Minimal fixed flow anesthesia for off-pump coronary artery bypass surgery: A parallel randomized trail

OBJECTIVES: The aim of the present study was to test a safety of a fixed minimal (0.5 l/min) fresh gas flow (FGF) anesthesia as a method ensuring adequate oxygenation during off-pump coronary artery bypass grafting operations. DESIGN: A randomized, prospective study. SETTING: Single-center clinical hospital affiliated with a university. PARTICIPANTS: 208 patients underwent off-pump coronary artery bypass surgery. INTERVENTIONS: All patients received endotracheal inhalational anesthesia with fixed minimal FGF. Half of them were anesthetized by sevoflurane and another half by isoflurane. The fresh (carrier) gas was pure oxygen in the control groups and a mixture of medical air and oxygen (FiO(2) 0.8) in the trial groups. MEASUREMENTS AND MAIN RESULTS: In the control groups inhaled oxygen concentration changed minimally during the operation. In the trial groups in 28.8 % of cases inhaled oxygen concentration dropped below preliminary margin (0.4). Body surface area (BSA) (B = 38.7; p = 0.002) and patient's age (B = −0.47; p = 0.004) were retained into final logistic regression model as independent predictors. We divided BSA into subcategories and analyzed data by survival cox regression with Forward LR method. Patients with BSA>2.3 (Exp.B = 183) and BSA [2.2–2.3] (Exp.B = 59) had high chance to get less than 0.4 of inhaled oxygen concentration compared to the patients with BSA <2.0 (p < 0.001). Exp(B) or OR for the patients’ age as independent predictor tested in multiple logistic regression was 0.628 In other words, for every year less the patient had 1/0.628 = 1.6 times more chance to reach the preliminary low margin (0.4) of oxygenation. CONCLUSIONS: Fixed minimal FGF 0.5 l/min with FiO(2) 0.8 may not be sufficient for the younger patients with BSA >2.0 to maintain inhaled oxygen concentration above 0.4. Using pure oxygen as a carrier gas during fixed minimal flow long term anesthesia is much safer and more reliable.