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 water26). 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 illness27).