Related Subjects:
|Metabolic acidosis
|Aspirin or Salicylates toxicity
|Ethylene glycol toxicity
|Renal Tubular Acidosis
|Lactic acidosis
📖 Introduction
- 🧪 Urinary excretion of weak acids and bases is strongly affected by urinary pH.
- 💧 Highly ionised molecules cross lipid membranes poorly → reduced tubular reabsorption → enhanced urinary excretion.
- ⚠️ Sodium bicarbonate use in lactic acidosis is controversial; may worsen intracellular acidosis. Most experts reserve it for pH < 7.0.
💉 Indications and Dose – Severe Metabolic Acidosis
- 🚑 Sodium Bicarbonate 8.4% (50–100 mL) via central line over 30–60 min → causes K⁺ to shift into cells.
- 💊 Sodium Bicarbonate 1.26% (1.5 L over 2 hrs) → aim urine pH >7.5 for toxin clearance (salicylate, methotrexate). Replace K⁺ due to losses.
- ❤️ TCA toxicity: if arrhythmias, QRS >0.16s, QT prolongation, or acidosis → give IV NaHCO₃ (50 mL 8.4%), repeat as needed.
- Aim pH 7.45–7.55 → ↑ protein binding, ↓ QRS width, stabilises arrhythmias, ↑ BP.
- 🔴 Severe metabolic acidosis (pH < 7.0): take expert advice. Some use 500 mL of 1.26% NaHCO₃ over 4 hrs. May be considered in refractory DKA.
⚠️ Complications
- 💧 Fluid overload.
- 🔄 Post-recovery or overshoot metabolic alkalosis (e.g. lactic acidosis → lactate converted to bicarbonate).
- ⚡ Electrolyte issues: hypernatraemia, ↑ urinary sodium excretion, hypokalaemia, ionised hypocalcaemia.
- 🦴 Risk of calcium phosphate precipitation → vascular calcification.
- 🌡️ Hyperosmolality.
- 🫁 ↑ pCO₂ → paradoxical intracellular acidosis, paradoxical CSF acidosis, impaired oxygenation.
- 📉 Prolonged QTc interval, arrhythmia risk.
- 💨 Hypercapnia.
- 🩸 Mild BP drop & haemodynamic instability (esp. in haemodialysis).
- 🔥 ↑ Lactate production in some cases.
💡 Pearls
- Bicarbonate is a bridge therapy - it buys time but doesn’t fix the underlying problem.
- Best evidence for use: TCA toxicity and toxin-induced acidosis (salicylates, methotrexate).
- In DKA, routine bicarbonate is not helpful; consider only if pH < 6.9.
- Overuse risks turning a patient from acidosis → dangerous alkalosis with electrolyte shifts.
📚 References
