What is the concentration of Na (meq/L) in normal saline?
**Core Concept**
Normal saline, also known as 0.9% sodium chloride solution, is a sterile solution containing sodium chloride in water. It is used as a fluid and electrolyte replenisher in various medical conditions. The concentration of sodium in normal saline is crucial in maintaining fluid balance and electrolyte homeostasis.
**Why the Correct Answer is Right**
Normal saline has a concentration of 0.9% sodium chloride, which translates to approximately 154 mEq/L of sodium. This concentration is crucial for maintaining isotonicity with human plasma, allowing for the free movement of fluids without causing hemolysis or cellular damage. The sodium ion (Na+) concentration in normal saline is regulated by the concentration of sodium chloride, which is 9 grams per liter.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because normal saline is isotonic, meaning it has the same osmotic pressure as human plasma, which contains approximately 135-145 mEq/L of sodium. Any concentration below this would be hypotonic.
**Option B:** This option is incorrect because normal saline does not contain 0.9% of sodium chloride, but rather 0.9% of sodium chloride dissolved in water, which is equivalent to 154 mEq/L of sodium.
**Option C:** This option is incorrect because normal saline is not hypertonic; it does not contain a higher concentration of sodium than human plasma.
**Clinical Pearl / High-Yield Fact**
When administering fluids, it is essential to consider the electrolyte content, particularly sodium, to avoid complications such as hyponatremia or hypernatremia. Normal saline is often used in emergency situations to rapidly expand intravascular volume, but it should be used judiciously to avoid diluting the serum sodium concentration.
**Correct Answer: B. 154**