AVP and Hyponatremia: Although hyponatremia is a frequent feature of sepsis and critical illness in general, and is particularly associated with pulmonary disease through the mechanism of the syndrome of inappropriate anti-diuretic hormone secretion (SIADH) and others, the prevalence and degree of hyponatremia in our patients who had symptoms of pneumonia for < 1 week is somewhat disproportionate to the expected and may represent a distinguishing feature [47].