Abstract
BACKGROUND: Pulmonary contusions (PCs) have historically been viewed as a serious complicating factor in thoracic injury. Recently, there has been conflicting evidence regarding the influence of PCs on outcomes; however, many studies do not stratify contusions by severity and may miss clinical associations. We sought to identify if contusion severity is associated with worse outcomes.
METHODS: A previously published chest wall injury database at an urban Level I trauma center was retrospectively reviewed. All severely injured subjects (defined as Injury Severity Score [ISS] ≥ 15) with moderate to severe thoracic injury (defined as a chest wall Abbreviated Injury Scale [AIS] ≥ 3) who required mechanical ventilation for > 24 h were stratified by contusion severity. Moderate to severe contusions were defined as AIS contusion ≥ 3 and Blunt Pulmonary Contusion 18 (BPC18) score ≥ 3.
RESULTS: Over 5 y, 3,836 patients presented with chest wall injuries, of which 1,176 (30.6%) had concomitant contusions. When screened for inclusion criteria, 339 subjects with contusions and 211 subjects without contusions (no-PC) were identified. Of these, 234 had moderate to severe contusions defined by AIS contusion ≥ 3 (PC-A) and 230 had moderate to severe contusions by BPC18 ≥ 3 (PC-B). Compared to no-PC, both PC-A and PC-B groups had significantly lower mortality (17.9% and 17.4%, respectively, vs 28.9%); however, PC-A and PC-B groups had longer durations of mechanical ventilation (6 and 7 d, respectively, vs 5 d), longer ICU length of stay (10 and 10 vs 8 d), and longer overall hospital length of stay (15 and 15 vs 13 d).
CONCLUSIONS: In severely injured polytrauma patients, PCs are seen with more severe chest injuries. Furthermore, moderate to severe contusions are associated with longer durations of mechanical ventilation, ICU length of stay, and hospital length of stay. Despite practice pattern changes, contusions appear to contribute significantly to the clinical course of the blunt chest wall injured patients.
Introduction
Pulmonary contusions (PCs) are a commonly encountered consequence of high-energy thoracic injury, affecting as many as 5.2% of all injured patients.1 In severely injured patients (Injury Severity Score [ISS] > 15), the incidence may be as high as 50%.2,3 Historically, contusions have been correlated with worse respiratory function, morbidity, and higher mortality. 4-6 Mortality in the setting of contusion ranges widely from 14–40%, and notable associations between contusions and ARDS have been identified.1,5-7 However, much of the current contusion understanding is derived from animal studies from the 1970s through 1990s. These studies tested the evolution of contusions using resuscitation strategies common to that time period, consisting mostly of high-volume crystalloid resuscitation directed at maintaining “normal” blood pressures.4 High-volume crystalloid resuscitation in the setting of injury has been found to exacerbate PCs,4 causing perturbations to oxygenation, increasing the need for intubation and advanced mechanical ventilation strategies. As a result, current management of the injured patient employs reduced crystalloids that may reduce PC consequences.
Recently, there has been conflicting evidence regarding the impact of PCs on clinical outcomes, and some studies have suggested there may be only minor, if any, clinical consequences of contusions following blunt chest injury.8-11 In 2008, Dinh and colleagues12 suggested that only contusions seen on initial presentation were of clinical importance. Rodriguez and colleagues9 came to the conclusion that in the era of pan-cross-sectional imaging isolated contusions and those PCs seen only on computed tomography imaging are of little clinical importance. In 2017, Chrysou and colleagues10 suggested that PCs are common but appear to have little effect on outcomes. These observations have been made over a heterogeneous array of methods and patient cohorts but followed a trend of analysis by differentiating only the presence or absence of contusions.
More recently, Dhar et al11 evaluated PCs in the setting of populations at high risk for respiratory complications. This high-risk population was defined as severely injured subjects (ISS ≥ 15) with moderate to severe thoracic injury who required mechanical ventilation for > 24 h. Finding no difference in outcomes between subjects with and without contusions, these authors echoed other studies concluding that PCs have contributed little to negative outcomes.9-12 The recent trend to treat contusions as either being present or absent as opposed to graduated by severity may disregard clinically important implications. Several injury severity scales exist to grade PCs. The most widespread of these scales are the Abbreviated Injury Scale (AIS)13 and the Blunt Pulmonary Contusion 18 (BPC18) score.14 By stratifying PCs by severity, a population in greater need for academic scrutiny and meticulous respiratory support and care may be realized. We hypothesized that stratification of PCs by severity in an injured population would reveal that PCs are associated with worse outcomes.
QUICK LOOK
Current Knowledge
Pulmonary contusions (PC) are a commonly encountered injury in the trauma patient, affecting as much as 5.2% of all injured patients. In recent years, there has been conflicting evidence on the impact of PCs on clinical outcomes. Some studies have suggested there may be only minor if any clinical consequences of PCs in the setting of blunt chest injury.
What This Paper Contributes to Our Knowledge
When present in a severely injured patient population requiring mechanical ventilation, more severe PCs demonstrated longer ICU and hospital lengths of stay. Subjects with any PCs were at an increased risk of developing respiratory failure for > 48 h when adjusted for age, gender, and comorbid diabetes.
Methods
A retrospective review of patients sustaining blunt chest wall injuries over a 5-y period at a single urban American College of Surgeons–verified Level I trauma center was performed utilizing an institutional trauma registry. All adult subjects (age > 15 y) sustaining bony chest wall injuries between January 2014 and December 2018 were included and screened for PCs. A portion of this database has been previously published;15 however, the current data set was expanded to include PC information as detailed below. Data gathering and analysis was conducted following University of Cincinnati Institutional Review Board approval (IRB # 2017–2673).
In keeping with prior methods published by Dhar et al,11 subjects included in the analysis had severe injuries (defined as ISS ≥ 15) with moderate to severe thoracic injury (defined as thoracic AIS ≥ 3) who required mechanical ventilation for > 24 h. In an effort to screen more specifically for bony injuries, chest wall AIS (which is isolated to rib cage and sternal fractures) was used in place of thoracic AIS, which can be skewed by nonpulmonary cardiac and great vessel injuries. These subjects were then divided into 2 subgroups: those meeting inclusion criteria with PCs and those without contusions (no-PCs). Subjects with PCs were scored by 2 separate scoring systems into moderate to severe groups according to the contusions/laceration AIS (PC-A) and the BPC18 score (PC-B). Details of the PC scoring systems can be seen in Figure 1. Records were reviewed for data including demographics, hospitalization data, tracheostomy, complications, and 30-d readmissions. All imaging (including initial digital chest roentgenogram and chest computed tomography CT scan if available) was reviewed by 2 authors (SWZ and CFJ) for injury pattern and contusion severity using both of the scoring systems above according to previously described methods.3,13,14 PC on imaging was defined as an area of increased lung parenchymal opacity without bronchial or vascular crowding. Moderate to severe contusion was defined as contusions/laceration AIS ≥ 3 and BPC18 ≥ 3. The AIS is the internationally recognized system for injury coding produced by the Association for the Advancement of Automotive Medicine, and scoring can range from 2–5. The BPC18 score is based on both the location and density of contusion and ranges from 1–18. Further clarification of the 2 scoring systems used with representative images can be seen in Figure 1.
Data were collected and analyzed using descriptive statistics and univariate analysis. Statistical analysis was performed using SPSS (Version 26; IBM, Armonk, New York) and SAS 9.4 (SAS Institute, Cary, North Carolina). Non-normally distributed continuous data were evaluated according to medians with interquartile ranges, and discrete data are presented as mean with percentage. Univariate statistics were evaluated using chi-squared or Fisher exact tests for categorical variables. Continuous variables were evaluated using nonparametric Mann-Whitney U tests. A multivariate logistic regression was used to assess whether the odds of respiratory failure are associated with a PC, while adjusting for other risk factors. Significance was determined by P < .05.
Results
Over 5 y, 3,836 patients presented with chest wall injuries, of whom 1,176 (30.6%) had concomitant contusions. A total of 550 subjects met inclusion criteria and had severe injuries. Of these 550 subjects, 211 (7.9%) were found to have no-PC and 339 subjects had contusions (28.8%). The 339 subjects with PCs were stratified into moderate-severe contusions by a contusion scoring method; 234 (19.8%) met criteria for severe contusion by AIS (PC-A) scoring and 230 (19.5%) when stratified by BPC18 scoring (PC-B) (Fig. 2). The distribution of subjects with PCs between the 2 scoring systems can be seen in Figure 3.
Baseline characteristics as well as injury characteristics between no-PC, PC-A, and PC-B can be seen in Table 1. Compared to no-PC, all subjects with PCs had multiple characteristics that were significantly different. Notably, the subjects with contusions were significantly younger and had fewer preinjury respiratory disorders or diabetes. Additionally, both the PC-A and PC-B groups had significantly worse injuries with higher ISS, more ribs fractured, sternal fractures, hemothoraces, pneumothoraces, and greater need for tube thoracostomy. Between the 2 scoring systems, the PC-B group had a significantly higher rate of drug use compared to no-PC, but there were no significant differences between the subjects grouped by PC-A and PC-B.
When comparing clinical outcomes (Table 2), there was a significantly higher mortality rate in no-PC compared to either PC-A or PC-B (28.9% vs 17.9% vs 17.4%, respectively, all P < .001). By contrast, both the PC-A and PC-B groups had longer duration of ventilatory support (median 6 and 7 d vs 5 d, P = .006 and .002 respectively), longer ICU length of stay (median 10 and 10 d, respectively, vs 8 d, P = .03 and .005 respectively), and longer overall hospital length of stay (median 15 and 15 d, respectively, vs 13 d, P = .003 and .002 respectively) than no-PC. There were significantly more cardiac complications in the no-PC group than PC-B (13.4% vs 7.4%, P = .041), but this did not meet significance between no-PC and PC-A (13.4% vs 7.7%, P = .050). Notably there were no differences in other pulmonary complications, tracheostomy, and readmission rates across all groups. There were no significant difference in outcomes between PC-A and PC-B.
To determine whether PCs affect respiratory failure, we analyzed our data to identify associations with respiratory failure as defined by mechanical ventilation > 48 h. Of the 550 subjects meeting inclusion criteria, 404 were identified to have acute respiratory failure. Those subjects with respiratory failure were more likely to have PCs as well as comorbid diabetes (Table 3). A multivariate logistic regression demonstrated PCs are associated with a 2.2 times increased risk of acute respiratory failure after adjusting for diabetes, age, and gender (Table 4).
Discussion
PCs are commonly encountered in trauma patients with blunt chest injury, and in our study, we found that nearly one-third of all subjects with chest wall injuries had a concomitant contusion. Our data demonstrate that contusions are not a homogenous population and more severe contusions, as assessed radiographically, are associated with worse clinical outcomes. By following previously published methods,11 we found that a high-risk chest wall injury population graded by contusion severity had significantly longer duration of ventilator needs, longer ICU stays, and longer hospital stays than similarly injured subjects without contusion. We also found that the moderate to severe contusion groups as assessed by either the contusions/laceration AIS or the BPC18 scale were not significantly different in chest wall injury or outcomes.
Our results differ from recent studies that suggest PCs do not significantly impact outcomes. In the study by Dhar et al,11 selecting a group of injured subjects requiring mechanical ventilation and stratifying by the presence or absence of contusion produced 2 groups without significant differences in age or comorbid conditions. By contrast, we found that our no-PC population was significantly older, which is in line with prior studies.3,16 It may then be unsurprising that this cohort of older subjects had higher rates of preexisting respiratory diseases as well as diabetes. This may also indicate that younger subjects have a greater likelihood of PCs due to the transmission of energy through a more compliant, less ossified chest wall. More important to outcome analysis, we found that both the PC-A and PC-B subpopulations had significantly worse overall and thoracic-specific injuries. No mention of chest wall injury analysis was made by Dhar et al11 beyond the thoracic AIS comparison, which was already part of the injury severity screening process. The significant differences we observed between those subjects with PCs and those without did not have a clear explanation, and further study may reveal that either injury mechanism or physiologic changes in the older population may reduce the likelihood of contusions. Regardless, despite using the previously described screening process, it is certainly possible that starting out with unequal populations may yield unequal outcomes.
When we analyzed our population for clinical outcomes, we identified marked increases in duration of critical care and hospital needs. When we calculate average duration of mechanical ventilation, we find our average of 10.5–11 d with and without contusion compares well with Dhar et al.11 However, noting the non-normal distribution of our data, we found that our median duration of mechanical ventilation was much shorter overall and also significantly shorter in the absence of contusions. This association was unaffected by excluding early deaths. The apparent discrepancy between our findings and those by Dhar et al11 is that the use of Student t test assumes that the data are distributed normally. Using a nonparametric test such as the Mann-Whitney U test is better suited to testing the independence of non-normally distributed groups.
The protracted time on the ventilator as well as increased ICU and hospital length of stay observed in our population are consistent with other studies.2,6 The apparent contrast between these findings and the overall unchanged rate of other complications (other than a trend toward significance for cardiac complications in the setting of contusions) does not have a clear explanation but may be due to the unequalness of those with and without PCs. However, the increased mortality in the no-PC group may be due to the older population having higher rates of chronic illness (respiratory disorder, diabetes, and psychiatric illness).
When we addressed the relationship between all PCs and the risk of respiratory failure, we demonstrated a 2.2 times increased risk of respiratory failure when adjusting for cofactors. This suggests that regardless of contusion severity all contusions in our severe-injury cohort are associated with increased risk of prolonged mechanical ventilation. This in turn may help explain the increased ICU and hospital stay observed, as those with respiratory failure would seemingly require a longer duration of higher-level care.
The contemporary case against the significance of contusions was well laid out by Robinson.17 In our study, under 20% of patients with contusions were studied, and the majority not studied had minor contusions that posed little clinical consequence. Four factors can be attributed to the diminished significance of contusions, including increased utilization of lung-protective ventilatory strategies, improved damage control resuscitation strategies that minimize crystalloid use, improved ICU sedation techniques, and better multimodal analgesia. It is unlikely that PC rates have decreased, as the widespread availability of cross-sectional imaging allows identification of more and lower severity contusions. Rather the rate at which PCs “blossom” and create physiologic stress is unclear, and the unpredictability is a challenge for clinicians. Being able to predict which contusions are at high risk for worsening, which may influence the timing of additional treatments such as surgical stabilization of rib fractures, is an important emerging topic of investigation. Also, identification of patients who are at an increased risk for respiratory failure may allow for implementation of early aggressive respiratory therapies. Conceptualizing PCs across a common spectrum of severity, as opposed to oversimplifying contusions as either present or absent, is an important step in this process.
Our current study has several limitations. First, as a retrospective review of a single institution, it is possible that our findings may represent a cohort of subjects unique to a particular region. Second, our study did not control for the reason for intubation, whether intubation was performed in the prehospital setting, concomitant severity of head injury, or need for emergency surgery. A variety of pathologies can lead to respiratory failure necessitating mechanical ventilatory support, which may influence hospital course. Furthermore, practice pattern variation in ICU supportive care may also affect outcomes observed. We feel that these limitations are relatively minor and likely do not change the overall trajectory of the care and response to care of the significantly injured trauma patient. Importantly, by excluding minor contusions, it is reasonable to expect that a moderate to severe PC group should have worse outcomes, but it was unanticipated that subjects with contusions and without contusions would have unequal baseline characteristics. Better characterization of PCs with particular emphasis placed on discerning factors associated with contusion progression is a necessary tool for injury prognostication and optimizing timing of interventions.
While the structure of this study was to analyze a high-risk cohort in keeping with prior published design, we must acknowledge that design improvements are possible. Future investigation should categorize PCs by severity including more minor contusions and examine the consequences of PC progression both radiographically and physiologically. This may yield novel characteristics that can inform better therapeutic decision-making and treatment strategies in patient with severe contusions.
Conclusions
We found that moderate to severe PCs were associated with significantly increased duration of mechanical ventilation, ICU length of stay, and overall hospital length of stay in a population at high risk for respiratory problems. All PCs were associated with increased risk of respiratory failure when adjusted for age, gender, and comorbid diabetes. We also demonstrated that the respective AIS and BPC18 score are effective for revealing contusions associated with worse outcomes. Future contusion studies should utilize graduated contusion severity to elucidate a subpopulation whose contusions will progress and display clinical consequences.
Acknowledgements
The authors would like to thank Dina Gomaa and Ann Salvator for their assistance in this work.
Footnotes
- Correspondence: Christopher F Janowak MD, University of Cincinnati, Department of Surgery, 231 Albert Sabin Way #ML 0558, Cincinnati, OH 45267. E-mail: christopher.janowak{at}uc.edu
Dr Zingg presented a version of this paper at the Chest Wall Injury Society Summit, held virtually April 22, 2020.
No funding was received for this work.
The authors have no conflicts to disclose.
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