To our knowledge, this is the first study reported the long-term prognosis of preoperative pneumonia and the influence of the preoperative pneumonia had on outcomes in patients admitted for hip fracture surgery or arthroplasty.
Outcomes of patients
In this retrospective study, the incidence of preoperative pneumonia in this vary population was higher (7.86%) than the previous studies (1%-3.2%)(7, 8, 14, 15). One possible cause for this phenomenon was that we applied a case-by-case reviewing method for the diagnosis of preoperative pneumonia, which may achieve more positive diagnosis for cases with mild symptoms than using data extraction method in medical record or social health database system(8).
In our cohort, outcomes of patients with preoperative pneumonia were generally worse than that of the normal patients (Table 2). Similar to previous study(16), hospital stays were longer for patients with preoperative pneumonia. In addition, we also observed a high ICU admission rate in these patients, which can be explained by high possibility of status aggravation after surgery of patients with preoperative pneumonia.
The overall 1-year mortality for hip fracture patients was 17.6%, which was close to previous studies(17, 18)(14%-22.8%) while patients with preoperative pneumonia had a 1-year mortality that significantly higher than that of patients without pneumonia (Table 2, 33.9% vs. 16.3%, p < 0.001). As depicted in Fig. 1, the survival rate of patients with preoperative pneumonia was decreasing over time and was significantly lower to those without the condition. The poor outcome of patients with preoperative pneumonia justified that it is necessary to evaluate potential risk factors for 1-year mortality in this group of patients.
Risk factors of 1-year mortality in patients with preoperative pneumonia
Through multivariate logistic regression, BMI < 18.5 kg/m2 was identified as one of the risk factors. As reported in population based observational studies(19, 20), low BMI (< 20 or 22 kg/m2 in this two study) was associated with high 30-day and 1-year mortality after surgery. A Meta-analysis by Nie et, al. revealed that this kind of survival advantage in relatively “obese” patients also existed in patients of various populations that diagnosed with pneumonia. A possible explanation other researchers(21) proposed was that patients with lower BMI may have more comorbidities than other patients, which caused the high mortality rate. However, we did not find a difference of the distribution for most of the comorbidities across different BMI groups (see Appendix). A more specified study with larger sample size may provide better static power to show the difference.
Another factor we discovered in the model was the type of anesthesia in hip fracture surgery or arthroplasty. Patients under regional anesthesia (epidural, spinal or peripheral neural blockade) were having a low 1-year mortality rate. Patorno et, al reported that regional anesthesia is associated with lower in hospital mortality for patients with hip fracture(22). While some studies failed to validate such an advantage(23, 24). According to a 2016 systemic review in Cochrane library(25) and another recent Meta-analysis(26), there were still no advantage of survival by regional anesthesia or more specifically peripheral neuro blockade. However, none of previous studies were focused on patients with preoperative pneumonia. The protective role of regional anesthesia in our study was possibly a result of avoiding further aggravation of pulmonary infection by avoiding intubation, deep sedation and mechanical ventilation.
CURB-65 score ≥ 3 was also indicated as a risk factor of 1-year mortality in patients with preoperative pneumonia. And in stratified analysis of odd ratios for 1-year mortality (Table 4), we found a linear correlation between CURB-65 score and 1-year mortality. However, compared to score 0, only when scores were higher than 3 that a significant increased risk of 1-year mortality existed. In COX regression (Fig. 2), the differences of survival rates were also not significant between patients with a CURB-65 score 0–2 and those free of pneumonia. Which indicating that patients with CURB-65 scores ≤ 2 may have similar long-term survival status to patients without pneumonia.
As a prediction tool for prognosis of patients with pneumonia, CURB-65 has been validated as a valuable scoring system for both 30-day and 1-year mortality in various populations(13, 27–29). Barlow et, al reported that patients that were diagnosed with community acquired pneumonia and rated with low CURB-65 scores (i.e. 0–1) did not differ much in 30-day mortality, which was similar to our findings(30). Other studies have shown that a cut-off value of 3 in CURB-65 had the strongest prediction value of mortality in these patients(13, 31). Our findings indicate that in patients admitted for hip fracture surgery or arthroplasty, CURB-65 score ≥ 3 indicated significant increased risk of 1-year mortality in patients with preoperative pneumonia. Whether the integration of severity evaluation with CURB-65 score and different therapeutic strategies can improve outcomes yet to be tested in further studies.
This study must be interpreted in context of multiple limitations. First, the nature of retrospective and single center study had resulted in limited power of ruling out potential confounding factors of the prognosis of patients. Second, we were not able to include functional analysis for patients enrolled in this study for sufficient reply from patients in follow up period. Which have compromised the evaluation of influences that preoperative pneumonia had on patients. Lastly, we don’t have complete data to include detail therapies (including antibiotic treatment, airway management, ventilation support and other complementary therapies) into the analysis. Some of these factors may affect the outcome of patients with preoperative pneumonia. These interventional factors need to be evaluated in more methodologically rigorous studies in the future.