Diagnostic value of " base deficit" in arterial blood gas analysis in comparison with hyperlactatemia as an indicator of tissue hypoperfusion in cardiac surgery

Hyperlactatemia is a well known index for tissue hypoperfusion which is not routinely measured in all surgical procedures. The aim of this study was to evaluate the diagnostic value of base deficit in detecting hyperlactatemia and also predicting its postoperative complications in cardiac surgery. In a prospective observational study, 487 patients who underwent elective coronary artery bypass grafting or valve replacement surgery were evaluated. The serum lactate level and arterial blood gas (ABG) tests were measured simultaneously 3-5 times during operation and every six hours until 24h after operation. Hemodynamic changes during the operation, and also postoperative major complications consisting cardiac, pulmonary, neurologic, renal, infectious complications and death were recorded. Criterion for hyperlactatemia was considerated serum lactate≥3 mg/dl and for metabolic acidosis, base deficit>5 mmol/L. Intraoperative frequency of "at least one episode of" base deficit>5 mmol/L was 41.3% and also hyperlactatemia was 56.3%. There were sensitivity (48%), specificity (68%) and PPV (66%) of base deficit>5 mmol/L in diagnosis of hyperlactatemia, considering pre-test probability (56.3%) of hyperlactatemia and calculating LR=1.49 for "base deficit>5 mmol/L ", the post-test probability of hyperlactatemia was estimated 70%. Considering frequency (pre-test probability) of 26.5% for postoperative complications and calculating LR=1.40 for both base deficit>5 mmol/L and hyperlactatemia, the post-test probability of postoperative complications was estimated 40% (in both tests). Because of importance of major postoperative complications, 40% probability of these events by observing base deficit>5 mmol/L or lactate≥3 mg/dl can be sufficiently alert the anesthesiologist to do proper interventions.