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Question:

The mother of a 7-year-old boy calls the clinic due to a 3-day history of diarrhea.  The patient initially had nausea with vomiting on the first day but has since been able to keep down crackers soaked in apple juice.  He now has voluminous watery diarrhea several times per day.  Several other children in his classroom have also been ill with similar symptoms.  The physician schedules the family to come to the office in 2 days and recommends an oral rehydration solution in the meantime.  The solution contains dextrose and sodium in equimolar amounts, as well as a small amount of potassium and citrate.  Which of following best describes the role of dextrose?

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Explanation:

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Oral rehydration solution

Glucose

  • Enhances sodium absorption through cotransport
  • Provides trivial calories

Sodium

  • Determines the intravascular volume status
    (major extracellular osmole)

Potassium

  • Replaces diarrheal potassium loss

Citrate

  • Converts to bicarbonate to buffer metabolic acidosis

Total osmolality ≈ 300 mOsm/L.

This patient has acute diarrhea likely due to viral gastroenteritis.  Because he is able to tolerate intake by mouth (ie, no severe nausea or ongoing vomiting), an oral rehydration solution (ORS), such as Pedialyte, is an appropriate treatment.  Acute diarrhea causes loss of total body water and electrolytes, which places patients at risk for several complications:

  • Hypovolemia is due to intestinal loss of sodium, the major extracellular osmole that maintains circulating volume status.  Sodium is absorbed at the gut brush border by 1:1 cotransport with glucose via sodium-glucose luminal cotransporter-1 (SGLT-1) lining the apical surface of enterocytes.  Therefore, all ORSs contain sodium and dextrose (ie, D-glucose) in equimolar amounts.
  • Metabolic acidosis (with normal anion gap) is due to loss of bicarbonate in diarrheal secretions.  ORSs typically contain citrate, which is metabolized to bicarbonate in the liver, providing a buffering capacity to help correct the acidosis (Choice A).
  • Hypokalemia is due to loss of potassium-rich diarrheal secretions.  ORSs typically contain a modest amount of potassium, quickly absorbed by passive diffusion in the small intestine.

Solutions such as fruit juices that have high sugar content (eg, glucose ≥50 g/L) are generally avoided because they may induce a superimposed osmotic diarrhea.  The total osmolality of ORSs is designed to be roughly isotonic to the gut lumen (Choice B).

(Choice D)  Dextrose is provided at 5% (eg, D5W) for intravenous fluids to prevent osmotic swelling and hemolysis of red blood cells, which would occur with true free water.  However, enterocytes are already bathed in a rich mucous layer containing osmoles; they do not lyse even when drinking pure water.

(Choice E)  Because the concentration of dextrose in ORSs is limited, they provide only a trivial caloric content (eg, 75 kcal/L).  Caloric deprivation is well tolerated during acute illnesses such as gastroenteritis; patients can safely fast for several days.  However, hydration and intravascular volume status must be maintained.

Educational objective:
Oral rehydration solutions contain equimolar amounts of dextrose (glucose) and sodium, which are absorbed through intestinal cotransport to maintain intravascular volume status.  They also contain potassium to compensate for gastrointestinal losses, and citrate to buffer metabolic acidosis.