Similar to the pleural cavity, the pericardial cavity is only a potential cavity formed by two serous membranes that are closely apposed to each other. The visceral pericardium lines the actual heart, while the parietal pericardium lines the actual pericardial cavity itself. In a disease-free state, the linings are separated by about 15-50 ml of fluid. The fluid provides generic lubrication and reduces friction by allowing the heart to move easily during both contraction and relaxation. Following injury (trauma) or onset of disease (medical), more fluid than normal, sometimes > 1000 ml may accumulate in this cavity. This aberrant accumulation is called an effusion, and it can severely impede cardiac output. In EMS we are very accustomed to associating these "tamponade" events with trauma, but we also need to realize that a host of medical causes are also behind this diagnosis. In order of incidence, in both pleural and pericardial space are: CHF, malignancy (cancer), pneumonia, and pulmonary embolism. Malignant disease or any of these conditions may already be known to the patient, so collecting a thorough patient history on the scene is paramount. Lung and Breast cancers are especially notorious for disseminating into both of these cavities. In cancers most of the time the problem stems from decreased reabsorption mainly due to neoplastic invasion of neighboring lymphatic vessels.
Due to gravity forces, pericardial effusions typically first appear posteriorly in the parasternal long-axis echocardiographic view and anteriorly in the area adjacent to the right atrium in the 4-chamber view. Hey.... here is yet another example demonstrating the vast utility of prehospital ultrasound in a critical care setting. As fluid continues to accumulate, the effusion becomes more circumferential like the above image. Loculated (localized pockets) effusions may be occasionally observed following cardiac surgery. Effusions may be asymptomatic or may have an impact (more or less severe) on cardiac hemodynamics, depending on the rate of accumulation.
On a personal note, the size of the effusion doesn't always correlate with a dramatic swing in the patient's clinical presentation. My mother was diagnosed with a non-small cell lung cancer. The mass extended across both sides of her left lung approximately 10 cm wide. During a bedside ultrasound an effusion was appreciated. She went to the cath lab and had 1,000 ml removed via pericardiocentesis and based on her vital signs you would have never known there was an issue. She had some fatigue and dyspnea, but nothing crazy. By the way, dyspnea is the most sensitive symptom. Her relative lack of hemodynamic instability can likely be attributed to the SLOW rate of accumulation. To contrast to her presentation, in rapidly accumulated fluid, the time for pericardium to stretch is insufficient and heart chambers (mostly the right ventricle due to the thinner-more compressible wall) collapse during diastole because of the high intrapericardial pressures. Thus, diastolic filling is impaired, the preload of the left ventricle is reduced, and finally cardiac output decreases. The images below adequately illustrates the forces at play specifically during the inspiration phase of the respiratory cycle.
PEARLS and closing thoughts
Size doesn't necessarily correlate with the presence of tamponade:
Rapid development of a small effusion may cause tamponade.
Gradual development of a large effusion may not cause tamponade.
Size does relate to the safety and ease of draining the effusion.
Size is estimated based on thickness in diastole:
Small (<1 cm): <300 ml.
Moderate (1-2 cm, circumferential effusion): ~400-600 ml.
Large (>2 cm): usually >700 ml.
Postoperative patients may have a focal clot in the pericardium that may be difficult to diagnose.
Initial fixes and management
Volume resuscitation and fluid loading can be beneficial in most patients. Volume depleted patients are more susceptible to experience RV collapse
Vasopressors - they can be a bridge to the invasive, but definitive treatment - the pericardiocentesis.
June 10, 2024
Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP
Pass with PASS, LLC