Bicarb in Metabolic Acidosis

The Resuscitationist has a great Instagram post about sodium bicarb in cardiac arrest, does it help or hurt? I’d expand this to just about any metabolic acidosis. IVP sodium bicarb used to be commonly given in these stations, especially during a cardiac arrest. It makes sense intuitively. Metabolic acidosis causes all sorts of cardiovascular problems including increased arrhythmias and poor contractility. Additionally, most vasopressors (vasopressin being the notable exception) won’t work in severe acidosis. So that just worsens things as the patient gets more hypotensive and you go up and up on the pressors to no effect.

So, it stands to reason that giving some bicarb would correct the acidosis (pH and HCO3 are inversely related in metabolic processes, after all) and fix all of our problems. So, why would you not want to give a couple of amps of bicarb?

Firstly, there isn’t any real evidence that it helps. Two studies mentioned in the IG post are pretty conflicting with one showing bicarbonate administration during cardiac arrest associated with earlier ROSC, but the other showing worse neurological outcomes. It may be beneficial in certain populations, including patients with severe metabolic acidosis and stage 2 or 3 AKI, some poisonings/overdoses (i.e. sodium channel blockers, TCA, salicylates, some toxic alcohols), and hyperkalemia (although a recent study question that as well).

So, there’s no real evidence it helps, but what’s the harm in trying? Well, firstly, I would argue that there’s always risk in medicine and so we shouldn’t be doing stuff “just because” if there is no evidence that it helps. But in the case of bicarb, it can actually hurt. Sodium bicarbonate (NaHCO3) gets metabolized and one of the byproducts is CO2. In a lot of cases, this isn’t really a big deal, but if your patient already has a respiratory acidosis (or is at risk for one), this is a really bad idea. It can also drop the ionized calcium, which again would be pretty bad in a critically ill patient.

So, no real evidence of benefit outside of certain situations. Possible harm. The better thing to do in most cases is to treat the cause of the metabolic acidosis. Having said that, I will sometimes give bicarb in a severe metabolic acidosis (pH < 7.2) in an unstable patient in order to buy some time. But, I’m cautious about it.

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