Serum Thrombomodulin as a Newly Identified Biomarker for Postoperative Lung Injury: A Prospective Observational Study

Postoperative lung injury after lung cancer resection is still a difficult problem to be solved. Thrombomodulin (TM) is a membrane-bound glycoprotein of endothelial cells, and its serum level is elevated in patients with acute lung injury or acute respiratory distress syndrome. In fact, TM is abundant in the pulmonary capillary vessels. Lung resection reduces the volume of pulmonary capillary vessels; however, the change in the serum levels of TM after lung resection remains to be investigated. We therefore analyzed the postoperative changes in the serum TM levels in 60 patients who underwent thoracotomy without lung resection (n = 3), partial resection of the lung (n = 15), or lobectomy (n = 42). Preoperative and postoperative day-1 laboratory data including the serum levels of TM and KL-6, a sialylated carbohydrate antigen (a biomarker for pulmonary fibrosis), and oxygenation index were collected. Unexpectedly, the postoperative serum levels of TM were lower than preoperative values in lobectomy group, whereas they remained unchanged after thoracotomy without lung resection and after partial resection of the lung. In addition, the serum TM level decreased proportional to the resected lung volume. Eight out of 42 patients with lobectomy presented high postoperative serum levels of TM, and 3 out of these 8 patients presented postoperative impaired oxygenation. Postoperative impaired oxygenation occurred only in patients with elevated TM levels; namely, an increase of serum TM is associated with impaired oxygenation after lung resection. In conclusion, serum TM is a possible biomarker for predicting the occurrence of postoperative lung injury.