As a last resort, the patient was rushed to a computed tomography scan (3:42 PM) revealing significant pneumopericardium, large bilateral pneumothoraces, and subcutaneous emphysema (Figure 1). No abdominal hemorrhage was seen. Chest tubes were inserted in both pleural cavities, but the circulation did not restore and the patient died a few hours later in multiorgan failure. Please see Figure 2 for a timeline of the case.
The patient undoubtedly remained in circulatory failure, despite coronary reperfusion and high doses of epinephrine, due to tension pneumothoraces and cardiac tamponade. Both constitute well-known reversible causes of circulatory failure and cardiac arrest,7 but these conditions in this case were not identified by specialists in cardiology and critical care. Pneumothoraces may be difficult to see with x-ray,8 especially in the supine position, but both pneumothorax and cardiac tamponade are expected to be disclosed with ultrasound. In this case, these were not detected despite the sonographers’ considerable experience with POC ultrasound.
Pneumothorax can be ruled out with a very high negative predictive value if one of several signs is seen with ultrasound. These signs include pleural sliding,9 B-lines (comet tails),10 and lung pulse,11 which all rely on the juxtaposition of both parietal and visceral layers of the pleurae. However, in this case, the absence of these signs could not be determined because air in the subcutis reflected ultrasound beams and constituted an effective barrier for visualization of deeper structures. Subcutaneous emphysema also precluded evaluation of any intraperitoneal fluid. Please see Supplemental Video File 1 (Supplemental Digital Content 1, http://links.lww.com/AACR/A142, showing an experimental cine loop of the liver, diaphragm with pleural sliding clearly visible) and Supplemental Video File 2 (Supplemental Digital Content 2, http://links.lww.com/AACR/A143, showing an experimental cine loop of the same anatomical location, but after injection of 10 mL of air into the subcutis). Cine loops from the actual patient case were regrettably not stored despite current recommendations.12 Storage would have furthered subsequent review and quality assurance.
Fluid in the pericardium that causes tamponade is often easily identified with ultrasound as a uniform black mass surrounding the heart. In contrary, ultrasonographic signs of pneumopericardium are highly elusive. When air accumulates in the anterior part of the pericardium, myocardial visualization is hindered as air becomes interpositioned between the ultrasound probe and the myocardium. However, if the air is dispersed during expansion in diastole, the myocardium may be seen in a cyclic manner with structures being visible in diastole, but not in systole. This phenomenon is termed as the air gap sign.13 Although several case stories testify to its clinical presence,14,15 the diagnostic performance of the air gap sign has not been reported and it is likely missed, especially in time critical scenarios such as the pericardiac arrest setting. Imaging of the inferior vena cava may have yielded a distended vein with no respiratory fluctuation compatible with obstructive shock, although recent, albeit experimental, studies have shown that right-side dilation may also occur in hypoxia and hypovolemia.16,17
Furthermore, this case highlights the significance of a multimodal approach to elucidate reversible causes of circulatory failure or cardiac arrest. During severe hemodynamic compromise, POC ultrasound examination, continuous x-ray, and auscultation were inconclusive in regard to pneumothorax. It cannot be ruled out that this critical diagnosis might have been revealed if even further attention had been payed to classical clinical signs of tension pneumothorax such as jugular vein distension, the presence of high ventilator inspiratory pressures, or lung percussion. In analogy, tamponade remains a clinical diagnosis and a negative cardiac ultrasound, even when conducted by a specialist, does not exclude tamponade regardless of the etiology being gas or fluid.18 Inconclusive POC ultrasound examinations are to be expected in critical care and should prompt further imaging modalities if available, but not delay clinical decision making.
In conclusion, the patient probably developed cardiac arrest from coronary occlusion, but likely eventually died of tension pneumothoraces and cardiac tamponade. Diagnosis of reversible causes was attempted with POC ultrasound, but subcutaneous emphysema precluded evaluation of the pleura and abdomen, whereas cardiac imaging provided a false-negative result for tamponade. This case highlights important limitations of an otherwise powerful diagnostic modality in the periarrest setting that are relevant to all clinicians working with patients in circulatory failure. Especially, the presence of subcutaneous emphysema and pneumothorax should be suspected if no recognizable structures including the pleural line, diaphragm, and liver can be visualized with ultrasound.
Name: Peter Juhl-Olsen, MD, PhD.
Contribution: This author helped acquire data and draft the manuscript.
Name: Rasmus Aagaard, MD.
Contribution: This author helped interpret the data and revise the manuscript.
Name: Anni Nørgaard Jeppesen, MD, PhD.
Contribution: This author helped interpret the data and revise the manuscript.
This manuscript was handled by: Mark C. Phillips, MD.
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