Base excess trumps lactate levels in predicting mortality after heart surgery
A low measure of base excess (BE) upon admission to the ICU following cardiac surgery was independently predictive of ICU mortality—more so than increased lactate levels, researchers reported in PLOS One.
“Cardiac surgery with use of cardiopulmonary bypass is known to induce distinct postoperative metabolic changes, which have a major influence on physiological processes,” wrote lead author Bjoern Zante, MD, with Bern University Hospital in Switzerland and University Heart Center Hamburg in Germany, and colleagues. “The underlying causes for respective acid-base disturbances after cardiac surgery are manifold and may best be reflected by changes in lactate-levels and base excess.”
Some analyses have suggested BE is predictive of mortality in subgroups of ICU patients, but there is little agreement on its value as a prognostic tool, the authors noted.
To further explore this potential relationship, Zante et al. studied data from 1,058 patients who were admitted to a cardiac surgery ICU at the University Medical Center Hamburg-Eppendorf in Germany from February 2009 through March 2010. The patients were a median of 69.8 years old, 67.6 percent male and had blood drawn immediately after ICU admission for blood-gas analysis.
Twenty-one patients died, or 2 percent of the entire study population. Multivariate regression analysis identified BE below -6.7 as the biggest independent predictor of ICU mortality, with levels below that threshold carrying a 4.78-fold risk of death.
Patients with BE below that level plus lactate at 3.9 mmol/L or lower were 2.56 times as likely to die in the ICU versus patients with both readings above those cutoffs.
“The highest mortality was found in the subgroup with hyperlactatemia and severe reductions in base excess,” Zante et al. wrote. “This appeared not surprising as this constellation may reflect severe lactic acidosis, which was related to a particular high ICU mortality previously and could be related to severe shock states.”
The authors noted their results could help clinicians identify a high-risk subset of patients early in the postoperative period.
“Subgroup analyses investigating different BE and lactate cutoff levels point towards BE as a key player in respect to mortality prediction in this clinical scenario,” they wrote. “Hence, lactate levels interpreted alone as a biomarker provides limited prognostic- and risk-stratification value. Thus, we advocate assessment of admission metabolic conditions after cardiac surgery in an effort to optimize risk stratification in the very early phase of postoperative care on the ICU.”
The authors acknowledged a handful of limitations with their study, including its small number of event rates, the retrospective, single-center design and lack of follow-up past the ICU stay, which may have shed light on midrange on long-term clinical outcomes associated with these metabolic indices.
Daniel joined TriMed’s Chicago editorial team in 2017 as a Cardiovascular Business writer. He previously worked as a writer for daily newspapers in North Dakota and Indiana.