BACKGROUND: One-lung ventilation (OLV) is commonly used in the majority of thoracotomies and thoracoscopic surgeries. During OLV, a decrease in partial pressure of arterial oxygen (PaO₂) occurs due to the right-to-left transpulmonary shunt that develops in the non-dependent lung, and is aggravated just after pleural opening. Here, we examined the occurrence, cause, and means of preventing drops in PaO₂ caused by pleural opening.

METHODS: Seventy patients, ASA PS I or II, who were scheduled for elective thoracotomy or thoracoscopic surgery, were prospectively examined. After OLV, patients were randomly allocated to one of four groups. In the Control group (n = 10), pleurae were not opened during studies. In the Open group (n = 20), pleurae were opened with the plug of the double-lumen endobronchial tube of the non-dependent lung opened. In the Closure group (n = 20), the plug was closed just before pleural opening. And in the continuous positive airway pressure (CPAP) group (n = 20), pleurae were opened after applying 5 cmH₂O CPAP of medical air to the non-dependent lung. Arterial blood gas analyses, hemodynamics, end-tidal CO₂, peak inspiratory airway pressure, lung compliance, and airway resistance were recorded 15 min after two-lung ventilation, 20 min after transition to OLV, just before pleural opening, and 1, 3, and 20 min after pleural opening. In the control group, data were recorded 15 min after two-lung ventilation and in seven intervals after transition to OLV (1, 3, 5, 10, 20, 25, and 45 min).

RESULTS: A significant decrease in PaO₂ was detected just after pleural opening in the Open and Closure groups. PaO₂ decreased in the Open group more than in the Closure group. However, in the CPAP group, no significant PaO₂ reduction was detected after pleural opening.

CONCLUSIONS: We found that PaO₂ decreased when pleurae were opened during OLV. This may be due to the sudden development of atelectasis in the non-dependent lung by exposure to atmospheric pressure. This decrease in PaO₂ can be relieved by closing the double-lumen endobronchial tube's plug of the non-dependent lung or by applying CPAP to the non-dependent lung when pleurae are opened.