Subcutaneous Emphysema – Causes, Diagnosis, Treatment

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Subcutaneous Emphysema is the de novo generation or infiltration of air in the subcutaneous layer of skin. Skin is composed of the epidermis and dermis, with the subcutaneous tissue being beneath the dermis.  Air expansion can involve subcutaneous and deep tissues, with the non-extensive subcutaneous spread being less concerning for clinical deterioration.   However, the development of subcutaneous emphysema may indicate that air is occupying another deeper area within the body not visible to the unaided eye. Air extravasation in other body cavities and spaces can cause pneumomediastinum, pneumoperitoneum, pneumoretroperitoneum, and pneumothorax.  The air travels from these areas along pressure gradients between intra-alveolar and perivascular interstitium, spreading to the head, neck, chest, and abdomen by connecting fascial and anatomic planes. Air will preferentially accumulate in subcutaneous areas with the least amount of tension until the pressure increases enough to dissect along other planes, causing extensive subcutaneous spread which can result in respiratory and cardiovascular collapse.

Pathophysiology

The development of subcutaneous emphysema is thought to be caused by the following mechanisms:

  • Injury to the parietal pleura that allows for the passage of air into the pleural and subcutaneous tissues
  • Air from the alveolus spreading into the endovascular sheath and lung hilum into the endothoracic fascia
  • The air in the mediastinum spreading into the cervical¬†viscera and other connected tissue planes
  • Air originating from external sources
  • Gas generation locally by infections, specifically, necrotizing infections

Causes of Subcutaneous Emphysema

Subcutaneous emphysema can result from surgical, traumatic, infectious, or spontaneous etiologies. Injury to the thoracic cavity, sinus cavities, facial bones, barotrauma, bowel perforation or pulmonary blebs are some common causes. Iatrogenic causes may occur due to malfunction or disruption of the ventilator circuit, inappropriate closure of the pop-off valve, Valsalva maneuvers that increase thoracic pressure, and trauma to the airway. Air may enter into the subcutaneous spaces via small mucosal injury in the trachea or pharynx during traumatic intubation, overinflation of endotracheal tube (ET) cuffs, or increased airway pressure against a closed glottis. Injury to the esophagus during gastric tube placement can also create communicating entry points for air passage. Air can enter the subcutaneous tissue via the cervical soft tissues during tracheotomy, via the chest wall during arthroscopic shoulder surgery, via the extremities as a result of industrial accidents, via bowel or esophageal perforation without pulmonary injury, or via a tube thoracos­tomy track or in the course of central venous access procedures, or percutaneous or transbronchial lung biopsy. Subcutaneous emphysema has also been observed following the insufflation of air during the course of modern era laparoscopy, and via the female genital tract during a pelvic examination, douche, postpartum exercise, or blowing into the vagina, especially during pregnancy.

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The¬†positive pressure applied by ventilator inspiration can promote the expansion of the gas through the communicating fascial planes down the partial pressure gradient.¬†While non-invasive ventilation correlates with lower rates of barotrauma, bag-mask ventilation in CPR and incorrect oxygen mask attachment that prevents¬†exhalation may have devastating outcomes.¬†There have also been case reports of epidural emphysema that migrates subcutaneously during¬†“air¬†loss of resistance” technique for¬†epidural catheters.¬†In another case report, a patient¬†developed massive bilateral subcutaneous emphysema without evidence of pneumothorax with post-operative nausea and vomiting.

Diagnosis of Subcutaneous Emphysema

History and Physical

Obtaining full history is critical to explore the causes of subcutaneous emphysema and its complications. On physical examination, the most common finding associated with subcutaneous emphysema is crepitus on palpation. Distention or bloating may be present in the abdomen, chest, neck, and face. Palpebral closure resulting in visual distortion and phonation changes from vocal cord compression may also be present. By palpating the affected area, a crackling sound and sensation (crepitus) are elicited. According to Medeiros, subcutaneous emphysema can also be appreciated by placing a stethoscope on the skin and thus emitting a high-frequency acoustic sound. However, crepitus is not in itself, a pathognomic finding for deeper structure air extravasation; although, it is a likely indication that air in another connecting fascial plane exists such as the mediastinum or pleura.  For patients that have extensive subcutaneous emphysema, hemodynamic or respiratory compromise may occur which is why it is imperative to investigate the cause of subcutaneous emphysema in each patient.

Grading classifications that help evaluate the extent of subcutaneous emphysema have received validation in some studies; however, it is not universally implemented or routinely used.

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There are suggestions that in patients who use inhalational corticosteroids may be at increased risk for tracheal injury with endotracheal intubation due to friable and thin mucosa. It is necessary to get a thorough medication history from patients, especially in those with asthma or COPD who are already at increased risk of developing subcutaneous emphysema.

Evaluation

Imaging including radiographic (X-ray) and computed tomography (CT) can help identify subcutaneous emphysema. On a radiograph, there are intermittent areas of radiolucency, often representing a fluffy appearance on the exterior borders of the thoracic and abdominal walls. On chest radiograph, a ginkgo leaf sign may be present, showing striations of gas along with the pectoralis major, resembling that of a ginkgo leaf. In addition to X-rays, CT will show dark pockets in the subcutaneous layer indicative of gas. CT may be sensitive enough to identify the source of injury causing the subcutaneous emphysema that may otherwise not be visible on an AP or lateral X-ray.

If cervical or facial subcutaneous emphysema develops during patient intubation, it is recommended to perform laryngoscopy before extubation to evaluate for impending airway compromise or pharyngeal emphysema. Additionally, if there is suspicion of airway injury as a result of intubation, bronchoscopy can help identify the location of the tracheal injury. Although air acts as a sound barrier when using ultrasound, subcutaneous emphysema may demonstrate by hyperechoic scattered densities. By placing the ultrasound probe on a region of skin without emphysema, pneumothorax is diagnosable by the absence of lung sliding and A-lines with 95% sensitivity.

Treatment of Subcutaneous Emphysema

Treatment of the underlying cause or precipitating factor should be considered first because it usually leads to gradual resolution of the subcutaneous emphysema. For mild cases that do not cause significant patient discomfort, observation is appropriate. Without compartment or deep tissue involvement, seen after exploratory laparotomy, for example, abdominal binders have been used for patient comfort. The resolution of subcutaneous emphysema will likely resolve in less than 10 days if the source controlled. In patients that experience continued discomfort or that require expedited resolution, high-concentration of oxygen is a well-known treatment, allowing for nitrogen washout and diffusion of gas particles in a patient with concomitant pneumothorax and/or pneumomediastinum.

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During endotracheal intubation, trauma can occur to the posterior trachea, causing a linear laceration of the mucosa. A tracheostomy may be required to bypass the tear and prevent further subcutaneous emphysema expansion or additional complications. In mucosa tears, empiric broad-spectrum antibiotics may also be of benefit to prevent the development of mediastinitis. For mechanically ventilated patients, reducing tidal volume, reducing positive end-expiratory pressure, and minimizing bronchospasm and air trapping can halt the progression and promote reabsorption. 

During laparoscopic procedures, insufflated CO2 management is typically by increasing the minute ventilation. However, in patients that develop slow onset and delayed hypercarbia despite minute ventilation adjustment may have CO2 escape into the subcutaneous layers. Therefore, post-operatively, in a patient that develops subcutaneous emphysema, be diligent in airway assessments, consider reintubation versus delayed extubation for airway protection and treat the respiratory acidosis/hypercapnia that may result from gas absorption.

In patients with extensive subcutaneous emphysema, there are reports that 2cm infraclavicular incisions bilaterally can reduce further subcutaneous expansion. In a case report, a patient with extensive subcutaneous emphysema following thoracostomy had successful treatment with a subcutaneous drain placed superficial to the pectoral fascia on low suction. Most experts reserve invasive therapy for cases of increasing airway impingement or cardiovascular compromise.

References

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