Obesity in Trauma Care

Obesity in Trauma Care

Authors:

Sarah Greenberger, MD, FACEP, Assistant Professor, The Ohio State University, Columbus, OH.

Howard A. Werman, MD, FACEP, Professor, The Ohio State University, Columbus, OH.

Peer Reviewer:

Jay Menaker, MD, Associate Professor, Department of Surgery, Associate Professor, Department of Emergency Medicine, University of Maryland School of Medicine, Baltimore; Physician Director of Quality Management, R. Adams Cowley Shock Trauma Center, Baltimore, MD.

Obesity is a growing public health concern affecting an estimated 103 million adults in the United States and more than 500 million adults worldwide. Obesity is defined according to body mass index (BMI), which is calculated by dividing weight in kilograms by height in meters squared. According to the World Health Organization, normal weight is defined as BMI 18.5-24.9 kg/m2, overweight is defined as BMI 25-29.9 kg/m2, obesity is BMI ≥ 30 kg/m2, and morbid obesity is defined as BMI ≥ 40 kg/m2.1 As more of the general population is obese, it is likely that the proportion of trauma patients who are obese will continue to rise as well, with important implications for emergency medicine and trauma specialists. The authors review the implications of obesity for acute care physicians managing trauma.

— Ann M. Dietrich, MD, Editor

Epidemiology

A 1993-2003 review of trauma patients found that the prevalence of obesity in this population increased from 0.4% to 1.5% over that 10-year period²; of note, another study found that the general risk of injury was 48% higher in morbidly obese patients than in normal-weight patients.³ Worldwide, the incidence of obesity nearly doubled from 1980 to 2008, with an incidence of 4.8% to 9.8% in men and 7.9% to 13.8% in women.⁴ It is projected that by 2020, three out of four patients in the United States will be overweight.⁵ Additionally, those characterized as obese (BMI > 40 kg/m²) and super-obese (BMI > 50 kg/m²) have increased by a factor of 7 and 12, respectively, in the past 25 years. Finally, a recent study showed that the greatest increase in prevalence of obesity is among children and adolescents, suggesting that knowledge of the particular challenges of obesity will be extremely important in trauma management of patients of all ages in the future.¹

Obesity predisposes people to a variety of injuries in the workplace.^6,7 In a study of almost 70,000 public sector employees, obese patients suffered a higher overall risk of occupational injury; multivariable adjusted hazard ratio (HR) was 1.21 (95% CI: 1.14-1.27). A relationship was observed for bone fractures (HR: 1.37; 95% CI: 1.10-1.70); dislocations, sprains, and strains (HR: 1.36; 95% CI: 1.25-1.49); concussions and internal injuries (HR: 1.26; 95% CI: 1.11-1.44); injuries to lower extremities (HR: 1.62; 95%: 1.46-1.79); and injuries to whole body or multiple sites (HR: 1.37; 95%: 1.10-1.70).⁶

Obesity places additional financial burdens on the health care system as well. The annual expenditures for health-related conditions for obese individuals is approximately $1500 greater than for non-obese patients.⁸ Given the increasing prevalence of obesity and the many effects it has on health, illness, and injury states, it is essential that medical facilities and emergency medicine providers understand and anticipate special concerns related to this unique patient population.

Physiologic Effects of Obesity

The notion that obesity affects overall health is well established in medical literature. Studies previously have linked obesity to everything from insulin resistance and consequent diabetes, to gastroesophageal reflux, to deep venous thrombosis.⁹

Cardiovascular System

Obesity has been shown to be an independent risk factor for cardiovascular disease. An increase of 10 kg above advised body weight is associated with a 3.0 mm Hg increase in systolic blood pressure and a corresponding 2.3 mm Hg increase in diastolic pressure.¹⁰ Additionally, patients often develop increased circulating blood volume and increased cardiac output in response to higher oxygen demands related to larger body habitus.¹¹ Childhood obesity contributes to high low-density lipoproteins and triglyceride levels, as well as low high-density lipoprotein levels, which confers an increased risk of cardiovascular disease in adulthood.¹³ Accelerated atherosclerosis occurs in the obese population, in part due to the effects of hyperlipidemia, diabetes, and prothrombotic state on the vasculature and the heart itself. Over time, these chronic cardiovascular changes can lead to consequent left ventricular hypertrophy and diastolic dysfunction, followed eventually by systolic dysfunction and dilated cardiomyopathy.^11,12 An additional factor contributing to left ventricular hypertrophy is the chronic increase in stroke volume that is required to support the increased metabolic demand of adipose tissue. Obesity also has been linked to the development of cardiomyopathy via the direct results of free fatty acid changes in the myocytes.

There is an increased risk of thromboembolism in obese patients, which has profound implications in the setting of trauma.¹² This risk is thought to be due to production of specific prothrombotic factors by adipose tissue, as well as to dysfunctional platelets found in obese patients. The prothrombotic state is believed to be a major contributing factor in the development of post-traumatic deep venous thrombosis and pulmonary emboli, as well as the increased incidence of stroke and acute myocardial infarction among obese patients.

Respiratory System

Obesity causes significant changes in respiratory physiology. At baseline, many obese patients have elevated respiratory rates and minute ventilation due to increased oxygen consumption and carbon dioxide generation.¹¹ Increased intra-abdominal fat pushes upward on the diaphragm, compromising ventilation, and airway resistance is compromised.¹⁴ This leads to a restrictive lung pattern. Lung compliance and volume are decreased in obese patients, whereas ventilation/perfusion mismatch is increased, which can impair oxygenation and lead to inadequate respiration.^9,12,15

Obesity hypoventilation syndrome, defined as baseline pO₂ < 75 mm Hg and pCO₂ > 45 mm Hg, is a function of obese patients' diminished respiratory drive and response to hypercapnia and is estimated to be present in 10-20% of patients.¹⁶ Obese patients are at risk of sleep apnea as well, which has been theorized to contribute to the occurrence of traumatic injury.⁶⁵ Obesity is also associated with an increased incidence of reactive airway disease.¹⁷

Gastrointestinal System

Obesity is associated with decreased gastrointestinal motility. Additionally, gastric volume typically increases and gastric content pH decreases in obese patients. Increased intra-abdominal pressure and diminished function of the lower esophageal sphincter may lead to hiatal hernia and gastroesophageal reflux.¹⁸ These findings increase the risk of aspiration pneumonitis during intubation procedures. Deposition of fat in the liver in hyperlipidemic states and direct organ damage by lipotoxicity can lead to nonalcoholic steatohepatitis in the obese. Other changes in the liver seen in obese patients include chronic elevations of liver enzymes, fatty liver, and cirrhosis. Finally, gallbladder disease is common in obese patients, potentially resulting in pancreatitis during recovery from traumatic injury.

Renal System

Visceral fat produces angiotensinogen, the effects of which can lead to glomerulonephritis and chronic renal failure. Other contributing factors to renal disease in obese patients include the high incidence of hypertension and diabetes. These changes are particularly important with regard to both fluid management and the use of renally excreted medications.

Endocrine System

Endocrine effects of obesity include increased activity of the hypothalamic-pituitary axis, which can be associated with heightened cortisol levels. Other hormones, including growth hormone, thyroid-stimulating hormones, glucagon, and prolactin, also are subject to sustained elevations. Many obese patients have "metabolic syndrome," characterized by hyperglycemia related to insulin resistance; as such, hyperglycemia poses a persistent challenge in both the early management and recovery phase of obese patients with traumatic injury. Various mechanisms for these changes have been proposed, including malfunction of target enzymes, signaling abnormalities, and increases in specific intracellular fatty acids. Obesity also has been linked to polycystic ovary disease, causing menstrual irregularities, infertility, and hirsutism; associated findings include hyperandrogenism and hyperinsulinemia.

Immunologic System

One of the many effects of obesity and consequent hyperglycemia is impaired neutrophil function, which can lead to weakened immunity and increased risk of infection.¹⁹ Recently, it has become apparent that obesity in and of itself has significant chronic pro-inflammatory effects; studies have demonstrated cytokine production — including TNF-alpha, interleukin-6, and interleukin-8 — by adipose tissue.^19,20,21 Greater levels of both C-reactive protein and interleukin-6 have been found specifically in critically ill obese patients after trauma, compared with non-obese patients, and these elevations have been associated with an increased incidence of multi-organ dysfunction.²² Trauma induces a complex immunological response with release of acute-phase proteins and cytokines that cause endothelial cell damage, dysfunction of vascular permeability, microcirculatory disturbances, and necrosis of parenchymal cells.²³ Adipokines (leptin and adiponectin) affect monocytes and macrophages, leading to a variety of physiologic changes, including further alterations in immunity, changes in endothelial cell function, and direct effects on the lung via pulmonary alveolar macrophage activation.¹⁹ Leptin appears to increase susceptibility to diet-induced obesity and metabolic impairment, whereas decreased levels of adiponectin contribute to insulin resistance and the development of type II diabetes. Given this pro-inflammatory state at baseline, obese patients may mount an especially heightened reaction to trauma that exceeds the normal post-injury inflammatory response seen in the non-obese population.¹⁹

Other Disease States

Obesity has also been linked to pseudotumor cerebri with chronic headaches, elevated intracranial pressure, and, occasionally, visual changes. Finally, obesity has been linked to several forms of cancer, including breast, colon, endometrial, and gallbladder. Each of these associated medical conditions represents significant co-morbidities that must be considered when caring for an obese trauma patient.

Injury Patterns in Obesity

Many studies have examined injury patterns in obese patients to ascertain the nature of obesity's effects on severity and region of injury. Prior studies have drawn some conflicting conclusions about the effects of obesity on severity of injury, but the majority of studies have found no clear link between obesity and severity of injury in either adult or pediatric populations.^19,24-28

Most of the literature regarding effects of obesity on pattern of injury comes from studies of blunt trauma, primarily motor vehicle collisions (MVCs). Observed variations in regional injury patterns have been attributed to differences in energy transmission when obese versus non-obese patients are involved in motor vehicle collisions.^29-31 One study that combined data from actual motor vehicle collisions, computer modeling, and crash simulations found that obese male drivers suffered more injuries to the upper body region — including the head, face, spine, and thorax — compared with normal-weight counterparts, whereas obese female drivers had slightly more risk of thoracic, abdominal, and extremity injuries. The authors speculated that different sex-related deposition of fat (in the lower body in women, in the upper body in men) and consequent differences in centers of gravity might account for these variations.³²

Additional studies have established some general patterns of injury for obese patients. As compared with the non-obese, obese patients suffering blunt trauma have fewer head injuries and liver lacerations, but extremity injuries and thoracic injuries (such as rib fractures and pulmonary contusions) seem to be more prevalent and severe in the obese population.^{21,26,27,29,30,33-37} The increased severity of extremity injuries is thought to be from greater forces transmitted by increased body mass to the arms and legs during motor vehicle collisions.²⁹

There is significant controversy about the role of obesity in extremity trauma. Increased stress from excess weight leads to early degenerative changes in joints and frank arthritis. Yet, obesity is thought to be protective for osteoporosis. Rapid weight reduction resulting from bariatric surgery can cause low bone density, which raises the risk of fractures from minor trauma,²⁰ although recent studies have challenged this assumption.³⁸ What is known is that obesity increases the likelihood of certain fractures (humerus, lower leg, ankle, vertebral), while being protective for other fractures (hip, pelvis, and wrist).

In contrast, researchers have speculated that obesity may confer relative protection for the abdomen. Arbabi et al conducted one of the early studies characterizing this phenomenon, finding that although the overall mortality and severity of skeletal trauma in patients were higher among the obese cohort, abdominal and pelvic injuries were lower in this group.²⁷ They postulated that a "cushion effect" may be present, whereby increased abdominal fat actually protects overweight patients from intra-abdominal injury by insulating the viscera, although in the morbidly obese population, significantly heightened energy transfer may overcome this "cushioning" effect.^21,27 Additionally, the older obese trauma population specifically may be more susceptible to intra-abdominal injury.³³

Regional patterns of injury in young obese children also appear to vary from those of obese adults. Although some studies have found similar patterns of injury in obese pediatric patients, others have found more thoracic and head injuries in younger populations (e.g., ages 2-13 years old) compared to obese adolescent patients, who have injury patterns more closely resembling those of obese adults, which may be due to changes in body proportion and restraint effects and usage with age.^35,39,40 One interesting theory regarding the increase in injury severity in obese patients relates to the imperfect fit of seatbelts with increasing BMI. The authors of one study postulated that the use of seatbelts introduces increased slack in the belt, resulting in increased excursion of the body and greater likelihood of contact with the interior in frontal, rollover, and other high-speed collisions.⁴¹

Even in the setting of minor trauma, obese patients demonstrate patterns of injury that differ from the non-obese populations. Substantial energy can be dissipated in the obese individual even at low velocities, resulting in comminuted fractures and soft-tissue damage, especially involving the distal end of the long bones. Ankle fractures in obese patients are more severe and more likely to be displaced than in non-obese patients. Obese patients also are at increased risk of re-displacement after reduction of these injuries.²⁰ Similarly, knee dislocations are more common with low-energy mechanisms of injury — like falls from standing height — in the setting of obesity as compared with the general population, and obese patients are also more likely to have nerve and vascular injuries associated with these low-energy injuries.^20,42 One recent study found that BMI averaged 49.1 kg/m² for those with low velocity knee dislocations, compared to an average BMI of 34.1 for patients with high impact knee dislocations.⁴³

Management Considerations

Evaluation and stabilization of obese trauma patients should proceed, as always, according to standard Advanced Trauma Life Support (ATLS) primary and secondary survey algorithms, but management of these patients may necessitate use of specialized equipment or modifications of standard trauma protocols. As yet, no formal guidelines are available for special considerations of the obese trauma population specifically.

Prehospital Considerations

Transport of morbidly obese patients from the scene of injury may be complicated by size or weight restrictions of transport vehicles loaded with medical equipment. Many ambulance stretchers have limited load capacity (300 kg) and may be unable to accommodate patients with a width exceeding 58 cm. Rotary and fixed-wing aircraft used in remote transfers certainly are weight-limited, too. Additional personnel beyond the regular number of prehospital responders may be necessary to aid in mobilizing a patient for transfer.

In general, special equipment, including stretchers, hoists, and even vehicle capacity, is not routinely available in many prehospital systems to care for those who are obese and, more specifically, morbidly obese. In both the prehospital and hospital settings, prior staff training in safe lifting techniques and adequate assistive devices, such as mechanized cots and winches or other lifting tools, can help minimize the potential for provider injury related to transfer and positioning of obese patients. Transport of bariatric patients previously has been associated specifically with increased risk of provider back injury.⁴⁴

Stabilization equipment such as cervical collars and extremity splints may fit improperly when applied to obese patients due to increased girth and relatively shorter necks; if equipment specifically designed for obese patients is not immediately available, prehospital providers may utilize dual backboards and blanket rolls or sandbags taped to both the patient and backboard to achieve spine immobilization for obese trauma patients.^20,45 Obese patients will generally not tolerate a full supine position due to respiratory compromise in this position; additionally, it has been postulated that fluid and blood product requirements may increase in obesity due to greater blood loss resulting from increased intrathoracic and intra-abdominal pressures in the supine position. This latter point may partially explain the findings of Nelson et al, who showed that the incidence of and mortality from hemorrhagic shock increases with increasing BMI.⁴⁶

Difficulty in extricating and transporting obese patients may result in substantial delays in transfer from the scene of injury to the emergency department setting. When possible, prehospital reports to receiving facilities should include advisement of obesity so that hospitals can ensure a gurney and/or hospital bed rated for obese patients is available when the patient arrives.

Circulation and Hemodynamic Monitoring

Additional equipment considerations include inadequacy of standard monitoring techniques in the obese trauma population. Monitoring equipment, such as standard blood pressure cuffs, may give inaccurate readings for obese patients. As arm size increases, standard cuff readings become increasingly inaccurate, so consideration should be given to alternative methods of measurement, both non-invasive and invasive. One study of 1240 obese patients whose blood pressures were measured using a standard cuff found inaccurate readings in patients with increased arm girth.⁵⁵ Most prehospital systems and many smaller hospitals may not be properly equipped to obtain accurate blood pressure readings for obese patients. Larger blood pressure cuffs or alternative placement of cuffs (e.g., forearm), arterial lines, and Doppler assessment of pulses may be necessary for hemodynamic assessment. Even when accurate readings are obtained, they may misrepresent an obese trauma patient's stability. One study found that metabolic derangements such as elevated lactate levels are not matched by lower systolic or mean arterial blood pressure in obese patients, so that other methods of measuring volume status may be necessary in order to determine adequacy of resuscitation.⁴⁶ Other monitoring devices, such as pulse oximetry and electrocardiogram tracings, may be inaccurate in the obese patient, as well.

Both peripheral and central vascular access may be more difficult to obtain in obese trauma patients. Dense soft tissue can obscure peripheral veins and normal anatomical landmarks — even limiting palpation of the clavicle or carotid pulsations — and also results in greater distances from skin to vessels, such that standard catheters may not be sufficiently long to allow venous cannulation.³⁴ Ultrasound guidance may be useful in this setting. Given the difficulty in obtaining and maintaining peripheral IVs, providers need to exercise caution that problems with vascular access do not delay early trauma care and resuscitation; for this reason, obese patients may require early intraosseous access and more frequent central venous line placement.²¹ When central venous lines are necessary, staff should ensure that patients do not spend excessive time in Trendelenburg, as is common for subclavian and internal jugular line placement, because this positioning can cause compromised respiratory function in obese patients who already have baseline reduced respiratory capacity.

Airway Management and Ventilation

Physiological changes in the obese may compromise respiratory function, especially in the setting of trauma. Early consideration should be given to oxygen supplementation and potential intubation. Obesity confers certain direct anatomic effects that should be considered in the airway management of obese trauma patients. Increased soft tissue characterizes the neck, face, and oropharynx of obese patients, and limited mouth opening is not uncommon. Deposition of fat in the neck, in particular, may contribute to decreased caliber and increased collapsibility of the airway, potentially complicating ventilation and intubation in this population. Baseline compromised respiratory function of obese patients can be exacerbated by depressant effects of anxiolytics and pain medication and by supine positioning due to spine immobilization, leading to alveolar collapse, poor oxygenation, and hypercapnia.¹⁶ Arterial and/or venous blood gases or end-tidal carbon dioxide capnography can be used to help monitor respiratory status. Clinicians should be alert to rising hypercapnia that may precede hypoxia, especially in obese patients who have chest wall trauma, remain immobilized, or have received opioid analgesia.¹⁶ When even non-rebreather masks fail to achieve adequate oxygenation, oxygen delivery via non-invasive positive-pressure ventilation should be considered, although this also raises the risk of gastric distention and aspiration.¹⁶ Nasogastric or orogastric tubes may help decompress the abdomen. In patients with a history of gastric banding, deflation of the band via the abdominal wall access port may help to decrease the likelihood of aspiration.²⁰

When non-invasive ventilation fails and intubation is required, bag-valve-mask ventilation may prove difficult due to excessive soft tissue of the face and neck. Use of oral or nasal airways or the two-person technique may help achieve better mask seal and more effective ventilation. Additionally, obese patients desaturate more quickly and require more time to return to normal oxygen saturation levels than do non-obese patients due to diminished functional residual capacity and consequent low oxygen reserve. This is particularly true for obese patients with obstructive sleep apnea.⁴⁷ Although positioning can be challenging in trauma patients for whom spinal precautions are a consideration, preoxygenation with head elevation to 25 degrees or via CPAP has been demonstrated previously to prolong time to desaturation in obese patients undergoing intubation.¹⁸ Passive oxygenation via high-flow nasal cannula during intubation can be useful, although only one attempt at intubation may be possible before oxygen levels drop to levels precluding further attempts.^18,48

The process of intubation itself can be complicated further by reduced mobility of the neck and limited visualization due to thick soft-tissue density in obese patients; generally, a short, thick neck portends a difficult airway.³¹ Brodsky found that a neck circumference specifically greater than 60 cm was associated with a difficult airway in 35% of cases.⁵⁰ Poor visualization of the tonsils, posterior pharynx, and soft palate has been associated with obesity. A ramped position, rather than the traditional sniffing position, may be more effective for achieving adequate laryngoscopy in these patients. Ramping uses blankets or wedges under the head, neck, and shoulders to align the external auditory canal parallel to the sternal notch, with the head and shoulders elevated relative to the chest. Video laryngoscopy has been shown to double the likelihood of successful intubation for patients considered to have difficult airways, including obese patients.⁴⁹ In several studies and multiple case reports, video laryngoscopy has been utilized successfully for intubation of obese patients for elective procedures, at times demonstrating superiority to traditional laryngoscopy in this population. Adequate visualization by video laryngoscopy in trauma patients may be hampered by blood in the oropharynx.¹⁸ In obese patients for whom intubation is predicted to be challenging, laryngeal mask airway, other supraglottic airway device, or awake fiberoptic intubation can be considered.¹¹ If an awake intubation is planned, nebulized or atomized lidocaine may be employed for topical anesthesia. In the setting of trauma, however, when patients may be unstable and aspiration is of particular concern, rapid sequence intubation may be preferable to awake intubation.

Despite these many challenges, intubation of obese trauma patients usually can be achieved. One review found no increase in failed intubation or need for surgical airway in trauma patients with higher BMIs.¹⁵ For obese patients requiring airway management but for whom endotracheal intubation is unsuccessful, cricothyrotomy and tracheostomy may be difficult due to increased soft tissue of the neck, resulting in a loss of normal landmarks and increased depth of the trachea. Tracheostomy tubes for obese patients may need to be longer and more angled than the tubes traditionally used for non-obese patients.¹⁸ A technique of using a gum-bougie in conjunction with a cricothyroidotomy has been described.

After the airway has been secured, obese patients are more prone to tube dislodgement. Therefore, careful attention to securing the tube, particularly during movement of the patient, is imperative. Initial ventilator settings should be based on ideal body weight rather than actual body weight to avoid barotrauma or volutrauma.¹¹ However, it should be noted that even post-intubation, mechanical ventilation can be difficult due to restrictive chest wall and altered pulmonary mechanics.

Resuscitation — and especially rapid sequence intubation — of obese trauma patients can be complicated by improper medication administration. Body habitus and fat stores have significant effects on drug metabolism and distribution. Doses of weight-based medications can be too high or too low depending on whether actual body weight or ideal body weight is used for calculation, so consultation with a pharmacist may be helpful.¹¹ Administration of lipophilic drugs is complicated by an increased volume of distribution in the obese due to greater fat stores. Common lipophilic drugs used in the trauma setting and for which actual body weight generally should be used in dosing include propofol, etomidate, lorazepam, and diazepam, although it has also been proposed that the induction dose of propofol be based on ideal body weight. In contrast, dosing for ketamine should utilize lean body mass (120% of ideal body weight).^18,51 Similarly, analgesic agents should be dosed on ideal body weight and titrated to effect. Dosing for succinylcholine should use total body weight, while hydrophilic nondepolarizing neuromuscular blockers like vecuronium or rocuronium should use ideal body weight.¹⁸ Several excellent reviews have recently been published on this topic.^52,53 (See Table 2.) Notably, these general conventions regarding dosing of drugs in obese patients are more theoretical than evidence-based, so further studies are needed to confirm the validity of these principles in practice.⁴¹

Medication delivery itself can also be complicated by obesity. Medications administered intramuscularly may actually be injected into adipose tissue, which is less vascularized than muscle, thereby reducing absorption.³⁴ Administration of local anesthesia, such as regional nerve blocks, may be hindered by loss of anatomic landmarks and inadequate needle length.

Initial Management of Injuries

It is not yet clear whether ideal or actual body weight should be used in determining the amount of fluids that should be given to hypovolemic obese trauma patients. Intra-abdominal pressure in the obese is chronically elevated at baseline, which could heighten the risk of abdominal compartment syndrome in obese patients receiving excessive fluid resuscitation. However, a retrospective European study suggested that obese trauma patients may be generally under-resuscitated, initially receiving less intravenous fluid volume when corrected for BMI than non-obese patients, leading to relative hypovolemia and persistent shock in this population.⁴⁶

Body habitus can limit assessment of injuries by physical exam. Recommendations for management of burns rely on visual estimation of body surface area (BSA) affected. Prior literature has proposed that the classic "rule of nines" is inaccurate in the obese population because of the effects of body habitus. Instead, a "rule of fives" has been suggested, in which the torso is assigned 50% of BSA, each leg is assigned 20%, 5% is assigned to each arm, and 2% is assigned to the head.⁵⁶

Similarly, diagnoses like flail chest that usually are made by observation may be difficult to visualize in obese trauma patients. Auscultation of breath sounds and palpation of abdominal organs or detection of progressive abdominal distention may be hindered by overlying adipose tissues. Obesity commonly displaces the umbilicus from the vertical midpoint, altering proximity of visible anatomic landmarks to underlying organ position and potentially skewing perceived likelihood of injury when considering location of wounds or tenderness on examination. Increased soft-tissue density also can hide vascular injuries in obese patients with lower extremity trauma, requiring evaluation by ankle-brachial index, CT angiography, or duplex ultrasound in order to detect injury.^1,30 As such, a lower threshold for observation and monitoring or diagnostic imaging may be necessary in the obese trauma population.

Considerations in Imaging

In the emergency department, evaluation of obese patients may be hampered by difficulty obtaining imaging studies. Thick soft tissue overlying deeper structures can limit the utility of plain radiographs, especially when portable radiographic equipment is used.^37,51 Increased abdominal fat — both subcutaneous and visceral — may attenuate ultrasound waves and make it difficult to penetrate deeply enough to obtain adequate visualization in screening for traumatic injuries with a FAST exam. In one review of scans performed by ultrasonographers and interpreted by radiologists, FAST sensitivity dropped from 85% in non-obese patients to 63% in obese patients.⁶⁵ Even patient positioning to allow optimal acoustic windows may be a challenge in the setting of obesity.³⁷ As such, a lower threshold for CT imaging in obese trauma patients may be prudent. Special protocols for CT imaging have been designed to reduce difficulties with beam penetration and noise associated with scanning obese patients, but non-bariatric centers may be unaware of these considerations. In those settings, image quality may be affected by increased noise and reduced beam penetration. CT and MRI scanners, especially in non-bariatric surgery hospitals, commonly have weight and girth restrictions. When patients exceed these limits and injury is suspected based on mechanism, symptoms, or hemodynamic instability, DPL or exploratory laparotomy might be necessary.^11,20,51

Other Management Considerations

Standard treatment for various traumatic injuries may need to be adjusted for obese patients, for whom body habitus might render such therapies ineffective. For example, a recent study revealed that the recommended catheter length for needle thoracostomy (5 cm) may be inadequate to relieve a tension pneumothorax in obese patients.⁵⁴ Similarly, various authors in the orthopedic literature have recommended deviating from standard management of many common fractures when obese patients are being treated. Halo fixators for cervical spine fractures are relatively contraindicated for obese patients due to body habitus. External fixation of pelvic fractures also is less likely to be successful in this population, so early symphyseal plating is recommended.²⁰ Similarly, anterograde intramedullary nailing of femur fractures appears to be more prone to complications than the retrograde approach in obese patients.

For obese trauma patients whose injuries are minor, special considerations include impaired mobility that may limit their ability to be discharged and might instead require placement at a rehabilitation facility. Additionally, standard assistive equipment, such as crutches, walkers, wheelchairs, and bedside commodes, may be unable to support the weight of obese patients. Case management, when available, may be useful in arranging specialized equipment and assistance for these patients.⁴⁵

Late Considerations

Although some reviews have failed to find a difference in mortality between certain obese and non-obese trauma population subsets, multiple other studies have demonstrated increased morbidity and mortality in obese patients compared with non-obese ones, especially in the critically injured population.^{2,9,20,21,26,28,33,46,57,58,61} A recent large analysis of almost 150,000 trauma patients in Pennsylvania concluded that severely obese trauma patients had twice the risk of complications and 30% greater mortality than non-obese counterparts.⁶¹ Specifically, obesity has been linked with higher rates of respiratory complications (pneumonia, acute respiratory distress syndrome, and ventilator days), urinary tract infection, decubitus ulcer, deep venous thrombosis, acute renal failure, bacteremia, multi-organ failure, hospital length of stay, and ICU length of stay.^{12,14,21,24,34,59} A recent study of severely injured trauma patients (ISS > 15) showed an increasing incidence of pneumonia among patients whose BMI was normal (1.6%), obese (2.0%), and morbidly obese (3.1%).⁶² Another study demonstrated a 30% increase in mortality and a two- to fourfold increase in wound complications, including infection and decubitus ulcers, for obese patients.⁶¹ Interestingly, a meta-analysis of 18 studies that found higher morbidity and mortality for obese patients compared with the non-obese did not find a clear linkage between injury severity score and obesity. As such, the authors noted that the increased complications in the obese trauma population, such as ARDS, renal failure, and multi-system organ failure, and even mortality itself, could not be attributed to more severe injuries in these patients.²⁴ On the other hand, in their analysis of more than 1200 trauma patients, Livingston et al failed to identify BMI as a significant predictor of mortality or morbidity.⁶³ Of note, outcomes for obese traumatic brain-injured patients have been found to be poorer than for non-obese patients with similar injuries; however, this effect seems to be due to baseline differences in study populations (especially in age, blood pressure on presentation, and concomitant injuries), rather than being due to obesity itself.³⁰ Given the higher risk of multiple system organ failure,¹⁹ infectious complications,³⁴ and thromboembolic events,⁶⁴ as a general rule, the threshold then for transferring an injured patient with obesity to a trauma center, and in those centers for admitting an injured patient to an intensive care unit setting, should be much lower.

Even less seriously injured patients face a myriad of complications after trauma due to the effects of obesity. These patients are at risk of slow wound healing due to increased tension on a wound — increasing the risk of wound dehiscence — and poor vascularization of adipose tissue, which reduces oxygenation to injured areas. Damage-control laparotomy specifically has been associated with a higher rate of infectious complications and a lower rate of primary fascial closure in obese patients compared with non-obese patients. Large pockets formed by nearby skin folds also can retain excess moisture in the vicinity of a wound and make adequate hygiene difficult. Precautions also should be taken in hospitalized obese trauma patients to prevent stasis ulcers. Special mattresses are available to accommodate higher weights, but regular repositioning can pose special challenges in this population.^{11,12,20,60,61}

Moreover, obesity increases the risk of thromboembolism, and early mobilization of obese patients after trauma can be difficult, yet standard deep venous thrombosis prophylaxis such as sequential compression devices (SCDs) and thromboembolic deterrent stockings (TEDs) cannot always be used in obese patients due to patient body habitus and limited equipment sizing. Low-molecular weight heparin prophylaxis has been recommended, although it has been suggested that obese patients may need adjusted dosing regimens to achieve therapeutic anticoagulation levels. Inferior vena cava (IVC) filters may also have a role in preventing pulmonary embolism in this setting.⁶⁰ Furthermore, obese patients may have various undiagnosed comorbid conditions, such as diabetes or hypothyroidism, that can complicate their recovery, so patients should be screened carefully for evidence of other chronic diseases.

Conclusion

The prevalence of obesity is steadily rising in the general population and can be expected to affect an increasing proportion of trauma patients. Obesity has known effects on health, and its effects on physiology have significant implications specifically for trauma patients. Initial stabilization, diagnosis, and management of obese trauma patients may differ from that of non-obese patients, particularly in the areas of prehospital stabilization, airway management, and hemodynamic support. Physical examination and diagnostic evaluation present additional pitfalls in initial assessment of the obese trauma patient. (See Table 3.) Even after the initial resuscitation period, obese patients face elevated complication rates and higher mortality than do non-obese patients.

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