The evaluations of pulmonary complications after lumbar spine surgery across the United States are elucidated in this study. The NIS database, being the largest fully paid, publicly available inpatient database, was considered as the reflection of national trends and less affected by selection bias, hence chosen to describe the trends of pulmonary complications (Malcolm et al. 2020). While multiple comparisons were not statistically adjusted in primary analyses, the dual-threshold filtering and large effect sizes enhance confidence in the reported associations. Future studies may incorporate formal correction when investigating marginal effects. On average, 3.5% of patients undergoing lumbar spine surgery were complicated with respiratory failure, aspiration, pneumonia, or PE.

From the results of the current study on pulmonary complications in patients undergoing lumbar surgery, it can be seen that the annual incidence of pulmonary complications showed a fluctuating trend from 2010 to 2019 (Fig. 2). It is possible that the diagnosis of pulmonary complications according to the ICD-9-CM had changed to ICD-10-CM after 2014, the definition of pulmonary complications changed accordingly (Supplementary Fig. 3). This coding overhaul fundamentally altered complication definitions and documentation requirements, likely contributing to artifactual trends during the transition period. The observed rise in the occurrence of pulmonary complications following lumbar spine surgery prior to 2014 could potentially be due to the increased awareness of this complication among hospital coders (Anderson et al. 2012). Moreover, the presence of underdeveloped anesthesia methods and medical procedures, insufficient knowledge, or even the protocols for alleviating discomfort may contribute to a higher occurrence of respiratory complications (Fineberg et al. 2013; Bozic et al. 2013). Subsequently, there was a growing focus on respiratory complications, which then experienced a reversal in trend starting from 2015. Potential reasons for these patterns encompass advancements in respiratory cleanliness, prevention of deep venous thrombosis, refined anesthetic and surgical approaches, optimization before surgery, and comprehensive care during the perioperative period (Malcolm et al. 2020). However, the incidence showed an increasing trend from 2017 to 2019. One possible explanation for this trend is the growing number of individuals undergoing lumbar spine surgery as the population ages rather than coding artifacts, though residual coding system adaptation effects cannot be entirely excluded (Yang et al. 2023).

Regarding to demographic data, individuals experiencing pulmonary complications were 3 years older compared to those unaffected by such issues. Furthermore, the elderly population were more likely to suffer pulmonary complications. Consistently, advanced age was a significant predictor for pulmonary complications, in logistic regression (Table 3). A potential explanation accounting for this trend may be that the number of elderly patients requiring lumbar surgery is increasing with population aging (Bozic et al. 2013), posing an additional risk for pulmonary complications (Fineberg et al. 2013). Meanwhile, elderly populations are known to have a weaker immune system and more comorbidities predisposing to pulmonary complications (Raj et al. 2022).

Interestingly, female gender was found to be a protective factor for pulmonary complications (Table 3; Supplementary Fig. 1 C & D). Possible explanations for the finding that men who had undergone lumbar spine surgery were more likely to have pulmonary complications are as follows. While the exact mechanisms require further investigation, studies have suggested that estrogen may suppress pro-inflammatory cytokines such as IL-6, and this mechanism was reported to be associated with pulmonary vascular leakage and lung injury (Raj et al. 2022; Kragholm et al. 2021).

The elevated total charges among patients with pulmonary complications (Table 2) stem from multiple factors. Most intuitively, pulmonary complications are inherently costly and morbid (Noh et al. 2022). Previous reports indicated that respiratory complications, such as respiratory failure and pneumonia, had the highest attributable costs ($52,466) among complications following noncardiac surgery at a single private medical center, including cardiovascular, thromboembolism, and infectious complications (Dimick et al. 2004). Additionally, prolonged length of stay (LOS) contributes significantly through supplementary expenditures for nursing care, perioperative management, rehabilitation, and diagnostic testing (Huang et al. 2023; Brauer et al. 2000; Demeure and Fain 2007) (Table 2). Patients experiencing pulmonary complications following lumbar spine surgery were likely to exhibit a significantly higher mortality rate. In prior research, preoperative comorbidities such as diabetes, uncomplicated solid tumor without metastasis, and chronic pulmonary disease were identified as predictive factors for mortality in patients with lung diseases (Raj et al. 2022). We suggest that the deteriorated cardiopulmonary health and weakened immune function typically associated with these comorbidities contributed significantly to the increased risk. (Fig. 3).

Urban or teaching hospitals was found to be associated with the incidence of pulmonary complications. This correlation may be attributed to the severity and complexity of patients'disease states, as well as the frequent occurrence of comorbid conditions.

To enhance treatment outcomes, prescreening and risk stratification are paramount in surgical practice, necessitating a thorough understanding of risk factors prior to surgery (Yang et al. 2020a). Logistic regression analysis was employed to gain deeper insights into these risks. A significant finding in this study was that a higher number of preoperative comorbidities served as a critical risk factor for pulmonary complications, suggesting that poorer preoperative health status can potentially elevate the risk of postoperative adverse events (Yang et al. 2023).

Notably, pulmonary circulation disorders and continuous positive airway pressure emerged as robust predictors of pulmonary complications following lumbar surgeries, presumably due to their association with compromised cardiopulmonary health and immune function (Malcolm et al. 2020; Raj et al. 2022). Pulmonary circulation disorders can impair lung function, predisposing patients to complications. In this paper, respiratory failure was categorized as a type of pulmonary complication, and continuous invasive ventilation represented one of the therapeutic modalities for its management. Given the non-modifiable nature of these factors, preoperative identification of patients harboring these risk factors was imperative as they were at a heightened risk for developing pulmonary complications. Recognizing high-risk patients allows clinicians to optimize pulmonary function preoperatively through targeted measures like adequate pain management, early ambulation, and respiratory muscle training, reducing the risk of postoperative pulmonary complications (Souza Possa et al. 2014; Mans et al. 2015).

Cardiac-related complications represented a significant and non-negligible challenge in the postoperative period following lumbar spine surgery. Key risk factors for pulmonary complications identified included congestive heart failure, valvular disease, acute myocardial infarction, cardiac arrest, and acute heart failure. These cardiac complications exacerbated cardiac congestion and compromise ejection function, leading to obstructed pulmonary circulation and potentially severe pulmonary complications. Preventing pulmonary complications is therefore paramount in patients with cardiac dysfunction.

Moreover, disturbances in the circulatory system also contributed to the elevated risk of pulmonary complications. Vascular diseases, such as peripheral vascular disorders and acute cerebrovascular disease, as well as anemia types including deficiency anemia and chronic blood loss anemia, could all impact a patient's circulatory status. Additionally, issues like blood transfusion and hemorrhage/seroma/hematoma emerged as potential risks for pulmonary complications following lumbar spine surgery. These conditions may reflect perioperative circulatory instability, thereby increasing the likelihood of developing pulmonary complications.

Of particular concern were deep venous thrombosis and coagulation dysfunction (including coagulopathy and thrombocytopenia), which were significant risk factors for pulmonary complications. The effectiveness of interventions to prevent DVT, such as chemoprophylaxis, is therefore critical (Muthu et al. 2023). Surgical trauma-induced coagulation dysfunction could not only lead to deep venous thrombosis but also precipitate various complications, including pneumonia and acute myocardial infarction. Even more alarmingly, the detachment of thrombi could directly result in pulmonary embolism, causing damage to lung tissues and further exacerbating the severity of pulmonary complications. The significant burden of these pulmonary sequelae underscores the value of preoperative risk stratification using tools like the validated GSU-Pulmonary Score prognostic model (NIHR Global Health Research Unit on Global Surgery and STARSurg Collaborative 2024).

Therefore, in the clinical management of patients undergoing lumbar spine surgery, it is imperative to conduct a comprehensive assessment of the patient's cardiac and circulatory status and implement effective preventive measures. This approach aimed to mitigate the risk of cardiac and circulatory-related complications, thereby reducing the occurrence of pulmonary complications and ensuring patient safety and successful recovery. Meanwhile, in clinical practice, it can be recommended that patients undergo preoperative pulmonary rehabilitation (respiratory muscle training and aerobic exercise) and early postoperative ambulation, which is conducive to better recovery.

The impact of neurological disorders on the development of postoperative pulmonary complications, specifically those arising from lumbar spine surgery, could not be ignored. In our meticulous investigation, we delved into the potential risk factors associated with these complications, encompassing various neurological conditions such as other neurological disorders, psychoses, postoperative delirium, and nerve injuries. These conditions can directly affect respiratory centers and muscle function, cause impairment, or indirectly disrupt cardiovascular homeostasis, adversely affecting lung health.

In the current study and prior literature, a significant correlation had been observed between weight loss, fluid and electrolyte disorders, and the occurrence of postoperative pulmonary complications, although the underlying mechanisms remain elusive. Furthermore, evaluations of patients undergoing both general and vascular surgeries revealed a significantly increased risk of postoperative respiratory failure among those with substantial weight loss, corroborating the close link between weight loss and adverse respiratory events postoperatively. Additionally, our study identified diabetes (uncomplicated), chronic renal failure, acute renal failure, and gastrointestinal complications as crucial risk factors, which, in conjunction with weight loss and fluid and electrolyte disorders, may collectively contribute to the heightened risk of postoperative pulmonary complications. Therefore, preoperative assessment and postoperative management should prioritize these factors to prevent and mitigate the occurrence of pulmonary complications, ensuring patient safety and smooth recovery.

Furthermore, we identified various factors, including alcohol abuse, drug abuse, septicemia, urinary tract infection, and wound infection, as potential contributors to the development of pulmonary complications. These factors were intimately linked to the diminution of immune function caused by the invasion of pathogenic microorganisms into the body, thereby heightening the likelihood of pulmonary diseases. During recovery, patients compromised immune systems are prone to pathogen invasion, which can initiate or exacerbate pulmonary complications. Consequently, a meticulous assessment and management of these potential risk factors was imperative to safeguard patients'recovery and mitigate the occurrence of pulmonary complications.

There are inherent limitations associated with utilizing NIS databases in the present study. Firstly, when performing retrospective analyses, similar to the conduct of other large database studies, discrepancies in coding and potential inaccuracies in data entry may arise (Kulkarni et al. 2010). Specifically, the transition from ICD-9-CM to ICD-10-CM coding systems during the study period (post-2014) introduces potential artifacts and inconsistencies in diagnostic and procedural classification. Consequently, the incidence of postoperative pulmonary complications reported in our study may represent an underestimation of the true occurrence. Secondly, as an administrative database, NIS relies on ICD-9 and ICD-10 coding, which lacks granularity (e.g., distinguishing specific types or severities within pulmonary diagnoses like pneumonia or respiratory failure) and has certain limitations compared to manual chart review. Meanwhile, the NIS only captures inpatient billing data; therefore, granular intra-operative details—such as surgical approach (open, MIS, or microscopic), anesthesia technique (general, spinal, or combined), operative duration, patient BMI, smoking status, and intra-operative vital signs—are unavailable. These unmeasured variables are known independent predictors of PPC; hence, residual confounding cannot be excluded. Thirdly, the NIS database does not capture long-term outcomes beyond the index hospitalization, limiting our analysis to in-hospital events only. Additionally, the lack of information on imaging studies, laboratory tests, treatment regimens, and vaccination status may have an impact on the results (Raj et al. 2022). Importantly, the observational nature of this study and these limitations preclude definitive causal inferences regarding the identified associations; they should be interpreted as risk indicators rather than proven causative factors. Despite its limitations, leveraging a comprehensive and representative national database like the NIS remains advantageous in uncovering trends and demographic insights, owing to its widespread adoption as a trusted research instrument (Malcolm et al. 2020; Rapacki et al. 2021). Moreover, the validity of the NIS database in precisely identifying patients undergoing specific orthopedic surgeries has been corroborated through validation studies with other databases (Rapacki et al. 2021).