What are the indications for sodium bicarbonate (NaHCO3) administration?

What are the indications for sodium bicarbonate (NaHCO₃) administration?

Before 1986, NaHCO₃ was routinely used during CPR, even without knowledge of the patient’s acid–base status. Acidosis inhibits myocardial contractility and also inhibits the effects of catecholamines. However, this inhibitory effect on catecholamines does not appear clinically signifi-cant at the range of pH commonly encountered and the catecholamine doses administered during resuscitation. The myocardial depressant effect of metabolic acidosis is delayed compared with that produced by the intracellular acidosis that follows the administration of NaHCO₃. As is apparent from the equilibrium equation,

[HCO₃⁻] + [H⁺] ⇔ [H₂CO₃] ⇔ [CO₂] + [H₂O]

every 50 mEq of bicarbonate administered produces large amounts of CO₂ gas. CO₂ gas freely diffuses across cellular membranes, and causes a paradoxical worsening of the intra-cellular acidosis. Intracellular CO₂ tensions of greater than 300 mmHg and pH values less than 6.1 have been recorded.

Carbicarb, a buffering agent that does not produce as much CO₂, has also been tried without significant improvements in outcome following CPR. Another probable explanation for the ineffectiveness of these buffering agents is that they also cause hypernatremia and hyperosmolality. Hyperosmolar solutions may decrease aortic pressures, and compromise survival. Initially, the leftward shift in the oxy-hemoglobin saturation curve following the administration of NaHCO₃ may theoretically decrease oxygen availability.

Thus, NaHCO₃ should only be given when the results of arterial blood gas analysis indicate a significant metabolic acidosis in the presence of severe acidemia (e.g., with an arterial pH <7.20). It currently holds a Class III indication in hypercarbic acidosis and thus may be harmful during CPR. NaHCO₃ is indicated in known hyperkalemia (Class I), bicarbonate-responsive acidosis (Class IIa), tricyclic anti-depressant overdose (Class IIa), to alkalinize urine in aspirin or other drug overdose (Class IIa), and for intubated and ventilated patients with a long arrest time or return of circulation after prolonged CPR (Class IIb). When NaHCO₃ administration is planned, the correct full dose is calculated as follows:

Patient’s weight (kg) × base deficit × 0.3

Many clinicians use half of the calculated dose initially. If blood gas results are unobtainable, an empiric dose of 1 mEq/kg can be administered in prolonged arrest situations.