Abstract Body (Do not enter title and authors here): Intro:
Cardiac tamponade is a common cause of obstructive shock, often necessitating urgent intervention. We delineate a rare case of cardiac tamponade and shock due to tension pneumomediastinum (TP).

Case Presentation:
A 53-year-old man with metastatic paranasal squamous cell carcinoma (SCC) was admitted to the Intensive Care Unit (ICU) for acute respiratory failure due to pneumonia requiring intubation. Shortly after an uncomplicated endotracheal intubation, he was noted to have worsening hypotension and tachycardia, and developed profound shock requiring multidrug vasopressor support. Physical examination revealed diffuse subcutaneous crepitus in the anterior chest and neck, peripheral edema, and pulsus paradoxus on the arterial line. Chest CT without contrast revealed massive pneumomediastinum tracking superiorly to soft tissues of the neck and inferiorly to below the diaphragm; there was no pericardial effusion, pneumothorax, or pneumoperitoneum seen. Transthoracic echocardiography findings were limited by poor windows, likely due to pneumomediastinum, but demonstrated overall preserved ejection fraction, dilated inferior vena cava with minimal respiratory variation, and no pericardial effusion. The leading diagnosis was obstructive shock secondary to tamponade physiology in the setting of TP. A multidisciplinary discussion with Cardiology, Cardiothoracic Surgery, Otolaryngology, and Interventional Radiology (IR) culminated in IR-guided mediastinotomy with drain placement, resulting in immediate hemodynamic improvement and reduction of the pneumomediastinum. He was rapidly weaned off vasopressors on day 2 and extubated on day 4 of ICU stay.

Discussion:
Cardiac tamponade is one of the most common causes of obstructive shock and is almost always due to a large or expanding pericardial effusion. Timely recognition of tamponade is essential due to its high mortality when left untreated. Here, we see a rare presentation of tamponade arising from TP in the setting of barotrauma from mechanical ventilation treated by mediastinotomy. Only a few such cases have been reported in literature, all of which were treated with mediastinal decompression. Notably, the patient's underlying SCC may have predisposed him to air dissection into the mediastinum, either via tumor-related tissue disruption or treatment-associated changes. This case highlights the importance of considering tamponade in the appropriate clinical setting even in the absence of pericardial effusion.