Pneumonia, a devastating complication in geriatric patients following hip fracture surgery, often results in seriously adverse outcomes. To our knowledge, the risk factors for postoperative pneumonia in this specific group are still debated. In this study, we incorporated the comprehensive risk factors in a large sample to obtain more reliable and applicable results. We found that the incidence of postoperative pneumonia was 5.7%, and age, sex (males), heart disease, respiratory disease, cerebrovascular disease, liver disease, preoperative stay and general anesthesia were identified as significant factors for postoperative pneumonia.
In this research, age was identified as an independent factor for pneumonia, consistent with most previous findings in previous studies [8, 18]. In a recent research, authors found this relationship was progressive with aging, and the risk was as 2.3, 3.9, and 5.6 times in patients aged 60‒69, 70‒79, ≥80 years as in patients aged 50 years . Similarly, another study found that individuals aged 80 years and older had a most strong magnitude of OR of 5.1 as compared with those under 50 years . This could perhaps be related that aging can lead to physiological degeneration of pulmonary function, primarily in the form of decline of breathing strength, lung compliance, cough reflex and respiratory defense, eventually bringing about pneumonia [21, 22]. In addition, aging also leads to impaired response of macrophages to injury repair and regeneration of functional tissue when stimulated by inflammation, aggravating local lung tissue damage, leading to reduced immune function and increased risk of pneumonia . Therefore, elderly patients, especially elder elderly patients ＞ 80 years should be always aware of the risk of pneumonia, and extracorporeal support and preoperative enhanced breathing exercises along with regimented temperature management are also necessarily warranted.
Although we found male sex having a moderate magnitude (OR, 2.27) of risk of pneumonia, its role was not consistent and the mechanism was also unclear and even controversy. Ekström et al  suggested that male patients have worse preoperative health status and higher comorbidity rate, consequently contributing to a two-fold increase in pneumonia in a prospective cohort study, contrasted with our finding that females had more prevalent comorbidities. Another study attributed this difference to the poorer pre-injury status , which, however, could not be captured in our study. Other studies also suggested the overwhelmingly predominated smokers and carriers of tracheobronchial conditions being males are the potential reason for risk of pneumonia, but we found that after adjustment for smoking and respiratory disease the males still showed the independent effect on pneumonia. These findings showed there may be other potential explanations or mechanisms for this association, and future study should elucidate this.
As is well known that co-morbidities status would substantially affect the postoperative complications, especially for those experiencing both trauma from a major fracture and subsequent surgery within a rather short period. In this study, we found several individual morbid conditions were associated with postoperative pneumonia: heart disease, respiratory disease, cerebrovascular disease and liver disease. These findings emphasized the clinical importance of inadequate physiologic reserve of organs and the undesirable systemic conditions [25, 26]. It is of particular note that chronic respiration disease, e.g. COPD, should be given special attention in practice due to the highest magnitude of risk for pneumonia and this finding was unsurprisingly consistent in literature [27, 28]. Anyhow, preoperative medical optimization is most, most important for the prevention of postoperative complications, not merely the pneumonia [29-31].
Early surgery within 48h and even within24h may be a most viable modifiable factor for prevention or reduction the occurrence of bed-rest-dependent complications, primarily pneumonia . Delaying surgery can cause pain, prolonged immobilization and the resultant weaken capacity of discharging phlegm, increasing the risk of developing pneumonia . We found 8% increased risk of postoperative pneumonia by an addition day of delay to surgery, in line with most previous studies [33, 34]. However, due to the setting of tertiary referral trauma center of our institution, it is impractical due to the fact that most patients referred to our institution had experienced 1-day delay, and the overheavy surgical capacity within a short period can post a considerable issue. Therefore, it is still a problem demanding solution for surgical room medical staff and operative surgeons to appropriately arrange such large number of hip fracture patients in as settings as such, and maybe a fast treatment channel for older elderly patients and specifically trained nurses allocated to qualified units can be established.
Anesthesia mode selection was also an essential consideration when managing complex major trauma in orthopaedic surgery fields [35, 36]. In the present study, general anesthesia was identified as an independent risk factor for development of pneumonia, consistent with findings of previous studies [20, 37]. This was explained by the general anesthesia being an invasive operation, which may cause damage to the respiratory system, affect the respiratory dynamics and muscle function and therefore reduce lung capacity. Meanwhile, intubation under general anesthesia can also impede the defense function, stimulate the increase of respiratory secretions, and finally induce occurrence of pulmonary infection . However, the evidence on anesthesia method affecting the postoperative pneumonia was inconclusive so far and selection of anesthesia was depending on numerous factors including patient comorbidities, anticipated surgical duration and surgical procedure, preference and of anesthesiologists on duty and personal factors from patients and their relatives. Therefore, although identified as a seemly modifiable factor, decision to select an anesthesia technique require multi-aspect communication and coordination.