5.2 Fluid, Electrolyte Imbalances & Arterial Blood Gas Analysis
Analyze life-threatening electrolyte shifts (potassium, sodium, calcium, magnesium) and master the ROME rule for arterial blood gas compensation.
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.
A client with end-stage renal disease who missed two hemodialysis sessions presents with extreme generalized muscle weakness. The serum potassium is 7.1 mEq/L. The 12-lead ECG shows tall, peaked T waves, prolonged PR interval, and widening of the QRS complex. Which intravenous medication must the nurse administer first?