The Influence of Different Breathing Modes on Oxygenation in a Lung Ventilation

Hypoxemia may develop in some patients, although one-lung ventilation (OLV) can be safely implemented to expand the field of vision and to facilitate surgical manipulation during lung surgeries. The main cause of hypoxemia is pulmonary shunt due to a single non-ventilated lung. Volume-controlled ventilation (VCV) is usually used as a mechanical ventilation modes, when OLV is implemented. Increased airway pressures in the ventilated lung cause the blood flow to be directed to the non-ventilated lung and the rate of pulmonary shunts further increases, thereby, leading to a deepening of hypoxemia. On the other hand, pressure-controlled ventilation-volume guaranteed (PC-VG) ventilation mode is used as a preventive ventilatory strategy during acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), and prevents uncontrolled increase in the alveolar pressure. Several studies comparing PC-VG with VCV have demonstrated that PC mode reduces the airway pressure and improves the partial arterial oxygen pressure (PaO2), particularly in patients with low preoperative forced vital capacity (FVC) values. In addition, the peak airway pressure (Ppeak) has been shown to decrease, while PaO2 increases due to decreased inspiratory current in the PC mode during ALI and ARDS. Therefore, the PC mode has been suggested to be an alternative ventilation mode to avoid high airway pressures during OLV In pressure-controlled ventilation-volume guaranteed (PC-VG) mode, The patients were provided with mechanical ventilatory support (Datex-Ohmeda Avance Anesthesia Machine, GE Healthcare, Madison WI USA) at a tidal volume of 7 mL/kg with 4 PEEP support to achieve an inspiration/expiration ratio of 1:2 and 50% FiO2.. During One lung ventilation (OLV), the tidal volumes of patients were reduced to 4 mL/kg and the respiratory frequency was increased up to 18-20. In the case of intraoperative hypoxia (Patients will be evaluated by the same consultant anaesthetist), certain maneuvers were performed for patient optimization including re-adjustment of tidal volume, increasing oxygen ratio, increasing PEEP, oxygen insufflation in non-ventilated lungs, fiberoptic confirmation of location of the intubation tube, and intermittent two-lung ventilation. The patients in PC-VG mode will monitored using the same mechanical ventilation mode from induction of anaesthesia to end of procedure.