or cardio-renal syndrome?

Cardiomyopathy, valvular disease,MI, and tamponade

115

What 2 causes of abnormal autoregulation can lead 2 pre-renal azotemia?

1. Blockade of angiotensin activity (ACEi or ARBs)
2. Prostaglanin inhibitos (NSAIDS which inhibit the enzyme cyclooxygenase)

116

What are psotaglandins?

A group of lipid compounds derived from essential fatty acids
-Originally isolated from the prostate (seminal fluid) in 1935

117

Where are prostaglandins found?

In all tissues and organs
-Autocrine (self-stimulatory)
-Paracrine (locally active)

118

What converts cell membrane phospholipids into arachidonic acid?

Phospholipase A

119

What converts arachidonic acid into prostaglandins?

Cyclooxygenase (COX)

120

What are the 3 drug categories that disrupt renal autoregulation?

1. NSAID
2. ACEi
3. ARB

121

What are some examples of NSAIDs?

1. Ibuprofen (motrin or alleve)
2. Naprosyn
3. Toradol
4. Vioxx
5. Celebrex

122

What are some examples of ACEi?

1. Catopril
2. Ramipril
3. Zestril
4. Lisinopril
5. Enalapril

123

What are some examples of ARBs?

1. Losartan
2. Irbesartan
3. Candesartan
4. Olmesartan

124

What do NSAIDs block?

Cyclooxygenase (prevents arachidonic acid from converting to PGG2 and PGH2)
-Ultimately prevent formation of prostacyclins which cause vasodilation and renin production

125

What way do NSAIDs shift the range for MAP?

To the right

126

What is the effect in the renal vasculature of an ACEi or ARB?

Dilated efferent arteriole with reduced intraglomerular pressure due to absent or blocked angiotensin II

127

What way to ACEi/ARB shift the range for MAP?

To the right

128

Overall effect of NSAIDs?

-Affterent arteriolar constrictionand efferent arteriolar vasodilation leading to decreased intraglomerular pressure

129

Overall effect of ACEi/ARB?

Efferent arteriolar vasodilation leading to decreased intraglomerular pressure

130

How do NSAIDs affect RBF/GFR/FF?

They decrease RBF and GFR proportionately so filtration fraction is still 0.20

131

How do ACEi and ARB affect RBF/GFR/FF?

They decrease RBF and super decrease GFR so filatraion fraction is less than 0.20 (because FF = GFR/RBF)

132

Who are the patients at highest risk for AKI due to impaired renal autoregulation?

1. CHF
2. Cirrhosis
3. Nephrotic
4. Renovascular disease- renal artery stenosis (bilateral)
*Use of ACEi or ARB in these patients requires very careful and frequent monitoring

133

What is COMPLETELY PROHIBITED in patients at highest risk for AKI due to impaired renal autoregulation?

NSAIDS

134

Is a normal individual with euvolemia at risk from NSAID or ACEi/ARB?

NO

135

Why are ACEi/ARB high recommended for patients with CKD?

The benefit of these agents in preserving renal function exceeds any potential risk of AKI... ACEi/ARB are reno-protective!
(Renal artery stenosis is excluded by clinical and radiologic studies)

136

What can intrinsic AKI lead to?

Acute tubular necrosis (ATN)

137

What are the 2 types of ATN and their %?

1. Ischemic (60%)
2. Toxic (40%)

138

Which part of the kidney has a higher oxygen delivery and oxygen content?

Cortex (v. medulla)

139

What is the O2 comsumption/O2 delivery ratio in the outer medulla?

79% --> The outer medulla operates in a delivate balance as it consumes almost all of the oxygen delivered

140

What structures are in the cortex?

1. Proximal Tubules: Pars Recta (further from the glomerulus) and Pars Convoluta (closer to the glomerulus)
2. Outer Medulla: Proximal tubules (pars recta) and TALH (thick ascending limb of henle)

141

What structures are in the outer medulla?

1. Proximal tubules: Pars Recta
2. TALH: Thick Ascending Limb of Henle

142

What structures are in the inner medulla?

1. Thin Descending Limb of the Loop of Henle
2. Thin Ascending Limb of the Loop of Henle
3. Collecting Duct

143

Where do you see ischemic injury in AKI?

Outer Medulla:
-Proximal Tubule: Pars recta
-TALH (major site)

144

Where do you see toxic injury in AKI?

Proximal tubule (pars convoluta) over the distal tubule

145

What can prolonged pre-renal azotemia lead to?

ATN

146

How does prolonged pre-renal azotemia lead to ATN?

Due to the high O2 requirements for sodium absorption, cellular ischemia will result if impaired delivery of blood remains prolonged
-Breakdown of cell membrane
-Entry of Ca and efflux of intracellular contents leading to cell death and sloughing of the renal tubular cell in the urine

147

What is progression of prolonged hypotension/shock/hypoperfusion os the kidneys (intrinsic AKI)?

This leads to pre-renal azotemia which can lead to ATN

148

Why is there an increased risk of ATN from toxins?

Increased risk secondary to:
1. High delivery of blood flow: 25% of CO
2. Concentration of toxins in the medulla and interstitium through the countercurrent mechanism
3.Organic transporters: Proximal tubule
4. Local metabolism to toxic compounds

149

What is a common clinical cause of ATN?

Radiology material:
-IV contrast is an iodinated compound that is directly toxic to the proximal tubule and extreme care must be taken when using these agens in patients with CKD

150

What are 2 drugs that can cause ATN?

1. Aminoglycosides: Antibiotics for gram - infections (gentamycin, tobramycin, amikacin)
2. Amphotericin: Antifungal agent

151

Where are aminglycosides toxic?

Proximal tubule

152

Where is amphotericin toxic?

Distal tubule (still considered a form of ATN

153

What are 2 intrinsic structures that can cause ATN?

1. Heme pigments: Released from damaged muscle cells (rhabdomyolysis) or damaged red cells (hemolysis) leading to toxicity in the proximal tubule
2, Light chains: More Kappa than Lambda from overflow proteinuria as a result of hemtopoeitic malignancy (myeloma) that cause proximal tubule damage

154

Can rhabdomyolysis cause both a false elevation of the creatinine and cause actual ATN?

Yes

155

Is pre-renal azotemia rapidly reversible?

Yes

156

Can you recover from ATN?

It will require 2-3 weeks for recovery and possible temporary or permanent dialysis

157

What does the diagnostic workup for AKI include?

1. Check volume status of the patient
2. Rule out obstruction
3. Urinary electrolytes
4. Urinalysis

158

What are signs of volume overload?

1. DOE (Dyspnea on exertion)
2. Orthopnea
3. PND (paroxysmal nocturnal dyspnea)
4. JVD (jugular venous distension)
5. Rales
6. LE (lower extremity) edema
7. Ascites
8. Peri-orbital edema
9. HTN (Systolic > 140 mmHg))
10. S4 gallop

159

What are signs of volume depletion?

1. Poor skin turgor
2. Dry mucosa : Axillae / oral cavity / vaginal- groin
3. Orthostatic hypotension: Decreased systolic (>20 mmHg) and diastolic BP (>10 mmHg) with upright position, Increased heart rate (> 100 bpm)
4. Absent edema
5. Absent JVD

160

Why is radiology used in the diagnosis of AKI?

Because obstruction can account for 10% of cases of AKI

161

What imaging techniques are used for diagnosis of AKI?

1. US: Preferred modality
2. MRI: No Gaolinium (In renal failure may lead to an irreversible systemic inflammatory condition with diffuse organ fibrosis- Nephrogenic systemic fibrosis)
3. CT Scan: No IV contrast (nephrotoxic)

162

What is done for laboratory evaluation of AKI?

1. Urine Na
2. FENA (Fractional Excretion of Sodium)
3. FEUREA (Fractional Excretion of Urea)
4. BUN/Cr ratio
5. Urine Specific Gravity
6. Urinary Sediment

163

What happens in pre-renal azotemia?

The kidney is underperfused so it will make every effort to restore the intravascular volume

164

How does the kidney try to restore the intravascular volume?

1. Sodium and water reabsorption (sympathetic nervous system): Proximal tubule, TALH, and distal tubule
2. Water reabsorption (ADH production): Collecting duct

165

What is the urine sodium concentration in pre-renal azotemia?

Markedly reduced... a random urine sodium will be under 20mEq/L (intense sodium avidity)

166

What is the urine sodium concentration in ATN?

Over 40mEq/L- No attempt at sodium retnention
-In ATN, the tubules are physically damaged so sodium cannot be retained adequately

167

What is the fractional excretion of sodium (FENA)?

It compares the clearance of sodium to the clearance of creatinine and is expressed as a %

168

What is FENA is a sodium avid state (the proximal tubule is absorbing as much sodium as possible)?

-Creatinine will continue to be secreted (also by the proximal tubule)
-Clearance of sodium will decrease while the clearance of creatinine does not decrease to the same degree
-As a ratio, the clearance of sodium / clearance of creatinine will decrease*

169

What does the calculation of FENA require?

Simultaneous:
-Urine sodium
-Urine creatinine
-Serum sodium
-Serum creatinine

170

What is the formula for FENA?

(Una/Pna)/(Ucr/Pcr) * 100

171

If FENA is under 1%?

Sodium retention (pre-renal azotemia)

172

If FENA os over 2%?

Sodium diuresis (ATN)

173

Is volume used in the calculation for FENA?

No, because it is the same in numerator and denominator and cancels itself out

174

What is a big problem with interpretation of FENA?

Diuretics

175

If a patient has effective diuresis therapy, what does this do to FENA?

I causes and increase in FENA...so
-Elevated FENA is not meaningful during diuretic therapy
-Need to stop diuretics 48 hours or more for the effect to wear off

176

What does a low FENA indicate in diuretic therapy?

Ineffective diuresis

177

What lab value can suggest pre-renal azotemia and what lab value confirms pre-renal azotemia?

Urina Na: Suggests
FENA: Confirms

178

Will a patient with pre-renal azotemia respond to fluid replacement?

YES... need to fill the intravascular compartment as quickly as possible

179

What is the BUN/Creatinine ratio?

A clinical tool to provide an indirect marker for volume status in the setting of renal failure

180

What is normal BUN/Cr ratio?

10-15:1

181

What happens to the BUN/Cr ratio in volume depletion?

-The BUN will increase to a greater extent than the creatinine secondary to obligate creatinine secretion in the proximal tubule and BUN reabsorption
-BUN/Cr ratio will increase above 20:1

182

What Happens to the BUN/Cr ratio in established renal injury (ATN or CKD)?

BUN and Creatinine will increase to the same proportion since the tubules are damaged to the same extent as the glomeruli preventing creatinine secretion
-Ratio stays the same

183

BUN/Cr ratio > 20:1 in the presence of an elevated creatinine?

Volume depletion --> Pre-renal azotemia

184

BUN/Cr ratio = 10-15:1 in the presence of an elevated creatinine?

Intrinsic renal failure (ATN or CKD)

185

Can the BUN/Cr ratio confirm pre-renal azotemia?

Yes

186

What is urea?

A nitrogenous compound derived from protein metabolism

187

What is BUN?

Blood urea nitrogen: An indirect measurement of the amount of urea by detecting only the 2 nitrogens within the molecule

188

Where is BUN absorbed?

In the proximal tubule with water passively

189

What happens to the absorption of BUN (urea) in patients with volume depletion?

It increases

190

What happens with regards to the handeling of creatinine?

It is absorbed also, but then i gets secreted in the tubule

191

So what is the Fractional excretion of urea in patients with volume depletion?

The fractional excretion of BUN (urea) compared to creatinine will decrease

192

What is the formula for fractional excretion of urea?

(U urea nitrogen/Pbun) / (Ucr/Pcr) * 100

193

If the fractional excretion of urea is under 35% what does this indicate?

Pre-renal azotemia

194

If the fractional excretion of urea is over 50% what does this indicate?

Intrinsic AKI (ATN or CKD)

195

When if the fractional excretion of urea useful?

In patients on diuretics which will increase the FENA and mask pre-renal azotemia
-Diuretics don't affect BUN absorption

196

What is urine specific gravity used for?

A marker for urinary concentration...this reflects the removal of water from the urine by the action of ADH on the collecting tubules

197

What is the definition of urine specific gravity?

The "weight" of urine compared to water

198

What is the specific gravity value of water?

1 (nothing can be less than this)

199

What does urine specific gravity correlate with?

The osmole concentration of urine (for every 30mosm/L increase in the urine, the specific gravity increases by 0.001)

200

What isosthenuria?

Urine that is neither concentrated nor diluted (the same osmolality as plasma)

201

What is the osmolality and specific gravity of isothenuria?

Osmolality: 300
Specific gravity: 1.010

202

What is concentrated urine?

Due to increased ADH
-Urine osmolality is greater than 450-500 and specific gravity is greater than 1.015

203

What kind of urine is seen with damaged tubules?

Isosthenuric (specific gravity of 1.010)
-Damaged tubules won't respond to ADH

204

Lab Values for Pre-renal Azotemia?

1. Urine Sodium: Under 20
2. Urine Osmolality: Greater than 500
3. Specific Gravity: Greater than 1.015
4. FENA: Under 1%
5. BUN/Cr: Over 20:1

205

Lab Values for ATN?

1. Urine Sodium: Over 40
2. Urine Osmolality: 280
3. Specific Gravity: 1.010
4. FENA: Over 2%
5. BUN/Cr: 10-15:1

206

What is seen on urinalysis in ATN?

1. Renal tubular cells
2. Granular casts
3. Muddy brown casts
4. Renal tubular cells casts

207

What are casts made of and where are they derived from?

Tamm-Horsfall glycoprotein (derived from the ascending limb of the loop of henle)

208

Are hyaline casts normal constituients?

YES... they are not indicative of renal disease**

209

Are granular casts normal constituents?

NO...they are indicative of acute tubular damage...NOT A NORMAL CONSTITUENT

210

Are granular casts present in pre-renal azotemia?

No

211

What are waxy casts indicative of?

CKD... the injury has been present for more than 3 months

212

Are RBCs, WBCs, RBC casts, waxy casts, or granular casts seen in evaluation of pre-renal azotemia?

No

213

Are RBCs, WBCs, RBC casts, waxy casts, or granular casts seen in evaluation of ATN?

Just granular casts

214

Are RBCs, WBCs, RBC casts, waxy casts, or granular casts seen in evaluation of CKD?

Just waxy casts

215

Are RBCs, WBCs, RBC casts, waxy casts, or granular casts seen in evaluation of CKD and AKI?

Waxy casts and granular casts

216

Can patients with CKD develop AKI?

YES

217

What is clue in urinalysis that a CKD patient developed AKI?

Granular and waxy casts

218

What are the 6 features of management of AKI?

1. HTN control
2. Anemia control
3. Dietary modification
4. Calcium and Phosphorous balance
5. Acid-Base Balance
6. Potassium Control

219

What is a natural accompaniment of all forms of AKI?

Impaired K secretion in the distal tubule

220

What needs to be initiated early in AKI?

Potassium dietary restriction

221

What factors predispose to increased K?

1. Catabolism
2. GI Bleed
3. Constipation
4. K sparing drugs (ACEi, All blockers, Bactrim, NSAIDS)

222

How do NSAIDs lead to hyperkalemia?

NSAIDs block prostaglandins, so they never cause renin secretion, which never causes aldosterone secretion (No aldosterone, no Na reabsorption, and K secretion) which leads to hyperkalemia

223

How do ACEi lead to hyperkalemia?

ACEi block conversion of angiotensin I to angiotensin II, which means that aldosterone is blocked, leading to hyperkalemia

224

How to ARB cause hyperkalemia?

ARB block antiotensin II receptors, which cause blockage of secretion of aldosterone, leading to hyperkalemia

225

How does trimpethoprim affect creatinine secretion?

It impairs creatinine secretion in the proximal tubule leading to false elevation of creatinine with normal GFR

226

What does the chemical structure of trimethoprim resemble and what is the effect of this?

It resembles amiloride, which is a K-sparing diuretic in the distal tubule and leads to hyperkalemia

227

What does hyperkalemia cause in terms of EKG?

1. Peaked T-waves
2. Loss of P wave (Sinus node failure)
3. Widening of QRS (Slow conduction)
4. Sine wave pattern (Cardiac arrest)

228

With normal K levels, what is the resting membrane potential and threshold potential?

Resting: -90mV
Threshold: -60mV

229

What is nerst equation for resting membrane potential (RMP)?

RMP = -61 log (K intracellular/K extracellular)

230

What does hyperkalemia do to the RMP?

Becomes less negative

231

What does hypokalemia do to the RMP?

Becomes more negative

232

In hyperkalemia is the threshold potential for spontaneous depolarization increased or decreased?

Its decreased (because hyperkalemia causes the RMP to become less negative)

233

Along with making the RMP less negative, what else does hyperkalemia do to the AP?

It can lead to an inability to repolarize since the RMP is above threshold potential

234

What does increased Ca do to the AP?

In increases the threshold potential

235

If Ca increases the threshold potential, what does this mean for treatment of hyperkalemia?

You can use Ca to treat hyperkalemia

236

What does K affect in the AP?

The resting membrane potential (it makes the RMP less negative and results in spontaneous depolarization, but prevents repolarization)

237

What does Ca affect in the AP?

If affects the threshold potential of the cell (Increase Ca will make the threshold potential less negative making it harder for the cell to depolarize)

238

What 4 things can be done to treat symptomatic hyperkalemia (EKG changes)?

1. Antagonize membrane effects (Calcium)
2. Redistribute K from extracellular to intracellular environement (insulin and beta-2 receptor stimulation)
3. Remove K from body (Exchange resin: Kayexalate, dialysis)
4. Bicarbonate therapy (only if severe acidosis is present)

239

What does exchange resin (Kayexalate) do?

Exchanges a K for a Na in the colon

240

What do insulin and beta-2 receptor stimulation do to redistribute K from extracellular to intracellular?

Increase the Na/K ATPase pump stimulation

241

What are 5 indications for dialysis in ARF?

1. Uncontrolled hyperkalemia
2. Intractable fluid overload
3. Uremia
4. Pericarditis
5. Intractable metabolic acidosis

242

Is there any proven benefit of any treatment in enhancing recovery of ATN?

No (Dopamine and diuretics- Lasix)

243

What is the purpose of treatment in ATN?

Supportive to allow time for tubular regeneration

244

What is dopamine?

A neurotransmitter that binds to peripheral receptors (D1/D2 receptors in the kidney)

245

What does dopamine do in the kidney?

1. Dilates the afferent and efferent arteriole (no change in GFR or FF)
2. Inhibits proximal tubular Na re-absorption (increased urine output and natriuresis)

246

Since ATN is a result of cell damage, what does this mean with regards to agents used?

No improvement can occur with agents that increase renal blood flow or cause a higher urine output

247

What are the 4 phases of AKI?

1. Initiating Phase
2. Oliguric Phase
3. Diuretic Phase
4. Recovery Phase

248

What is the initiating phase?

Time of exposure to hemodynamic or toxic insult

249

What is the oliguric phase?

-Period of oliguria (67%)
Urine volume is under 400cc/day

250

When do most patients die from AKI?

In the oliguric phase

251

What is the duration of AKI during the oliguric phase?

10-14 days

252

What is the diuretic phase?

-Increasing urine output (non-oliguric)
-No change in renal function

253

What is the recovery phase?

-May last 3-12 months before full functional recovery occurs (acid base/water homeostasis)

254

What are 4 outcomes of ATN and their associated %?

1. Death: 50%
2. Complete recovery: 15%
3. Partial recovery: 30%
4. Dialysis dependent: 5%

255

What are 5 causes of death in AKI and their associated %?

1. Pneumonia: 35%
2. Gram negative sepsis: 30%
3. GI Bleed: 10%
4. Cardiac: 20%
5. Hyperkalemia: 5%

256

What 5 things does the buildup of uremic toxins do in AKI that can lead to death?

1. Impairs immune system (decreases antibody production)
2. Reduces the function of PMNs (phagocytosis)
3. Increase the permeability of the skin and GI barriers to bacterial translocation
4. Decreases platelet function (GI BLEED)
5. Na and water overload (CHF/MI)
*The first 3 lead to infection

257

What are the 9 things in the check-list approach to AKI?

1. Document with repeat values for BUN and Cr
2. Assess for spurious increases in BUN and Cr
3. Look at BUN/Cr ratio
4. Evaluate hemodynamic status
5. Look for nephrotoxin exposure
6. Examine the urinary sediment and urinary indices- FENA, Urine Na, Specific gravity
7. Order radiologic evaluation of the kidneys
8. Follow course of electrolytes / volume status / nutrition on a daily basis
9. Watch the potassium level !