Association of base excess with adverse outcomes following cardiac surgery: a retrospective study

Base excess (BE) is a key parameter in the assessment of acid-base balance, reflecting the body’s ability to handle acid loads and offering valuable insights into a patient’s metabolic condition.

In the immediate postoperative phase following cardiac surgery, factors such as anesthesia and potential tissue hypoxia—resulting from hypoperfusion during extracorporeal circulation—can trigger a transition from aerobic to anaerobic metabolism. This shift leads to a lactic acidosis and a negative BE. Additionally, other contributors such as bicarbonate loss and the buildup of organic acids may exacerbate metabolic acidosis.

BE is emerging as a significant prognostic indicator, as altered levels may correlate with complications and mortality. This retrospective study will explore the association between BE and adverse outcomes in patients undergoing cardiac surgery with extracorporeal circulation.

A retrospective study was performed in a tertiary care center. All patients who underwent cardiac surgery with extracorporeal circulation in 2023 were included. Clinical and surgical data was obtained from the electronic medical records. BE was routinely measured immediately before surgery, within 1 hour after extracorporeal circulation finalization, on admission to the cardiac intensive care unit (CICU), and 24 hours after surgery. Its values are presented as medians and interquartile ranges (IQR) and compared with Wilcoxon’s test. Statistical significance was considered with p < 0.05.

A total of 117 patients were included. Their basal characteristics and surgical data are presented in Table 1. The hospital mortality was 6%.

Before surgery, BE was similar in survivors and non-survivors: 0.70 mEq/L, with an IQR of -1.70 to 0.50, and -1.10 mEq/L with an IQR of -2.95 to -0.45, respectively (p = 0.28). On arrival to the CICU, BE was lower in non-survivors (-6.80 mEq/L, with an IQR of -7.40 to -5.00) compared to survivors (-3.30 mEq/L, with an IQR of -4.90 to -1.60), with a statistically significant difference (p = 0.02). The evolution of BE can be observed in Figure 1.

Discussion/Conclusion: This retrospective clinical study has demonstrated a significant relationship between BE and mortality in the immediate postoperative period following cardiac surgery. The analyzed data indicate that non-surviving patients exhibited lower BE values compared to survivors, suggesting that a less favorable acid-base balance is associated with worse clinical outcomes. These results highlight the significance of monitoring BE as a prognostic indicator in this patient population, potentially facilitate the early identification of at-risk patients and guide appropriate clinical interventions. Additional prospective studies are necessary to validate these findings and to assess the therapeutic implications of monitoring and improving BE in the setting of postoperative cardiac surgery.

Perioperative evolution of base excess