Osmolality and Solute Concentration—Their Relationship with Oral Hydration Solution Effectiveness: An Experimental Assessment

Abstract

ABSTRACT. The role of electrolyte, carbohydrate, and base composition, a s well a s osmolality, of oral hydration solutions (OHS), was investigated using a nonabsorbable marker and tritiated water in an in vivo intestinal perfusion system in rats. The O H S tested were the World Health Organization recommended formula, containing 90 mEq/ liter sodium and 11 1 m M glucose, which was taken a s the reference solution; five variants of this solution with different sodium and glucose concentrations; and two solutions without sodium, i.e. isotonic glucose and deionized water. Also tested were one solution with acetate in lieu of bicarbonate, and two commercial preparations where citrate substituted for bicarbonate. The best water absorption rates were obtained with World Health Organization-type O H S characterized by a combination of low osmolality and moderate sodium and glucose content. Hypotonic O H S (190, 220, and 155 mosmol/kg) in which the sodium:glucose ratios were 60:30, 60:60, and 3055, respectively, produced mean jejunal water transport rates of 3.46, 3.20, and 2.91 pl/min/cm, respectively, whereas the standard World Health Organization O H S (330 mosmol/kg) resulted in a rate of 1.36 pl/min/cm ( p < 0.001). Similar good water absorption was achieved when Ac was the base (270 mosmol/kg and 60:111 sodium:glucose ratio) and with one of the commercial solutions (245 mosmol/kg and 50:111 sodium:glucose ratio). The reference World Health Organization O H S allowed for sodium absorption, a s did the O H S with sodium:glucose ratios of 90:45,60:30,60:60, and acetate-containing 60:111. Sodium a t a concentration of 30 mEq/liter or less resulted in the efflux of this electrolyte. High glucose concentration and lower osmolality exacerbated this effect. The results obtained in this investigation may assist in better evaluating O H S and in selecting modified formulae geared to specific hydration needs and possible replacement of water and sodium losses. (Pediatr Res 19: 894-898,1985 OHS, the cost factor, and other considerations (1-4). The most important points involved in the formulation of OHS have been sodium and carbohydrate concentrations and osmolality. The rationale for the amount of sodium, potassium, and chloride provided in the OHS has been related to the degree of potential electrolyte losses during the illness (5, 6).Several field and experimental studies have tested the suitability of the OHS proposed by the WHO, containing 90 mEq/liter sodium, or of a variant with a lower sodium content (7-10). It is generally accepted that both can accomplish rehydration, with the WHO formula also allowing for the replenishment of sodium. The amount of glucose added (20 g/liter or 1 1 1 mM) has been considered optimum.Earlier reports had provided conflicting information on the stoichiometry of sodium:glucose cotransport and the fluxes of electrolytes and water, either from in vitro (1 1-14) or from in vivo studies, including animal experimentation (15, 16) and clinical trials (I 6, 17).We previously evaluated the rela...

Effect of Bicarbonate or Base Precursor on Water and Solute Absorption from a Glucose-Electrolyte Solution in the Human Jejunum

“…There was greater absorption of sodium but not of water from the acetate-containing solution compared with the bicarbonate con taining solution. In the perfused rat jejunum a similar effect has been shown where a GES containing acetate produced increased so dium and similar water absorption com pared with GES containing bicarbonate or citrate [26],…”

Studies of water and electrolyte movement from oral rehydration solutions (rice‐ and glucose‐based) across a normal and secreting gut using a dual isotope tracer technique in a rat perfusion model

“…However, similar studies with reduced¯ow rates (0.2 mL/min) failed to show Na + absorption. 8 Moreover, maximal glucose absorption has been demonstrated at¯ow rates of 0.36 mL/min.…”

“…However, unidirectional¯ow of water has been determined using a single tracer by a number of researchers. 8,9 Male Wistar rats (150±270 g) were fasted for 18 h with free access to water. After the fasting period, 50 lCi of tritiated water (Amersham), was administered orally via a gavage.…”

Water and Solute Absorption From Carbohydrate-Electrolyte Solutions in the Human Proximal Small Intestine: A Review and Statistical Analysis

“…• Water absorption is proportional to the pore size in the cell membranes of the intestine (Travis & Menzies, 1992) and negatively correlated to osmolality (Hunt, Elliott, Fairclough, Clark, & Farthing, 1992;Shi et al, 1995;Wapnir & Lifshitz, 1985). This osmotic effect on water absorption is gradually attenuated from the duodenum to the jejunum and ileum.…”

“…Intestinal water absorption is inversely related to the osmolality of the solution (Cunha Ferreira et al, 1992;Hunt, Carnaby, & Farthing, 1991;Wapnir & Lifshitz, 1985;Wapnir, Litov, Zdanowicz, & Lifshitz, 1991). Hypotonic solutions (~200 mOsm/kg) produce greater water absorption than iso-or hypertonic solutions (Hunt et al, 1989;Hunt, Thillainayagam, et al, 1992).…”