In our study, POP occurred in 143 (19.7%) of 727 patients who underwent VATS lobectomy (Table 1). Patients with POP had higher PLOS and total hospital care costs than no-POP patients (Table 2). Three independent risk factors for POP after VATS lobectomy were identified: BMI grading ≥24.0 kg/m2, right lung lobe surgery and total intravenous crystalloid infusion grading in the postoperative 24 h ≥ 1500 mL (Table 3).
The incidence of POP after lung resection varies. Simonsen et al. [4] reported frequencies of 3.6% and Lee et al. [9] documented a prevalence of 6.2%, whereas, Arslantas et al. [11] noted that POP occurred in 18.7% patients after lung resection. One of the reasons for this fluctuation is due to the differences in the definitions of POP. In the current study, POP were defined similarly to Arslantas et al. [11] and Allou et al. [12], including a new pulmonary infiltrate on chest X-ray, leukocyte count > 10.0 × 109/L and fever. Our incidence of POP was 19.7%, which was compatible with the reported frequency [11] .
Our study showed that BMI grading ≥24.0 kg/m2 was an independent risk factor for POP after VATS lobectomy. The result of the present study corresponded with the earlier studies, which reported that overweight or obese patients have an increased risk of POP [15,16,17]. Obese patients often have reduced lung volume, altered ventilation pattern, decreased immune function, and comorbid conditions, which are risk factors for intra- and postoperative complications [16,17,18]. Overweight and obesity are spreading worldwide, and thoracic surgeons will encounter more overweight patients in need of surgery in the future [19]. Although a BMI ≥ 24.0 kg/m2 is not a surgical contraindication, it is necessary to pay close attention to overweight patients, and to strengthen respiratory exercise before lobectomy to reduce the risk of POP.
To the best of our knowledge, this is the first report to identify that right lung lobe surgery is an independent risk factor of POP after VATS lobectomy (Table 3). The incidence of POP was 23.0% (103 /448) after right lung lobe surgery and 14.3% (40/279) after left lung lobe surgery, respectively (Table 3). The reasons why right lung lobe surgery has an increasing risk of POP are unclear. The lung volume of right lung is larger than the volume of left lung (right/left lung volume, 1.22 ± 0.14) [20], so right lung lobe surgery has a greater impact on lung function and has a greater trauma than left lung lobe surgery, thus leading to an increasing risk of POP. Therefore, for patients with right lung lobe surgery, it is especially necessary to strengthen the training of respiratory function and cough ability before surgery, and take some measures to prevent lung infection after surgery, to avoid the occurrence of POP.
Finally, our study showed that total intravenous crystalloid infusion grading in the postoperative 24 h ≥ 1500 mL was an independent risk factor of POP after VATS lobectomy. In this study, POPs were all diagnosed 24 h after operation, so POP was not the reason for increased intravenous crystalloid infusion in the postoperative 24 h. Excessive intravenous fluid infusion would cause pulmonary edema and impair gas exchange, thereby placing patients at heightened risk for infection and respiratory failure [11, 13]. Shin et al. found that excessive perioperative fluid is associated with increased risk of postoperative pulmonary complications and increased 30-day mortality [13]. A meta-analysis of several trials suggested that larger fluid volumes increase the chances of postoperative pneumonia and pulmonary edema [21]. The harmful effects of fluid excess are frequently manifested in the lungs, especially after pulmonary lobectomy. Arslantas et al. conducted a study of perioperative fluid administration and the results showed that excessive perioperative infusion fluid during anatomic lung resections could increase postoperative pulmonary complications [11]. Our findings support the view that liberal postoperative fluid infusion has harmful effects on postoperative lung function and adds to the current understanding of the postoperative fluid management in several ways.
Some studies have reported risk factors for POP following lung cancer surgery. Lee noted that age ≥ 70 years, intraoperative red blood cell transfusion and forced expiratory volume in 1 s < 70% were independent risk factors of POP after lung cancer surgery [9]. Simonsen reported that major risk factors for POP following lung cancer surgery are advanced age, obesity, chronic pulmonary disease, alcoholism and atrial fibrillation [4]. The POP risk factors for VATS lobectomy in our study differ from the above studies, thus adding new content to the POP risk factors study.
Our study is one of the few to show risk factors for POP after VATS lobectomy. However, this study has potential limitations. First, it was a single-centre retrospective study. Second, antibiotics were used prophylactically in every patient, thereby masking the discovery of risk factors for POP. Finally, the study population only included adult patients who underwent VATS lobectomy, which limits the generalisability of the findings.