The concentration of sodium ions in the standard WHO oral rehydration solutions is:
The core concept here is the composition of ORS solutions. The key point is the sodium concentration, which is crucial for effective rehydration without causing electrolyte imbalances. The WHO guidelines specify the exact concentration to ensure it's isotonic and safe.
Now, the correct answer is likely 75 mmol/L. The old formula had 90 mmol/L, but the newer version adjusted it downward. Let me verify that. Yes, the updated WHO ORS (from 2002) uses 75 mmol/L sodium, along with 20 mmol/L potassium, 10 mmol/L calcium, and 100 mmol/L glucose. The glucose helps with sodium absorption via the SGLT1 transporter in the intestines.
Looking at the options, even though they aren't provided, typical distractors might include the old 90 mmol/L, or other concentrations like 60 or 100. Each of these would be incorrect because they don't match the current WHO standard. For example, 90 mmol/L is the older version, while 60 might be too low to be effective. 100 could be a trick option if someone confuses it with another component like glucose.
The clinical pearl here is remembering the updated sodium concentration and understanding why it was changed. Students should note that the ORS is hypotonic (245 mOsm/L) compared to the previous isotonic solution, reducing the risk of hyponatremia. Also, the glucose-sodium co-transport is essential for fluid absorption.
Putting it all together, the correct answer is 75 mmol/L. The explanation should highlight the change in WHO guidelines and the rationale behind adjusting sodium levels. The other options are incorrect because they either refer to outdated formulations or incorrect concentrations. The high-yield fact is the current sodium concentration and the reason for the update to prevent complications.
**Core Concept**
The World Health Organization (WHO) oral rehydration solution (ORS) is a standardized hypotonic solution designed to treat dehydration. Its sodium concentration is critical for osmotic balance, fluid absorption via the sodium-glucose co-transporter (SGLT1), and prevention of hyponatremia during rehydration.
**Why the Correct Answer is Right**
The current WHO ORS formulation contains **75 mmol/L sodium**. This concentration was reduced from the older 90 mmol/L to lower the risk of hyponatremia, especially in children with diarrhea. Sodium drives water absorption in the intestines by coupling with glucose via SGLT1, and the adjusted concentration maintains an osmolarity of 245 mOsm/L (hypotonic), enhancing safety and efficacy.
**Why Each Wrong Option is Incorrect**
**Option A:** If this were 60 mmol/L, it would be too low to effectively drive fluid absorption via SGLT1.
**Option B:** If this were 90 mmol/L, it reflects the outdated isot