Two-Lung and One-Lung Ventilation in Patients - Anesthesia ...

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36 CARDIOVASCULAR ANESTHESIA BARDOCZKY ET AL. ANESTH ANALG POSITION AND Fio 2 DURING OLV 2000;90:35–41 1.0 eight patients) throughout the study. The patients had mild pulmonary hyperinflation (functional residual capacity 120%). All patients were premedicated with midazolam 3 to 5 mg IM, approximately 30 min before the induction of anesthesia. In the operating room, all patients had an epidural catheter inserted around the T7 level, and after the administration of a test dose, an epidural anesthesia was started with 8 mL of 2% lidocaine with 100 g fentanyl and was maintained with a continuous infusion of epidural bupivacaine 0.5% (2–5 mL/h). The patients were anesthetized with a variable-rate (3–6 mg kg 1 min 1 ) continuous infusion of propofol and inhaled isoflurane (0.4%–0.6%) in 40% or 60% oxygen in air or pure oxygen. Muscle relaxation was achieved with pancuronium. In all patients, the bronchus of the dependent lung was intubated with a double-lumen endotracheal tube (DLT) (Broncho-cath tm ; Mallinckrodt Laboratories, Athlone, Ireland) of an appropriate size determined by the height of the patient (10). The correct position of the DLT was determined with fiberoptic bronchoscopy in both the supine and the lateral positions. The electrocardiogram, heart rate, systemic arterial blood pressure, noninvasive arterial oxygen saturation, and end-tidal CO 2 were continuously monitored. Constant tidal volume of 10 mL/kg was delivered with a Siemens 900C ventilator (Siemens ® Elema tm , Solna, Sweden) throughout the study. The ventilatory pattern consisted of a volume-controlled, square-wave flow pattern, at a rate of 10 breaths/min. Inspiratory time (T I/T TOT) was 0.33 and end-inspiratory pause was 10% of the total respiratory cycle. All measurements were performed with zero applied endexpiratory pressure. Ventilatory variables were kept constant during the study, both during TLV and OLV. This investigation was performed with the chest closed and before the surgical procedure. After intubation in the supine position and fiberoptic control of the correct DLT position, the two lungs were ventilated with the above-described ventilatory pattern for 15 min. End-inspiratory and end-expiratory occlusions were performed to determine the mechanical characteristics of the respiratory system (peak inspiratory airway pressure, end-inspiratory plateau pressure, and intrinsic positive end-expiratory pressure) and arterial blood gas samples were drawn. Then, the tracheal lumen of the DLT was clamped, and the would-be operated nondependent lung was allowed to deflate to atmospheric pressure. After 15 min of OLV and data collection, TLV was restored with unaltered ventilatory settings, and the patient was turned to the lateral decubitus position. TLV and turning and positioning of the patients generally lasted approximately 30 min. At the end of this period, ventilatory data were recorded, an arterial blood gas sample drawn, and the nondependent lung collapsed again, now with the patient in the lateral decubitus position. After 15 min, respiratory mechanics and gas exchange data were collected again. Pao 2, alveolar-arterial oxygen tensions difference [P(A-a)o 2] were calculated by using standard equations. Demographic data and preoperative pulmonary functions of the three groups were comparable (Kruskall-Wallis test). The data obtained in the two positions were compared with the Wilcoxon matched pair test. The data caused by Fio 2 differences were analyzed with the Kruskall-Wallis test. Values of P 0.05 were considered as statistically significant. Data were presented as median (range). Results Demographic characteristics, preoperative pulmonary function tests, and the values of the preoperative arterial oxygen and carbon dioxide tensions of the 24 patients are shown in Table 1. The differences were not statistically significant among the three groups. Right- and left-sided thoracotomies were comparable in the three groups and among the groups (Kruskall- Wallis test). Initiating OLV with unaltered ventilatory settings increased peak inspiratory pressures significantly in all three groups (Tables 2–4). Effects of the Position During the period of TLV, the position of the patient (supine versus lateral) did not significantly influence the variables related to gas exchange in the three groups of patients (Tables 2–4). In contrast, in the OLV assessment stages, the Pao 2 values in the lateral position were always significantly higher than in the supine position: Group 0.4, 63 (57– 144) vs 101(72–201) mm Hg (P 0.02); Group 0.6, 155 (114–235) vs 268 (162–311) mm Hg (P 0.02); Group 1.0, 301 (216–422) vs 486 (288–563) mm Hg (P 0.02) (Wilcoxon’s matched pair test). The values of P(A-a)o 2 showed similarly significant changes, but in the opposite direction (Tables 2–4 and Figure 1). While turning the patients from the supine into the lateral position, no changes were observed regarding the variables related to the mechanical properties of the respiratory system (peak inspiratory airway pressure, end-inspiratory airway pressure, and intrinsic positive end-expiratory pressure), during neither TLV, nor OLV (not significant, Wilcoxon matched-pair test). Effects of FIO 2 In the three groups of patients ventilated with different Fio 2 values, the differences of Pao 2 values observed between the supine and lateral TLV periods were not significant. In contrast, the increases of Pao 2
ANESTH ANALG CARDIOVASCULAR ANESTHESIA BARDOCZKY ET AL. 37 2000;90:35–41 POSITION AND Fio 2 DURING OLV Table 1. Demographic Characteristics, Preoperative Pulmonary Function Studies, and Preoperative Arterial Blood Gas Values of 24 Patients During Thoracic Surgery values observed between the lateral and supine OLV were significantly higher when the Fio 2 was higher (P 0.02, Kruskall-Wallis test) (Figure 2). Pao 2 was decreased and P(A-a)o 2 was increased during OLV in comparison with the TLV values in both the supine and the lateral positions and at every level of Fio 2. However, these changes were more pronounced in the supine position (Group 0.4: 61 [17–132] vs 19 [5–39]) mm Hg; Group 0.6: 68 [9–150] vs 14 [4–44] mm Hg; Group 1.0: 107 [5–268] vs 65 [18–205] mm Hg; P 0.05, Wilcoxon’s matched pair test). When turning the patients from the supine to the lateral position, Pao 2 increased significantly when comparing the periods of OLV. These Pao 2 increases (lateral-supine) were significantly larger when higher Fio 2 values were used (Figure 2). When comparing the periods of TLV, no significant differences in Pao 2 increases (lateral-supine) were found, regardless of the Fio 2 values administered (Figure 2). There were no significant changes in mean arterial pressure or heart rate in any of the patients during the study period. Discussion Fio 2 Group 0.4 (n 8) Group 0.6 (n 8) Group 1.0 (n 8) Age (yr) 59 (46–62) 60 (24–72) 64 (44–78) Height (cm) 175 (169–183) 169 (154–180) 167 (162–184) Weight (kg) 75 (51–105) 69 (55–86) 65 (56–98) FEV1 (% predicted) 76 (35–81) 79 (51–84) 80 (53–85) FRC (% predicted) 152 (122–195) 145 (121–182) 145 (122–181) RV (% predicted) 170 (128–177) 156 (131–196) 151 (124–193) TLC (% predicted) 115 (99–131) 115 (98–138) 112 (77–135) Paco 2 (mm Hg, room air, supine) 37 (31–41) 37 (29–43) 40 (36–47) Pao 2 (mm Hg, room air, supine) 78 (66–90) 82 (68–102) 72.5 (64–95) Data are median (range). Fio 2 fraction of inspired oxygen, FEV1 forced expiratory volume in 1 s, FRC functional residual capacity, RV residual volume, TLC total lung capacity. Table 2. Respiratory Mechanics and Gas Exchange Data Obtained During TLV and OLV with Patients in the Supine and in the Lateral Positions, Fio 2 0.4 (n 8) Supine Lateral TLV OLV TLV OLV Ppeak (cm H 2O) 21 (12–35) 29 (17–40) 20 (12–35) 29 (17–42) Pplateau (cm H 2O) 14 (7–23) 18 (9–26) 13 (9–19) 18 (12–24)† PEEPi (cm H 2O) 1.5 (0–2) 2.5 (0–6) 1 (0–3) 3 (0–8) Paco 2 (mm Hg) 38 (34–47) 39 (32–49) 40.5 (35–47) 38.5 (36–45) Pao 2 (mm Hg) 124 (81–240) 63 (57–144) 132 (102–296) 101 (72–201)‡ P(A-a)o 2 (mm Hg) 118 (12–170) 181 (94–197) 117 (16–166) 131 (44–177)‡ Data are median (range). TLV two-lung ventilation, OLV one-lung ventilation, Ppeak peak inspiratory airway pressure, Pplateau end-inspiratory airway pressure, PEEPi intrinsic positive end-expiratory pressure, P(A-a)o 2 alveolar-arterial oxygen tension difference. * P 0.02, † P 0.05 (OLV versus TLV). ‡ P 0.02 (lateral versus supine OLV). In this study, we investigated arterial oxygenation with the patient in the supine and in the lateral positions during TLV and OLV in patients with mild pulmonary hyperinflation scheduled for thoracic surgery. We found significantly higher Pao 2 and lower P(A-a)o 2 when OLV was performed in the lateral position. Recent developments in thoracic surgery have widened the scale of surgical interventions and changed certain traditions, including the patient positioning. Single-lung transplantation (12) and resection of unilateral emphysematous bullae (3) are performed with the patient in the lateral decubitus position, while double-lung transplantation, lung volume reduction surgery, and minimally invasive coronary artery surgery are performed with the patient placed in the supine position (1,2,13). In both conditions, to facilitate the surgeon’s task, variable periods of OLV are required during these procedures. To explain the preservation of blood oxygenation in the presence of a large fraction of atelectatic lung, as
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