While two-thirds of diabetic ketoacidosis and hyperglycemic hyperosmolar states are associated with infections, many episodes develop with minimal or no apparent causation. In these settings, dehydration may be the clinical presentation of the altered diabetic state and can be quite profound, with deficits of whole-body water exceeding 5 L. In these individuals, weakness and confusion further reduce fluid intake and lead to greater dehydration.

The concentration of sodium chloride in the sweat of patients with cystic fibrosis (CF) is considerably higher than that of age-matched healthy individuals. In some patients, sweat sodium and chloride levels may approach their plasma concentrations. In contrast, sweat sodium and chloride levels of healthy individuals seldom exceed 60 to 70 mmol/L. As a result, patients with CF may lose excessive amounts of sodium chloride, particularly when their sweating rates are elevated during physical exercise or exposure to climatic heat (Bar-Or et al., 1992; Kriemler et al., 1999; Orenstein et al., 1983).

Unlike healthy people, whose body fluid osmolality rises as a result of sweating, the osmolality of CF patients does not increase due to high concentrations of sodium and chloride in their sweat. The excessive loss of these ions results in significantly lower serum sodium and chloride concentrations, as well as lower serum osmolality. Furthermore, drinking water while exercising in the heat can also contribute to the decrease in serum osmolality experienced by CF patients (Kriemler et al., 1999; Orenstein et al., 1983). Without elevated serum osmolality, these patients are deprived of a major trigger for thirst and, as a result, dehydration ensues. A study with 10- to 14-year-old CF patients showed that during a 3-hour intermittent exercise program in 31° to 33°C (88° to 91°F), voluntary drinking of water was only half that of age-matched controls, and the CF patients’ level of dehydration was threefold that of the controls (Bar-Or et al., 1992) (Figure 4-19).

One can stimulate the thirst of patients with CF, as with healthy individuals, by increasing the sodium chloride content in the fluid ingested. Indeed, when 11- to 19-year-old patients with CF were given a flavored drink containing 50 mmol/L of sodium chloride, their voluntary drinking increased, which was sufficient to prevent dehydration during a 3-hour exposure to exercise in the heat. Lower concentrations of sodium chloride in the drink were insufficient to trigger adequate drinking (Kriemler et al., 1999).