acute renal failure intro Flashcards
Internal vs external balance
External balance refers to the relationship between intake from the outside and output to the outside. Internal balance refers to shifts between intra and extracellular fluid spaces.
- Understand the physiologic determinants of glomerular filtration rate at a single nephron level
Starling forces: • Glomerular capillary hydrostatic pressure (PGC). • Glomerular capillary oncotic pressure (πGC). • Tubular hydrostatic pressure (PT). • Oncotic pressure in the tubule (πT). • A term that takes into account the surface area and permeability of the glomerular capillary membrane (Kf).
Which factor controls single nephron glomerular filtration rate the most
Hydrostatic pressure in glomerular capillary is most important, which favors glomerular filtration. Capillary oncotic pressure and tubular hydrostatic pressure oppose filtration. Tubular oncotic pressure is essentially aero because the glomerulus prevents filtration of proteins into the tubules.
Compare filtration at the afferent arteriole vs efferent arteriole sides of the glomerulus
Filtration decreases from the afferent arteriole to the efferent arteriole b/c glomerular oncotic pressure increases as fluid is filtered out and proteins are concentrated
Clinical ways to estimate GFR
Plasma based: Urea (BUN) is indirect and not used, and creatinine (most common), or Cockcroft and gault formula. Urine based: clearance formula
Urea in the kidney and GFR
Urea is a nitrogenous waste that is endogenously produced, is freely filtered by the glomerulus, and is not secreted. It is, however, reabsorbed at several tubular sites, and thus, its clearance tends to underestimate GFR
Creatinine for measurement of GFR
Creatinine is a nonenzymatic breakdown product of creatine that exists in high and fairly stable concentrations in human muscle as well as some other tissues. Creatinine production reflects muscle mass. It is freely filtered by the glomerulus, is not reabsorbed, but is secreted to a variable degree. It tends to overestimate GFR by 10-20%
- Understand how to calculate glomerular filtration rate based on plasma
Cockcroft and Gault formula estimates creatinine clearance which estimates GFR. Creatinine clearance = [(A) x (140 - age) x weight]/ (72 x SCr) Where: • the creatinine clearance is in ml/min • A=l.0 if male, 0.85 if female • Age is in years • Weight is in kg • Serum creatinine is in mg/dL Cockcroft and Gault formula estimates creatinine clearance which estimates GFR. Creatinine clearance = [(A) x (140 - age) x weight]/ (72 x SCr) Where: • the creatinine clearance is in ml/min • A=l.0 if male, 0.85 if female • Age is in years • Weight is in kg • Serum creatinine is in mg/dL Cockcroft and Gault formula estimates creatinine clearance which estimates GFR. Creatinine clearance = [(A) x (140 - age) x weight]/ (72 x SCr) Where: • the creatinine clearance is in ml/min • A=l.0 if male, 0.85 if female • Age is in years • Weight is in kg • Serum creatinine is in mg/dL
- Understand how to calculate glomerular filtration rate based on urine
Patient collects urine over 24 hr period and has blood draw to determine plasma creatinine. Then calculate: ClCr (ml/min) = (UCr mg/dL) V (ml/min)/ PCr (mg/dL). Where ClCr is creatinine clearance, Ucr is urine creatinine conc., V is urine flow rate (ml/min), PCr is plasma creatinine conc.
What causes decreased afferent arteriolar resistance and how does it affect GFR? Increased afferent?
Decreased afferent: NO, PGE2, PGI2, high protein diets cause increased GFR. Increased afferent: NSAIDS, adenosine, norepinephrine, endothelin, thromboxane decreases GFR.
What causes decreased efferent arteriolar resistance and how does it affect GFR? Increased efferent?
Decreased efferent: ACEI and ARBs decrease GFR. Increased efferent: angiotensin II increases GFR
Normal lab values for plasma: Na, K, Cl, CO2, glucose, creatinine, BUN, phosphorus, Ca, cholesterol, osmolality, plasma anion gap
- Na- 140 ± 3 mEq/L
- K- 4.5 ± 0.6 mEq/L
- Cl- 104 ± 3 mEq/L.
- Total CO2 (tCO2)- 27 ± 2 mEq/L
- Glucose (Fasting)- 90 ± 30 mg/dL
- Creatinine- 1.0 ± 0.3 mg/dL
- BUN- 12 ± 4 mg/dL
- Phosphorus- 4.0 ± 1.0 mg/dL
- Calcium- 9.5 ± 1.0 mg/dL
- Cholesterol- 140-200 mg/dL
- Osmolality- 285 ± 3 mosm/kg H2O
- Plasma Anion Gap = Na – (Cl + tCO2) = 9 ± 2 mEq/L • Na- 140 ± 3 mEq/L
- K- 4.5 ± 0.6 mEq/L
- Cl- 104 ± 3 mEq/L.
- Total CO2 (tCO2)- 27 ± 2 mEq/L
- Glucose (Fasting)- 90 ± 30 mg/dL
- Creatinine- 1.0 ± 0.3 mg/dL
- BUN- 12 ± 4 mg/dL
- Phosphorus- 4.0 ± 1.0 mg/dL
- Calcium- 9.5 ± 1.0 mg/dL
- Cholesterol- 140-200 mg/dL
- Osmolality- 285 ± 3 mosm/kg H2O
- Plasma Anion Gap = Na – (Cl + tCO2) = 9 ± 2 mEq/L • Na- 140 ± 3 mEq/L
- K- 4.5 ± 0.6 mEq/L
- Cl- 104 ± 3 mEq/L.
- Total CO2 (tCO2)- 27 ± 2 mEq/L
- Glucose (Fasting)- 90 ± 30 mg/dL
- Creatinine- 1.0 ± 0.3 mg/dL
- BUN- 12 ± 4 mg/dL
- Phosphorus- 4.0 ± 1.0 mg/dL
- Calcium- 9.5 ± 1.0 mg/dL
- Cholesterol- 140-200 mg/dL
- Osmolality- 285 ± 3 mosm/kg H2O
- Plasma Anion Gap = Na – (Cl + tCO2) = 9 ± 2 mEq/L
Normal lab values for urine: Na, K, creatinine, osmolality, specific gravity, pH
- Na- low < 10 mEq/L, high> 40 mEq/L
- K- must be considered in light of plasma potassium.
- Creatinine- usually viewed in concert with plasma creatinine; a UCr/PCr value greater than 20 suggests avid tubular water reabsorption, a value less than 10 suggests less avid water reabsorption.
- Osmolality (again, no “normal range) 285 is isotonic -normally can dilute to less than 50-100 mosm/kg H2O, -normally can concentrate to greater than 1000 mosm/ kg H2O
- Specific gravity- 1.010 is isotonic (< this is dilute, > this is concentrated)
- pH- normally, when faced with an acid load, can decrease urine pH to < 5.2• Na- low < 10 mEq/L, high> 40 mEq/L
- K- must be considered in light of plasma potassium.
- Creatinine- usually viewed in concert with plasma creatinine; a UCr/PCr value greater than 20 suggests avid tubular water reabsorption, a value less than 10 suggests less avid water reabsorption.
- Osmolality (again, no “normal range) 285 is isotonic -normally can dilute to less than 50-100 mosm/kg H2O, -normally can concentrate to greater than 1000 mosm/ kg H2O
- Specific gravity- 1.010 is isotonic (< this is dilute, > this is concentrated)
- pH- normally, when faced with an acid load, can decrease urine pH to < 5.2• Na- low < 10 mEq/L, high> 40 mEq/L
- K- must be considered in light of plasma potassium.
- Creatinine- usually viewed in concert with plasma creatinine; a UCr/PCr value greater than 20 suggests avid tubular water reabsorption, a value less than 10 suggests less avid water reabsorption.
- Osmolality (again, no “normal range) 285 is isotonic -normally can dilute to less than 50-100 mosm/kg H2O, -normally can concentrate to greater than 1000 mosm/ kg H2O
- Specific gravity- 1.010 is isotonic (< this is dilute, > this is concentrated)
- pH- normally, when faced with an acid load, can decrease urine pH to < 5.2
Define acute kidney injury
rapid reduction in glomerular filtration rate manifested by a rise in plasma creatinine (Pcr) concentration, urea and other nitrogenous waste products. Azotemia is the state where clearance of nitrogenous wastes is reduced
Broad categories of disorders that cause acute kidney injury
- Pre-renal azotemia: a decrease in GFR due to decreases in renal plasma flow and/or renal perfusion pressure. 2. Post-renal azotemia or obstructive nephropathy: a decrease in GFR due to obstruction of urine flow. 3. Intrinsic renal disease: a decrease in GFR due to direct injury to the kidneys (may be due to a variety of insults).
Define uremia
constellation of signs and symptoms of multiple organ dysfunction caused by retention of “uremic toxins” and lack of renal hormones due to acute or chronic kidney injury. Symptoms include nausea, vomiting, abdominal pain, diarrhea, weakness and fatigue.
