MO176IS IT REALLY INDICATED TO INCREASE FLUID INTAKE IN ELDERLY PATIENTS DURING SUMMER MONTHS?

Background and Aims Thirst mechanism is essential to maintain an adequate osmolarity and homeostasis. During summer heat waves, there is an increased morbidity and mortality in elderly patients that has led to generally recommend an increase in fluid intake in all elderly patients beyond thirst stimulation, even in those independent patients with free access to water. The aim of this study was to observe the differences in calculated serum osmolarity (cOsm) between young, elderly and very elderly patients who were neither institutionalized nor hospitalized, in different seasons throughout the year. Method We conducted a retrospective cross-sectional study in outpatients between 18-104 years old that had undergone a blood test between July 2019 and January 2020, in which serum osmolarity could be calculated. Patients with serum creatinine above 1.5 mg/dl were excluded. Results The study included 45236 blood samples from 41132 patients, 56.1% were female. 50% of patients were between 18 and 65 years old, 45.4% were between 65 and 85 years old and 4.6% were >85 years old. The mean cOsm in patients between 18-65 years was 288.3 mOsm/kg, compared to 289.8 mOsm/kg in those between 65- 85 years old (p<0.0001). In patients >85 years, mean cOsm was 289.4 mOsm/kg. When comparing cOsm between different seasons of the year, cOsm in summer months was about 1 mOsm/kg higher than in autumn-winter (288.9 mOsm/kg vs 287.8 mOsm/kg in young patients, p=0.0001; 290.5 mOsm/kg vs 289.4 mOsm/kg in elderly patients, p=0.0001). In the very elderly (>85 years) the difference was smaller and non-significant (289.6mOsm/kg vs 289.1mOsm/kg). Conclusion Under physiologic conditions, patients >65 years have a slightly higher calculated serum osmolarity than younger patients, nevertheless staying within normal range. These differences only increase in 1 mOsm/kg during the summer months. Therefore, it is not indicated to force an increase in fluid intake in the elderly or very elderly population under physiologic conditions.