The increase in CO2 production induced by NaHCO3 depends on blood albumin and hemoglobin concentrations.
OBJECTIVE
To evaluate the origin of H+ ions participating in the generation of CO2 coming from sodium bicarbonate infusion during metabolic acidosis. We hypothesized that these H+ ions come from a back-titration of the main non-bicarbonate buffers present in the blood, i. e. the hemoglobin and the albumin, and thus postulated that the rate of CO2 release from a bicarbonate load is dependent on the concentration of these buffers.


METHODS
Prospective clinical and experimental study.


METHODS
Surgical intensive care unit of a university hospital.


METHODS
(1) Sixteen stable sedated and artificially ventilated critically ill patients with a mild base deficit. (2) Acidotic human blood (bicarbonate 5 mM, pH 7.0) of hematocrit 5, 10, 20 and 40% regenerated from a mixture of frozen fresh plasma and packed red blood cells.


METHODS



METHODS
infusion of 1.5 mmol/kg sodium bicarbonate over 5 min. Regenerated blood: 25 mM sodium bicarbonate load.


RESULTS



METHODS
continuous measurement of CO2 production (VCO2) on the expired gas using a metabolic monitor and arterial blood gas analysis before (T0), at the end (T5) and at 10, 30 and 60 min after the beginning of the bicarbonate infusion. The increase in VCO2 was 18 +/- 7% leading to a rise in PaCO2 from 39.6 +/- 2.3 at T0 to 46.2 +/- 2.7 mmHg at T5. The increases in VCO2 and in PaCO2 were significantly correlated to the albumin (r = 0.73, p < 0.005 and r = 0.70, p < 0.005, respectively) and to the hemoglobin (r = 0.51, p < 0.05 and r = 0.65, p < 0.01, respectively) concentrations. Regenerated blood: gas analysis 1 min after the bicarbonate load. The increase in PCO2 was closely related to the hematocrit (Ht) of the blood as it was 15.9 +/- 7.5 mmHg for Ht 5%, 29.0 +/- 9.6 for Ht 10%, 44.2 +/- 5.9 for Ht 20% and 71.0 +/- 3.5 for Ht 40% (n = 5 for each, p < 0.001).


CONCLUSIONS
The importance of the release of CO2 from a bicarbonate load is dependent on the concentration of the blood non-bicarbonate buffers. It is therefore likely that the adverse effects of bicarbonate therapy linked to the CO2 generation are more important in patients with high blood albumin and hemoglobin concentrations.
Département d'Anesthésie-Réanimation, Hôpital Saint-Roch, Nice, France. jacques.levraut@unice.fr
J
J
Levraut
P
P
Garcia
C
C
Giunti
C
C
Ichai
M
M
Bouregba
J P
JP
Ciebiera
P
P
Payan
D
D
Grimaud
D000138:Acidosis / Q000188:drug therapy*; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000378:metabolism*; D005260:Female; D006454:Hemoglobins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007262:Infusions, Intravenous; D007362:Intensive Care Units; D007773:Lactates / Q000097:blood; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012709:Serum Albumin / Q000187:drug effects / Q000378:metabolism; D017693:Sodium Bicarbonate / Q000008:administration & dosage / Q000627:therapeutic use*
D006454:Hemoglobins; D007773:Lactates; D012709:Serum Albumin; D002245:Carbon Dioxide; D017693:Sodium Bicarbonate