The mediastinal space is a narrow space between organs in the mediastinum that is filled with loose connective tissue to accommodate organ activities and changes in volume. The connective tissues of the mediastinal space extend upwards and are continuous with the connective tissues of the neck. The pre-tracheal space is located between the upper mediastinum, trachea, bifurcation of trachea, and aortic arch. It communicates upward with the pre-tracheal space in the neck. Gas can diffuse upwards to the neck when pneumomediastinum occurs (Fig. 2B). A layer of superficial fascia exists between the mediastinal space and the skin. This layer of superficial fascia is dense and gas cannot easily diffuse through it. The pre-tracheal space lies behind the superficial fascia of the neck, in a rhombic region formed between the anterior borders of the bilateral sternocleidomastoid muscles and the anterior borders of the bilateral sternohyoid muscles (Fig. 2A). This area contains the anterior jugular vein, the jugular venous arch, and the inferior thyroid vein. When performing this procedure, blunt dissection must be used to reduce the risk of injury to these veins .
It is much more difficult to control the anatomical layer accessed by the incision when using a needle or small incision to expel gas. Thus, the superficial fascia may not be punctured due to fear of causing vascular and nerve injury, resulting in the drainage of only small volumes of gas outside the superficial fascia. Even if the superficial fascia has been punctured and gas can be effectively expelled for a short while, the superficial fascia contraction will cause the puncture site to rapidly close, and subsequently, gas cannot be effectively drained.
In the single incision drainage strip method, although the drainage strip can enter the sub-superficial fascial space, the position of drainage strip cannot be easily fixed. Thus, it tends to slip out into the anatomical layers beyond the superficial fascia when the forceps are withdrawn, leading to ineffective drainage.
We used curved forceps for blunt dissection to create a drainage tunnel, which had a clear anatomical level and precise location, thus preventing damage to the trachea and veins. The drainage strip passed through a longer route accurately inside the pre-tracheal space to connect the pneumomediastinal space with the skin incision for sufficient drainage. The significant differences in arterial partial pressure of oxygen and partial pressure of carbon dioxide in the 12th hour of mechanical ventilation between the two groups suggest that the surgery could relieve the pressure of tension pneumomediastinum on the airway, heart, and lungs, improve blood circulation, promote the diffusion and mutual exchange of carbon dioxide and oxygen, leading to the significant difference in total length of mechanical ventilation between the two groups. The two ends of the drainage strip were located outside the skin and were fixed, which facilitates observation. The treatment duration was shortened due to high efficiency of the operation. Nevertheless, this procedure raised the risk of infection and skin scarring.
This study aims to provide a standard and effective drainage method for tension pneumomediastinum occurring from various causes, as well as to provide a reference for the treatment of tension pneumomediastinum caused by COVID-19. Clinicians should carefully consider the following points before selecting this method: familiarity with the local anatomical structure of the pre-tracheal region, as failure to accurately enter the pre-tracheal space will lead to ineffective operation; the method has the risks of damaging the trachea and increasing the infection routes.
Respiratory function improvements could not be completely attributed to drainage of the tension pneumomediastinum, as the treatment of primary diseases such as pneumonia and respiratory distress syndrome also resulted in gas absorption. The contribution of drainage could not be accurately determined since the sample size was too small and additional control groups were lacking, affecting the accuracy of the conclusion.