The incidence of PPCs in elderly patients after thoracic surgery was 31.0%. This study identified nine independent predictors of PPCs. These nine candidates were used to construct a novel nomogram with good predictive performance for PPCs. This nomogram is a valuable tool for predicting the risk of PPCs in elderly patients who have undergone thoracic surgery. Each indicator in the nomogram contributes points, and a higher total point value indicates a greater likelihood of developing PPCs. The convenience of obtaining these indicators in clinical practice allows for easy evaluation of a patient's vulnerability to PPCs using the nomogram. The main advantage of the nomogram lies in its ability to identify high-risk patients promptly. By calculating the total points obtained from each indicator, healthcare professionals can assess the risk level and take appropriate measures to mitigate potential complications. This early identification enables the implementation of timely interventions, improving postoperative outcomes for elderly patients undergoing thoracic surgery.
Previous studies have identified a large number of risk factors for PPCs, especially advanced age and thoracic surgery [4, 9, 10, 17–19]. However, there is currently no research focusing on the risk factors for PPCs in elderly patients undergoing thoracic surgery. We identified nine independent risk factors for PPCs in elderly patients undergoing thoracic surgery: preoperative presence of COPD, elevated leukocyte count, higher PaCO2 levels, location at surgery, thoracotomy, intraoperative hypotension, blood loss > 100 mL, surgery duration > 180 min and malignant tumor. Some of the results were consistent with previous studies on PPCs.
COPD patients face a higher risk of PPCs due to a variety of complex and diverse physiological and anatomical reasons. The significant reduction in pulmonary function resulting from chronic bronchitis, emphysema, and other diseases limits compensatory ability after surgery, thereby increasing the risk of postoperative respiratory failure [20, 21]. Additionally, postoperative effects can exacerbate respiratory distress and contribute to respiratory muscle fatigue and failure. The chronic inflammation observed in COPD patients leads to an increase in respiratory secretions, which can result in mucus retention and potential lung infections. Moreover, increased airway hyperresponsiveness in COPD patients can lead to bronchospasm, which is further aggravated postoperatively, causing airway obstruction and heightened respiratory distress. Structural changes in lung tissues, including inflammation and emphysema, result in alveolar damage and reduced lung elasticity in COPD patients. These factors collectively contribute to decreased ventilatory function during the postoperative recovery process, thereby heightening the risk of complications such as lung atelectasis [22].
An increase in the leukocyte count may indicate that the body is in a state of stress or inflammation, which will have a series of effects on PPCs. Studies have shown that diseases that cause elevated leukocyte counts before surgery, such as preoperative acute pulmonary infection and sepsis, are independent risk factors for PPCs [17, 23–25]. However, the effect of preoperative leukocyte counts elevated but within the normal range on PPCs is complex. A normal immune response can help reduce the inflammatory response after surgery and contribute to lung recovery. The immune system functionality in the elderly typically experiences a decline with advancing age. At the same time, the overall health status, chronic diseases, and medication regimens of patients also impact their white blood cell count. Therefore, even though the white blood cell count may fall within the normal range, it may have already exceeded the upper limit of normalcy within the elderly population. Consequently, an elevated leukocyte count, even within the normal range, may represent a certain physiological or pathological condition that requires further evaluation and monitoring.
Preoperative elevation of PaCO2 can have significant consequences on the body's acid-base balance and respiratory function. High levels of PaCO2 can lead to acidosis, which can have detrimental effects on hemodynamics and respiratory function. In this acidotic state, the lungs become more vulnerable to damage, further impacting postoperative pulmonary function and leading to an increase in the risk of PPCs. Moreover, elevated PaCO2 levels can also inhibit the function of immune cells, disrupting the normal response of the immune system. This impaired immune response decreases the ability to effectively combat infections and inflammation, further increasing the risk of postoperative pulmonary infections and complications [26, 27]. Furthermore, patients with COPD are particularly susceptible to postoperative PPCs due to elevated PaCO2 levels. COPD patients have compromised pulmonary function, airway obstruction, and disrupted gas exchange, leading to increased PaCO2 levels. Additionally, the compromised respiratory muscle function and inadequate ventilation commonly observed in COPD patients contribute to the increase in PaCO2 levels, further exacerbating the risk of complications. Therefore, closely managing and monitoring PaCO2 levels and respiratory function are essential to ensure safe and successful postoperative recovery.
Esophageal surgery is a crucial method for treating various esophageal-related diseases, such as esophageal cancer and esophageal hiatal hernia. Esophageal surgery presents unique challenges due to the complex anatomical structures involved and the larger surgical area. In the treatment of esophageal cancer, partial or total removal of the esophagus may be necessary, which can entail handling structures such as the accessory gastric artery and lymphatic drainage of the lungs, increasing the complexity of the surgery. In contrast, mediastinal surgery and lung surgery typically focus on the mediastinum or lungs, resulting in a smaller surgical area. Consequently, esophageal surgery has a greater impact on surrounding lung tissues, increasing the risk of PPCs. Esophageal surgery often utilizes more invasive techniques, such as thoracotomy or thoracoabdominal surgery [28]. Thoracotomy during surgery can cause a certain degree of interference in the physiological balance of the thoracic cavity. For example, the disappearance of negative pressure in the pleural cavity causes a decrease in venous blood return to the heart, affecting the homeostasis of the respiratory and circulatory systems. These conditions can lead to complications such as postoperative atelectasis and restricted respiratory function [29]. In contrast, mediastinal surgery and lung surgery are generally thoracoscopic or minimally invasive surgeries and have relatively smaller impacts on the lungs [30]. Thus, thoracotomy is an independent risk factor for PPCs.
Esophageal surgery is associated with a higher risk of intraoperative hypotension because of the longer operation time and greater intraoperative blood loss than pulmonary and mediastinal surgery. These are also independent risk factors for PPCs found in this study.
An increased operation time leads to the infusion of additional anesthetics, fluids, or blood products, which may affect the patient's cardiovascular function and lead to intraoperative hypotension. In addition, the duration of operation was closely related to the duration of mechanical ventilation. This extended use of mechanical ventilation can result in various complications, including pulmonary overinflation, pressure-related injuries, respiratory muscle atrophy, loss of surfactant, and increased susceptibility to pulmonary infections [31]. Esophageal surgery patients are particularly at a higher risk of experiencing these complications due to the potential for aspiration and reflux of gastric contents into the lungs. To mitigate the negative impact of prolonged mechanical ventilation, healthcare providers should prioritize minimizing the duration of ventilation and promoting early extubation whenever feasible. Additionally, alternative ventilation methods, such as continuous positive airway pressure (CPAP), can be utilized to reduce the dependence on mechanical ventilation and decrease the risk of complications [32].
Increased surgical bleeding can have significant implications for patients undergoing thoracic surgery, particularly in relation to PPCs. Surgical bleeding often results in a decrease in blood volume, ultimately leading to decreased cardiac output and subsequent hypotension. This impairs tissue perfusion during surgery, especially in elderly patients with already decreased organ function, thereby further escalating the risk of PPCs. Furthermore, significant blood loss during surgery can result in postoperative anemia, a condition that impairs the delivery of oxygen to tissues, consequently increasing vulnerability to PPCs. In addition to these challenges, increased intraoperative bleeding can impair immune function, heightening the risk of infections, particularly in elderly patients who already have reduced immune function. Moreover, increased bleeding may lead to the transfusion of blood products, which can lead to transfusion-related reactions and complications, such as transfusion-related acute lung injury (TRALI), further increasing the incidence of PPCs [33].
Elderly patients are particularly susceptible to intraoperative hypotension, primarily due to a combination of factors [34, 35]. Elderly patients often enter the operating room in a state of frailty, more underlying diseases, or low physiological reserve, which increases their vulnerability to the hemodynamic effects of anesthetics during the induction phase of anesthesia [36]. The occurrence of hypotension can lead to poor blood circulation in the lungs after surgery. This decrease in lung blood circulation, both during and after the procedure, can lead to disruptions in pulmonary circulation, compromising blood supply and oxygenation to the lung tissue and increasing the likelihood of pulmonary complications. This effect is particularly pronounced in elderly patients due to the natural decline in vascular and cardiac function, further exacerbating the risk of PPCs.
Malignant tumor patients, particularly elderly individuals, often face numerous challenges related to their health. Previous studies have focused on the analysis of risk factors for PPCs after thoracic malignant tumor surgery, such as esophageal and cancer lung cancer, or that a history of malignancy is an independent risk factor for PPCs [19, 37–39]. Although the relationship between thoracic malignancy and PPCs after thoracic surgery is unclear, our study showed that thoracic malignancy is an independent risk factor for PPCs after thoracic surgery. The presence of the tumor itself, along with various treatments, such as surgery, radiation, and chemotherapy, can induce hypoalbuminemia, anemia, and a weakened immune system. These factors contribute to a greater susceptibility to PPCs in patients with malignant thoracic tumors. One notable effect of thoracic tumors is their ability to invade the pleura and lead to the accumulation of fluid in the chest cavity. The proliferation and infiltration of tumor cells can cause pleural effusion, pneumonia, and other PPCs, particularly in elderly patients who have compromised immune function. The impact of tumors is more severe in this population than in other populations due to their weakened immune systems, which increase vulnerability to tumor effects. Moreover, the growth of malignant thoracic tumors can result in preoperative lung dysfunction. As the tumor expands, it can compress or invade lung tissue, leading to a decrease in lung function. This impairment in lung function, coupled with natural aging and a decrease in lung tissue in elderly patients, further increases the risk of preoperative lung dysfunction and increases the likelihood of experiencing PPCs. In the case of malignant thoracic tumors, surgical resection may require a larger resection area or a longer operation time. Both open surgery and thoracoscopic surgery can cause damage to the tissues and organs within the chest cavity. This additional trauma exacerbates the impact on lung function and heightens the risk of experiencing PPCs.
Strengths and limitations
To our knowledge, our study represents the inaugural endeavor to develop and validate a nomogram of risk factors for PPCs in elderly thoracic surgery patients. Although the use of a nomogram for assessing the risk of PPCs in elderly patients after thoracic surgery is beneficial, it is important to acknowledge some limitations. First, this particular study was a single-center retrospective study, meaning that PPCs may have been missed or misdiagnosed. First, this particular study was a single-center retrospective study. Despite strict inclusion criteria and rigorous experimental design, potential biases may interfere with the study results and conclusions. Second, the case data may not have fully captured all instances of PPCs and underlying diseases in the patients, and some necessary data points may be missing or incomplete, which may have caused bias. Third, the leukocyte count was within the normal range. This is because all the patients in this study were scheduled for elective surgery, and our center generally postpones the operation if there is an acute infection or an increase in white blood cell count caused by other reasons before surgery. This approach may provide fewer indications for individual patients. However, this demonstrated the differential trend of this indicator between the two groups, thus furnishing a navigational cue for forthcoming inquiries. In future studies, multicenter, large-sample, prospective studies and subgroup analyses should be included to validate our results, and the data quality should be improved to increase the robustness of the studies.