AVP and Anxiety: Iatrogenic hyponatremia is relatively frequent in the pediatric perioperative population because of its association with several factors, such as increased secretion of vasopressin (antidiuretic hormone, ADH) in sick children due to non-osmotic stimuli (pain, stress, nausea, anxiety, and opioids) and/or intraoperative hypovolemia, which, together with the infusion of hypotonic fluids during the perioperative period, leads to excess free water (157).