[Metabolic acidosis after cardiac surgery with cardiopulmonary bypass revisited with the use of the Stewart acid-base approach].
BACKGROUND
According to the Stewart approach of acid-base regulation, chloride from either volume replacement or cardiopulmonary bypass (CPB) priming solution may induce metabolic acidosis. The alternative hypothesis stands in volume dilution with solutions free of bicarbonate.


OBJECTIVE
Evaluate the acid-base status of patients undergoing cardiac surgery with CPB priming containing chloride and bicarbonate.


METHODS
Prospective study.


METHODS
Twenty-eight patients were prospectively included. Priming of CPB contained 47.4 mmol/l of bicarbonate and 97.7 mmol/l of chloride. Arterial blood samples were taken at 3 timings: prior (T1) and after (T2) CPB, and on arrival in the ICU (T3). Following measurements were performed: Na(+), K(+), Cl(-), Mg(++), Ca(++), phosphates, albumin, lactate and arterial blood gases.


RESULTS
After CPB respiratory acidosis was observed. There was a significant increase of chloride with a decrease in apparent strong ion difference (SIDa). At the same time bicarbonate and base excess (BE) remained constant. A significant but weak correlation between BE and SIDa existed (r(2) = 0.06, p=0.024). On the contrary, no correlation was found between variations of BE and SIDa. However, the correlation was stronger between values and variations of bicarbonate and BE (respectively r(2)=0.605, p<0.0001 and r(2)=0.495, p<0.0001).


CONCLUSIONS
No metabolic acidosis occurred after cardiac surgery when CPB was primed with bicarbonate. Therefore, it appears that chloride administration is not the main mechanism being involved in the acid-base regulation. This reinforces the hypothesis that metabolic acidosis during CPB may mainly be due to dilution of bicarbonate.
Guéret
G
G
Département d'anesthésie réanimation, CHU la Cavale-Blanche, boulevard Tanguy-Prigent, 29609 Brest, France. gildas.gueret@chu-brest.fr <gildas.gueret@chu-brest.fr>
Rossignol
B
B
Kiss
G
G
Wargnier
J-P
JP
Corre
O
O
Bezon
E
E
Carre
J-L
JL
Arvieux
C-C
CC
D000136:Acid-Base Equilibrium / Q000502:physiology*; D000138:Acidosis / Q000209:etiology*; D000368:Aged; D001639:Bicarbonates / Q000737:chemistry; D002315:Cardiopulmonary Bypass; D013504:Cardiovascular Surgical Procedures / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies
D001639:Bicarbonates