AVP and susceptibility to pneumonia measurement: The pathophysiological mechanisms behind the occurrence of the syndrome of inappropriate antidiuretic hormone secretion in pneumonia as in COVID-19 are not fully elucidated but may be due to a non-osmolar release of AVP secondary to intravascular fluid depletion, activating the baroreceptors, which in turn activates the rennin-angiotensin-aldosterone system [19].