Which of the following crystalloid solutions has the most similar electrolyte composition to plasma and is considered a 'balanced' solution?

Explanation

## Balanced Crystalloid Solutions in Perioperative Fluid Therapy ### Definition of Balanced Solutions **Key Point:** Balanced crystalloids are designed to mimic the electrolyte composition of plasma more closely than normal saline, reducing the risk of hyperchloremic metabolic acidosis and hypernatremia. ### Electrolyte Composition Comparison | Solution | Na⁺ (mEq/L) | K⁺ (mEq/L) | Cl⁻ (mEq/L) | Ca²⁺ (mEq/L) | Mg²⁺ (mEq/L) | Lactate (mEq/L) | pH | |---|---|---|---|---|---|---|---| | **Plasma** | 140 | 5 | 103 | 2.5 | 1.5 | — | 7.4 | | **Lactated Ringer's** | 130 | 4 | 109 | 3 | 0 | 28 | 6.5 | | **Normal Saline** | 154 | 0 | 154 | 0 | 0 | 0 | 5.0 | | **5% Dextrose in Water** | 0 | 0 | 0 | 0 | 0 | 0 | 3.5 | | **3% Hypertonic Saline** | 513 | 0 | 513 | 0 | 0 | 0 | 5.0 | ### Why Lactated Ringer's is "Balanced" 1. **Chloride concentration** is lower (109 mEq/L vs. 154 in normal saline), reducing hyperchloremic acidosis risk 2. **Potassium and calcium** are present, mimicking plasma composition 3. **Lactate buffer** (28 mEq/L) is metabolized by the liver to bicarbonate, providing mild alkalinizing effect 4. **Osmolality** (~273 mOsm/L) is closer to plasma (~290 mOsm/L) ### Clinical Pearl **High-Yield:** Large-volume normal saline infusions (>1 L) cause: - Hyperchloremic metabolic acidosis (excess Cl⁻ overwhelms renal excretion) - Hypernatremia (Na⁺ 154 mEq/L vs. plasma 140) - Increased risk of acute kidney injury and poor outcomes Lactated Ringer's avoids these complications and is now preferred for perioperative fluid resuscitation in most guidelines. ### Contraindications to Lactated Ringer's **Warning:** Avoid in: - Severe hepatic dysfunction (cannot metabolize lactate → lactic acidosis) - Hyperkalemia (contains 4 mEq/L K⁺) - Hypercalcemia (contains 3 mEq/L Ca²⁺) ### Mnemonic **Mnemonic: "LR is BETTER" = Balanced Electrolytes, Tailored composition, Tissue-friendly, Eliminates acidosis, Reduces complications** [cite:Miller's Anesthesia Ch 41]