5.2 Fluid, Electrolyte Imbalances & Arterial Blood Gas Analysis

🎯 Key NCLEX-RN® Clinical Takeaways

• Hyperkalemia (> 6.5 mEq/L with peaked T waves): Administer IV Calcium Gluconate FIRST to stabilize the cardiac membrane.
• Severe hyponatremia (< 120 mEq/L): Correct slowly with 3% saline (max 8-10 mEq/L/24hr) to prevent fatal Central Pontine Myelinolysis.
• Hypocalcemia: Chvostek's and Trousseau's signs signal neuromuscular tetany post-thyroidectomy; treat with IV Calcium Gluconate.
• ABG ROME rule: Respiratory Opposite, Metabolic Equal. Partial compensation: pH abnormal with both PaCO2 and HCO3- abnormal.

Electrolytes maintain cellular resting membrane potentials. Potassium imbalances are the most immediately lethal. Hyperkalemia impairs ventricular conduction, causing peaked T waves, widened QRS, and ventricular fibrillation. Calcium gluconate acts immediately to stabilize the myocardium.

Sodium imbalances produce neurological dysfunction. Hyponatremia causes cerebral edema, stupor, and seizures; rapid correction causes osmotic demyelination and locked-in syndrome.

Arterial blood gases reflect respiratory and metabolic balance. Respiratory acidosis (hypoventilation in COPD/opioids) features low pH and high CO2. Metabolic acidosis (DKA/septic shock) features low pH and low bicarbonate, compensated by Kussmaul breathing.

⚠️ Common Pearson VUE / NCLEX Traps

• Giving insulin before calcium in hyperkalemia with peaked T waves; the patient can fibrillate while waiting for insulin to work.
• Rapidly correcting chronic hyponatremia above 10 mEq/L per day, causing irreversible osmotic demyelination syndrome.