Relationship of Obesity and Severe Penetrating Thoracic and Abdominal Injuries in Adolescent Patients

Key Takeaways

• Adolescent trauma patients with and without obesity presenting after isolated abdominal or thoracic knife wounds had similar rates of severe injury, operative intervention, and mortality.

Introduction

The prevalence of obesity in adolescents has steadily increased in the United States from 10.5% in 1988 to 21.2% in 2018. ¹ Furthermore, injury is the leading cause of death in adolescents, causing more than 60% of deaths annually. ²

Due to a rising prevalence of obesity and a higher rate of mortality in the adolescent population following trauma, the relationship between obesity and injury is of particular interest to trauma providers. Some authors have proposed possible protective mechanisms of excess body mass, such as the “cushion effect,” where abdominal fat functions as insulating tissue from blunt abdominal trauma ³ and the “armor phenomenon,” where subcutaneous fat distribution limits the wound depth from a penetrating injury (ie, stab wound or gunshot wound). ⁴

Previous authors have investigated if obesity is truly associated with decreased injury severity and morbidity after trauma in the adult population with varied results. A higher body mass index (BMI) has been associated with a lower mortality^5,6 and injury severity score (ISS) ³ for adult blunt trauma patients, and a recent meta-analysis by Chen et al, concluded that an armor phenomenon may exist for adolescents with obesity that sustain thoracoabdominal stab injuries, but this may not lead to improved outcomes. ⁴ In fact, some studies have found that patients with obesity have a longer length of stay (LOS) in the intensive care unit (ICU) after trauma ⁷ and obesity is an independent risk factor for complications such as nosocomial infections, ⁸ prolonged mechanical ventilation, and postoperative pulmonary complications. ⁹

However, studies in the adolescent population evaluating the effect of obesity on injury after penetrating trauma are limited. In children, studies have reported differences in injury patterns between patients with obesity and without obesity but have failed to demonstrate a significant difference in mortality, length of stay, or complications. However, this may be due to limitations of sample size inherent to a single-center study design.^10-12

Therefore, this study aims to examine the association between obesity in adolescents and severe penetrating torso injuries using a large national database. We hypothesize that adolescents with obesity presenting after penetrating thoracic and abdominal trauma have a lower rate of severe traumatic injury and mortality.

Methods

Results

Demographics, Comorbidities, and Injury Profile

From 12,181 adolescent trauma patients, 1603 (13.2%) had obesity. The median age was similar between cohorts with and without obesity (16 vs 16 years-old, P = .08). Both groups had a similar rate of all comorbidities, except patients with obesity, who had higher rates of hypertension (.9% vs .3%, P < .001) and diabetes (.9% vs .3%, P < .001). In terms of mechanisms of injury, the cohorts had a similar rate of gunshot wounds (65.5% vs 68%, P = .05) but adolescents with obesity had a higher rate of stab wounds (34.6% vs 32.1%, P = .042). Overall mortality was similar between cohorts (4.6% vs 5.8%, P = .053) (Table 1).

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Table 1.

Demographics of Patients With Penetrating Injuries Stratified by Obese vs Non-obese.

Characteristic	Obese (n = 1603)	Non-obese (n = 10578)	P-value
Age, years, median	16 (15, 17)	16 (15, 17)	.086
Male, n (%)	1242 (77.5%)	9059 (85.7%)	<.001
ISS	4 (1, 10)	5 (1, 10)	<.001
Race, n (%)			<.001
White	689 (43%)	3996 (37.8%)
Non-white	914 (57%)	6582 (62.2%)
Mechanism of injury
Gunshot wound, n (%)	1050 (65.5%)	7189 (68%)	.050
Stab wound, n (%)	555 (34.6%)	3393 (32.1%)	.042
Comorbidities, n (%)
ADHD	102 (6.4%)	693 (6.6%)	.80
Hypertension	14 (.9%)	34 (.3%)	<.001
Diabetes	14 (.9%)	35 (.3%)	.001
Smoking	142 (9%)	1029 (9.8%)	.29
Substance abuse	81 (5.1%)	614 (5.9%)	.24
PRBC transfused, n (%)	150 (10%)	1288 (13%)	.002
AIS severe, n (%)
Thorax	55 (3.4%)	514 (4.9%)	.012
Abdomen	70 (4.4%)	459 (4.3%)	.96
Mortality, n (%)	74 (4.6%)	615 (5.8%)	.053

ISS = injury severity score, ADHD = attention-deficit/hyperactivity disorder, PRBC = packed red blood cells, AIS = abbreviated injury scale.

In terms of injuries, the cohort without obesity had a higher median ISS (4 vs 5, P=<.001) as well as a higher rate of severe AIS for the thorax (3.4% vs 4.9%, P = .012). Also, patients without obesity presented with a higher rate of lung injuries (13.3% vs 16.5%, P = .001) (Table 2).

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Table 2.

Clinical Outcomes of Patients With Isolated Thoracic Injuries Caused by Gun and Stab Wounds, Stratified by Obese vs Non-obese.

Characteristic	Thoracic Injuries Caused by Gunshot Wounds			Thoracic Injuries Caused by Stab Wounds
	Obese (n = 138)	Non-obese (n = 1069)	P-value	Obese (n = 73)	Non-obese (n = 586)	P-value
Injured organ, n (%)
Lung	44 (31.9%)	383 (35.8%)	.36	24 (32.9%)	235 (40.1%)	.23
Liver	0 (.0%)	1 (.1%)	.71	0	0
Spleen	0	0		0	0
Kidney	0	0		0	0
Pancreas	0	0		0	0
Small intestine	0	0		0	0
Colon	0	0		0	0
Rectum	0	0		0	0
Bladder	0	0		0	0
Type of surgery, n (%)
Respiratory	16 (11.6%)	135 (12.6%)	.73	6 (8.2%)	42 (7.2%)	.74
Gastrointestinal	12 (8.7%)	87 (8.1%)	.82	3 (4.1%)	23 (3.9%)	.93
Urinary	6 (4.3%)	70 (6.5%)	.31	2 (2.7%)	20 (3.4%)	.76
HBP	0	0		0	1 (.2%)
Cardiovascular	2 (1.4%)	37 (3.5%)	.20	4 (5.5%)	19 (3.2%)	.32
Mortality, n (%)	3 (2.2%)	67 (6.3%)	.053	1 (1.4%)	6 (1%)	.78
Length of stay, days, median	3 (1, 6)	3 (1, 7)	.70	2 (1, 4)	3 (2, 4)	.06
Total ICU length of stay, days, median	3 (2, 6)	3 (2, 6)	.76	2 (1.75, 3.25)	2 (2, 4)	.86
Total ventilator days, days, median	3 (1.5, 5.5)	3 (2, 5.75)	.84	1.5 (1, 31.25)	2 (1, 2)	.64

HBP = hepatic-biliary-pancreatic, ICU = intensive care unit.

Outcomes for Adolescent Trauma Patients With Isolated Abdominal Injury

Adolescents with obesity with isolated abdominal gunshot wounds had a similar rate of severe abdominal injuries (12.1% vs 10.2%, P = .46) and mortality (1.2% vs 1.9%, P = .53) compared to patients without obesity. Both groups also had a similar median LOS, ICU LOS and ventilator days (all P > .05).

Adolescents with obesity with isolated abdominal stab wounds had a similar rate of severe abdominal injury (5.1% vs 2.8%, P = .28) and mortality (0% vs .7%, P= .46) compared to patients without obesity. However, there was a higher rate of gastrointestinal surgery required in non-obese patients, compared to obese patients (8.9% vs 18.9%, P = .029). Although there was no difference in median LOS, ICU LOS or ventilator days between cohorts (all P > .05) (Table 3).

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Table 3.

Clinical Outcomes of Patients with Isolated Abdominal Injuries Caused by Gun and Stab Wounds, Stratified by Obese vs Non-obese.

Characteristic	Abdominal Injuries Caused by Gunshot Wounds			Abdominal Injuries Caused by Stab Wounds
	Obese (n = 165)	Non-obese (n = 1055)	P-value	Obese (n = 79)	Non-obese (n = 599)	P-value
Injured organ, n (%)
Lung	0	1 (.1%)	.69	0	0
Liver	14 (8.5%)	115 (10.9%)	.34	5 (6.3%)	46 (7.7%)	.66
Spleen	3 (1.8%)	15 (1.4%)	.69	1 (1.3%)	7 (1.2%)	.94
Kidney	10 (6.1%)	62 (5.9%)	.92	1 (1.3%)	17 (2.8%)	.41
Pancreas	3 (1.8%)	27 (2.6%)	.56	0	7 (1.2%)	.33
Small intestine	26 (15.8%)	171 (16.2%)	.88	4 (5.1%)	41 (6.8%)	.55
Colon	23 (13.9%)	156 (14.8%)	.77	2 (2.5%)	21 (3.5%)	.65
Rectum	2 (1.2%)	13 (1.2%)	.98	0	6 (1%)	.37
Bladder	2 (1.2%)	21 (2.0%)	.49	0	3 (.5%)	.52
Type of surgery, n (%)
Respiratory	7 (4.2%)	62 (5.9%)	.39	0	15 (2.5%)	.15
Gastrointestinal	46 (27.9%)	321 (30.4%)	.50	7 (8.9%)	113 (18.9%)	.029
Urinary	20 (12.1%)	152 (14.4%)	.43	2 (2.5%)	32 (5.3%)	.28
HBP	9 (5.5%)	67 (6.4%)	.65	0	28 (4.7%)	.50
Cardiovascular	2 (1.2%)	3 (.3%)	.08	0	0
Mortality, n (%)	2 (1.2%)	20 (1.9%)	.53	0	4 (.7%)	.46
Length of stay, days, median	3 (2, 8)	3 (2, 8)	.60	2 (1, 3)	2 (1, 4)	.004
Total ICU length of stay, days, median	3 (2, 7)	3 (2, 6)	.84	1 (1,2)	2 (1, 3)	.07
Total ventilator days, days, median	3 (1, 5.25)	3 (2, 5)	.65	0	2 (1, 2.5)	1.00

HBP = hepatic-biliary-pancreatic, ICU = intensive care unit.

Discussion

The effect of obesity in penetrating trauma is still controversial. With an alarming increase in the prevalence of obesity in adolescents, it is imperative to understand injury patterns in this population to guide workup and treatment algorithms. This national analysis found that adolescent patients with obesity had a significantly lower rate of isolated severe thoracic injury caused by gunshot wounds, but a similar rate of severe thoracic injuries caused by stab wounds. In addition, there was also a similar rate of severe isolated abdominal injuries caused by gunshot or stab wounds. Also, all populations studied had similar rates of mortality for adolescent trauma patients with and without obesity.

There are few studies comparing obese vs non-obese penetrating trauma.^13-18 Furthermore, most studies in general evaluating obesity exclude patients less than 18 years old and focus on blunt trauma outcomes.^3,5,6,15,16 In adult patients sustaining abdominal stab wounds, Bloom et al found decreased rates of peritoneal violation, severity of abdominal injury, and ISS with increasing BMI. In fact, patients in the thinnest group required an operation three times more often than those in the most obese category (BMI <18.5, 67% vs BMI >35, 20%, P = .03). ¹⁴ Patel et al also reported that adult (>16 years of age) patients with obesity were less likely to have abdominal fascial penetration and sustained fewer visceral injuries compared to overweight and normal weight cohorts. ¹⁷ That said, adolescent firearm injuries are increasing and now comprise the most common cause of injury-related death in this population. ¹⁹ Similar to adults, Castle et al performed a retrospective review of the National Trauma Data Bank and found a lower rate of operation needed for overweight and pediatric patients with obesity (ages 2-18 years old) sustaining penetrating thoracoabdominal trauma. However, they did not perform separate analysis regarding the mechanism of injury (eg, gunshot vs stab wounds) and location of injury. ¹² In furtherance of these findings, this current study found that specifically, adolescents with obesity with isolated thoracic injuries caused by gunshot wounds had a lower rate of severe injuries. This is the first study to the knowledge of these authors to evaluate the “armor effect” in an adolescent population and may be helpful for providers when considering the possibility of tangential injury if clinically appropriate.

Mortality is obviously an important outcome and is also truly objective. In regards to adult penetrating trauma, Osborne et al found similar mortality between obese (BMI >30) and non-obese (BMI <30) patients in a limited sample size of 132 subjects. ⁶ Drury et al compared three BMI groups (normal weight, overweight, and obese) in adults who suffered either blunt or penetrating trauma, and although not statistically significant, the authors highlight that the overweight BMI group had the lowest mortality rate while the normal BMI group had the highest mortality rate. ¹⁶ In contrast, Owattanapanich et al studied isolated abdominal injuries caused by gunshot wounds in patients ≥16 years old, comparing patients with BMI >30 (obesity) vs patients BMI <30. Patients with obesity had increased mortality (6.5% vs 4.2%, P = .010) as well as hospital length of stay, ventilator days, and hospital acquired pneumonia. On subsequent multivariate logistic regression, obesity was independently associated with increased mortality (OR, 1.636; P = .021). ¹³ In contrast, this current national analysis of adolescents found a statistically similar rate of mortality after isolated thoracic and abdominal trauma caused by gunshot or stab wound. A possible explanation for the differences in outcomes between our study and the previously presented study is the patient population investigated. Our study analyzed a younger cohort, which despite having obesity, has not had the time to develop obesity-related medical complications from diabetes and/or metabolic syndrome. Thus, they may receive the armor effect (protective effect of having increased truncal mass to prevent internal injury) without the detriment of the long-term metabolic complications associated with obesity.

As a large retrospective database study, there are inherent limitations to this study including coding errors, missing information, and reporting bias. Additionally, given the retrospective design, the findings cannot be interpreted as causation and serve primarily to establish correlation and warrant further exploration. Furthermore, the use of BMI as a surrogate for estimating body fat and thus obesity is an important limiting factor as well. Although BMI is widely accepted and is the most readily available tool for stratifying patients by weight, it is truly excess body fat rather than the excess weight that correlates with ill-health. Given that BMI is calculated based on just height and weight, it fails to account for other factors like age, sex, and muscularity that play a role in determining a patient’s body fat. ²⁰ In addition, the notably unstandardized fashion in which height and weight are collected across the country is an important limitation. Many trauma centers directly measure these values; however, it is possible that using bed weights which may include clothes or other objects and skew weight data. Furthermore, other trauma centers may rely on self-reported values or estimates. Despite these limitations, this study is strengthened by its large national population.

Conclusion

This analysis, spanning three years of data from the TQIP database, demonstrated that adolescent trauma patients with obesity presenting after isolated thoracic or abdominal knife wounds had similar rates of severe injuries and mortality compared to adolescents without obesity. However, adolescent patients with obesity presenting after an isolated thoracic gunshot wound had a nearly 25% relatively lower rate of severe injury. As such, trauma providers should consider this information when making emergent decisions regarding the work-up and treatment of firearm injuries in adolescent trauma patients.