Monday, January 26, 2015

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. 

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:
     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 7.044 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 scoresWhen 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

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.

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