Severe electrolyte disturbances

Sodium Disorders - Salty Situations

• Hyponatremia (<135 mEq/L): Check serum osmolality (Osm).

  • Hypotonic (<280 mOsm): True hyponatremia. Assess volume status.

    Volume Status	Urine Na+	Causes
    Hypovolemic	>20	Renal loss (diuretics)
    	<10	Extra-renal loss (GI, skin)
    Euvolemic	>20	SIADH, Hypothyroidism, Adrenal Insuff.
    Hypervolemic	>20	CHF, Cirrhosis, Nephrotic Syndrome

  • Isotonic (280-295): Pseudohyponatremia (↑lipids/protein).
  • Hypertonic (>295): Hyperglycemia, mannitol. $Na_{corr} = Na_{meas} + 2.4 \times \frac{Glucose-100}{100}$.

• Hypernatremia (>145 mEq/L): Always hypertonic; net water loss.

  • Causes: Dehydration, Diabetes Insipidus (Central vs. Nephrogenic).

• ⚠️ Correction Rate is Key

  • Hyponatremia: Correct slowly to prevent Osmotic Demyelination Syndrome (ODS). Rate <8-10 mEq/L/24h.
  • Hypernatremia: Correct slowly to prevent cerebral edema.

⭐ Central Pontine Myelinolysis (a type of ODS) from rapid correction of chronic hyponatremia presents with spastic quadriparesis, pseudobulbar palsy, and altered consciousness.

Potassium Disorders - K's Kardiac Karma

• Hypokalemia (<3.5 mEq/L):

  • Causes: Diuretics (loop/thiazide), RTA, GI loss (diarrhea, vomiting), hyperaldosteronism.
  • ECG: Flattened T waves, prominent U waves, ST depression.
  • Tx: Oral/IV KCl. Max IV rate: 10-20 mEq/hr. Always check & correct ↓Mg²⁺ first!

• Hyperkalemia (>5.5 mEq/L):

  • Causes: CKD, ACEi/ARBs, K⁺-sparing diuretics, crush injury/rhabdo, adrenal insufficiency.
  • ECG: Peaked T waves, wide QRS, sine wave pattern → V-fib.
  • 📌 Mnemonic (Tx): C BIG K Drop (Calcium, Bicarb/Beta-agonist, Insulin, Glucose, Kayexalate, Diuretics/Dialysis).

⭐ In hyperkalemia with ECG changes, give IV Calcium Gluconate first to stabilize the cardiac membrane before lowering potassium.

Calcium Disorders - A Bone to Pick

• Hypercalcemia (>10.5 mg/dL)

  • Causes: Primary Hyperparathyroidism (outpatient), Malignancy (inpatient), Thiazides.
  • Symptoms: "Stones, bones, groans, psychiatric overtones."
  • EKG: Short QT interval.
  • Tx: Aggressive IV fluids, calcitonin (rapid), bisphosphonates (slow onset, long duration).

• Hypocalcemia (<8.5 mg/dL)

  • Causes: Hypoparathyroidism (e.g., post-thyroidectomy), CKD, Vitamin D deficiency.
  • Symptoms: Perioral numbness, tetany, seizures.
  • Signs: 📌 Chvostek (facial tap), Trousseau (carpal spasm).
  • EKG: Long QT interval.
  • Tx: IV Calcium Gluconate.

⭐ Malignancy is the most common cause of hypercalcemia in hospitalized patients, often via PTHrP (e.g., Squamous Cell Lung Cancer).

Magnesium & Phosphate - The Understudies

• Hypomagnesemia (< 1.8 mg/dL)
  • Causes: Diuretics (loops/thiazides), PPIs, diarrhea, alcohol abuse.
  • Effects: Torsades de Pointes, tetany, prolonged PR/QT intervals.
• Hypophosphatemia (< 2.5 mg/dL)
  • Causes: Refeeding syndrome, DKA, chronic antacid use.
  • Effects: Acute muscle weakness (incl. diaphragm), rhabdomyolysis, cardiac dysfunction.

⭐ Refractory Hypokalemia? Always check magnesium levels. Hypomagnesemia prevents renal K⁺ reabsorption and intracellular correction.

High-Yield Points - ⚡ Biggest Takeaways

• Hyperkalemia with EKG changes (peaked T waves) requires immediate IV calcium gluconate for cardiac stabilization.
• Correcting chronic hyponatremia too quickly risks osmotic demyelination syndrome; correcting hypernatremia too quickly risks cerebral edema.
• Hypocalcemia presents with neuromuscular excitability (Chvostek/Trousseau signs) and QT prolongation.
• Severe hypercalcemia management starts with aggressive IV fluid hydration to enhance renal excretion.
• Refractory hypokalemia often indicates underlying hypomagnesemia; always replete magnesium first.