Question

What is the osmolarity of the new (reduced osmolarity) ORS in mmol per litre?

• A. 270
• B. 245
• C. 290
• D. 310

Hint:

The reduced osmolarity formula sums sodium, glucose, chloride, potassium and citrate.

Answer 1

The Correct Option is B

Step 1: The original WHO oral rehydration solution had an osmolarity of about 311 mmol per litre. Studies showed a lower osmolarity solution reduced stool output, vomiting and the need for unscheduled intravenous fluids.

Step 2: The reformulated new ORS, called the reduced osmolarity ORS, has a total osmolarity of 245 mmol per litre, achieved by lowering the sodium and glucose concentrations.

Step 3: Its key contents are sodium 75, glucose 75, chloride 65, potassium 20 and citrate 10 mmol per litre, summing to 245 mmol per litre.

Step 4: Among the options, 310 is close to the old formula and 270 and 290 are distractors, so the correct value for the new ORS is 245.