Which of the following is the most likely cause of this patient’s condition?
- A) High cardiac preload
- B) Low cardiac afterload
- C) Low cardiac output
- D) High cardiac output
This patient arrives in the Emergency Department after sustaining penetrating chest trauma and is found to be hypotensive, tachycardic, and with a low oxygen saturation on room air. The first step in evaluating any trauma patient involves the primary survey. The primary survey is also known as the “ABCDEFs” of trauma. This stands for Airway, Breathing, Circulation, Disability, Exposure, and FAST exam (Focused Assessment with Sonography in Trauma). Each letter should be assessed in alphabetical order to avoid missing a time sensitive life-threatening condition. The primary survey should be conducted prior to taking a full history. After the primary survey, a more detailed physical exam (secondary survey) is conducted, followed by interventions and a focused patient history.
The FAST exam is a quick sonographic exam that requires the practitioner to look at 4 anatomical areas for signs of internal injuries. The 4 areas are the right upper abdominal quadrant, left upper abdominal quadrant, pelvis, and subxiphoid (cardiac) areas. The addition of views for each lung (1 view for each lung) is known as an E-FAST, or extended FAST exam. The presence of an anechoic (black) stripe on ultrasound indicates the presence of free fluid. In the setting of trauma, free fluid is assumed to be blood. The presence of free fluid on a FAST exam is considered a “positive FAST exam”. This patient’s ultrasound shows fluid in the pericardiac sac which in combination with the patient’s hypotension and tachycardia, this supports a diagnosis of cardiac tamponade. See the image below for labelling.
Cardiac tamponade is considered a type of obstructive shock. As with other types of obstructive shock, such as pulmonary embolism and tension pneumothorax, there is a state of reduced preload and elevated afterload. This causes a reduction in cardiac output (Choice C) which leads to hypotension, tachycardia, and circulatory collapse. High cardiac preload (Choice A), low cardiac afterload (Choice B), and high cardiac output (Choice D) do not occur in cardiac tamponade. Treatment for cardiac tamponade includes IV hydration to increase preload, bedside pericardiocentesis, and ultimately, a surgical cardiac window performed by cardiothoracic surgery. Correct Answer: C
References
- Avila, J. (2020). Pericardial tamponade. Core ultrasound. https://www.coreultrasound.com/pericardial-tamponade/
- Simon, E. (2017). EM@3AM – Cardiac tamponade. EmDocs. http://www.emdocs.net/em3am-cardiac-tamponade/
