Chylothorax, although relatively rare, is known as a serious complication and has a variety of causes. In thoracic surgery, chylothorax is caused by a thoracic duct injury due to mediastinal lymph node dissection, especially when performed for primary lung cancer. The incidence of postoperative chylothorax following lung resection is estimated to be 0.25–3% [3, 6] and is known to occur more often in the right thoracic cavity . Previous studies have reported that lobectomy, right side surgery, robotic surgery, and pathological N2 disease are the most common causes of chylothorax . In addition, Uchida et al.  stated that the most frequent chyle leak point was the #4R lymph node.
To date, there have been multiple discussions regarding the treatment methods for postoperative chylothorax [2–4, 9–11]. The principles of conservative treatment include efficient pleural drainage, sufficient residual lung expansion, and pleurodesis for reducing the dead space in the thoracic cavity. Furthermore, we attempted to close the fistula by reducing lymphatic flow in the thoracic duct using a low-fat diet, fasting, and total parenteral nutrition . The first choice of treatment is conservative treatment, and it is reported that approximately 70–80% of the cases are relieved by conservative treatment alone .
Since chyle contains triglycerides, lymphocytes, proteins, and electrolytes, the loss of a large amount of chyle results in malnutrition and impaired immune function . Therefore, for cases in which conservative treatment is ineffective, surgical treatments involving closure of the damaged site of the thoracic duct or ligation of the thoracic duct are considered. Regarding surgical indications, Shimizu et al.  argued that reoperation should be performed if drainage fluid ≥ 500 mL is obtained on the first day following fasting and total parenteral nutrition. In addition, Takuwa et al.  concluded that reoperation should be considered if there is drainage ≥ 500 mL per day after starting a low-fat diet (≤ 10 g).
In our study, conservative treatment was successful if the amount of drainage was < 500 mL on the first day after starting a low-fat diet. Furthermore, when the drainage on the first day was ≥ 500 mL, the cases in which the drainage tended to decrease within 3 days recovered by conservative treatment. This suggests that even in cases in which the chyle leakage exceeds 500 mL daily, if a patient's general condition is maintained, the course could be observed conservatively at least until the third day. There was no noticeable difference in the duration of chest drainage between the surgery group and the conservative treatment group, and the maintenance period did not exceed 2 weeks even in the conservative treatment group. However, even if the drainage decreased by the third day, in the case where the drainage still exceeds 500 mL per day, the drainage period may be prolonged.
The present study has certain limitations. First, this study was a retrospective review that only included patients from a single institution. Second, the assessment regarding the properties of pleural effusion was subjective, and there was no objective index excluding the amount of drainage.
There was no clear protocol regarding the indication of pleurodesis in our hospital, and it was decided by the discretion of the attending physician. Although changes in the drainage amount did not suggest any indications for pleurodesis in this study, past reports have revealed that chylothorax could be controlled by pleurodesis using drugs such as OK-432 . A sufficient therapeutic effect could be expected in cases in which the expansion of the residual lung is well attained and the dead space in the thoracic cavity is small despite the drainage volume being large. Therefore, since this is a less invasive treatment than reoperation, future research based on the accumulated cases is warranted.