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78 Cards in this Set

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What is renal function?
the ability of the kidney to excrete solids
Approximately how many nephrons are there per kidney?
1 million
How many nephrons must be destroyed for renal failure to occur?
60-78%
What is renal failure?
The loss of renal function either acute or chronic that results in azotemia and syndrome of uremia
What is azotemia?
an increase of nitrogenous wastes in the blood
What is uremia?
a complex of symptoms due to azotemia that can be relieved by dialysis
What are the three areas of renal function?
Renal Plasma Flow (RPF)
Glomerular Filtration Rate (GFR)
Tubular Reabsorption
What is normal renal plasma flow and how is it measured?
Approximately 1200 ml/min (dependent on BP) measured by clearance tests and renal blood flow tests
What is the glomerular filtration rate and how is it measured?
The amount of fluid flowing through the glomeruli into the tubules at a given time; measured by clearance tests
What is tubular reabsorption and how is it measured?
the reclaiming of needed elements; measured by concentration tests
What is the easiest way to test tubular reabsorption?
First morning specimen
What is the first thing to go in renal failure?
Concentrating ability
What are the three different kinds of renal disease and give examples of causes
Pre-renal (blood flow, pressure, volume)
Intrarenal (abnormal filtration or absorption)
Post-renal (BPH, bilateral blockage)
What do clearance tests do?
reflects the ability of the kidney to "clear" the plasma of a specific substance; measures how much of a substance is cleared from the blood/minute
What are the clearance tests used for?
Measure RPF and GFR
When is RPF decreased?
Shock, lowered Na levels, low clearance results
What is the principle used to determine GFR?
If the substance passes unaltered through nephron the amount excreted = amount entering glomerulus
How are the plasma concentration and clearance related?
They are inversely proportional
What are three variables that affect clearance?
# of nephrons functioning
Efficiency with which they function
Amount of blood entering the nephron
What is the clearance equal to?
The amount of plasma (ml) flowing through the glomeruli per minute with complete removal of the substance
What is Inulin?
It is a metabolically inert sugar that is not metabolized, absorbed, or secreted it is the reference method of clearance tests
What is Urea?
Produced by the liver, end product of protein metabolism (Also known as BUN)
What are the Pros of using the Urea Clearance test?
There is no effect from tubular cells, passive reabsorption by tubules, plasma concentration remains constant
What are the Cons of using Urea Clearance test?
non-renal events can affect the concentration, plasma levels increase if increased protein breakdown, if the kidneys reabsorb water the urea is reabsorbed with the water
What is the metabolism of creatinine?
Creatine phosphate converted to creatine in synthesis of ATP from ADP (catalyzed by CK) in process small amounts of creatine are irreversibly converted to creatinine, which is removed by the kidneys
What does creatinine depend on?
Muscle mass (therefore higher in men than women); the amount of creatinine from creatine is constant/person
If a patient is hypovolemic how can this affect the Cr level?
Because a little Cr is secreted into urine as it moves through the tubules it may be enough to give you an impression that the patient's Cr Cl is ok when it's not
What do serial determinations detect?
Changing renal function
What are the normals for Cr Cl?
85-125 Males
75-115 Females
55-85 Children
What are the normal serum levels for Cr?
Men (0.7 - 1.2)
Women (0.6 - 1.1)
What Cr clearance would be considered a chronic kidney disease?
Anything less than 60
What is Serum Cystatin C and how is it used?
A low molecular weight protein that is filtered at the glomerulus and not reabsorbed, but metabolized in tubules; cannot be used to directly measure clearance, may be more accurate to measure GFR than serum Cr, testing only available in a limited # of labs
How much can Kidneys concentrate urine in relationship to plasma?
Kidneys can concentrate urine 4 times the plasma concentration
How much can kidneys dilute urine in relationship to plasma?
1/4 of plasma concentration
How do concentration tests show impairment in tubular reabsorption?
Tubules should be able to excrete wastes and reabsorb needed elements with low water intake
What is the simplest concentration test?
First morning specimen
What specific gravity or osmolality indicates adequate concentrating ability and what two things cannot be present?
Sp. Gr. > = 1.025
Osmo > = 850
No protein or glucose
What percent should a normal 12-14 hour fluid restriction show?
75% of maximal ability to concentrate urine
What percent should a normal 24 hour fluid show?
100% of maximal ability to concentrate urine
When is fluid restriction contraindicated?
Cardiac patients, renal disease, elderly, electrolyte disorders
When is the concentration test impaired?
Diabetes insipidus, sickle cell anemia, pyelonephritis, glomerulonephritis
What four molecules largely determine osmolality?
Na, Cl, HCO3-, Glucose, Urea
How and where is osmolality regulated?
Regulated by the reabsorption of water and electrolytes anywhere in the distal tubules and collecting ducts.
What is the calculation for osmolality?
2(Na) + Glucose/18 + BUN/2.8
How do you correct osmolality for suspected alcohol use?
Add Ethanol/4.6 to the osmolality final number
What is the normal urine osmolality? Serum osmolality?
Urine: 300-900 mOsm/kg H2O
Serum: 289-308 mOsm/kg H2O
What is the normal urine osmolality to serum osmolality ratio?
1:1 to 3:1
If the urine to serum osmolality ratio is <1:1 what is the problem?
Distal tubular damage (inability to concentrate urine)
If the urine to serum osmolaltiy ration is >3:1 what is the problem?
decrease in GFR (Glomerular disease)
If you have a constant specific gravity of 1.010 what should you consider?
Chronic renal disease
What happens to osmolality and sodium in the hyperglycemic patient and how?
Increased osmolality, decreased serum sodium; the high concentration of glucose in ECF draws H2O out of ICF and dilutes Na in ECF (Cellular Fluid)
For every 100 mg/dL increase in glucose how much does the serum Na decrease?
1.6 meq/L
What is the corrected Na formula?
Measured Na + (1.6 meq/L x (measured glucose - 100))/100
What is SIADH and when does it occur?
It is the most common cause of euvolemic hypotonic hyponatremia; occurs when ADH secretion is a result of nonphysiologic stimuli
What does ADH do to renal tubular epithelial cells?
Causes them to reabsorb water
What is the most common cause of SIADH?
Ectopic hormone production by bronchogenic carcinoma
What is the normal ADH result on osmolality and volume?
Increased osmolality and decreased volume
What is SAIDH's result on Serum Osmolality and Serum Na? Urine?
Decreased Serum Osmolality and decreased Serum Na
Increased Urine Osmolality and Increased urine Na
What is Fanconi's syndrome?
a defect in renal tubular reabsorption; patients having proximal renal tubular acidosis with a nonanion gap metabolic acidosis
What is Fanconi's Syndrome characterized by?
Bicarbonaturia, Uricosuria, gluycosuria, amino-aciduria, and phosphaturia
What does it mean for tubular function if you have glycosuria with normal serum glucose?
proximal tubular dysfunction
What does it mean for tubular function if you have inappropriate secretion of Na, K, HCO3-?
Distal tubular dysfunction
What is Blood Urea Nitrogen (BUN)?
The end product of metabolism, produced by the liver
What is Creatinine?
Product of the breakdown of creatine (found in muscles)
What is the normal BUN/Cr ratio?
10:1 to 20:1
When is the BUN/Cr ratio increased?
Prerenal (increased production of urea)
Postrenal (increased tubular reabsorption of urea)
What does a BUN/Cr ratio of <15:1 mean?
Intrarenal (acute tubular necrosis)
Because intrarenal affects both BUN and Creatinine levels
What does elevated BUN and creatinine show?
Impaired GFR
What is the Fractional Sodium Excretion (FNa) and how do you calculate it?
Renal failure index
(urine sodium x plasma creatinine)/(urine creatntine x plasma sodium)
If the value of the FNa is < 1.0 what does this mean?
Prerenal cause (underperfusion) - the kidneys respond to decreased blood flow by conserving Na
If the value of the FNa is > 1.5 what does this mean?
Intrarenal cause (acute tubular necrosis) - there is tubular damage; inability to conserve Na
What is Microalbumin?
The urinary excretion of albumin that is below the detection capability of urine dipsticks, but above the upper limit of normal for healthy individuals
What does a measurement of microalbumin identify?
Patients who are at risk for diabetic nephropathy
How do you screen for microalbumin and what affects the screening?
Urine albumin to Cr ratio
A ratio between 30 to 300 mg/g establishes the presence of microalbuminuria
The results are affected by NSAIDs and ACE inhibitors and influenced by the urine volume
What is oliguria? What causes it?
Marked decrease in urine flow - caused by dehydration, shock, obstruction, hypotension, nephrotoxic drugs
What is polyuria? What can cause it?
Marked increase in urine flow - caused by DM, Diabetes Insipidus, diuretics, caffiene, alcohol
What is nocturia?
Increased volume of urine at night
What is anuria?
No urine flow