Vasopressin (also known as anti diuretic hormone, ADH) is synthesized in the supraoptic and paraventricular nuclei of the hypothalamus, and often released into the posterior pituitary gland or neurohypophysis through the vasopressin-releasing neurons.
A TRIPHASIC response usually follows pituitary surgeries; they are:
PHASE ONE: CENTRAL DIABETES INSIPIDUS/HYPERNATREMIA.
There’s decreased release of vasopressin following pituitary surgery due to trauma or ischemia/shock of the vasopressin-releasing neurons in the hypothalamus. This results in the passage of large amount of diluted urine (polyuria) and increased thirst (polydypsia). In response to the polyuria in this phase, extracellular sodium level rises (a condition known as HYPERNATREMIA) in a bid to compensate for the water loss.
Monitor urinary output every hour.
Ensure strict intake and output monitoring.
Measure urine specific gravity.
Give fluid replacement with 5% dextrose water (free water).
Administer IV Desmopressin (DDAVP).
PHASE TWO: OLIGURIA/HYPONATREMIA
In this phase, there’s leakage of vasopressin from the posterior pituitary gland, leading to the excessive release of pre-synthetic vasopressin – a condition known as syndrome of inappropriate anti diuretic hormone (SIADH). This condition potentiates fluid retention; which is further complicated by the interventions given in phase one. Hyponatremia is the expected response to fluid retention. Therefore, urinary output is reduced and patient becomes oliguria.
PHASE THREE: CHRONIC DIABETES INSIPIDIS/HYPERNATREMIA.
Individuals may or may not enter this phase. It takes the death of 80-90% of vasopressin-releasing neurons to develop a chronic diabetes insipidus. The normal, uncomplicated pituitary surgery should resolve in phase two.
DDAVP means 1-Desamino 8-D Arginine Vasopressin.