Pericardial Effusion

The nurse managing pericardial effusion must understand the pressure-volume relationship within the pericardial space and its hemodynamic consequences. The pericardium has a steep pressure-volume curve: once the pericardial reserve volume is exceeded, small additional fluid increments cause large pressure increases. Intrapericardial pressure normally ranges from -5 to +5 mmHg. As effusion accumulates, intrapericardial pressure rises and eventually equals right atrial pressure (normally 0-8 mmHg), then right ventricular diastolic pressure, then left atrial and left ventricular diastolic pressure. This equalization of diastolic pressures is the hemodynamic hallmark of tamponade. Pulsus paradoxus (exaggerated respiratory variation in arterial pressure) occurs because during inspiration, increased venous return to the right heart causes the interventricular septum to shift leftward within the fixed pericardial space, directly compressing the left ventricle and reducing left ventricular stroke volume. During expiration, the septum shifts rightward, temporarily improving LV filling. This mechanism is called ventricular interdependence. Echocardiographic signs of tamponade include: right atrial collapse during systole (earliest sign), right ventricular diastolic collapse, IVC plethora without respiratory variation (greater than 2.1 cm without inspiratory collapse), and exaggerated mitral inflow velocity variation...