Endocrine Abstracts

Introduction

Institutional campaigns, and some health care professionals, encourage the elderly to drink large quantities of fluids, regardless of their level of thirst. Furthermore, SIADH-inducing medications can often cause dryness of mouth. Thus, patients when diagnosed with SIADH can have a high fluid intake (FI), drinking in the absence of thirst. However, fluid restriction, considered the first step in therapy of mild/moderate SIADH hyponatremia, has a poor evidence base, shows an irregular response, can interfere with the intake of protein in solid foods, and should not be used in intense heat. We studied the response of SIADH patients with a history of drinking large volumes of fluids without thirst (HHFI) to simple ’hygienic’ fluid intake (HFI) measures.

Methods

Retrospective study of 34 patients diagnosed with SIADH and HHFI in a monographic hyponatremia outpatient clinic of a University hospital in Madrid, Spain. HFI: patients were instructed to drink only when thirsty, unless eating solids, and rinse without swallowing when dryness of the mouth and not thirst was present. Those attaining eunatremia were classified by Urine Osmolality (UOsm). Patients with Primary Polydipsia (UOsm ≤ 100 mOSm/kg) were excluded. Serum Sodium (SNa) in mmol/l. UOsm in mOsm/kg. Eunatremia was defined as a SNa 135–145. SPSS 25.

Results

Mean age 72 (SD: 15) years, 20/34 (58.2%) women. Nadir SNa: 123 (SD: 6.7). The initial daily fluid Intake ranged from 2.5–10 l, median: 3.2 l [IQR 2.99–4.00]. Mean SNa at the start of HFI: 130 (SD: 5). Following HFI, 26/34 (76.5%) attained eunatremia: mean SNa 138.7 (SD: 3) P < 0.01. When classified by UOsm at diagnosis, eunatremia was achevied by 8/10 (80%) with UOsm 101–200; by 5/9 (56%) with UOsm 201–280; by 8/10 (80%) with UOsm 281–600, and 3/5 (60%) with UOsm > 600. When a UOsm cut-off point of 280 was used, 14/19 (73.6%) with UOsm 101–280 reached eunatremia, and 11/15 (73.3%) with UOsm > 280. In no patient was nutritional status worsened. 8/10 non-responders were treated with tolvaptan, achieving eunatremia. 2/10 non-responders were lost to follow-up.

Conclusions

Some SIADH patients at diagnosis have a history of drinking large volumes of liquids in the absence of thirst. Instruction directed towards limiting fluid intake to drinking when thirsty and at meals, as well as distinguishing between thirst and dryness of mouth, can permit attainment of eunatremia in a majority of these subjects, regardless of UOsm at diagnosis.