Approach to PU/PD Flashcards
Define polyuria
> 50ml/kg/day of urine
define polydipsia
> 100ml/kg/day intake (dogs)
50ml/kg/day (Cats)
what are the main differentials for primary polydipsia
centrally mediated disease (neoplasia, endocrine effects, compensating for losses)
OR
physiology ( toxicity, exercise, high temps)
what does ADH do
increases aquaporin density and increases reabsorption from tubules.
what is osmotic diuresis
if urine contains solutes above normal values (e.g. glucose in diabetes mellitus) this ‘draws’ water into the tubules increasing output.
what is medullary solute washout
loss of solutes from the medulla, also leads to a concentration gradient and osmotic water loss.
how can increased GFR lead to polyuria
hypertension will lead to increased filtration in excess of the kidneys resorptive capability.
Is primary nephrogenic diabetes insipidus common
No rare
what are the 2 substances that commonly cause osmotic diuresis
glucose
sodium
describe Fanconi’s syndrome
Proximal tubular disease and loss of glucose, but amino acids, bicarb, electrolytes, lactate, etc.- basically animasl looses ability to reabsorp anything
List 2 things that can cause reduced medullary/interstitial tonicity
low protein diet
medullary washot
what is a Phaeochromocytoma
Catecholamine producing tumour of the adrenal gland i.e. adrenaline
RARE
If you see signs of dehydration in animal that is PU/PD what is most likely cause
primary polyuria
If you see a USG with >1.030 with normal hydration in PU/PD patient what should you think
normal- owner wrong
or
primary polydipsia driving intermittent polyuria-
If you see a USG with >1.030 with dehydration what should you think
animal is normal and dehydrated
OR
check for:
- glucosuria- diabetes mellitus
- Fanconis
- renal tubular glycosuria
If you see a USG with <1.030 with normal hydration what should you think
Consider primary polydipsia again, but consistently present.
means that they are pushing more fluid through kidneys
If you see a USG with <1.030 with dehydration what should you think
Consider primary polyuria and intrinsic renal disease or extrinsic disease affecting renal function.
If you see a USG with <1.006 (Hyposthenuria what should you think
Diabetes insipidus
primary polydipsia
hypercalcemia
hyperadrenocorticism
what is considered active dilution by kidneys
<1.006 USG
what do you do if you suspect primary polydipsia
Could this just be physiological
Toxin exposure
GI losses
rule out 3rd space loss- POCUS
check fro haem and biochem- look for endocrine and osmolarity changes
describe how to work out osmalility of blood
(Na + glucose + BUN) x 2 = osmolality
all values straight from biochem
what is the normal osmalalility of blood
dog 290-310
cat 308-335
what is azotaemia
elevated urea and creatinine
what is warning sign for a phaeochromocytoma
inappropriate hypertension
because it —> Produces adrenaline —> vasoconstricts peripheral vessels —-> increasing central blood pressure
describe what causes pre-renal azotaemia
fluid loss i.e. haemoconcentration and reduced renal blood flow (eventually becomes renal also due to renal hypoxia)
give fluids
what can cause post-renal azotaemia
obstruction or uroabdomen
why is post renal azotaemia dangerous
Hyperkalaemia can develop rapidly—> bradycardia
what can cause renal azotaemia
AKI
or
chronic renal failure
describe the difference in phosphorus between AKI and CKD
AKI- – Phosphorous increase is marked.
CKD- Phosphorous increase is more moderate, and consistent with the creatinine elevation
describe how to tell the difference between AKI and CKD
phosphorus
clinical signs
CKD- 2/3rd renal mass loss
anaemia- CKD- due to reduced EPO production
what does water deprivation test differentiate between
primary polydipsia, central diabetes insipidus and nephrogenic diabetes insipidus.
what do you see with water deprivation test with primary polydipsia
USG improves with just water deprivation
what do you see with water deprivation test with central diabetes insipidus
USG improves with vasopressin (ADH)
what do you see with water deprivation test with nephrogenic diabetes insipidus
USG never improves
which is more commonly the primary issue, polyuria or polydipsia
polyuria
what can cause primary polyuria
Intrinsic renal issue or extrinsic effect on kidneys
-ADH decrease
osmotic diuresis
medullary solute washout
interstitial tonicity reduction
increased GFR
CKD
AKI
what is interstitial tonicity reduction
reduced concentration gradient across the interstitium
what can cause a decrease in ADH
no ADH production - central diabetes insipidus
OR
reduced ADH sensitivity - nephrogenic diabates insipidus
what is central diabetes insipidus
no ADH production or release
what is nephrogenic diabetes insipidus
reduced ADH sensitivity or response
List some common causes of secondary nephrogenic diabetes insipidus
cushings
Addisons
hyperthyroidism
pyometra
hypercalcaemia
drugs
what can cause a post obstructive diuresis
blocked cats
what diagnostic test distinguishes between primary PU or PD
USG
what does a low osmolality indicate
primary polydipsia
List some diagnostic tests to look for a PD cause
history
POCUS
bloods
neuro exam
how can we identify renal azotaemia
USG will be isosthenuric, electrolyte disturbances are likely present
why is the water deprivation test controversial
if you do the test and your animal is polyuric, not polydipsic, it will die
how can you differentiate between psychogenic polydipsia and diabetes insipidus
modified water deprivation test and ADH administration
What are the possible mechanisms behind primary polyuria?
ADH or its receptor,
Osmotic diuresis,
Medullary solute washout
Interstitial tonicity reduction
increased GFR
List the 5 main differentials for polyuria caused by reduced ADH sensivity/response?
Cushings
addisons
hyperthyroidism
pyometra
hypercalcaemia
What are the main differentials for polyuria caused by osmotic diuresis?
Diabates Mellitus
post-obstructive diuresis- e.g. blocked cats
Addison’s
result of diuretics
What disease is common in Basenjis relating to glucose diuresis causing a proximal tubular disease?
Fanconi’s syndromes
What do we want to look for on clinicial exam with the PU/PD patient?
Body condition
signs of dehydration
neuro-signs
dermatological conditions
signs of other body systems
Why is it important to do a POCUS with a PU/PD patient with suspected primary PD?
Rule out third space loss
What next steps would we undertake with a PU/PD patient with suspected primary PU?
Triage if needed, POCUS, urinalysis, biochem and haem, bp, further imaging +/- FNA/renal biopsy
How do we rule out pre-renal azotaemia
give fluids and see if urea and creatinine restore to normal
What is the top differentials for pre-renal azotaemia
Addisons
How do we diagnose an obstruction or uroabdomen?
POCUS to check for blockages or free fluid
Why can CKD result in non-regenerative anaemia?
Due to damage, kidneys produce less EPO (erythropoietin) = less RBC are produced`
what do you when performing a water deprivation test
over 3-5days you can gradually restrict water and then complete removal of water until 5% dehydration is achieved. If doesn’t improve give ADH (vasopressin).
