Clinical implications of blood gas analysis of chest tube drainage

Blood gas analysis of chest tube drainage following thoracostomy for experimental and clinical penetrating chest injuries was evaluated to determine its usefulness in predicting the etiology of the injury. Twenty dogs were divided into four groups and sustained right chest injury as follows: Group I--closed chest lung laceration; Group II--open chest lung laceration; Group IIII-gunshot wounds; Group IV--thoracotomy and injection of autologous, mixed venous blood. All animals and 14 patients who sustained penetrating chest injury were made simultaneously from chest tube draininage, systemic artery, and central vein in all dogs and patients. Eight patients (Group A) had pneumothorax; six patients (Group B) did not. Mean control canine aortic PO2 and pulmonary arterial PO2 values in Group I did not differ significantly from those in the other three canine groups, nor from the two human groups. Group II dogs exhibited chest tube PO2 which was significantly (p less than 0.01) above aortic PO2. In Group IV, chest tube PO2 was increased significantly above pulmonary arterial blood. Patients without pneumothorax had values for PO2 in chest tube drainage and aorta which were not significantly different, whereas when pneumothorax was present, PO2 of chest tube drainage was significantly higher than that of aortic PO2. Thus blood gas determinations on chest tube drainage may reflect the nature of the injury; however, the presence of air in the pleural space can result in oxygenation of contained blood well above systemic arterial levels.