A churning sound in the precordial region (also known as the mill-wheel murmur) is consistent with air in the heart chambers. This finding is characteristic of venous air embolism. Other common features of this condition include sudden hypotension, tachycardia, jugular vein distension, signs of respiratory distress, and, in patients who are being mechanically ventilated, a sudden fall in end-tidal carbon dioxide.
Venous air embolism develops when air enters the venous circulation. This can occur during neurosurgical procedures, especially those that require the patient to be in a sitting position. In this position, the negative (subatmospheric) pressure of the cranial veins due to them being at a higher level than the heart can result in air being sucked into the cranial veins. Other causes of venous air embolism include vascular interventions (e.g., insertion or removal of central venous catheters), penetrating lung injuries, and barotrauma. Management procedures depend on the suspected site of embolism and include compression of the suspected entry site, correction of hypoxia and hypotension, and placing the patient in a head-down position (e.g., Trendelenburg position) or in the left lateral decubitus position (Durant maneuver), both of which help trap the air emboli in the right ventricular apex and therefore prevent further obstruction of the pulmonary outflow tract. If the patient remains unstable following these procedures, direct aspiration of air through a central venous catheter may be considered.
Epinephrine and high-dose corticosteroids are indicated in anaphylactic shock, which can manifest with sudden onset tachycardia, hypotension, signs of respiratory distress (e.g., hypoxia, wheezing), and a decrease in end-tidal carbon dioxide. Many agents used in the operating room (e.g., neuromuscular blocking agents, antibiotics) can lead to anaphylaxis. However, jugular vein distension and a mill-wheel murmur are characteristic of venous air embolism, not anaphylactic shock. Although vasopressors can be used in hemodynamically unstable patients with venous air embolism, steroids are not generally recommended.
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