When I was doing Internal Medicine as a resident and as Chief Resident of Internal Medicine I spent a lot of time in the intensive care units. I was fascinated by the degree of Subcutaneous Emphysema observed in patients on ventilators. The picture above is representative of the bloated appearance observed in these patients, and the gas would frequently extend down the arms and of course the chest. When you pressed or squeezed these areas you could feel the skin crackle…this is called crepitations.
Naturally I wanted to understand it further. The classic disease associated with crepitations related to gas in the skin is gas gangrene…an infection caused by anaerobic bacteria producing gas in the infected area. I do have clinical slides of this but I thought the images were too graphic to display here. I wanted to know what other conditions caused subcutaneous emphysema. The first article I wrote on this was published in the Journal of the Association of Military Dermatologist in 1991. This was a comprehensive review and I will be displaying the drawings I did for this article below.
The most common cause of Subcutaneous Emphysema is related to chest trauma and ventilator use. Thoracic pressures applied by a ventilator to inelastic lungs can result in rupture of the alveoli…the small sacks involved in oxygenation of blood. The air then tracks along the linings of structures that penetrate the chest, neck and abdomen, such as the esophagus, trachea, aorta, etc. In the drawing above follow the black spaces between the various sections and you will appreciate the path that air takes to get to the subcutaneous tissues of the skin.
In this cross section of the neck follow the dead spaces from the lungs up the prevertebral space and the danger space. Gas can then spread along the retropharyngeal space to the carotid sheath which becomes a highway to the face and neck. Understand this anatomy and you will understand why the face, neck and upper chest areas are frequently involved.
Now, what else can cause Subcutaneous Emphysema? In this drawing I show you the most common causes by region. I even found cases of Subcutaneous Emphysema caused by liquid nitrogen treatments to the skin, where the physician applied direct contact of the tip of the canister to the skin, forcing nitrogen into the subcutaneous tissues. As a warning to my fellow dermatologists…don’t do this. For those of you that don’t believe me…click HERE. I wrote another article on Subcutaneous Emphysema in relationship to disorders which need to be considered a potential medical emergency. The reference is in my CV on the home page, but it was published in Advances in Dermatology in 1996. To read more about Subcutaneouos Emphysema click HERE and HERE. I know this blog post is very technical…but I find it very fascinating stuff and hope you do too…