Discussion

In this study, we assessed the development of PTCs in the USA during a 10-year period from 2007 to 2017. We hypothesized that temporal PTC incidences would have dropped during the investigative time frame, but that a number of patients remain at risk. Of the 12 selected PTC categories, we did indeed identify significant reductions in the PTC incidence of acute renal failure, ARDS, myocardial infarction, organ space and superficial SSI, pneumonia, pulmonary embolism, cardiac arrest, and sepsis. In contrast, the incidence of deep SSI, DVT, and stroke increased over time when multivariate modeling was considered. Although the graphical representation in figure 1 suggests an overall drop in PTC incidence, multivariate modeling thus indicates a slight increase in certain PTCs, which runs counter to the study hypothesis.

In the last study year, where treatment protocols would presumably be optimal compared with the previous years, 27 943 (2.8%) patients experienced one or more PTCs. To put this number into perspective, the global burden of injury in the 2017 study estimated that 520 million patients worldwide suffered traumatic injuries in that year.20 If numbers can be extrapolated, this would mean that an excess of 14 million patients could have suffered a PTC globally in 2017 alone. Although these numbers should be interpreted in the light of the many differences in trauma systems worldwide, they still suggest that a sizeable number of patients remain unresponsive to current prophylaxis protocols and could potentially benefit from precision medicine-based approaches.

Several factors should be considered when interpreting the data, and caution should be exercised when interpreting the presented results. The annual volume of trauma patients in the TQIP data set increased from 2007 (506 257) to 2017 (997 970), and the underlying demographics and injury characteristics also varied over the years. The fluctuations in complication rates could thus in part be due to data from additional trauma centers with demographic and injury characteristics variations being added to the data set. As treatment protocol adjustment after feedback from the TQIP would take time to implement, the rapid increase in the number of participating centers may thus create a setting where centers would enter TQIP with suboptimal PTC incidence rates, which would be gradually corrected once TQIP feedback was obtained and time for protocol optimization was allowed for. Furthermore, as is the case for many retrospective databases, there is likely a significant issue of under-reporting in the data set. As such, a recent study from Japan, investigating 184 214 patients, reported a PTC rate of 12.8%,21 as opposed to 2.8% in this study. Although obvious differences in number and definitions of reported PTC exist between data sets, the presented results should be interpreted in light of the underlying data set. Although TQIP likely also suffers from under-reporting, it is less clear whether such an under-reporting should exhibit a temporal trend. As such, it is likely that the findings of a relatively stable PTC trend for most complications reflect reality, although at a higher incidence than reported here.

Also, the results should be interpreted in the light of the inherent variance in reporting standards between sites this and most other retrospective quality registers suffer from. Indeed, studies have indicated that a degree of interobserver variability exists in TQIP, which could affect the presented results.22

The observed reduction in the incidence of pulmonary complications, including ARDS and pneumonia, can likely be associated with the development and adherence to resuscitation and ventilator-associated pneumonia (VAP) protocols during the last decade, including outcomes of research collaboratives such as the ARDS Network.23 High incidences of pneumonia are well documented as a major cause of PTC,2 and VAP continues to be a preventable burden for critically ill patients. Studies on prevention strategies have shown variable success, focusing on treatments including non-invasive positive pressure ventilation, optimal bed position, better oral care, and removal of subglottic secretions.24 25 Hospitals adhering to ventilator optimization strategies have reported good drops in incidence statistics.26

ARDS incidences are likely also affected by developments in resuscitation strategies, as well as accelerated patient mobilization efforts.27 As such, the gradual shift from large-volume crystalloid resuscitation toward a permissive hypotensive and balanced blood transfusion regimen has likely played a role in reducing ARDS incidences28–30 nationwide.

Acute renal failure, associated with increased morbidity and mortality as well as hospital LOS,31 also exhibited reduced incidence during the study period. This is likely associated with the development of and adherence to risk assessment protocols targeting renal failure, mainly through optimizing renal perfusion.32 Of note, the second most common reason for renal failure is sepsis, which also exhibited reduced incidence during the study period.

Collectively, it is likely that these improvements are due to increased adherence to updated resuscitation and treatment protocols, including sepsis, as well as resuscitation and treatment guidelines such as those championed by trauma societies.33 34

For thrombosis ORs, we observed a decrease in pulmonary embolism, but a slight increase in DVT and stroke ORs over time when multivariate modeling was considered. Although thrombosis prophylaxis protocols have received much attention,35 with an apparent drop in unadjusted DVT rates over time, multivariate modeling suggested that this could be due to changes in the underlying demographics and trauma characteristics of included patients. As such, current prophylaxis protocols have been unsuccessful in further reducing DVT and stroke incidences over time when patient covariates are considered, thus highlighting a focus area for further research and development.

Although myocardial infarction and cardiac arrest incidence rates decreased in this study, the observed trend for DVT and stroke thus mirrors the rise in cardiovascular disease-related mortality in the general US population during the last decade36 and could potentially be related to changes in lifestyle factors, including diet, smoking, and a general increase in sedentary lifestyle.36 For DVT, the observed increase in adjusted incidence is in line with a general embolism-associated mortality increase in USA since 2008.37 38 Interestingly, this did not translate into an increased incidence of pulmonary embolism in this study, which could potentially be associated with focus on vena cava filters in high-risk patients,39 although this cannot be concluded from these data.

For infectious complications, we observed a reduction in ORs of organ space and superficial SSI, although an increase in deep SSI OR was observed concurrently. Whether this represents real fluctuations associated with changes in treatment strategies (eg, increase in non-operative management strategies) or simply a shift in SSI classification practices cannot be readily deduced from these data. Incidences of SSI have in other studies decreased and were largely associated with small bowel and vascular bypass surgery.40 41 The reduction in SSI incidence observed here is thus in line with previous reports from non-trauma surgical patients. These results should, however, be interpreted with caution. The structure of the TQIP database did not allow for a consistent registration of the nature, indication, and type of surgical procedures. As such, fluctuations in the number of major surgical procedures performed during the investigative time frame could have impacted on the results.

Overall, although selected PTC incidences have shown a temporal decrease (pneumonia and ARDS), other PTCs have failed to show a clear development. Although these exhibited slight increases or reductions, it is questionable whether the magnitude of these fluctuations is of clinical relevance (figure 1). Furthermore, although most of these alterations are statistically significant, this should be analyzed in light of the large number of patients present for analysis.

The study has several limitations. First, this is a retrospective study dependent on the quality and correctness of data sources from the TQIP database. As such, PTCs may have been missed by the curators. Second, although we have sought to control for relevant confounders, the results may still be affected by factors not included in the regression model. Such factors could potentially include the number of major surgical procedures performed, as this could have impacted on PTC incidences, specifically Venous Thromboembolisms (VTE) and SSI rates. Third, data from the TQIP database are limited to trauma centers participating in the program, which may not completely mirror other centers throughout the USA or elsewhere. Fourth, although the sensitivity analysis did not indicate a major effect of the missing data, interpretation of the presented results should be seen in light of the fact that TQIP data quality and data completeness generally increased toward the final years of the study period. The increase in the number of participating hospitals could also have affected data quality as well as reported outcomes, either due to variations in data definitions or differential outcomes between participating centers. It would thus have been interesting to identify hospitals present in TQIP throughout the study time frame to assess PTC variations in these. TQIP, does, however, not allow for an identification of the individual center, which precludes us from making this analysis. Also, the use of advanced directives could have impacted on the level of treatment offered to patients. The TQIP data set does, however, only contain information on such decisions from 2013 and onwards, which was considered incompatible with the analysis approach.

The TQIP data structure was changed during the study period, with the number and types of PTCs recorded differing from 2007 to 2017. Ideally, a uniform data set would have been optimal, and fluctuations in data definitions and recorded variables could thus impact on the results. The TQIP data set adheres to the definition standard set forth by the National Trauma Data Bank, as defined in the National Trauma Data Set (NTDS) standards. There are annual updates of the PTC definitions, and variations could thus affect the presented results. A review of the NTDS changelogs did, however, reflect minor changes with perceived limited impact on the presented findings. For comparative purposes, we provide an overview of the 2007 vs 2017 PTC definitions in online supplemental table 1.

Finally, certain PTCs such as venous embolisms are critically dependent on imaging studies for their detection. The TQIP data set does not allow for an assessment of the use of imaging modalities. As such, whether changes in the frequency of imaging studies could have impacted on the presented findings cannot be deduced from these data but may impact on the results. Collectively, interpretation of the presented results should thus be done with these limitations in mind.

Even with these limitations, we conclude that incidences of PTC remain largely stationary over time, with a slight decrease or increase for selected PTCs. A number of patients remain unresponsive to current treatment prophylaxis and could be candidates for future precision medicine-based approaches.