Page 83 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Sodium and Water: Hypernatremia and Hyponatremia 73

History of polydipsia/polyuria

Rule out iatrogenic causes

Normal physical exam Apparently sick

Verify by measurement at home, if necessary

CBC, biochemical profile, urinanalysis

Negative Positive

Rule out (confirm with specific tests):
•Hyperthyroidism •Postobstructive diuresis •Hepatic failure
•Renal failure •Pyometra •Polycythemia
•Diabetes mellitus •Hypoadrenocorticism •Hypercalcemia
•Renal glucosuria •Hyperadrenocorticism •Hypokalemia

Nondehydrated Dehydrated
Rehydrate
Water deprivation test Creatinine clearance test
Rehydrate
Positive Negative Intermediate Normal Decreased
APP CDI Patrial CDI CDI RI
NDI APP + MSW NDI
APP + MSW RI APP

Exogenous ADH test

Positive Intermediate Negative
CDI APP + MSW NDI
APP + MSW

Partial water deprivation or Hickey-Hare test

Positive Negative
APP NDI
Figure 3-15 Clinical approach to the patient with polydipsia and polyuria. APP, Apparent psychogenic
polydipsia; CBC, complete blood count; CDI, central diabetes insipidus; MSW, medullary solute washout; NDI,
nephrogenic diabetes insipidus; RI, renal insufficiency with solute diuresis. (From Fenner WR. Quick
reference to veterinary medicine, 2nd ed. Philadelphia: JB Lippincott, 1991: 110.)

MODIFIED WATER DEPRIVATION mOsm/kg in normal dogs after 24 hours of water depri-
TEST vation. 116 At this time, 2 to 3 U of aqueous vasopressin
was administered subcutaneously and the urine osmolal-
A modified water deprivation test has been described for
the diagnosis of polyuric disorders in dogs. Water is ity determined at 1 and 2 hours after injection. Further
removed from the animal’s cage and the urinary bladder increase in urine osmolality after administration of vaso-
pressin should not exceed 10% in normal dogs. In this
emptied, after which urine osmolality or specific gravity is
study, dogs with CDI showed an average 292% increase
measured and the bladder emptied on an hourly basis.
in urine osmolality after aqueous ADH, dogs with partial
Maximal urine solute concentration is defined as occur-
CDI an average 28% increase, and dogs with hyperadre-
ring whenever less than a 5% increase in urine osmolality
nocorticism an average 20% increase. The time required
occurs on sequential determinations. This maximal con-
to develop dehydration ranged from 3 to 11.5 hours in
centration occurred at a mean urine osmolality of 1414