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Penetrating injury patients treated at high-volume penetrating trauma centers have lower mortality

Fu, Chih-Yuan, MD; Bajani, Francesco, MD; Tatebe, Leah, MD; Butler, Caroline, MD; Starr, Frederic, MD; Dennis, Andrew, DO; Kaminsky, Matthew, MD; Messer, Thomas, MD; Schlanser, Victoria; Kramer, Kristina, MD; Poulakidas, Stathis, MD; Cheng, Chi-Tung, MD; Mis, Justin, RN; Bokhari, Faran, MD

Journal of Trauma and Acute Care Surgery: June 2019 - Volume 86 - Issue 6 - p 961–966
doi: 10.1097/TA.0000000000002245
ORIGINAL ARTICLES
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BACKGROUND The recognition of the relationship between volume and outcomes led to the regionalization of trauma care. The relationship between trauma mechanism-subtype and outcomes has yet to be explored. We hypothesized that trauma centers with a high volume of penetrating trauma patients might be associated with a higher survival rate for penetrating trauma patients.

METHODS A retrospective cohort analysis of penetrating trauma patients presenting between 2011 and 2015 was conducted using the National Trauma Database and the trauma registry at the Stroger Cook County Hospital. Linear regression was used to determine the relationship between mortality and the annual volume of penetrating trauma seen by the treating hospital.

RESULTS Nationally, penetrating injuries account for 9.5% of the trauma cases treated. Patients treated within the top quartile penetrating-volume hospitals (≥167 penetrating cases per annum) are more severely injured (Injury Severity Score: 8.9 vs. 7.7) than those treated at the lowest quartile penetrating volume centers (<36.6 patients per annum). There was a lower mortality rate at institutions that treated high numbers of penetrating trauma patients per annum. A penetrating trauma mortality risk adjustment model showed that the volume of penetrating trauma patients was an independent factor associated with survival rate.

CONCLUSION Trauma centers with high penetrating trauma patient volumes are associated with improved survival of these patients. This association with improved survival does not hold true for the total trauma volume at a center but is specific to the volume of the penetrating trauma subtype.

LEVEL OF EVIDENCE Prognostic/Epidemiology Study, Level-III; Therapeutic/Care Management, Level IV.

From the Department of Trauma and Burn Surgery (C-Y.F., F.B., L.T., C.B., F.S., A.D., M.K., T.M., V.S., K.K., S.P. C-T.C., J.M., F.B.), Stroger Hospital of Cook County, Rush University, Chicago, Illinois; and Department of Trauma and Emergency Surgery (C-Y.F., C-T.C.), Chang Gung Memorial Hospital, Chang Gung University, Taoyuan City, Taiwan.

Submitted: August 9, 2018, Revised: January 15, 2019, Accepted: January 30, 2019, Published online: March 1, 2019.

Address for reprints: Faran Bokhari, MD, Department of Trauma and Burn Surgery, Stroger Hospital of Cook County, Rush University, 1950 West Polk St, Chicago, IL, 60612; email: fbokhari@cookcountyhhs.org.

The abstract has been accepted for a poster at the Annual Meeting of American Public Health Association, November 10–14, 2018 in San Diego, CA. (ID 2064.0).

The centralization of complex health care services, such as transplant and oncology, improves outcomes.1–3 Several studies have demonstrated a similar association between the creation of trauma care and outcomes.4–7 In a landmark article, Mackenzie et al.8 demonstrated that adjusted-mortality rates are significantly lower when care is provided in a trauma center compared with when it is provided in a nontrauma center.

Mechanisms of traumatic injury can be diverse. Penetrating, blunt, and burn injuries require different skill sets from the treating trauma team. Geographic patterns of injury can result in some centers receiving high volumes of specific subtypes of injury. To the best of our knowledge, the association between treatment at a trauma center receiving a high-volume of a certain type of injury and outcomes has not been explored. We sought to define the current volume and nature of penetrating trauma treated within Level I/II trauma centers in the United States, and to explore the association between the volume of penetrating trauma cared for at a center and outcomes. The data from our own center, the John H Stroger Jr. Hospital of Cook County (CCH), which is the largest Level I trauma center in Cook County, Illinois was also analyzed. We hypothesized that trauma centers with a high volume of penetrating trauma patients might be associated with a higher survival rate for penetrating trauma patients.

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MATERIALS AND METHODS

A retrospective cohort analysis of penetrating injury patients in our registry at the CCH and the National Trauma Data Bank (NTDB) for Level I/II trauma centers was undertaken for the years 2011 to 2015. The NTDB is largest data bank of collected information about traumatic injuries and outcomes in the United States.9 The CCH serves as the largest combined Level I adult and Level I pediatric trauma center for Cook County. This institution is surrounded by West/East Garfield Park and the South Side of Chicago, both of which have high violent crime rates.10,11

The inclusion criteria for the current study were penetrating injuries (origin file: RDS_ECODE and RDS_ECODEDES) treated in Level I/II trauma centers either accredited by the American College of Surgery or state law (origin file: RDS_FACILITY). Patients who were dead on arrival or those with missing key values were excluded. Patients with missing records of age, vital signs, Injury Severity Score (ISS), and trauma mechanisms were excluded (N = 154,567 within 5 years, 5.0%).

Systolic blood pressure/pulse in the emergency department (origin file: RDS_VITALS), age (origin file: RDS_DEMO), using ventilator or not (origin file: RDS_DISCHARGE), region of injury (origin file: RDS_AIS98PCODE) and ISS (origin file: RDS_ED) of penetrating trauma patients in all Level I/II trauma centers from the NTDB were evaluated. Trauma centers at the top and bottom 25% of penetrating trauma patients numbers per year were compared. The relationship between the number of penetrating injury patients per year and their survival rate in Level I/II trauma centers was evaluated.

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Statistical Analysis

All original files from the NTBD with required data were merged and analyzed using R (V3.3.1).12 Nominal data are presented as a percentage and were compared using the χ2 test, whereas numerical data are presented as the mean and standard deviation and were compared using Student’s t test. A value of p less than 0.05 was considered statistically significant. Linear regression analysis was used to evaluate independent factors for the survival rate of penetrating injury patients and create a risk adjustment model with above factors for mortality of penetrating trauma patients.13 Microsoft Excel (V15.32) was used for data entry and generating the associated figures. Collinearity analysis was performed to evaluate the multicollinearity between total volume and volume of penetrating trauma. The variance inflation factor value is 2.817 and thus multicollinearity is low (variance inflation factor < 10).14 Therefore, both total volume and volume of penetrating trauma were included in our regression model.

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RESULTS

During the 5-year study period, 2,935,917 (587,183 per year) patients were evaluated in the NTDB, which included 442 Level I/II trauma centers. The proportion of penetrating injuries was 9.5%, and the mortality of overall penetrating injuries was 4.0%. Of the penetrating injury patients, 18.3% had an ISS of 16 or greater, and their mortality rate was 19.8%.(Table 1).

TABLE 1

TABLE 1

Figure 1A illustrates the distribution of injury severity across penetrating injury volume among the national trauma centers (442 Level I/II trauma centers): CCH is labeled for clarity. With regard to volume, the top 25% of Level I/II centers treat greater than 167 penetrating injury patients per year, and the bottom 25% of Level I/II centers treat 36.6 or less penetrating injury patients per year (Fig. 1B). Compared with the low-volume centers (≤36.6 patients/year), patients in the high-volume centers (≥167 patients/year) are significantly severely injured (ISS: 8.9 vs. 7.7, p < 0.001). Furthermore, high-volume centers treated significantly more patients with hypotension (9.0% vs. 7.6%, p < 0.001), more patients requiring mechanical ventilation (17.4% vs. 13.7%, p < 0.001) and more patients with head, torso, and both head plus torso injuries. High-volume centers had a higher proportion of gunshot wounds (GSWs) versus stab wounds (52.5% vs. 38.9%, p < 0.001). Increase in survival was significant for patients with an ISS of 25 or higher in high-volume penetrating trauma centers compared to low-volume centers (71.7% vs. 66.8%, p < 0.001) (Table 2).

Figure 1

Figure 1

TABLE 2

TABLE 2

Figure 2 indicates the relationship between the number of penetrating injury patients (per year) and their survival rate. A comparison of slopes among all ISS, ISS of 16 or higher and ISS of 25 or higher (Fig. 2A, B, C) shows that the volume effect is significant for the survival rate of severely injured penetrating injury patients (ISS ≥ 16 and ISS ≥ 25). (p < 0.001).

Figure 2

Figure 2

Table 3 shows a risk adjusted model to evaluate independent factors associated with the survival of penetrating injury patients. There are statistically significant inverse relationships between penetrating trauma survival and ISS (B value = −0.285, p < 0.001), age (B value = −0.076, p = 0.001) and the need for mechanical ventilation (B value = −0.147, p < 0.001). The number of penetrating injury patients is an independent factor associated with improved survival rate (10 patients per year: B value = 0.011, p = 0.032), whereas the effect of the number of all (blunt and penetrating) trauma patients is not significant (p = 0.452) (linear regression in Table 3).

TABLE 3

TABLE 3

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DISCUSSION

Among all high-income nations, the United States still leads in firearm-related injury mortality.15,16 Blunt trauma, however, is the predominant mechanism of traumatic injury in the US. Several epidemiological studies have examined the incidence and mortality rates of penetrating trauma in various geographies.15–19 In general, the rate of penetrating injuries was estimated to be less than 10% of all adult traumas. A discrepancy exists in the distribution and severity of penetrating injuries among Level I/II trauma centers (Fig. 1). Previous studies have demonstrated an inverse relationship between socioeconomic status and traumatic injury.20,21 In the United States, the number of penetrating injury patients treated in a single institution ranges from 2.6 to 890.6 per year (Fig. 1). Twenty trauma centers treat more than 400 penetrating injury patients per year.

There is evidence of a volume-outcome relationship where higher surgical volume results in lower postoperative mortality.1–3 In our study, the total number of all trauma patients does not improve the survival of penetrating trauma patients (p = 0.452, Table 3). The volume effect is more complex and specific to injury subtype treated. Figure 2 shows a positive relationship between survival rates of penetrating injury patients in institutions and the numbers of penetrating injury patients treated in a specific institution. This effect was especially significant in patients with more severe injuries (ISS ≥ 16 or ISS ≥ 25) (Figs. 2B and C).

In the current study, we used 167 penetrating injury patients per year as the high cutoff value (top 25%) and 36.6 penetrating injury patients per year as the low cutoff value (bottom 25%) to evaluate survival in trauma centers (Fig. 1B). A comparison between the institutions with high and low volume of penetrating injury patients (167 vs. 36.6 patients per year) showed that high-volume institutions (>167 penetrating injury patients per year) showed a distinct survival advantage with a higher grade of injury (ISS ≥ 25). For all ISS, number of penetrating patients does not affect survival either for all centers grouped together or the top and bottom quartiles (Fig. 2A and Table 2). However, these high-volume centers (for all ISS) were associated with survival rates for penetrating trauma equivalent to low-volume centers, which treated less severe and less ill patients (survival rate, 96.0% vs. 96.3%, p = 0.230). For ISS ≥ 16 (which includes patients with ISS ≥25) survival is better for all centers but not for the top versus the bottom quartiles (Fig. 2B and Table 2). For ISS of 25 or higher, survival is better not only for all centers but also for the top and bottom quartiles (Fig. 2C and Table 2). This suggests that the difference in survival among the centers is driven primarily by the survival of more severely injured patients (survival rate for ISS ≥ 25: 71.7% vs. 66.8%, p < 0.001) (Table 2).

While it is hard to make generalizations, one would assume that penetrating injury to head can lead to a higher mortality and that penetrating extremity injury is more salvageable than penetrating injury to the torso. Another assumption might be that GSWs are more lethal than stab wounds. Our data found that the higher-volume centers treat more penetrating injuries to the head, torso and extremities and more GSWs in general than low volume centers (52.5% vs. 38.9%, p < 0.001). The AIS scores of the head, and not torso or extremities, were significantly higher in the high-volume centers.

Gunshot wounds usually occur in populations with lower socioeconomic status, and most violence occurs in neighborhoods with concentrated poverty and housing.22–25 In addition to increased law enforcement efforts against gun violence, equal attention should be paid to improving medical survival from GSWs. Delayed surgical intervention for significant injuries, such as torso penetrating injuries, can increase trauma-related morbidity and mortality rates.26,27 Therefore, a trauma center that provides rapid transportation and timely treatment is necessary for people who are victims of GSWs. Furthermore, while the trauma centers analyzed have very similar expert personnel, in a high-volume penetrating center the personnel are exposed to more penetrating trauma. The results of the current study suggest that increased penetrating volume is associated with better survival.

Improved outcomes of trauma patients who were treated at trauma centers have been previously reported. However, volume effect has not been evaluated based on mechanism of injury. The management of a non-penetrating injury can be as complicated as the management of penetrating injury.28,29 Therefore, volume-related improved outcomes may exist not only for penetrating injury patients. We evaluated whether the salutary patient volume effect is specific to penetrating injuries. A risk adjustment model using linear regression analysis was created to evaluate independent risk factors that were related to the survival rate of penetrating trauma patients. Older age, using ventilator, and higher ISS show significantly negative effects on the survival of penetrating trauma patients. Trauma centers show improved survival rates of penetrating trauma patients associated with increased number of penetrating injury patients treated per year (p = 0.032). Although it is difficult for emergency medical service personnel to evaluate injury severity at the scene, penetrating injury patients is more easily identified. Triage of the right severity penetrating injury to the correct regional trauma center is more complex. The a priori assessment of a higher ISS injury and triage to a “high-volume penetrating trauma center” would need a discussion, evaluation, and consensus within each region.

A nationwide data bank with a large sample size was evaluated in the current study, but the conclusions are limited due to the retrospective nature of the data and some missing elements in the NTDB. In addition, the functional outcome of penetrating injury patients and the cost-effectiveness of subspecialized trauma centers were not evaluated. We were not able to evaluate if concentrating penetrating trauma in a few centers would actually improve overall survival in a local trauma system. This would depend on the location of penetrating hotbeds and the deleterious effect of further decreasing penetrating trauma patients going to already low penetrating trauma centers. Further studies with a prospective design and long-term follow-up are needed.

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CONCLUSION

Severely injured penetrating trauma patients have a higher survival when treated at high-volume penetrating trauma centers. The reason for improved survival in a penetrating injury trauma center is more complex than a simple overall volume effect.

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DISCLOSURE

The authors have no commercial associations or sources of support from any grant, funding source or commercial interest including pharmaceutical or device companies that might pose a conflict of interest.

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Keywords:

Penetrating trauma; trauma center; high volume

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