Postoperative Pneumonia in Geriatric Patients With a Hip Fracture: Incidence, Risk Factors and a Predictive Nomogram

Abstract

Objectives: To evaluate the incidence and risk factors of postoperative pneumonia (POP) in geriatric patients with a hip fracture after surgery, to design a predictive nomogram, and to validate the accuracy of the nomogram.

Design: Retrospective study.

Setting: A tertiary hospital affiliated to a medical university.

Patients/participants: We retrospectively studied 1285 surgical-treated geriatric patients with a hip fracture from April 2010 to April 2018.

Intervention: Surgical treatment was performed on the patients of this study. The procedure methods were classified as: total hip arthroplasty, hemiarthroplasty, percutaneous fixation, intramedullary nail fixation, and plate/screw fixation.

Main outcome measurement: The primary interest of end point of this study is the development of POP during the postoperative period. The postoperative period in this study was defined as the time from 24 hours after surgery to discharge. The diagnostic criteria for pneumonia were set according to the guidelines built by the Infectious Diseases Society of America and the American Thoracic Society (Guidelines for the Management of Adults with Hospital-Acquired, Ventilator-Associated, and Healthcare-Associated Pneumonia, 2005). Potential variables for developing POP were identified using logistic regression analyses initially and were further selected via the method of LASSO. Then the independent risk factors were identified by multivariable regression analyses. A predictive nomogram was built based on the multiple regression model, and the calibration abilities of the nomogram was measured by Harrel C-index, calibration plot and Hosmer-Lemeshow test, respectively. Decision curve analysis was carried out to assess the net benefit due to threshold probability and an on-line questionnaire survey was conducted among the clinicians to assess the applicability of the nomogram coherently.

Results: Of the 1285 patients, 70 (5.4%) developed POP. COPD, number of comorbidities, ASA classification >2, preoperative dependent functional status and cognitive impairment were identified as independent risk factors of POP. The nomogram built based on the results showed good accordance between the predicted probabilities and the observed frequency. The decision curve analysis confirmed the clinical utility of the nomogram when the threshold probabilities were between 5% and 65% due to the net benefit, while the results of on-line questionnaire among 200 clinicians showed that 91.5% of the participants had a mental threshold of intervention between 5-50%.

Conclusion: (1). COPD, number of comorbidities, ASA classification >2, preoperative dependent functional status and cognitive impairment are independent risk factors for POP. (2). The nomogram built in this study has a good accordance between the predictive risk and the observational incidence. The results of decision curve and questionnaire among clinicians show well applicability of the nomogram.

Keywords: geriatric; hip fracture; nomogram; postoperative pneumonia.

Figure 1.

Predictive nomogram for postoperative pneumonia. This predictive nomogram was constructed based on the multivariable model. To use the nomogram, a vertical line is drawn up to the top point row to assign points for each variable. Then, the total number of points is calculated, and a vertical line is drawn downward from the total point row to obtain the probability of POP.

Figure 2.

Calibration plot. The calibration curve showed good concordance between predicted probability and actual probability.

Figure 3.

Decision curve plot. In the decision analysis curve, the nomogram was compared with the null model for its added value, which turned out that the nomogram was applicable when thresholds were in the range between 0.05 and 0.65, due to the net benefit.