From the Guidelines
Low osmolarity oral rehydration solution (ORS) is recommended as the first-line therapy for mild to moderate dehydration in infants, children, and adults with acute diarrhea from any cause. This recommendation is based on the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1. The guidelines suggest that reduced osmolarity ORS is safe and effective for rehydrating patients with mild to moderate dehydration, regardless of the cause of diarrhea.
Key Points
- Low osmolarity ORS is recommended for mild to moderate dehydration in all age groups 1.
- Nasogastric administration of ORS may be considered in infants, children, and adults with moderate dehydration who cannot tolerate oral intake 1.
- Isotonic intravenous fluids such as lactated Ringer’s and normal saline solution should be administered in cases of severe dehydration, shock, or altered mental status and failure of ORS therapy 1.
- Maintenance fluids should be administered after rehydration, and ongoing losses in stools should be replaced with ORS until diarrhea and vomiting are resolved 1.
Evidence Summary
The safety and efficacy of ORS have been evaluated in several studies, including a meta-analysis of 17 RCTs involving 1811 patients aged <18 years from high-income and low-income countries 1. The results showed no important clinical differences in failure to rehydrate, weight gain at discharge, hyponatremia or hypernatremia, duration of diarrhea, or total fluid intake at 6 or 24 hours between children receiving ORS and intravenous rehydration therapy.
Recent Guidelines
Recent guidelines, such as the 2022 ESPEN practical guideline on clinical nutrition and hydration in geriatrics, also emphasize the importance of proper hydration in older adults, recommending subcutaneous or intravenous fluids for those with measured serum or plasma osmolality >300 mOsm/kg who appear unwell 1. However, the primary recommendation for low osmolarity ORS remains based on the 2017 IDSA guidelines for the management of infectious diarrhea 1.
From the Research
Low Osmolarity Solutions
- Low osmolarity solutions are used in oral rehydration therapy to treat dehydration caused by diarrheal illness 2
- The World Health Organization recommends a reduced osmolarity oral rehydration solution (ORS) with a glucose-containing solution 2
- Hypotonic oral rehydration solutions have been shown to produce maximum water absorption in the intestine, making them a potential optimal replacement treatment for patients with acute diarrhea 3
- The composition of these solutions can vary, but they typically contain sodium, potassium, and glucose in specific concentrations 3
Osmolality and Osmolarity
- Osmolality and osmolarity are measures of the concentration of solutions, with osmolality referring to the number of milliosmoles of solutes per kilogram of water and osmolarity referring to the number of milliosmoles of solutes per liter of solution 4, 5
- The normal range of plasma tonicity is 275-295 mOsm/kg of water, and the difference between measured and calculated osmolality is called the osmolal gap 5
- Effective osmolality, or tonicity, can be calculated using the equation: Eosm = 2 [Na+] + glucose/18 5
Clinical Applications
- Low osmolarity solutions are used to treat dehydration and maintain hydration during vigorous exercise 2
- Serum osmolality is an important measure in clinical practice, particularly in the diagnosis of disorders related to sodium, glucose, and water balance, kidney diseases, and small molecule poisonings 6
- Hypertonic states can have significant clinical consequences, including neurologic symptoms and even death, and should be promptly diagnosed and managed 6