Figure 49-5 Conditions during thoracotomy in the lateral decubitus position when pulmonary artery (PA) catheter data may be inaccurate. A, During right thoracotomy with a PA catheter located in the collapsed right lung (one-lung ventilation [1 LV]), cardiac output (CO) may be lower than when the right lung is ventilated. The thermistor in the collapsed lung may be exposed to abnormal flow patterns or vascular wall interference. B, When the PA catheter is in the nondependent lung and the nondependent lung is exposed to continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP), pulmonary artery wedge pressure (Ppaw) may be inaccurate. Nondependent lung CPAP or PEEP may cause zone 1 conditions in the nondependent lung. Ppaw is probably always reasonably accurate when the PA catheter is in the dependent lung, even if the dependent lung is exposed to PEEP. (From Benumof JL: Anesthesia for Thoracic Surgery. Philadelphia, WB Saunders, 1987.)