Correcting Acidosis or Just adding CO2?: On Sodium Bicarbonate for Metabolic Acidosis
Clinical Scenario:
You are working in the emergency department when an elderly male is brought in by EMS after being found unresponsive at home with an
unknown downtime. The paramedics report a possible seizure. His finger stick glucose registers as critical high. Post-intubation for poor GCS, his initial labs reveal an ABG of 6.8/20/90 and a lactate of 18. As you are signing out the patient to the ICU, the ICU team requests a sodium bicarbonate infusion. You wonder, will
sodium bicarbonate administration improve outcomes or correct acidosis faster when compared to normal
saline?
Physiology & Literature Review:
Other than well-defined indications for sodium bicarbonate administration (such as treatment of Na-channel blockade in TCA overdose or to induce alkalinization in salicylate toxicity), one should be skeptical about administering sodium bicarbonate simply for acidosis. On the one hand if a patient is acidotic, it makes intuitive sense that you should try to alkalinize them, which is why sodium bicarbonate has been used so often in the past. On the other hand, there is evidence to show that administration of sodium bicarbonate shifts the oxygen dissociation curve, increasing hemoglobin affinity to oxygen, and resulting in paradoxical tissue hypoxia and causes an increase in lactate production. In addition, it causes an intracellular acidosis. Despite this, because it tends to be part of the "code cocktail", it is often administered anyway.
Other than well-defined indications for sodium bicarbonate administration (such as treatment of Na-channel blockade in TCA overdose or to induce alkalinization in salicylate toxicity), one should be skeptical about administering sodium bicarbonate simply for acidosis. On the one hand if a patient is acidotic, it makes intuitive sense that you should try to alkalinize them, which is why sodium bicarbonate has been used so often in the past. On the other hand, there is evidence to show that administration of sodium bicarbonate shifts the oxygen dissociation curve, increasing hemoglobin affinity to oxygen, and resulting in paradoxical tissue hypoxia and causes an increase in lactate production. In addition, it causes an intracellular acidosis. Despite this, because it tends to be part of the "code cocktail", it is often administered anyway.
Rise in EtC02 after bicarb (Dr. Sacchetti video) |
The effect of administration of Sodium bicarbonate on the end-tidal CO2 in an intubated patient with severe metabolic acidosis is well demonstrated by this video by
Dr. Alfred Sacchetti. While we disagree in giving a bicarb drip as
mentioned in the video, it does demonstrate the acid-base physiology in
real time.
A small randomized-controlled trial published in Critical Care Medicine more than 20 years ago gave either a blinded bolus of saline or sodium bicarbonate to patients with lactic acidosis vasopressor support [1]. They then checked ABGs one hour later. While sodium bicarbonate did increase the venous bicarb level, improved pH, it did not improve
hemodynamics.
Regarding two common metabolic acidosis scenarios seen in the emergency department, Diabetic ketoacidosis, the evidence suggests that sodium bicarbonate has the potential to cause harm:
Regarding two common metabolic acidosis scenarios seen in the emergency department, Diabetic ketoacidosis, the evidence suggests that sodium bicarbonate has the potential to cause harm:
1. Diabetic ketoacidosis: A recent retrospective observational cohort study examined the effect of sodium bicarbonate on 86 patients in DKA with a pH less than 7.0. 44 patients received sodium bicarbonate and 42 did not. There was no difference in time
to resolution of acidosis (pH greater than 7.2) or hospital length of stay between the two groups.
However, there was a significant increase in insulin and fluid
requirements in the sodium bicarbonate group. With regard to pediatrics, the PECARN study examining DKA in the pediatric population found that one of the only risk factors for cerebral
edema (once again a retrospective analysis) was administration of sodium bicarbonate [3].
2. Lactic Acidosis: Regarding
lactic acidosis, an article from Korea retrospectively
looked at 103 patients with acidosis (CO2 less than 20) and lactate
greater
than 3.3 mmol and compared those that got bicarb (69) to those that did
not
(34) [4]. Patients who received sodium bicarbonate had increased mortality, but this was confounded by the fact that these patients had lower initial pH, higher initial lactate, and higher
APACHE 2 scores. When
they ran their regression analysis, the only two things that were
independently
associated with mortality were Sequential Organ Failure Assessment
(SOFA) and
bicarb administration (95% CI 1-251). When the authors did a subgroup
analysis by excluding less ill patients (SOFA less than 8), they found again that administration of sodium bicarbonate was associated with death. They also found that those
that received sodium bicarbonate cleared their lactate more slowly.
Take home points:
Sodium bicarbonate may increase serum pH, but may worsen rather than improve prognosis. Other than indications where sodium bicarbonate is the treatment for the acidosis (such as TCA overdose), the treatment for metabolic acidosis is to correct the underlying cause, whatever it may be.
Submitted
by Wes Watkins, PGY-4
Edited by
Louis Jamtgaard, PGY-3 @Lgaard
Faculty
reviewed by Evan Schwarz @TheSchwarziee
References:
1. Mathieu D, Neviere R, Billard V, Fleyfel M, Wattel F (1991) Effects of
1. Mathieu D, Neviere R, Billard V, Fleyfel M, Wattel F (1991) Effects of
bicarbonate
therapy on hemodynamics and tissue oxygenation in patients with
lactic-acidosis: a prospective, controlled clinical study. Crit Care Med 19:
1352– 1356.
2. Adeva-Andany, M. M.,
Fernández-Fernández, C., Mouriño-Bayolo, D., Castro-Quintela, E., &
Domínguez-Montero, A. (2014). Sodium Bicarbonate Therapy in Patients
with Metabolic Acidosis. The Scientific World Journal, 2014.
3. Glaser
N, Barnett P, McCaslin I, et al; Pediatric Emergency Medicine Collaborative
Research Committee of the American Academy of Pediatrics: Risk factors for
cerebral edema in children with diabetic ketoacidosis. The Pediatric Emergency
Medicine Collaborative Research Committee of the American Academy of
Pediatrics. N Engl J Med 2001; 344:264–269
4. Kim, H. J., Son, Y. K., & An, W. S. (2013). Effect of Sodium Bicarbonate Administration on Mortality in Patients with Lactic Acidosis: A Retrospective Analysis. PloS one, 8(6), e65283.
4. Kim, H. J., Son, Y. K., & An, W. S. (2013). Effect of Sodium Bicarbonate Administration on Mortality in Patients with Lactic Acidosis: A Retrospective Analysis. PloS one, 8(6), e65283.