Relationship between preoperative red blood cell distribution width and postoperative pneumonia in patients with hip fracture: a retrospective cohort study

Abstract Background and Objective: The relationship between preoperative red blood cell distribution width and postoperative pneumonia in elderly patients with hip fracture remains unclear. To investigate whether preoperative red blood cell distribution width is associated with postoperative pneumonia in elderly patients with hip fracture. Methods The clinical data of patients with hip fractures in the department of orthopedics of a hospital from January 2012 to December 2021 were retrospectively analyzed. Logistic regression model and generalized additive model were used to identify both linear and nonlinear relationships between red blood cell istribution width and postoperative pneumonia. A two-piecewise regression model was performed to calculate the saturation effect. Subgroup analyses were performed using stratified logistic regression models. Results The study included 1444 patients in total. The incidence of POP was 6.30% (91/1444), the mean age of the patients was 77.55 ± 8.75 years, and 73.06 percent of them (1055/1444) were female. After full adjustment for covariates, preoperative red blood cell distribution width had a nonlinear relationship with postoperative pneumonia. The two-segment regression model showed an inflection point of 14.5%. On the left side of the inflection point, the incidence of postoperative pneumonia increased by 52% for every 1% increase in red blood cell distribution width (OR:1.52, 95% CI :1.08–2.16, P = 0.0173). On the right side of the inflection point, the effect size was not statistically significant (OR: 0.80 ,95% CI: 0.58–1.11, P = 0.1878). Conclusion The relationship between preoperative red blood cell distribution width level and postoperative pneumonia incidence is nonlinear in elderly hip fracture patients. The incidence of postoperative pneumonia is positively correlated with red blood cell distribution width when it is below 14.5%. A saturation effect is observed when red blood cell distribution width reaches 14.5%.