The frequency of rib fractures in this study was 48.3%, and most were bilateral, multiple, and severe. By analysing the propensity score-matched cohort, we found that multiple rib fractures after successful resuscitation were associated with the development of pneumonia within 7 days after hospital admission independent of other risk factors for pneumonia. To the best of our knowledge, while numerous studies have reported on rib fracture caused by chest compression [5–8] and the development of pneumonia after resuscitation [9–15], none have ever addressed this issue.
As the result of a dedicated effort to improve the survival outcome of OHCA, a significant number of resuscitated OHCA patients may develop pneumonia following multiple rib fractures. The management of pneumonia during the post-resuscitation period is critical. Pneumonia can prolong the duration of mechanical ventilation and length of intensive care unit stay, and may worsen the prognosis . Several studies have reported various factors associated with the development of pneumonia, such as mechanical ventilation, TH, use of muscle relaxants, and lack of prophylactic antibiotics [9–15]. However, these factors are commonly present in resuscitated patients, as in our study participants. When the study participants were compared according to the presence or absence of multiple rib fractures before propensity score matching, the aforementioned factors were more frequently observed in the multiple rib fracture group. Because the incidence of pneumonia was also higher in this group, it appears that these risk factors were related to the development of pneumonia. However, after adjustment for these factors using propensity scores, our analysis indicated that multiple rib fractures were independently associated with the development of pneumonia during the post-resuscitation period.
The mechanisms through which rib fractures cause pneumonia are generally explained by pain , decreased vital capacity , and changes in chest wall dynamics that distort the movement of chest wall muscle . The frequency of pneumonia increases with the number of rib fractures, particularly in elderly patients  and those with frail chest injuries . Most of the rib fractures observed in this study were bilateral and multiple, and these patients were likely to develop pneumonia within 7 days after hospitalisation. To optimise post-resuscitation care, serious chest wall injuries (e.g., multiple rib fractures) should be carefully evaluated in resuscitated CA patients.
Early surgical fixation of multiple rib fractures or flail chest due to chest trauma improves survival by shortening the duration of mechanical ventilation [19, 20, 31]. Similarly, early surgical fixation of fractured ribs can benefit post-resuscitated OHCA patients who experience pneumonia following CPR-related chest wall injuries. Because it is almost impossible to eliminate CPR-related chest wall injuries without compromising the survival of patients with sudden OHCA, physicians need to consider this CPR-associated complication when treating resuscitated patients with OHCA to optimise post-resuscitation care. Further investigation of this issue will reveal its impact on communities and assist in establishing a surgical indication for CPR-related rib fractures.
Our study has several limitations. Firstly, the study was conducted in a single institution over a short observation period to minimise the heterogeneity of the study population. The 2015 resuscitation guideline was applied to our study. In addition, the diagnostic criteria for rib fractures and pneumonia may differ among institutions or investigators. For this reason, we had to establish the diagnostic criteria for this study. Consequently, the sample size is small, and generalization of the present is difficult. Hence, a multicentre study under the same setting is warranted. Secondly, due to the small number of study participants, we were unable to adjust for many confounders using multivariate analysis. Therefore, these findings were obtained through calculation of propensity scores using variables with a small number of risk factors. Although we examined as many risk factors for the development of pneumonia as possible, the possibility of unknown confounding factors cannot be completely ruled out. Differences in patient background between the two groups after propensity score matching were assessed using standardized differences. Although the factors for witnessed and initial shockable rhythm were not fully adjusted for, the lack of difference in the duration of CPR is not expected to have a significant impact on the results of this study. Thirdly, clinical findings (e.g., pain) may not be reflected in the diagnosis of rib fractures because we studied sedated patients after resuscitation and evaluated only imaging findings. However, with careful diagnosis, the frequency of rib fractures in the present study was similar to that observed in other studies .