Urology Flashcards
Poydipsia
water intake >90-100ml/kg/day in dogs, 50 cats
Polyuria
urine output >50ml/kg/d
Nephrogenic Diabeties Insipidus
Partial or complete lack of response to ADH in the kidneys.
Primary: congenital lack of ADH receptors, rare
Secondary: variety of causes. Most common cause of PU/PD in small animals.
Osmotic diuresis
Concentration of osmotic solute in glomerular filtrate exceeds the proximal tubular capacity for reabsorption therefore impairs passive reabsorption of water, leading to increased obligatory water loss.
Causes of osmotic diuresis
Glucosuria Chronic Kidney Disease Post-obstructive diuresis Osmotic diuretic administration (mannitol) High salt diet
Central diabetes insipidus
ADH deficiency
Causes of central diabetes insipidus
idiopathic
trauma
brain neoplasia
post-hypophysectomy (pituitary tumour removal)
Low renal medullary tonicity
Due to increased renal tubular flow and volume. Decreased reabsorption of sodium and urea, reduces medullary interstitial hypertonicity.
Causes of low renal medullary tonicity
Renal medullary washout - PU/PD cases due to large volumed of urine. Patients on IVFT. Hepatic disease CKD Hypoadrenocorticism Hyperthyroidism Low protein diet
Primary polydipsia
‘psychogenic polydipsia’ poorly understood.
?behavioral
?altered function or inappropriate stimulation of the hypothalamic thirst centre?
May have a role in PU/PD associated with hyperthyroidism, hepatic disease and GI disease.
Drugs which may cause PU/PD
Glucocorticoids
Anti-epileptics
Progestogens
Diuretic treatment
Cancers which can cause PU/PD via paraneoplastic hyperglycaemia
Lymphoma & anal sac carcinoma
Water deprivation test
Should only be performed if the only potential differentials left for PU/PD are CDI, NDI and primary polydipsia.
Ideally discuss with a specialist beforehand.
Designed to determine weather endogenous ADH is released in response to dehydration and if the kidneys can respond normally to it.
Therapeutic desmopressin trial
Can be considered in lieu of a water deprivation test. Involves monitoring water intake and urine output following administration of desmopressin (synthetic ADH)
Dysuria
difficult or painful urination
