thereby further compromising the extracellular volume and stimulating vasopressin release. Na+ and/or K+ depletion alone would not be expected to cause marked hyponatremia because water excretion normally increases as the serum Na+ concentration falls. However, because thiazides interfere with renal water excretion, they impair this normal osmoregulatory response. Thus, as in most patients with hyponatremia, urine osmolality is inappropriately high relative to the osmolality of plasma and often exceeds it
The reason why individuals with reduced body mass are more prone to complications from diuretics remains puzzling. Plasma Na+ level is determined by the ratio between the amount of exchangeable Na+ and potassium (K+) and the total body water Thus, it is conceivable that Na+ concentration might change to a greater degree in a subject with smaller body size, and hence less total body water. Besides, small body mass or muscle wasting might also signify underlying illness