renal pathophysiology Flashcards
Kidneys receive ____ of the total cardiac output
15-25%
How much of the kidney blood flow goes to the renal cortex?
95%
How much of the kidney blood flow goes to the medulla?
5%
How many L/min of blood flows through the renal arteries?
1-1.25 L/min
Where is the glomerulus located?
renal cortex
Kidneys autoregulate their blood flow between
60-160 mmHg mean arterial pressures
Autoregulation of renal blood flow is an
intrinsic mechanism that causes vasodilation and vasoconstriction of renal afferent arterioles
Where does Na+ move in the nephron?
proximal convoluted tubule, descending loop, ascending loop, distal convoluted tubule
where do potassium sparing diuretics work in the nephron?
the end of the distal convoluted tubule before the collecting duct
where do thiazides work in the nephron?
beginning of the distal convoluted tubule
where do loop diuretics work in the nephron?
ascending limb of the loop of Henle
where do osmotic diuretics work in the nephron?
end of the proximal convoluted tubule and descending limb of the loop of Henle
Where does Acetazlamide work in the nephron?
beginning of the proximal convoluted tubule
the resistance in the efferent arterioles creates ____ within the glomerulus to provide force for _____
hydrostatic pressure; ultrafiltration
the glomerular capillaries are lined with
endothelial cells called podocytes
Glomerular filtration rate definition
the rate at which blood is filtered through all of the glomeruli measure overall kidney function
Urinary excretion = _____ - ______ + ______
filtration - reabsorption + secretion
SNS activation will _____ renal blood flow
reduce
If blood pressure decreases the SNS will stimulate
the RAAS
Antidiuretic hormone (ADH) is released in response to ____ stretch receptors in the atrial and arterial wall
decreased
ADH is released in response to ____ osmolality of the plasma
increased
osmolality is monitored by the
hypothalamus
what causes an increased osmolality?
dehydration
ADH is synthesized in the ____ and is released from the ____
hypothalamus; posterior pituitary
the half life of ADH is ____ minutes
16-24 minutes
2 primary functions of ADH
increases reabsorption of sodium and water in the kidneys
causes vasoconstriction and PVR to increase blood pressure
perioperative causes of ADH release include
hemorrhage, positive pressure ventilation, upright position, nausea, medications
What is renin?
an enzyme secreted by the kidneys that hydrolyzes angiotensin to angiotensin I
where is renin released from?
the juxtaglomerular cells located near the afferent arterioles
what makes renin be released?
decreased arterial blood pressure
decrease in sodium load delivered to the distal tubules
SNS (beta 1 receptor)
angiotensin I is converted in the ___ by ____ into ____
lungs; angiotensin converting enzyme; angiotensin II
angiotensin II is a ___ and stimulates the ___ to secrete ____
potent vasoconstrictor; hypothalamus; ADH
Aldosterone is a ___ hormone released from the ____
mineralcorticoid; adrenal gland
plasma half life of aldosterone is
20 minutes
aldosterone stimulates epithelial cells in the distal tubule and collecting ducts to
reabsorb sodium and water
Aldosterone does the complete opposite of what hormone?
Atrial natriuretic hormone
Which diuretic blocks aldosterone receptors?
spironolactone (potassium sparing)
definition of pre-renal failure
sudden and severe drop in BP or interruption of blood flow to the kidneys from severe injury or illness
definition of intra-renal failure
direct damage to the kidneys by inflammation, toxins, drugs, infection, or reduced blood supply
definition of post-renal failure
sudden obstruction of urine flow due to enlarged prostate, kidney stones, bladder tumor, or injury
some causes/examples of pre-renal failure
hypoperfusion vs hypovolemia
skin loss, fluid loss, hemorrhage, sequestration, vascular occlusion
pre-renal failure will activate RAAS to conserve
sodium and water
nephrotoxic drugs include
aminoglycosides (gentamicin, tobramycin), chemotherapeutic drugs (carboplatin, cisplatin), NSAIDs, PCNs, radiocontrast dye
patients with parenchymal disease will have trouble concentrating ___ leading to ___ urine sodium and ___ osmolality
urine; high; low
CHF and liver failure can lead to ___ ultimately causing ___
hypovolemia, decreased CO, decreased effective circulating volume; pre-renal AKI
NSAIDs, ARBs, ACEi, cyclosporines can lead to ___ and ultimately cause ___
impaired renal autoregulation; pre-renal AKI
bilateral ureteropelvic obstruction and bladder outlet obstruction leads to
post-renal AKI
ischemia, sepsis, and nephrotoxins can lead to ___ ultimately causing ___
acute glomerulonephritis and tubular damage; intrinsic renal AKI
vasculitis, TTP/HUS, and malignant HTN can lead to __ ultimately causing ___
vascular damage; intrinsic renal AKI
oliguric
<0.5 mL/kg/hr
polyuric
> 2.5 L/day of non concentrated urine
risk for renal failure GFR criteria
increased creatinine x 1.5 or GFR decrease >25%
injury for renal failure GFR criteria
increased creatinine x 2 or GFR decrease > 50%
failure for renal failure GFR criteria
increased creatinine x3 or GFR decrease >75% or creatinine >4mg per 100 mL
high sensitivity urine output criteria for risk of renal failure
UO <0.5 mL/kg/hr x 6 hours
urine output criteria meeting injury for renal failure
UO <0.5 mL/kg/hr x 12 hours
high specificity urine output criteria for failure in renal failure
UO <0.3 mL/kg/hr x 24 hours or anuria x 12 hours
for each year after age ___ creatinine clearance decreases by ____ and renal plasma flow by ____
50; 1.5 mL; 8 mL
risk factors for acute renal failure/injury
age, preexisting renal dysfunction, certain surgical procedures (Cardiac bypass, aortic aneurysms, ventricular dysfunctions), sepsis (hypovolemia, hemolysis, DIC, infections, acidosis), neprhotoxic agents, diabetes, HTN
ways to prevent renal insult?
hydration, blood pressure control
3rd most common cause of hospital acquired acute renal injury
contrast induced nephropathy
treatment for contrast induced nephropathy
prevention is important!
supportive, careful fluid and electrolyte management
dialysis may be required in some cases
which kind of radiocontrast agents are the most problematic in causing contrast induced nephropathy
iodinated contrast agents
what are some risk factors that place a patient at increased risk of contrast induced nephropathy?
pre-existing kidney disease, DM, HTN, dehydration, obesity, only having one kidney, hepato-renal syndrome
as high as ___ in patients with diabetic nephropathy develop contrast induced nephropathy
50%
contrast induced nephropathy is worsened by ___ and ___
hypoxia and hypoperfusion
pathophysiology of contrast induced nephropathy
activation of cytokine induced inflammatory mediators by reactive free radicals, the excreted contrast media generates an osmotic force in the renal tubules causing an increase in sodium and water excretion which will increase intratubular pressure, reducing GFR, and contributing to the development of acute renal failure
oliguria is often a sign of
inadequate systemic perfusion
monitors to assess fluid status intraoperatively
urinary catheter, TEE, CVP, blood pressure, SVV
assume pre-renal oliguria is related to
FLUID until proven otherwise
when should diuretics NOT be given?
in the setting of intravascular hypovolemia
selective dopamine DA1 receptor agonists cause
renal arteriolar vasodilation
examples of selective dopamine DA1 receptor agonists
fenoldopam, “low dose” dopamine
dopamine < 3 mcg effects
modest increase in CO
increases renal blood flow
decreases proximal tubule Na+ absorption
increases splanchnic blood flow
dopamine 3-10 mcg effects
increases contractility
minimal change in HR and SVR
increases renal blood flow
increases splanchnic blood flow
dopamine > 10 mcg effects
increases HR
vasoconstriction
could increase or decrease renal and splanchnic blood flow
hispanic americans have a ___ greater risk for developing kidney failure than non-hispanic americans
1.5 times
ESRD rates nearly ___ higher among African Americans
4 fold
Native Americans are about ___ more likely to be diagnosed with kidney failure
1.8 times
what increases the risk of developing kidney disease and limit access to preventive measures and treatment in communities with socioeconomic and cultural differences?
language barriers, education and literacy levels, low income, unemployment, lack of adequate health insurance, certain culture specific health beliefs and practices
chronic renal failure characteristics
slow, progressive, irreversible
definition of chronic renal failure
decreased functioning nephrons and renal blood flow, GFR, tubular function, and reabsorptive capacity
common causes of chronic renal failure
glomerulonephritis, pyelonephritis, diabetes, vascular or hypertensive insults, congenital defects
chronic renal failure stages
decreased renal reserve
renal insufficiency
end stage renal failure or uremia
someone with chronic renal failure is usually asymptomatic until ___
< 40% of normal nephron remain
renal insufficiency in chronic renal failure is defined as
10-40% of functioning nephrons remain
compensated, little renal reserve
end stage renal failure or uremia in chronic renal failure is defined as
> 95% of nephrons are nonfunctioning
GFR is < 5-10% of normal
severely compromised electrolyte, hematologic, and acid-base balances, uremia is eventually lethal, dialysis dependent
chronic renal failure manifestations
hypervolemia acidemia hyperkalemia cardiorespiratory dysfunction anemia bleeding disturbances
treatment of chronic renal failure
hemodialysis, peritoneal dialysis, kidney transplant
specific gravity
measurement of solutes in the urine indicating the kidneys ability to excrete concentrated urine and reflects tubular function
urine osmolality
number of moles of solute per kilogram of solvent
it is more specific than specific gravity
ability to excrete concentrated urine indicates
good tubular function
proteinuria
> 150mg is excreted per day indicating failure of the renal tubules to reabsorb protein
when > 750 mg indicative of severe glomerular damage
urinary pH
inability to excrete an acid urine in the presence of acidosis is indicative of renal insufficiency
when would you see proteinuria?
pre-eclamptic patients
glucose is freely filtered at the
glomerulus
glucose is reabsorbed in the
promixal tubule
glycosuria signifies
that the ability of the renal tubules to reabsorb glucose has been exceeded by an abnormally heavy glucose load and is usually indicative of diabetes mellitus
blood urea nitrogen
not a direct renal function, is influenced by exercise, bleeding, steroids, and tissue breakdown
BUN is elevated in kidney disease once GFR is reduced to
75%
serum creatinine
muscle tissue turnover and dietary intake of protein
creatinine is freely filtrered at the ___ and is neither __ or ___
glomerulus; reabsorbed; secreted
what is the best measure of glomerular function?
glomerular filtration rate
normal GFR
125 mL/min
patients are usually asymptomatic until GFR decreases to
< 30-50% of normal
creatinine clearance (mL/min) =
[(140-age) x lean body weight (kg)] / [plasma creatinine (mg/dL) x 72]
conditions causing elevation of serum creatinine independent of GFR
ketoacidosis, cephalothin, cefoxitin, flucytosine, ASA, cimetidine, probenecid, trimethoprim
conditions causing decrease of serum creatinine independent of GFR
advanced age, cachexia, liver disease
electrocardiogram in renal disease reflects
the toxic effects of potassium excess more closely than determination of the serum potassium concentration
what can you give to someone who is hyperkalemic
CaCl, insulin (5-10 units), D50, albuterol, hyperventilate, RBCs, Kayexelate
what clinical situations contribute to increased K+ in renal failure patients?
protein catabolism, hemolysis, hemorrhage, transfusion, metabolic acidosis, exposure to meds that inhibit K+ entry into cells or K+ secretion in the distal nephron
during blood storage there is a slow but constant leak of ___ from the cells into the plasma as a result of ___
potassium, failure of the sodium/potassium ATPase pump
what do you see on ekg with hyperkalemia?
peaked T waves and/or small/indiscernible P waves
how long are RBCs stored in blood bank?
42 days
the plasma level of potassium may increase by ____ per day of refrigerator storage
0.5-1 mmol/L
the risk of potassium overload can be minimized by selecting
blood collected less than 5 days old and by washing the unit before infusion to remove extracellular potassium
the use of ___ during transfusion may also decrease potassium loading
potassium absorption filters
other factors that play a role in the increase of potassium levels with blood transfusions include
the patient’s circulating volume, and the rate and volume of the transfusion
ultrasound can assess ___
kidney size, hydronephrosis, vaculature, obstructions, and masses
CT can assess/detect ___
stones of all kinds, masses (with contrast)
MRI can assess ___ and is a nice alternative to ___ and ___
detailed tissue characterization, alternative to contrast CT, reduced radiation exposure
what is a common agent used in MRA
gadolinium
general anesthesia on renal function
PPV and decreased CO leads to depression of renal blood flow, GFR, urinary flow, and electrolyte secretion
regional anesthesia on renal function
parallels with degree of SNS blockade, decreased venous return, and decrease in blood pressure
indirect perioperative effects on renal function
circulatory, endocrine, sympathetic nervous system, patient positioning
