Unit 10 - Kidney part 2 Flashcards
objective of countercurrent system in descending loop of Henle
concentrate urine by transferring water from tubular fluid to peritubular interstitium & ultimately returning to blood
why does UF become more dilute in the peritubular interstitium
water can’t follow Na+
fluid becomes more dilute, interstitium becomes more concentrated
how does ADH affect water and solutes
increases water reabsorption only (not solutes)
how does aldosterone affect water and solutes
- increases Na+ and water reabsorption
- increases K+ and H+ excretion
where in the nephron does PTH promote calcium reabsorption
distal tubules
where does the kidney expend most of its O2
Na/K-ATPase in basolateral membrane of tubular cells (the side that faces peritubular capillaries)
MOA of carbonic anhydrase inhibitors
noncompetively inhibit carbonic anhydrase in cells that make up proximal tubule
reduces reabsorption of bicarb, Na+, and water
MOA of carbonic anhydrase inhibitors
noncompetively inhibit carbonic anhydrase in cells that make up proximal tubule
reduces reabsorption of bicarb, Na+, and water
2 effects of HCO3- loss to urine via carbonic anhydrase inhibitors
- akaline urine
- mild hyperchloremic metabolic acidosis
3 uses of acetazolamide
- open angle glaucoma
- high altitude sickness
- central sleep apnea
why can acetazolamide be used in high altitude sickness
mild metabolic acidosis ↑ resp drive
why is acetazolamide used in central sleep apnea
mild metabolic acidosis ↑ resp drive
why is acetazolamide used in open angle glaucoma
carbonic anhydrase inhibition ↓ aqueous humor production and ↓ IOP
complicatinos of acetazolamide use
- metabolic acidosis
- hypokalemia
- may exacerbate CNS depression from severe hypercarbia in pts with COPD (loss of bicarb ions in urine = reduced buffer)
function of carbonic anhydrase
facilitates production of H2CO3
location of osmotic diuretic action
inhibit water reabsorption in proximal tubule (primary site) & loop of Henle
dose of acetazolamide
200-500 mg
MOA of osmotic diuretics
- They inhibit water reabsorption in proximal tubule (primary site) & loop of Henle
- Pull ECF volume into intravascular space - increases plasma osmolarity, which reduces brain water (↓ ICP) and augments RBF
uses of mannitol
- preventing AKI (little evidence to support)
- ↑ ICP
- differential diagnosis of acute oliguria (mannitol ↑ UOP if prerenal, no effect with intrinsic injury)
complications of mannitol use
- CHF
- pulmonary edema
- cerebral edema if blood-brain barrier is disrupted
adverse effect of osmotic diuretics in pts with CHF
transient increase in intravascular volume can cause pulmonary edema
MOA of loop diuretics
- disrupt Na-K-2Cl transporter in medullary region of thick portion of ascending loop of Henle (primary site)
- Amount of Na+ that remains overwhelms the distal tubule’s reabsorption capability - large amount of dilute urine excreted
electrolytes lost to urine with loop diuretics
- Na+
- K+
- Ca2+
- Mg2+
- Cl-
loop diuretic dosing
- Furosemide: 20-200 mg
- Bumetanide: 0.5-2 mg
- Ethacrynic acid: 25-100 mg
clinical uses of loop diuretics
- acute pulmonary edema
- AKI
- CHF
- hypercalcemia
- HTN
- anion overdose
- ↑ ICP
- mobilization of edema fluid
complications assoc with loop diuretics
- hypokalemic hyperchloremic metabolic alkalosis
- hypocalcemia
- hypomagnesemia
- hypovolemia
- ototoxicity
- reduced lithium clearance
Ototoxicity ethacrynic acid > furosemide
MOA of thiazide diuretics
inhibit Na-Cl co-transporter in distal tubule
how do thiazide diuretics affect serum calcium
increase
* Inhibition in distal tubule activates Na-Ca antiporter
* ↑ Ca2+ reabsorption and ultimately increasing serum Ca2+
unique side effects of thiazide diuretics
hyperglycemia, hypercalcemia, hyperuricemia
clinical uses of thiazide diuretics
- essential HTN
- mobilize edema fluid
- CHF
- osteoporosis (↓ Ca2+ excretion)
MOA of Amiloride & triamterene
inhibit K+ secretion and Na+ reabsorption in collecting ducts
function is independent of aldosterone
MOA of spironalactone
aldosterone antagonist
by blocking aldosterone at mineralocorticoid receptors, it inhibits K+ excretion and Na+ reabsorption into collecting ducts
doses of K+ sparing diuretics
- Spironolactone: 12.5-100 mg
- Amiloride: 5-10 mg
- Triamterene: 50-150 mg
uses of K+ sparing diuretics
to reduce K+ loss in a patient receiving a loop or thiazide diuretic, secondary hyperaldosteronism
adverse effects of K+ sparing diureics
hyperkalemia, metabolic acidosis, gynecomastia
increases risk of hyperkalemia with K+ sparing diuretics
concurrent NSAIDs, beta blockers, or ACE inhibitors
2 reasons amiloride is administered
- reduce K+ loss in pt on loop or thiazide diuretic
- secondary hyperaldosteronism
5 side effects of K+ sparing diuretics
- hyperkalemia
- metabolic acidosis
- gynecomastia
- libido changes
- nephrolithiasis
3 tests of glomerular function
- BUN
- Cr
- CrCl
normal BUN
10-20 mg/dL
normal serum Cr
0.7-1.5 mg/dL
normal CrCl
110-150 mL/min
tests of tubular function (concentrating ability)
- fractional excretion of Na+
- urine osmolality
- urine Na+
- urine specific gravity
normal fractional excretion of Na+
1-3%
normal urine osmolality
65-1400 mOsm/L
normal urine Na+ concentration
130-260 mEq/day
normal urine specific gravity
1.003-1.030
primary metabolite of protein metabolism in the liver
urea
etiologies of BUN < 8 mg/dL
Dehydration
Decreased urea production: Malnutrition, severe liver disease
etiologies of BUN 20-40
- Dehydration
- Increased protein input: High protein diet, GI bleed, Hematoma breakdown
- Catabolism: trauma, sepsis
- Decreased GFR
etiologies of BUN > 50
decreased GFR
metabolic byproduct of creatine breakdown
creatinine
production of creatinine is directly proportional to:
muscle mass (↓ in women and elderly)
lab test that is a useful indicator of GFR
Serum Creatinine
Undergoes renal filtration but not reabsorption
100% increase in serum Cr indicates:
50% reduction in GFR
why is BUN not a great indicator of GFR
Because urea undergoes filtration & reabsorption
how does BUN:Cr help evaluate hydration
Since BUN undergoes filtration AND reabsorption, but creatinine undergoes filtration but NOT reabsorption, the ratio of these substances in the blood can help evaluate state of hydration
normal BUN:Cr
20:1
BUN:Cr > 20 suggests:
prerenal azotemia
most useful indicator of GFR
CrCl
GFR calculation
calculating CrCl in women
Multiply value by 0.85 to account for smaller muscle mass
lab that relates sodium clearance to creatinine clearance
Fe(Na+)
Fractional Excretion of Sodium
what does Fe(Na+) < 1% suggest
prerenal azotemia
more sodium is conserved relative to the amount of creatinine cleared
what does Fe(Na+) > 3% suggest
impaired tubular function
more sodium is excreted relative to amount of creatinine cleared
what does urinary sodium level indicate
working kidneys can conserve sodium, failing kidneys waste sodium
UA result that indicates glomerular injury
Large amount of protein in urine (> 750 mg/day or +3 by UA)
what does urine specific gravity assess
weight of urine relative to sterile water
Measures kidney’s ability to concentrate or dilute urine
urine specific gravity
what does urine specific gravity indicate
Higher number = more concentrated urine (more solutes)
Lower number = less concentrated (less solutes)
Better test of tubular function than specific gravity
urine osmolarity
fractional excretion of Na+ in prerenal oliguria vs. acute tubular necrosis
oliguria: < 1
tubular necrosis: > 3
urinary Na+ in prerenal oliguria vs. acute tubular necrosis
oliguria: < 20
tubular necrosis: > 20
urine osmolality in prerenal oliguria vs. acute tubular necrosis
oliguria: > 500
tubular necrosis: < 400
BUN:Cr in prerenal oliguria vs. acute tubular necrosis
oliguria: > 20:1
tubular necrosis: 10-20:1
sediment prerenal oliguria vs. acute tubular necrosis
oliguria: normal, poss hyaline casts
tubular necrosis: tubular epithelial cells, granular casts
fundamental basis of AKI
The nephron (particularly the proximal tubule and thick ascending limb of the loop of Henle) has a high ATP consumption, and research reveals that impaired energetics is the fundamental basis of AKI
The most common cause of perioperative kidney injury
ischemia-reperfusion injury
Patients at risk for AKI during perioperative period:
- Pre-existing kidney disease
- Prolonged renal hypoperfusion
- Congestive heart failure
- Advanced age
- Sepsis
- Jaundice
- High-risk surgery (Use of aortic cross-clamp and liver transplant)
greatest risk: pre-existing kidney disease, CHF, advanced age, sepsis
problem with using UOP as surrogate of renal perfusion
oliguria is often result of physiologic response to perioperative stress (↑ ADH release during surgery)
RIFLE Criteria
Risk, Injury, Failure, Loss, End-stage kidney disease
Risk in RIFLE criteria
Cr > 1.5x baseline
UOP < 0.5 mL/kg/hr for > 6 hours
Injury in RIFLE Criteria
SCr 2x baseline
UOP < 0.5 mL/kg/hr for > 12 hrs
Failure in RIFLE criteria
SCr Increased to > 3x baseline or increase > 0.5 mg/dL to absolute value of > 4 mg/dL
UOP < 0.3 mL/kg/hr > 12 hrs or anuria for > 12 hrs
Loss in RIFLE criteria
Need for renal replacement therapy > 4 weeks
End-Stage in RIFLE criteria
Need for renal replacement therapy > 3 months
End-Stage in RIFLE criteria
Need for renal replacement therapy > 3 months
AKIN classification of kidney injury
Acute Kidney Injury Network
Risk in AKIN classification of kidney injury
SCr increased > 1.5-2x baseline or > 0.3 mg/dL
UOP < 0.5 mL/kg/hr for > 6 hours
injury in AKIN classification of kidney injury
SCr increased > 2-3x baseline
UOP < 0.5 mL/kg/hr for > 12 hrs
failure in AKIN classification of kidney injury
SCr increased > 3x baseline or
SCr increase > 0.5 mg/dL to absolute value > 4 mg/dL or
Need for renal replacement therapy
UOP < 0.3 mL/kg/hr > 12 hrs or
Anuria for > 12 hours
KDIGO classification of kidney injury
Kidney Disease Improving Global Outcomes
risk in KDIGO
Scr Increased > 1.5-2x baseline within past 7 days or increased > 0.3 mg/dL within 48 hours
UOP < 0.5 mL/kg/hr for > 6 hrs
failure in KDIGO criteria
SCr Increased > 3x baseline or increase to absolute value of > 4 mg/dL or need for renal replacement therapy
UOP < 0.3 mL/kg/hr > 12 hrs or anuria for > 12 hours
cause of prerenal injury
Hypoperfusion
Perfusion impaired as a result of hypovolemia, decreased CO, systemic vasodilation, renal vasoconstriction, or ↑ IAP
treatment of prerenal injury
halt progression to ATN: restore RBF with IVF, HD support, PRBCs
confirms diagnosis of prerenal azotemia
Improved UOP following IVF bolus
why should NSAIDs be avoided in pts at risk of renal injury
decrease prostaglandin synthesis and cause constriction of renal vasculature
cause of intrinsic renal injury
Parenchymal Dysfunction
Intrinsic causes of acute tubular necrosis
ischemia & nephrotoxic drugs
causes of intrinsic renal injury
Can be caused by injury of the tubules, glomerulus, or the interstitial space
cause of postrenal kidney injury
obstruction
Source can arise anywhere between collecting system and urethra (Foley, ureteral stones, neurogenic bladder)
cause of postrenal kidney injury
obstruction
Source can arise anywhere between collecting system and urethra (Foley, ureteral stones, neurogenic bladder)
etiologies of prerenal injury related to depleted vascular volume
- Hemorrhage
- Dehydration
- GI losses (V/D, NG tube)
- Cirrhosis
- Nephrotic syndrome
etiologies of prerenal injury related to decreased CO
- CHF
- Sepsis
- Cardiogenic shock
etiologies of prerenal injury related to systemic vasodilation
- Sepsis
- Anaphylaxis
- Cirrhosis
etiologies of prerenal injury related to renal vasoconstriction
- Early sepsis
- Hepatorenal syndrome
- Hypercalcemia
- NSAIDs
- Iodine-containing IV dye
what kind of kidney injury does abdominal compartment syndrome cause
prerenal
etiologies of intrinsic kidney injury that cause tubular injury
- Ischemia – hypoperfusion
- Myoglobin
- Free hgb (transfusion rxn)
- Antibiotics
- Contrast agents
- Chemotherapeutics
etiologies of intrinsic kidney injury that cause Tubulointestinal Injury
- Acute allergic interstitial nephritis
- Infection
- Infiltration
etiologies of intrinsic kidney injury r/t glomerular injury
- Inflammatory disease
- Hemolytic uremic syndrome
- Thrombotic thrombocytopenic purpura
etiologies of intrinsic renal injury r/t renal vasculature
- Toxemia of pregnancy
- Hypercalcemia
- Contrast agents
- Malignant hypertension
- Scleroderma
etiologies of intrinsic renal injury r/t renal vasculature
- Toxemia of pregnancy
- Hypercalcemia
- Contrast agents
- Malignant hypertension
- Scleroderma
etiologies of postrenal injury
- Retroperitoneal tumor
- Hematoma
- Fibrosis
- Surgical trama to ureter
- Hematoma
- Nephrolithiasis
- Blood clots/debris
- Tumor
- Stricture
- Infection
- Enlarged prostate
- Bladder obstruction
- Stones
- Neurogenic bladder
urinary tract obstruction
etiologies of postrenal injury
- Retroperitoneal tumor
- Hematoma
- Fibrosis
- Surgical trama to ureter
- Hematoma
- Nephrolithiasis
- Blood clots/debris
- Tumor
- Stricture
- Infection
- Enlarged prostate
- Bladder obstruction
- Stones
- Neurogenic bladder
urinary tract obstruction
how is risk of prerenal azotemia decreased
by maintaining MAP > 65 and providing appropriate hydration
fluids associated with an increased risk of renal morbidity
hydroxyethyl starches
consequence of using diuretics to attempt to convert oliguric to nonoliguric AKI
increases risk of additional renal injury & mortality
why does vasopressin maintain GFR and UOP better than NE or neo
preferentially constricts efferent arteriole
antibiotics to avoid in pts at high risk for renal injury
aminoglycosides
target serum glucose for preventing AKI in critically ill patients
110-149 mg/dL
most common causes of CKD
1 - diabetes
2 - HTN
stages of CKD
- Normal = GFR > 90 mL/min
- Mildly decreased = GFR 60-89
- Moderately decreased = GFR 30-59
- Severely decreased = GFR 15-29
- Kidney failure (requires dialysis) = GFR < 15
s/s uremic syndrome
anemia, fatigue, N/V, anorexia, coagulopathy
most accurate predictor of bleeding risk in pt with uremic syndrome
bleeding time
PT, PTT, and plt count in pts with uremic syndrome
normal
1st line treatment of uremic bleeding
desmopressin (von Willebrand factor 8)
when should dialysis be performed in uremic pt needing surgery
within 24 hours of surgery
improves bleeding time
why are pts with CKD anemic
- Decreased erythropoietin production leads to normochromic normocytic anemia
- Excess PTH also contributes to anemia by replacing bone marrow with fibrotic tissue
treatment of anemia in CKD
exogenous EPO or darbepoetin + iron supplementation
Blood transfusion is not a first-line treatment because it increases the risk of HLA sensitization and future rejection of a transplanted kidney
side effect of exogenous EPO admin
HTN
what causes HTN in CKD
result of RAAS activation leading to sodium retention and fluid overload
most common cause of death in CKD
CAD
Assume all patients with CKD have CAD
common CV complication with uremia
pericarditis
acid-base balance in CKD
- Decreased excretion of non-volatile acid contributes to a gap metabolic acidosis
- Non-gap acidosis is the result of a loss of HCO3- ions
oxyhgb assoc curve in CKD
Acidosis shifts the oxyhgb dissociation curve to the right (partially compensates for anemia)
serum K that necessitates dialysis
6
treatments of hyperkalemia
- Glucose (25 - 50g) + insulin (10 - 20 units)
- Hyperventilation (for every 10 mHg ↓in PaCO2, the serum K+ level ↓ by 0.5 mEq/L).
- Sodium bicarbonate (50 - 100 mEq)
why is CaCl given for hyperkalemia
does not alter serum potassium concentration but raises threshold potential in the myocardium and reduces the risk of lethal dysrhythmias
2 causes of Renal osteodystrophy
- Decreased vitamin D production
- Secondary hyperparathyroidism
why are pts with CKD at higher risk of bone fractures
- Inadequate supply of vitamin D impairs calcium absorption in the Gl tract
- The body responds ↑ PTH, which demineralizes bone to restore serum calcium concentration
- decreased bone density = increased fractures
phosphate level in CKD
increased
Phosphate clearance parallels GFR
phosphate level in CKD
increased
Phosphate clearance parallels GFR
respiratory effects of CKD
- Increased intravascular volume and uremia create a restrictive ventilatory defect
- Volume overload may lead to pulmonary edema
- Metabolic acidosis is compensated by respiratory alkalosis (hyperventilation)
why do CKD patients have decreased baroreceptor response & delayed gastric emptying
ANS dysfunction
when is PD favored over HD
in patients who can’t tolerate fluid shifts associated with HD (CHF or unstable angina)
most common event during dialysis
hypotension
due to intravascular volume depletion and osmotic shifts
most common event during dialysis
hypotension
due to intravascular volume depletion and osmotic shifts
most common event during dialysis
hypotension
due to intravascular volume depletion and osmotic shifts
leading cause of death in dialysis patients
infection
5 indications for dialysis
- Volume overload
- Hyperkalemia
- Severe metabolic acidosis
- Symptomatic uremia
- Overdose with a drug that is cleared by dialysis
what leads to gap metabolic acidosis in CKD patients
decreased excretion of non-volatile acids
FDA recommended rate of sevo admin
1 L/min for no more than 2 MAC hours
After 2 MAC hours, FGF should increase to 2 L/min
Factors assoc. with increased compound A production:
- high concentrations over a long period of time
- low FGF
- high temp of CO2 absorbent
- increased CO2 production
is succs safe in renal failure?
Renal failure does not cause upregulation of extrajunctional receptors, so succinylcholine is safe in patients with renal failure and a normal potassium level
succs infusion shuold not be used - metabolite is renally excreted
propofol dosing in CKD
may need an upward dose adjustment due to hyperdynamic circulation & disruption of BBB secondary to uremia
is precedex safe to use in CKD
yes - biotransformed by liver
duration may be prolonged
Primary function of the kidneys
eliminate toxins from the body
what area of the kidneys is at particular risk from nephrotoxic agents
tubules
what determines extent of nephrotoxic effects
Concentration of toxin & duration of exposure
2 mechanisms by which radiographic contrast media causes nephrotoxicity:
- Ischemic injury due to vasoconstriction in renal medulla
- Direct cytotoxic effects
when do s/s AKI begin after nephrotoxic agents are admin
Signs of AKI begin at 24-36 hours and peak between 3-5 days
narcotics best for use in renal failure pts
fentanyl, sufentanil, remifentanil, alfentanil
methods to prevent AKI from contrast dye
- IV hydration with 0.9% NS before contrast
- low or iso-osmolar contrast
- bicarb
sequelae of direct muscle trauma, muscle ischemia, or prolonged immobilization that damages kidneys
Rhabdomyolysis and myoglobinemia
binds oxygen inside of the myocyte
myoglobin
where is myoglobin filtered when released into circulation
at the glomerulus
renal consequences of Rhabdomyolysis and myoglobinemia
tubular obstruction and acute tubular necrosis
CK level assoc with increased risk of kidney injury
> 10,000 units/L
prevention of AKI from myoglobin
- Maintain RBF and tubular flow with IV hydration
- Osmotic diuresis with mannitol
- Keep UOP > 100-150 mL/hr
- Administer sodium bicarb and/or acetazolamide to alkalize urine
side effects of tacrolimus
HTN, renal vasoconstriction
neuraxial anesthesia level required for TURP
T10
5 nephrotoxic antibiotics besides aminoglycosides
- ampho B
- vanc
- sulfonamide
- tetracyclines
- cephalosporins
2 immunosuppressant agants that are nephrotoxic
- tacro
- cyclosporine
5 conditions that cause rhabdomyolysis & myoglobinemia
- direct muscle trauma
- muscle ischemia
- immobilization
- MH
- succs in DMD
absorbed irrigation volume in a TURP
estimated as 10 - 30 mL/min of resection time
height of irrigation solution used in TURP
no more than 60 cm above OR table
TURP time should be limited to:
1 hour
TURP time should be limited to:
1 hour
characteristics of ideal irrigation fluid used in TURP
provides good surgical visibility (should be clear), is isotonic, and nontoxic
fluids that are contraindicated as irrigant solutions when monopolar electrocautery used in TURP
0.9% NaCl or LR
highly ionized - good conductors of electricity
cons of using water in TURP
Increased risk TURP syndrome:
classic triad in TURP syndrome
- HTN with increased pulse pressure
- reflex bradycardia
- AMS
cons of glycine use in TURP
Increased ammonia - dec LOC
Transient postop visual syndrome
s/s transient postop visual syndrome with glycine in TURP
- Blindness or blurry vision x 24-48 hours
- Inhibitory neurotransmitter in the eye
cons of 3.3% sorbital for TURP
Hyperglycemia
Osmotic diuresis
Lactic acidosis (w/ massive absorption)
cons of 5% mannitol for TURP
Osmotic diuresis
Transient plasma expansion (risk LV failure)
what causes TURP syndrome
absorption of a large volume of hypo-osmolar irrigation solution
serum Na+ assoc with increased complications from TURP syndrome
< 120
Serum Na+ level associated with seizure, coma, and lethal ventricular arrythmias
< 110 mEq/L
hematologic effects of TURP syndrome
hemolysis
treatment of TURP syndrome if Na+ > 120
restrict fluids and give lasix
treatment of TURP syndrome if Na+ < 120
give 3% NaCl at < 100 mL/hr (d/c when Na+ > 120 mEq/L)
complication of obturator n. stimulation in TURP
can cause lower extremity movement, which may cause the resectoscope to puncture the bladder wall
presentation of bladder puncture in TURP
- abdominal and shoulder pain
- reduction of irrigation fluid return is an early sign of bladder rupture
presentation of bladder puncture in TURP
- abdominal and shoulder pain
- reduction of irrigation fluid return is an early sign of bladder rupture
management of pt with bladder perforation in TURP
- HD support
- serial assessment of H&H and transfusion as indicated
- will require emergent suprapubic cystostomy or possibly exploratory laparotomy
rough estimate of blood loss during TURP
2-5 mL blood per minute of resection time
absolute contraindications to ESWL
pregnancy, bleeding disorder or anticoagulation (risk bleeding)
relative contraindications to ESWL
- pacemaker/ICD
- calcified aneurysm of aorta or renal artery
- untreated UTI
- obstruction beyond renal stone
- morbid obesity (further distance from energy source to stone)
Complications of ESWL
- dysrhythmias
- organ perforation
common side effect after ESWL
hematuria
common side effect after ESWL
hematuria
Often used when ESWL has been ineffective
Percutaneous Nephrolithotripsy
most common position for Percutaneous Nephrolithotripsy
prone
complications of Percutaneous Nephrolithotripsy
- TURP syndrome (large amount of irrigant used)
- pneumothorax
typical pt position for laser lithotripsy
lithotomy
labs elevated in renal osteodystrophy
2 P’s
phosphate
parathyroid hormone
most potent stimulators of ADH release
hypernatremia
hypovolemia
why is vasopressin a good choice for a potent vasopressor when preserving renal function is particularly important
it constricts the efferent arteriole, increasing GFR