AVP and Hyponatremia: The latter, in the presence of high circulating plasma-AVP levels on admission, might have had a clinically meaningful impact on PNa levels at the end of surgery.18 Of note, almost all of the patients were able to excrete net free water, which is essential in preventing clinically important changes in PNa concentrations.19 This is also reflected in the assessment of water and electrolyte balance (Table 1), which shows that the amount of water and sodium retained was rather isotonic, thus preventing the appearance of hyponatremia.