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Abstract

Introduction: Marked elevation of lactate following cardiac surgery is associated with increased morbidity and mortality. While high lactate with low central venous oxygen saturation (ScvO2) suggests global hypoperfusion amenable to interventions that address the imbalance between oxygen supply and demand, the approach to patients with high lactate and normal ScvO2 is less clear. The purpose of this study was to identify differences in perioperative characteristics between cardiac surgery patients with markedly elevated lactate and normal ScvO2 upon intensive care unit (ICU) arrival who experienced major complications (MC) versus those without MC. Methods: A retrospective chart review was conducted on 43 patients who underwent cardiac surgery with cardiopulmonary bypass (CPB) between September 2010 and December 2011 and presented with lactate ≥ 4 mmoL/L and ScvO2 ≥ 70% upon ICU arrival. Perioperative characteristics assessed included preoperative ejection fraction (EF), EUROscore, complete blood count, serum chemistries, CPB time and perfusion rate, aortic cross clamp time, cumulative dose/duration of vasoactive therapy, blood loss, vital signs, urine output, lactate, ScvO2, arterial blood gases, ventilator data, chest x-rays, central venous pressure (CVP) and crystalloids/blood products administered. Results: Of the 43 patients evaluated, 14 had MC and 29 had no MC. The most frequent MC was prolonged mechanical ventilation, which occurred in 11/14 patients, followed by sepsis (3), stroke (3), renal failure (2), and pulmonary embolism (1). Comparing the MC and no MC groups, respectively, perioperative characteristics found to be significantly different included median EF (40 vs. 53%, p = 0.0009), cumulative intraoperative epinephrine (701 vs. 200 mcg, p < 0.0001), PaO2/FiO2 (PF) ratio on day 1 (169 vs. 242, p = 0.031), Lung Injury Score on day 1 (1.4 vs. 1, p = 0.029), Multiple Organ Dysfunction Score on days 1, 2 and 7 (7 vs. 5; 5.5 vs. 2; 3 vs. 0, all p < 0.01), vasopressor duration > 24 hr (42.8 vs. 3.4%, p = 0.003), mean CVP at 8 hr (14 vs. 11 mmHg, p = 0.002) and presence of systemic inflammatory response syndrome on day 7 (42.9 vs. 10.3%, p = 0.040). Additionally, mortality was significantly higher in the MC group (21.4 vs. 0%, p = 0.030). Median EUROscore (9 vs. 6, p = 0.149), CPB time (74 vs. 56 min, p = 0.129), aortic cross clamp time (52 vs. 37 min, p = 0.214), intraoperative blood loss (1,550 vs. 1,000 mL, p = 0.156), PF ratio on day 2 (184 vs. 292, p = 0.076) and incidence of intraoperative hypotension (64.3 vs. 48.3%, p = 0.353) were all numerically higher in the MC group as well. Conclusions: The majority of patients presenting with a markedly elevated lactate level in the setting of a normal ScvO2 upon ICU arrival following cardiac surgery experience an uneventful course. However, significant differences in several perioperative characteristics were identified in patients who experienced MC compared to those without MC. Mild to moderate lung injury and a protracted CPB/vasopressor-induced microcirculatory derangement likely contributed to prolonged mechanical ventilation and other adverse outcomes.