Effectiveness of low levels of nonventilated lung continuous positive airway pressure in improving arterial oxygenation during one-lung ventilation

Continuous positive airway pressure (CPAP) of 5 and 10 cm H₂O applied to the nonventilated lung is effective in improving arterial oxygenation during one-lung ventilation (1-LV). The effectiveness of lower levels of CPAP on improving oxygenation, however, has not been reported, possibly because of limitations of previous methods of CPAP delivery. Recently, a disposable, self-assembled CPAP system capable of delivering CPAP over a wide range of pressures has been introduced (Mallinckrodt Medical, Inc., St. Louis, MO). The purpose of this study was to evaluate the effectiveness of 2 and 5 cm H₂O of CPAP delivered with this device in improving PaO₂. In thoracic surgical patients during 1-LV. Twenty patients scheduled for thoracotomy were anesthetized and a left-sided endobronchial tube was placed with fiberoptic bronchoscopic guidance. Patients were ventilated with a tidal volume of 12 mL/kg, an FIO₂ of 1.0, and the respiratory rate was adjusted to maintain PaCO₂ at 40 ± 4 mm Hg. Patients were randomized to receive nonventilated lung CPAP at either the 2 (Group I) or 5 (Group II) cm H₂O pressure setting of the device. Application of CPAP followed 20 min of stable 1-LV in the lateral decubitus position. Compared with two-lung ventilation, PaO₂ (mean ± SD) was significantly less with I-LV (Group I, 126 ± 75 mm Hg, and Group II, 173 ± 79 mm Hg). Application of the assigned CPAP resulted in an increase in PaO₂ compared to 1-LV (Group I, 270 ± 112 mm Hg, and Group II, 386 ± 66 mm Hg; P ≤ 0.05). Nonventilated lung airway pressure with the CPAP system at the 2 and 5 settings was 2.6 ± 0.4 and 5.5 ± 0.5 cm H₂O, respectively. These results demonstrate that during 1-LV, improvement in arterial oxygenation with nonventilated lung CPAP can be achieved with both the 2 and 5 cm H₂O CPAP settings of the Mallinckrodt CPAP system.