Serum Bicarbonate Concentration Correlates with Arterial Base Deficit in Critically Ill Patients

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Abstract
Background: Base deficit (BD) and lactate concentration have been established as endpoints of resuscitation (EOR) in critically ill patients. However, obtaining these data has traditionally required an arterial blood gas (ABG) sample. We hypothesized that the more easily available serum bicarbonate (SB) concentration could approximate BD and potentially serve as a useful EOR of critically ill or septic patients. We evaluated retrospectively the correlation of SB with BD in a cohort of surgical intensive care unit patients. Materials and Methods: Clinical data from April 1996 through April 1998 were recorded in a computerized application from 1,712 critically ill adult patients. The data were downloaded daily and imported into a relational database for storage and analysis. A subset of paired SB and ABG samples obtained simultaneously was analyzed by linear regression to determine the correlation coefficients (r) and coefficient of determinations (r2) for the respective analyses. Results: A total of 26,690 BD and 16,737 SB determinations were available in the database. Of these, 5,301 BD and SB samples were drawn simultaneously on the same patient. The correlation coefficient for these data pairs was 0.91, and the coefficient of determination was 0.83. The base deficit was predicted by the equation: BD = 22.43 - (0.9522 × SB) (p < 0.0001). Conclusion: In this large data set, there was a close inverse correlation between SB and BD in critically ill or septic patients. The predictive equation explains 83% of the variability for BD values. A prospective study comparing SB to BD and lactate could confirm SB as a useful marker of resuscitation.