• Marco Ranucci, Giovanni Carboni, Mauro Cotza, Paolo Bianchi, Umberto Di Dedda, Tommaso Aloisio, and Surgical and Clinical Outcome Research (SCORE) Group.
• Department of Cardiothoracic-Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, San Donato Milanese (Milan), Italy.
• Plos One. 2015 Jan 1; 10 (5): e0126939.

ObjectiveThe nadir hematocrit (HCT) on cardiopulmonary bypass (CPB) is a recognized independent risk factor for major morbidity and mortality in cardiac surgery. The main interpretation is that low levels of HCT on CPB result in a poor oxygen delivery and dysoxia of end organs. Hyperlactatemia (HL) is a marker of dysoxic metabolism, and is associated with bad outcomes in cardiac surgery. This study explores the relationship between nadir HCT on CPB and early postoperative HL.DesignRetrospective study on 3,851 consecutive patients.Measurements And Main ResultsNadir HCT on CPB and other potential confounders were explored for association with blood lactate levels at the arrival in the Intensive Care Unit (ICU), and with the presence of moderate (2.1 - 6.0 mMol/L) or severe (> 6.0 mMol/L) HL. Nadir HCT on CPB demonstrated a significant negative association with blood lactate levels at the arrival in the ICU. After adjustment for the other confounders, the nadir HCT on CPB remained independently associated with moderate (odds ratio 0.96, 95% confidence interval 0.94-0.99) and severe HL (odds ratio 0.91, 95% confidence interval 0.86-0.97). Moderate and severe HL were significantly associated with increased morbidity and mortality.ConclusionsHemodilution on CPB is an independent determinant of HL. This association, more evident for severe HL, strengthens the hypothesis that a poor oxygen delivery on CPB with consequent organ ischemia is the mechanism leading to hemodilution-associated bad outcomes.

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