Effects of increased expiratory pressure on blood gas tensions and pulmonary shunting during thoracotomy with use of the Carlens catheter.

THE ORIGINAL USE Of the Carlens catheter in thoracic surgery was to prevent contamination of healthy lungs with secretions. Today it is widely used also to obtain an optimal operating exposure by excluding the lung in the opened hemithorax from the anaesthetic system3 Extremely low arterial oxygen tensions may occur with this technique because of intentional collapse of the non-dependent lung and atelectasis in the dependent lung, resulting in excessive pulmonary shunting. 2 It is known that during thoracic surgery, with the patient in the lateral decubitis position and the nondependent pleural space open, the mediastinum tends to shift towards the dependent lung by gravity and further increases the possibility of atelectasis on that side. To overcome this shifting, some positive airway pressure in the dependent lung throughout the expiratory phase is often required. 3 It has been reported that higher arterial oxygen tensions can be obtained with increased expiratory pressures during non-thoracic surgery. 4 Theoretically, controlled ventilation during thoracic surgery with increased expiratory pressures could prevent both mediastinal shifting and atelectasis, expand collapsed alveoli, and decrease pulmonary shunting in the dependent lung. This, in turn, would increase arterial oxygen tensions. This study was an effort to evaluate this concept.