Exam 4 - Polyuria/Polydipsia Flashcards
what is polyuria for a dog?
urine production > 50 ml/kg/day
what is polydipsia for a dog?
water intake > 100 mg/kg/day
owner may mistake polyuria for pollakiuria, but most owners can measure water intake
what is isosthenuria?
usg 1.008-1.012
what is hyposthenuria?
usg 1.001-1.007
what represents minimally concentrated urine in dogs & cats?
dogs - usg <1.030
cats - usg <1.035
thirst is mainly controlled by what? what else can cause thirst?
mainly controlled by dehydration of osmoreceptors
non-osmotic factors such as decreased arterial blood pressure & increased body temperature can stimulate thirst
T/F: thirst is abnormally stimulated in patients with primary polydipsia
true
what is required of the body to be able to form concentrated urine?
body must produce ADH & renal tubules must respond to ADH
requires that the renal medullary interstitium be hypertonic & that at least 1/3 of the total nephron population be functional
so that in the presence of ADH, the distal portion of the distal convoluted tubule & collecting duct to become permeable to water where water is reabsorbed from the tubular lumen
hypertonicity of the renal medullary interstitium produces osmotic pressure that drives the water resorption & the kidneys maintain body fluid composition & volume
what is the mechanism causing pu/pd in a patient with diabetes mellitus? what diagnostics can you use to prove this?
osmotic diuresis due to glucosuria
blood glucose levels & measure urine glucose
what is the mechanism causing pu/pd in a patient with renal failure? what diagnostics can you use to prove this?
osmotic diuresis of remnant nephrons & structural disruption of medullary concentration gradient
measure BUN, creatinine, SDMA, & do a urinalysis
what is the mechanism causing pu/pd in a patient with bacterial pyelonephritis? what diagnostics can you use to prove this?
renal parenchymal damage + e. coli endotoxin competes with ADH on renal tubules
do a urine culture, abdominal ultrasound, & excretory urogram
what is the mechanism causing pu/pd in a patient with hypercalcemia? what diagnostics can you use to prove this?
inhibits binding of ADH to receptors on renal tubules
measure serum or plasma calcium
what is the mechanism causing pu/pd in a patient with hyperadrenocorticism? what diagnostics can you use to prove this?
glucocorticoids inhibit ADH release & inhibit the effects of ADH on renal tubules
do a LDDST, ACT stim test, or urine cortisol:creatinine ratio
what is the mechanism causing pu/pd in a patient with hyperthyroidism? what diagnostics can you use to prove this?
increased medullary blood flow & psychogenic
run a serum T4
what is the mechanism causing pu/pd in a patient with hepatic insufficiency? what diagnostics can you use to prove this?
loss of medullary concentrating gradient (low urea)
possibly psychogenic
do a chemistry panel, bile acids, blood ammonia, & abdominal imaging
what is the mechanism causing pu/pd in a patient with a pyometra & e. coli septicemia? what diagnostics can you use to prove this?
endotoxin competes with ADH binding sites on renal tubules
good history, cbc, abdominal imaging, & cultures
what is the mechanism causing pu/pd in a patient with post-obstructive diuresis? what diagnostics can you use to prove this?
osmotic diuresis due to retained solutes (especially urea)
take a good history & look at patient urine output
what is the mechanism causing pu/pd in a patient with hypoadrenocorticism? what diagnostics can you use to prove this?
mineralocorticoid deficiency results in sodium loss & renal medullary wash out
measure serum Na, K, & do an acth stim test
what is the mechanism causing pu/pd in a patient with diabetes insipidus? what diagnostics can you use to prove this?
primary - decreased ADH production
nephrogenic - defect in renal response to ADH
do a modified water deprivation test (diagnosis of exclusion)
what is the mechanism causing pu/pd in a patient with psychogenic issues? what diagnostics can you use to prove this?
primary - unexplained increase in water intake + renal medullary washout
do a modified water deprivation test (diagnosis of exclusion)
what is the mechanism causing pu/pd in a patient with an iatrogenic cause? what diagnostics can you use to prove this?
take a good history & look at fluid therapy
what is the mechanism causing pu/pd in a patient with primary hyperaldosteronism? what diagnostics can you use to prove this?
resistance to the effects of ADH in renal tubules & disturbed regulation of ADH release
measure serum Na/K, take blood pressure measurements, do an abdominal ultrasound, & acth stim test (aldosterone)
what is the mechanism causing pu/pd in a patient with acromegaly? what diagnostics can you use to prove this?
results in diabetes mellitus causing pu/pd
measure IGF-1 levels & do a ct scan
what is the mechanism causing pu/pd in a patient with renal glucosuria? what diagnostics can you use to prove this?
osmotic diuresis due to glucosuria
measure bg & urine glucose
what is the mechanism causing pu/pd in a patient with hypokalemia? what diagnostics can you use to prove this?
nephrons are less responsive to ADH
measure blood K
what are some history clues that lead to a suspicion of pu/pd in companion animals?
litterbox needs to be changed more often
dog needs to go outside to urinate more often/has accidents in the house
water bowl needs to be refilled more often or pet is seeking more water sources
last estrus cycle!!!
T/F: water intake can usually be measured but urine output is more difficult to measure
true
what should you look for on physical exam when working a patient up for pu/pd? what are some common findings?
palpate the liver & kidneys
endocrine alopecia and/or pendulous abdomen may suggest hyperadrenocorticism
palpate the thyroid glands
lymphadenopathy
anal sac mass
recent onset cataracts suggesting diabetes mellitus
T/F: if a patient presents for pu/pd & has a usg < 1.030, it is reasonable to evaluate for causes
true
what is commonly seen on a cbc of a patient with pu/pd?
stress leukogram - absence may support hypoadrenocorticism
evaluate for inflammatory leukogram - may support pyelonephritis
polycythemia
what is commonly seen on chemistry panels of patients with pu/pd?
BUN, creatinine, SDMA - low urea disrupts medullary concentration gradient, so you need to evaluate for azotemia and/or elevated SDMA
liver enzymes - may be elevated with liver disease or cushings/feline hyperthyroidism
calcium - high levels can cause pu/pd
hyperglycemia - diabetes mellitus or euglycemia with primary renal glucosuria
albumin - may be decreased with liver disease, addison’s & some renal diseases or can be increased with dehydration
why may you have a hyposthenuric usg in a pu/pd patient?
psychogenic polydipsia or absent ADH/abnormal response to ADH
if you have a usg that is less than or equal to 1.007, what does that exclude as a cause of pu/pd?
generalized renal dysfunction is excluded
what is the preferred collection method for urine culture for a patient that is pu/pd?
cystocentesis
T/F: lower urinary tract infections are not expected to cause polyuria but do cause pollakiuria
true
how can an owner monitor the pet at home for polydipsia?
measure water intake at home for 2-3 days by measuring the amount of water put in the bowl & the amount left at the end of the day while isolating other pets & home & restricting other water sources
what is normal water intake a day for a dog? what classifies them as polydipsic?
<60 ml/kg/day is normal
> 100 ml/kg/day is abnormal
what is the mechanism of thirst from decreased blood volume caused by?
angiotensin II stimulates thirst
what is required for the body to have normal urine concentrating ability?
adequate renal tubular function
hypertonic renal medullary interstitium (urea & Na)
ADH from the hypothalamus
renal tubular response to ADH
what is the autoregulatory system in the kidneys?
made up by the macula densa cells in the walls of the late distal tubules that maintains gfr despite changes in arterial blood pressure
what happens to the autoregulatory system if filtrate is flowing too slowly?
vasodilation of the afferent arterioles occurs & there is an increase in gfr
what happens to the autoregulatory system if filtrate is flowing too rapidly?
vasoconstriction of the afferent arterioles occurs & there is a decrease in gfr
what is gfr?
amount of fluid filtered from the blood into the capsule each minute
what is net filtration pressure in the nephron?
result of forces that push fluids into bowman’s capsule against those that push fluids out
what makes up the process of urine formation in the nephrons?
begins with glomerular filtration - hydrostatic pressures forces fluids & solutes through the membrane
net filtration pressure - result of forces that push fluids into bowman’s capsule against those that push fluids out
gfr - amount of fluid filtered from the blood into the capsule each minute
what is included in active tubular resorption in nephrons?
glucose, amino acids, vitamins, & most ions are transported with Na on carrier molecules
what is included in passive tubular resorption in nephrons?
sodium movement by active transport establishes a strong osmotic gradient - water moves by osmosis out of the filtrate
other substances follow the concentration gradient out of the filtrate (solvent drag)
what resorption is happening in the descending loop of henle?
impermeable to sodium & freely permeable to water
sodium outside of the tubule causes water to leave the tubule & sodium concentration inside the tubule increases
what resorption is happening in the ascending thin loop of henle?
permeable to sodium & impermeable to water - sodium leaves the tubule by diffusion so that the contents become more dilute
what resorption is happening in the ascending thick loop of henle?
sodium actively transported out by the Na-K-Cl cotransporter
when is ADH released?
released in response to plasma osmolality (excess water loss) or reduced blood volume (detected by baroreceptors)
what is the action of ADH?
increases water resorption in the collecting ducts - acts on the distal & collecting tubules making them permeable to water so that water is resorbed into the interstitial space (blood stream) & urine is more concentrated
