Postoperative Pulmonary Infection in Elderly Patients With Hip Fracture: More Attention Needed

Background: Postoperative pulmonary infection is a serious complication in elderly patients with hip fracture, it’s necessary to identify the inuencing factors of pulmonary infection in patients with hip fracture. Methods: Elderly patients with hip fractures admitted from January 1, 2020 to July 31, 2021 were included. The characteristics of patients with pulmonary infection and no infection were evaluated and compared. Logistic multivariate regression analyses were conducted to assess the risk factors of pulmonary infection. Results: 267 patients with hip fracture were included, the incidence of pulmonary infection in patients with hip fracture was 13.11%. There were signicant differences in the age, diabetes mellitus, anemia, hypoalbuminemia, anesthesia method and duration of surgery between infection and no infection group, no signicant differences in the gender, BMI, hypertension, hyperlipidemia, type of fracture, preoperative oxygen saturation, white blood cell count, platelet count, red blood cell count, creatinine, alanine aminotransferase, aspartate aminotransferase, estimated blood loss during surgery were detected between infection and no infection group. Logistic regression analysis showed that age ≥ 70y(OR2.326 , 95%CI1.248~3.129), diabetes mellitus(OR2.123, 95%CI1.021~3.551), anemia(OR3.199,95%CI1.943~5.024), hypoalbuminemia(OR2.377, 95%CI1.211~3.398), general anesthesia(OR1.947, 95%CI1.115~3.038), duration of surgery ≥ 120min(OR1.621 , 95%CI1.488~2.534) were the risk factors of pulmonary infection in elderly patients with hip fracture(all p<0.05). Escherichia Coli(33.33%), Klebsiella pneumoniae(28.57%), Staphylococcus aureus(21.43%) were the most common bacteria of pulmonary infection. Conclusion: There are many risk factors for pulmonary infection in elderly patients with hip fractures after surgery.

death of the patient [5,6]. Therefore, the prevention and treatment of postoperative pulmonary infection in patients with hip fractures is of great signi cance to the prognosis of patients.
The rate of new pulmonary infections after hip fracture is 8. [12][13][14][15][16][17][18][19].05% [7,8]. Once patients have lung infections, the risk of death within 30 days after surgery is 8 times that of other patients without pulmonary infections [9]. It can be seen that for postoperative patients with hip fracture, timely and reasonable preventive interventions for pulmonary infections are needed to improve the prognosis of patients [10]. To ensure the rationality of the implementation of preventive interventions for pulmonary infections after hip fractures in the elderly, it is necessary to understand a series of risk factors that may be associated with pulmonary infections. At present, although there are several reports on the risk factors of pulmonary infection after hip fracture surgery, due to the limitations of various research subjects, regions and populations, a uni ed understanding has not been reached so far. Based on this background, we retrospectively analyzed the clinical data of elderly hip fracture patients undergoing surgical treatment in hospital in recent years, aiming to analyze the risk factors that may be associated to the hospitalacquired pulmonary infections in elderly hip fracture patients after surgery, to provide reference for the clinical development of reasonable plan for the prevention and treatment of pulmonary infection after hip fracture.

Ethical consideration
In this study, all methods were performed in accordance with the relevant guidelines and regulations.
Approval from the ethical committee of Wuhan Fourth Hospital (approval number: A10085c) had been obtained in this study, and all the included patients were well informed and written informed consents had been obtained from all the included patients.

Patients
We selected elderly patients with hip fractures admitted from January 1, 2020 to July 31, 2021 as the study patients. The inclusion criteria of this study were: (1) The hip fracture was con rmed by MRI or Xray. (2) The patient received arti cial hip replacement or internal xation in our hospital. (3) The clinical data was complete. (4) Age > 60 years old. (5) The patients were informed and agreed to participate in this study. Exclusion criteria in this study were: (1) Patients with other infectious diseases diagnosed before surgery. (2) Those who have received surgical treatment for fractures of the same site in the past (3) Patients who were not willing to participate in this study.

Diagnostic criteria for pulmonary infection
We referred to the relevant diagnostic criteria for hospital-acquired pneumonia in the "Guidelines for the Diagnosis and Treatment of Hospital-Acquired Pneumonia" of the Chinese Medical Association Respiratory Medicine Branch [11]. The criteria were: (1) After the operation, the patient's original respiratory disease-related symptoms aggravated, or sputum coughing, thick sputum coughing. (2) The patient developed fever after the operation. (3) Physical examination results showed signs of lung consolidation, and pulmonary rales could be heard on auscultation. (4) White blood cell count < 4 ⋅10 9 /L or > 10⋅10 9 /L. (5) The chest X-ray lm showed patchy in ltrates or interstitial changes. After excluding patients with lung cancer, tuberculosis, pulmonary embolism and other pulmonary diseases, in the above items, if the patient meets any of (1)~(4) and also meets item (5), the diagnosis can be con rmed for pulmonary infection.

Bacteria identi cation
The sputum of elderly patients with pulmonary infection was collected. The specimen was collected as early morning sputum, and the in uence of oral bacteria was removed after gargle. And we asked the patient to cough as much as possible to take deep sputum. The coughed sputum would be sent to the sterile container for inspection in time. Bacterial culture of sputum samples was conducted in the laboratory of our hospital, the inspection instrument for identifying the bacteria was the automatic microbial identi cation and drug sensitivity analyzer XE100 (France BioMérieux).

Data collection
The two authors retrospectively reviewed the original records of patients' medical records and collected the following relevant patient information: gender, age, body mass index(BMI), hypertension, diabetes mellitus, hyperlipidemia, anemia, hypoalbuminemia, type of fracture, preoperative oxygen saturation, preoperative laboratory examination including white blood cell count, platelet count, red blood cell count, creatinine, alanine aminotransferase, aspartate aminotransferase, anesthesia method, duration of surgery, estimated blood loss during surgery.

Statistical analysis
We used SPSS 24.0 statistical software for data analysis. The measurement data were expressed as mean ± standard deviation, and the t test was used for group comparison. And the count data was expressed as the cases and percentage, Chi-square test was used for group analysis. The variables with statistical differences in the univariate analysis were further included in the logistic multivariate regression analysis. p < 0.05 indicated that the difference was statistically signi cant in this present study.

Results
The characteristics of patients 267 postoperative patients with hip fracture were included in this study nally, of whom 35 patients had been diagnosed as pulmonary infection, the incidence of pulmonary infection in patients with hip fracture was 13.11%. As presented in Table 1, there were signi cant differences in the age, diabetes mellitus, anemia, hypoalbuminemia, anesthesia method and duration of surgery between infection and no infection group(all p < 0.05), no signi cant differences in the gender, BMI, hypertension, hyperlipidemia, type of fracture, preoperative oxygen saturation, white blood cell count, platelet count, red blood cell count, creatinine, alanine aminotransferase, aspartate aminotransferase, estimated blood loss during surgery were detected between infection and no infection group(all p > 0.05). The variable assignments of multivariate logistic regression were presented in Table 2. As indicated in  Anesthesia method X 5 General anesthesia = 1, lumbar anesthesia = 2 Duration of surgery(min) X 6 ≥ 120 = 1, < 120 = 2  Table 2 The variable assignments of multivariate logistic regression   Table 4 The pathogen distributions of pulmonary infection in patients with hip fracture (n = 42)

Discussions
The incidence of pulmonary infection in elderly patients with hip fractures after surgery differs in regions with different economic levels [12], but the overall incidence is still relatively high, which is worthy of attention. In addition, postoperative lung infection will further increase the risk of death in such patients [13]. Studies [14,15] have shown that lung infection is an independent risk factor for death after hip fracture in the elderly. Previous study [16] has found that 14% of elderly hip fracture patients with lung infections died within 30 days, while the case fatality rate of patients with non-pulmonary infections is only 1.7% within 30 days. Another study [17] has showed that the risk of death for patients with pulmonary infection after hip fracture is 7.36 times higher than that of patients without lung infection after surgery. Therefore, the prevention of pulmonary infection should be strengthened clinically in order to reduce the complications and mortality. The results of this study have found that the incidence of pulmonary infection in patients with hip fracture is 13.11%, which is similiar to previous reports [18,19].
And we have found that age ≥ 70y, diabetes mellitus, anemia, hypoalbuminemia, general anesthesia, duration of surgery ≥ 120min were the risk factors of pulmonary infection in elderly patients with hip fracture, early intervention targeted on those in uencing factors should be taken to reduce the development of postoperative pulmonary infections.
Regarding the in uence of age on postoperative pulmonary infections in elderly patients with hip fractures, many studies [20,21] have reached different conclusions. A study [22] has reviewed 1,429 patients undergoing hip fracture surgery, and the results have showed that the higher the age, the greater the probability of postoperative lung infections. This may be because elderly patients have more underlying diseases and the body's immune function is reduced, which is extremely easy under the invasion of pathogenic bacteria, combined with fracture trauma, surgical stress, and long-term bed rest caused a further decline in immunity, which induced pulmonary infection [23][24][25]. However, some studies[26-28] have pointed out that the occurrence of postoperative lung infections should be attributed to the increase in the number of comorbidities that accompany age, rather than age itself. However, it is currently recognized that the incidence of hip fractures in elderly patients increases with age, and surgery is the current main treatment method. Therefore, surgery cannot be given up on the grounds of advanced age, and other controllable patients should be evaluated. For patients with more risk factors, we should adopt targeted interventions to reduce the risks of postoperative pulmonary infections.
Malnutrition has been proven to be one of the important risk factors for postoperative pulmonary infection in elderly patients with hip fracture. In addition to low BMI, serum albumin is also an important indicator of nutritional status [29]. Studies [30,31] have pointed out that low serum albumin levels increase the risk of pneumonia, because wounds, fracture healing, and muscle strength recovery require a large amount of protein supplementation. When protein is insu cient, muscle strength and limb function decline, causing the prolonging duration of bed time [32]. Besides, some patients are in a state of malnutrition when they are admitted to the hospital, coupled with increased catabolism caused by trauma and surgery, and increased demand for nutrients, resulting in a further sharp decline in nutritional status, weakened immunity, and increased risk of pulmonary infection [33]. Therefore, elderly patients with hip fractures should be screened for nutrition before surgery, and nutritional support interventions should be implemented before surgery to reduce the risk of pulmonary infections due to malnutrition.
Diabetes may be one of the risk factors for postoperative lung infection in elderly patients with hip fracture. Some studies [34,35] have found that patients with diabetes before surgery are prone to pulmonary infection after surgery, which is consistent with the results of this study. However, some studies [36,37] have pointed out that diabetes has nothing to do with the occurrence of postoperative lung infections in elderly patients with hip fractures. Study [38] has reported that when the patient's blood glucose is > 200 mg/dL, it will increase the incidence of pneumonia. Diabetes may be associated with postoperative lung infections in elderly patients with hip fractures, but this relationship may only exists when blood sugar is high [39]. The reason may be that when the blood sugar of diabetic patients is too high, the plasma osmotic pressure will also increase, which inhibits the phagocytic ability of immune cells in the blood and is prone to infection [40,41]. However, due to the small sample size of related studies, there may be biases in the results. Further researches are needed to con rm the role of diabetes in the future.
Studies [42,43] have reported that the longer duration of surgery is an important risk factor for postoperative pulmonary infection in elderly patients with hip fractures, which is more consistent with the results of this study. The prolonged operation time may be caused by a variety of factors, such as severe osteoporosis and complex fracture morphology [44]. The prolongation of the operation time can lead to an increase in blood loss during the operation, and the prolongation of the patient's intraoperative hypothermia time, resulting in a decrease in their resistance, thereby increasing the postoperative pulmonary infection [45]. In addition, during general anesthesia surgery, the cough re ex is suppressed, and prolonged surgery leads to rapid proliferation of lower respiratory tract bacteria, which may lead to the occurrence of pneumonia [46]. Therefore, medical staff should shorten the operation time as much as possible, and pay attention to monitoring the patient's body temperature and keep warm during the operation.
At present, many scholars [47,48] believe that general anesthesia is related to the occurrence of pulmonary infections after surgery. Because local anesthesia does not affect the patient's spontaneous breathing, does not inhibit the protective cough re ex, and at the same time avoids tracheal intubation, thus reducing the risk of postoperative pulmonary infection. But the shortcoming of the study is that doctors are more inclined to adopt general anesthesia for patients with more severe illness, which may cause selection bias. In addition, it's been reported [49] that the incidence of pulmonary infection after local anesthesia is lower than that of patients under general anesthesia. However, when subgroup analysis is performed, only in patients with femoral intertrochanteric fractures, the difference in the results of the study is statistically signi cant, while in the femoral neck There is no such trend among fracture patients. However, the speci c reasons are not clear, and further studies are needed in the future. Furthermore, this study has found that the bacteria in lung infections are mainly gram-negative bacteria. This result suggests that the detection of pathogenic bacteria should also be paid attention to in actual clinical treatment, and reasonable antimicrobial treatment should be selected in combination with patient drug sensitivity test to improve anti-infection effects.

Conclusions
In summary, there are many risk factors for hospital-acquired pulmonary infection after hip fracture in the elderly, for patients with age ≥ 70y, diabetes mellitus, anemia, hypoalbuminemia, general anesthesia, duration of surgery ≥ 120min, they may have higher risks of postoperative pulmonary infection. Actively correct the patient's anemia, treat comorbidities, and improve lung function before surgery, and give patients targeted intervention after surgery, to a certain extent, may reduce the risk of hospital-acquired pulmonary infections after surgery. For patients who have already developed pulmonary infections, bacterial culture and drug sensitivity testing should be carried out as soon as possible to ensure the rationality of the use of antibacterial drugs.
Abbreviations BMI: body mass index Declarations Ethics approval and consent to participate In this study, all methods were performed in accordance with the relevant guidelines and regulations. Approval from the ethical committee of Wuhan Fourth Hospital (approval number: A10085c) had been obtained in this study, and all the included patients were well informed and written informed consents had been obtained from all the included patients.

Consent for publication
Not applicable.

Availability of data and materials
All data generated or analyzed during this study are included in this published article.

Competing interests
The authors declare that they have no competing interests.

Funding
None.
Author contributions P Z designed research; Y Y, P Z conducted research; Y Y, P Z analyzed data; Y Y, P Z wrote the rst draft of manuscript; P Z had primary responsibility for nal content. All authors read and approved the nal manuscript.