Instituting positive pressure ventilation in a patient with cardiac tamponade can result in cardiovascular collapse due to the critical impedance of cardiac filling. The increase in intrathoracic pressure is added to intrapericardial pressure, which worsens the Starling resistor pathophysiology of cardiac tamponade. Supine positioning, with or without positive pressure, can further impede filling. An anterior clot or effusion can, with gravity, worsen right atrial and RV compression when the patient is supine. Increased diaphragmatic splinting in a patient already in respiratory distress will limit the negative intrathoracic pressure generated in spontaneous ventilation; this further compromises the gradient for venous return to the RA.

References

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