Question

Which of the following is an isotonic, alkalinizing, replacement solution?

• A. Normal saline
• B. Ringer's solution
• C. Ringer's lactate
• D. 5% dextrose in 0.45% saline solution

Hint:

Fluids containing metabolizable anions like lactate, acetate, or gluconate are converted into bicarbonate by the liver or muscles.
This makes them alkalinizing solutions, which are highly useful for managing metabolic acidosis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Fluid therapy is a cornerstone of veterinary critical care.
Crystalloids are categorized based on their osmolarity relative to plasma (isotonic, hypotonic, hypertonic), their primary clinical purpose (replacement vs. maintenance), and their impact on acid-base balance (acidifying vs. alkalinizing).

Step 2: Detailed Explanation:
Let us evaluate each fluid option:
- Normal Saline (0.9% NaCl) (A): This fluid is isotonic but contains high concentrations of sodium and chloride (\(154 \text{ mEq/L}\) each).
The high chloride content can lead to hyperchloremic metabolic acidosis, making it an acidifying solution.
- Ringer's Solution (B): This is an isotonic solution containing sodium, chloride, potassium, and calcium, but it lacks any buffering agent, making it slightly acidifying.
- Ringer's Lactate (Lactated Ringer's Solution, LRS) (C): This is an isotonic crystalloid solution designed for volume replacement.
It contains sodium, chloride, potassium, calcium, and sodium lactate.
In the body, the liver metabolizes the lactate ions into bicarbonate ions (\(\text{HCO}_3^-\)).
This generation of bicarbonate provides a buffering effect, making Ringer's lactate an alkalinizing solution ideal for correcting metabolic acidosis.
- 5% Dextrose in 0.45% Saline (D): This is initially a hypertonic solution.
Once the dextrose is metabolized, it becomes hypotonic and acts as a maintenance fluid rather than an alkalinizing replacement solution.

Step 3: Final Answer:
Ringer's lactate is the correct example of an isotonic, alkalinizing, replacement solution.