Why do we care?

Approximately 12% of patient survive from a cardiac arrest. We know that bystander cardiopulmonary resuscitation (CPR) is essential as it decreases the interval of lack of blood flow to vital organs. Aside from this, following ACLS protocols and early defibrillation for ventricular fibrillation is associated with better outcomes. Administer sodium bicarbonate during cardiac arrest is a controversial topic and current ACLS guidelines do not recommend it unless it is for hyperkalemia, tricyclic antidepressant overdose or preexisting metabolic acidosis like diabetic ketoacidosis. 

Why consider using sodium bicarbonate in an arrest?

During CPR, blood flow is reduced to 70% of normal blood flow and the cardiac output is approximately 15%. This causes acidosis from anaerobic metabolism and failure of ventilation.

As a result, the above equation to shift to the left, causing depletion of bicarbonate. Some argue that by giving bicarbonate, one can shift this equation to the right. Essentially, the metabolic acidosis can be converted to respiratory acidosis and then the carbon dioxide can be blown off by hyperventilating the patient. This will improve the pH and allow cells to function under optimal condition.

Why sodium bicarbonate is a terrible idea?

Some scholar argue that hyperventilation is a bad idea as it decreases coronary and cerebral perfusion pressure secondary to increased intrathoracic pressure and decreased venous return. It also worsens intracellular acidosis as the bicarbonate administration shifts the equation to the right producing carbon dioxide, but instead of returning to the lungs to be blown off, the carbon dioxide quickly diffuses across the cell membrane where the reverse equation occurs and more hydrogen ions are produced. Sodium bicarbonate further causes hypernatremia and increases osmolarity. 1 amp of sodium bicarbonate increases sodium by 1 meq, extracellular volume (ECV) by 250 ml and raises pH by 0.10 units. So if you have a pH of 7, and you want to increase it to 7.4 - think of the changes you are making to the sodium and the ECV. 

So what does the literature show?

Vukmir et. al. conducted a double-blind, perspective, randomized, placebo-controlled trial where they gave sodium bicarbonate to half the patients in cardiac arrest and normal saline to the other half. They did not find a difference in their primary end point of ED survival between the two groups. However, during secondary analysis, they found that in patient with prolonged cardiac arrest (defined as greater than 15 minutes), there was a 2-fold increase in survival with bicarbonate administration. They concluded that this is the group that can derive the greatest benefit from bicarbonate administration. However, they interpreted the data incorrectly as they did not include all the patients who had bicarbonate administered. When this group was included, the result was not statistically significant. 

Ahn et. al. also conducted a double-blind, perspective, randomized, placebo-controlled trial where they gave sodium bicarbonate to half the patients in cardiac arrest and normal saline to the other half. This was a pilot study with a sample size of only 50 patients. They also hyperventilated their patients to ensure that carbon dioxide would be blown off, which was has not been done in any previous trials.  They found patients who were administered bicarbonate had a higher pH and a higher bicarbonate levels than the normal saline group however, no difference was seen in ROSC or good neurological survival. 

So never use sodium bicarbonate?

Literature suggests that administration of sodium bicarbonate does not increase ROSC. Limit the use of sodium bicarbonate to patients with hyperkalemia, TCA overdose and those with preexisting metabolic acidosis like DKA. 

References:

1) Vukmir, R. B., Katz, L., & Sodium Bicarbonate Study Group. (2006). Sodium bicarbonate improves outcome in prolonged prehospital cardiac arrest. The American journal of emergency medicine, 24(2), 156-161.

2) Ahn, S., Kim, Y. J., Sohn, C. H., Seo, D. W., Lim, K. S., Donnino, M. W., & Kim, W. Y. (2018). Sodium bicarbonate on severe metabolic acidosis during prolonged cardiopulmonary resuscitation: a double-blind, randomized, placebo-controlled pilot study. Journal of Thoracic Disease, 10(4), 2295.