Study population
Between July 2016 and June 2017, 45 adult patients scheduled for selective totally thoracoscopic ablation for stand-alone atrial fibrillation were enrolled in this study. Patients with concomitant severe valvular heart disease, history of cardiac or lung surgery, left ventricular ejection fraction lower than 30%, left atrium more than 70 mm, left atrial appendage (LAA) thrombi, and contraindications to pulmonary artery catheterization were excluded. This study was approved by the institutional review board of Xinhua hospital. All patients voluntarily agreed to participate in this study and written informed consent was received from each patient the day before the surgery.
Anesthesia management
After peripheral vein cannulation, a dose of 2 mg of midazolam was intravenously injected to sedate the patients. A right-sided radial artery cannula was then implanted for monitoring arterial blood pressure and analyzing baseline blood gas condition. General anesthesia was induced with midazolam (0.05 mg/kg), etomidate (0.3 mg/kg), fentanyl (3 μg/kg) and rocuronium (0.6 to 0.9 mg/kg), followed by the insertion of a left-sided double-lumen endotracheal tube ( 32, 35 or 37 French, Covidien, Mansfield, MA, USA). Subsequently, a Swan-Ganz catheter (#744F75, Edwards Lifescience, Irvine, CA, USA) was placed in the pulmonary artery to measure central venous pressure (CVP), mean pulmonary arterial pressure (mPAP), pulmonary artery wedge pressure (PAWP), cardiac index (CI), etc. Anesthesia was maintained with a continuous infusion of propofol (4 to 6 mg·kg−1·h−1), remifentanil (0.15 to 0.3 μg·kg−1·min−1) and rocuronium (0.6 mg·kg−1·h−1). All patients received positive controlled ventilation with a tidal volume of 5 to 8 ml/kg and a fraction of inspired oxygen of 0.6 to 1.0, at a respiratory rate of 10 to 12 breaths/min. The thoracoscopic surgical ablation was totally conducted on the left side of chest wall. Therefore, patients were placed in the right lateral decubitus position and left lung collapse was requested. Various strategies including increasing FiO2, endotracheal suction, adjusting position of double-lumen tube and two-lung ventilation were used if SpO2 was lower than 90% during one-lung ventilation. The procedure was performed in alignment with a previous study [15]. Briefly, bipolar radiofrequency ablation was conducted across 3 circles and 2 lines on the left atrium. Ablation of three circles included lesions of the right pulmonary vein (including right superior and inferior pulmonary veins), the left pulmonary vein (including right superior and inferior pulmonary veins) and the circle crossing over the left inferior pulmonary vein and the right superior pulmonary vein. Two linear ablations were referred to linear lesions from the left pulmonary vein to the left atrial appendage and from the left inferior pulmonary vein to the mitral valve annulus. Subsequently, the ganglionic plexus on the epicardium was ablated and the left atrial appendage was removed using a stapler. When the operation ended, the patients were transferred to intensive care unit for extubation and recovery.
Cerebral rSO2 monitoring
Cerebral rSO2 was monitored using a near-infrared reflectance spectroscopy (NIRS)-based cerebral oximeter (EGOS-600A series, Suzhou Engin Biomedical Electronics Co., Ltd, Jiangsu, China). After cleaning the patient’s skin surface with alcohol, two sensors were placed bilaterally on the forehead. To reduce light contamination, a black belt was used to cover the sensors during the surgery. The left and right rSO2 were simultaneously detected at baseline (T0), 15 min after anesthesia induction (T1), 15 min after one-lung ventilation (T2), after right pulmonary vein ablation (T3), after left pulmonary vein ablation (T4), and 15 min after two-lung ventilation (T5). The average rSO2 value was calculated at each time point.
Hemodynamic evaluation and blood gas analysis
Hemodynamic changes during the surgery were assessed at the same time points as the rSO2. The hemodynamic measurements included heart rate (HR), systolic arterial pressure (SAP), diastolic blood pressure (DAP), mean arterial pressure (MAP), central venous pressure (CVP), mean pulmonary arterial pressure (mPAP), pulmonary artery wedge pressure (PAWP), cardiac index (CI), pulmonary vascular resistance index (PVRI) and systemic vascular resistance index (SVRI). Concurrently, arterial blood gas was analyzed by measuring pH, arterial carbon dioxide tension (PaCO2), ratio of arterial oxygen pressure to fractional inspired oxygen (PaO2/FiO2), arterial oxygen saturation (SpO2), hemoglobin (Hb), hematocrit (Hct), base excess (BE) and lactate (Lac) using an ABL 825 hemoximeter (Radiometer Copenhagen, Denmark).
Statistical Analysis
Continuous data are presented as the mean ± standard deviation or median with interquartile range as appropriate. Categorical data are expressed as the number (percentage) of patients. The normality of continuous data was tested with Shapiro–Wilk method. Comparisons of rSO2, hemodynamic and laboratory parameters at different time points were performed using a one-way repeated-measures ANOVA followed by post hoc Bonferroni analysis if the data met the assumption of normality, or nonparametric Friedman test would be applied. If rSO2 showed significant difference at a specific time point, the changes of rSO2 (△rSO2), hemodynamic and blood gas parameters from the baseline value were calculated. Then, a univariate analysis was first performed to illustrate possible influencing factors of △rSO2 with Pearson or Spearman correlations. The variables with P value less than 0.2 were further incorporated into a multivariate linear regression analysis (stepwise method). Statistical significance was considered if P value was less than 0.05. All the statistical analyses were conducted using IBM SPSS software version 20 (SPSS Inc., Chicago, IL, USA).