Hypothesis: Serum bicarbonate (HCO(3)) measurement may accurately and reliably be substituted for the arterial base deficit (BD) assay in the surgical intensive care unit (ICU).
Design: Retrospective criterion standard analysis.
Setting: Surgical ICU in a tertiary care facility.
Patients: Consecutive sample of non-trauma-related surgical ICU admissions from January 1996 to January 2004 with simultaneously obtained serum HCO(3) and arterial BD levels.
Main outcome measures: Correlation between HCO(3) and BD at admission and during the ICU stay; predictive value of serum HCO(3) for significant metabolic acidosis and ICU mortality.
Results: The study included 2291 patients with 26 063 sets of paired laboratory data. The mean +/- SD age was 52 +/- 16 years and mean ICU stay was 5.8 +/- 9.8 days. There were 174 ICU deaths (8%). Serum HCO(3) levels showed significant correlation with arterial BD levels both at admission (r = 0.85, R(2) = 0.72, P<.001) and throughout the ICU stay (r = 0.88, R(2) = 0.77, P<.001). Serum HCO(3) reliably predicted the presence of significant metabolic acidosis (BD > 5) with an area under the receiver operating characteristic curve (AUC) of 0.93 at admission and 0.95 overall (both P<.001), outperforming pH (AUC, 0.80), anion gap (AUC, 0.70), and lactate (AUC, 0.70). The admission serum HCO(3) level predicted ICU mortality as accurately as the admission arterial BD (AUCs of 0.68 and 0.70, respectively) and more accurately than either admission pH or anion gap.
Conclusions: Serum HCO(3) provides equivalent information to the arterial BD and may be used as an alternative predictive marker or guide to resuscitation. Low HCO(3) levels should prompt immediate metabolic acidosis evaluation and management.