Significant diaphragm elevation suggestive of phrenic nerve injury after thoracoscopic lobectomy for lung cancer: an underestimated problem

BACKGROUND: Phrenic nerve injury (PNI) during lung cancer surgery, without apparent nerve section or damage, is still not well-studied. The aim of our study is to find an easy and objective way to evaluate a significant diaphragm elevation (SDE) suggestive of inadvertent PNI and its incidence and impact on lung cancer patients undergone video-assisted thoracoscopic surgery (VATS) lobectomy. METHODS: Extent of diaphragm elevation was first examined on chest X-ray in a cohort of patients with invasive thymoma in whom phrenic nerve was intentionally transected. The result was then used as the criterion to diagnose a SDE suggestive of PNI in another cohort of VATS lobectomy patients. Fluoroscopy test was used to validate the results. Spirometry test was repeated to evaluate pulmonary function loss after surgery. RESULTS: Diaphragm elevation was 24.24%±6.2% in 22 invasive thymoma-patients, with 30% elevation adopted as the criterion to diagnose SDE suggestive of PNI. In 753 VATS lobectomy patients, 56 (7.4%) were diagnosed of SDE. On Fluoroscopy test, diaphragm movement was significantly less in patients with diaphragm elevation >30% than those without (5.0 vs. 11.0 mm, P=0.003), together with a significantly smaller diaphragm movement ratio on the operation (OP) side than on the contralateral side (17% vs. 42%, P=0.018). Although no difference in postoperative complications was found, reduction in FEV1, FVC, and DLCO was significantly greater in patients with a SDE than those without (P=0.009). CONCLUSIONS: Patients with more than 30% diaphragm elevation after VATS lobectomy is highly likely to have PNI and should undergo fluoroscopic validation. Inadvertent PNI during VATS lobectomy is an underestimated phenomenon and is associated with significantly greater loss of pulmonary function.