The Effect of Two Airway Interventions, During One Lung Ventilation, on Blood Oxygen Content

Patients requiring one lung ventilation (OLV) for open thoracic surgery will be ventilated (breathing performed by a breathing machine) during anesthesia using a lung protective ventilation strategy (small breath volumes at 6ml/kg). During thoracic surgery the anesthesiologist is able to ventilate only one lung by inserting a special breathing tube, allowing the surgeon to operate on the non ventilated (diseased) lung. In a randomized trial two interventions used to improve blood oxygen levels during one lung ventilation will be compared . The two interventions are: 1. Continuous Positive Airway Pressure (CPAP) applied to the non ventilated (non breathing) lung and 2. Positive End Expiratory Pressure following a lung Recruitment Maneuver (RM-PEEP) to the ventilated (breathing) lung. CPAP is performed by applying a steady flow of oxygen to the non ventilated (non breathing) lung at a continuous gentle pressure of 5cmH20. To perform a Recruitment Maneuver (RM) the anesthesiologist inflates the ventilated (breathing) lung with oxygen, holding the breath for 25 seconds so all the lung is opened up. Immediately after the recruitment maneuver PEEP will be applied. PEEP is an action which also helps keep the lung open, maintaining the benefits achieved by the RM. It is performed by adjusting settings on the ventilator (breathing machine). The ventilator creates and applies a gentle pressure (5cmH20) to the ventilating lung at the end of each breath. The outcome measure will be the oxygen content in blood (PaO2), measured in mmHg, using blood sample analysis. The null hypothesis is that compared to CPAP, RM-PEEP does not significantly increase the oxygen content of blood during OLV when using a lung protective ventilation strategy.