When sodium bicarbonate earns its place, and when it is just reflex.
Whiteboard by Daniel Patino, MD (@DanPatino7). Transcribed for The Curbside.
Bicarb is one of the most reflexively pushed drugs in the department and one of the least evidence-backed. The physiology tells you why. The indication list tells you when.
Two ways to give it
Bicarbonate push
1 amp
50 mL
8.4% NaHCO3, 50 mEq
Osmolarity about 2,000 mOsm/L
Roughly twice as hypertonic as 3% saline
Isotonic infusion
Isotonic
1 L D5W or sterile water
50 to 150 mEq bicarbonate
Rate 100 to 250 mL/hr
Faster if hypovolemic or volume-tolerant
Why a push can do nothing
CO2 + H2O ⇌ H2CO3 ⇌ HCO3− + H+
Bicarbonate binds acid (H+) and converts to CO2 and water.
You then have to breathe that CO2 off by raising minute ventilation (tidal volume or rate).
If minute ventilation is fixed or falling, there is no benefit. You have swapped a metabolic acidosis for a respiratory one.
Clearing the CO2 from a single amp can take 20 to 30 minutes.
Other effects of a push
Osmotic load. Raises intravascular volume by up to a quarter liter, and the risk of cerebral edema.
Hypernatremia. One amp is 50 mEq of Na+.
Extravasation. Causes tissue necrosis.
Left-shifted O2 curve. Alkalemia means less oxygen offloaded at the tissue.
Hypocalcemia. Alkalemia raises calcium binding to albumin, dropping ionized Ca2+, contractility, and blood pressure.
Where it lands, by indication
Cardiac arrestAgainst
No survival benefit, may worsen it, and no longer part of ACLS. Falling ventilation and hypoperfusion trap the CO2 the push creates.
DKAAgainst
No benefit in mortality, hemodynamics, or time to resolution of acidosis, even below pH 7.0 (Gamba, Lever, Duhon). Some societies still suggest it below pH 6.9, without conclusive evidence.
Lactic acidosisAgainst
No benefit in isolated lactic acidosis. MIMIC-III showed no mortality benefit at pH <7.2 in sepsis with metabolic acidosis, except in the AKI subgroup. Treat the underlying cause.
Acute kidney injuryFor
BICAR-ICU: lower mortality and less renal replacement therapy in the AKI subgroup at pH <7.2.
HyperkalemiaMixed
Alkalinization shifts K+ into cells, but a push's osmotic load drags it back out. Net effect is neutral to minimal. An isotonic infusion works better because it carries no osmotic load.
NAGMAFor
Reasonable at pH <7.2. Resuscitate with isotonic bicarb for severe diarrhea or renal bicarb losses. Consider a push if there is concurrent hyponatremia.
The one line to remember
A bicarb push only helps if the patient can blow off the CO2 it creates. No minute ventilation, no benefit. And when the goal is volume, the isotonic infusion avoids the osmotic hit of a push.