If a patient shows signs of an air embolism from her PICC line, what is the appropriate action?

Placing the patient in the left lateral decubitus and Trendelenburg position is the appropriate action when signs of an air embolism are observed. This position helps trap any air bubbles in the right atrium of the heart, preventing them from entering the pulmonary circulation, which could lead to serious complications. The left lateral decubitus position allows gravity to minimize the chance of air traveling into the central circulation, and the Trendelenburg position elevates the patient's legs above their heart, promoting venous return and further reducing the risk of air reaching critical areas.

This technique is a recognized emergency response in cases of venous air embolism, prioritizing patient safety and mitigating potential harm. It is crucial to stabilize the patient and minimize further risk while assessing the situation and providing appropriate medical intervention. Other actions, like removing the line immediately or "milking" the line, do not directly address the immediate need to prevent the air from moving towards vital organs, thus making those alternatives less suitable in this emergency scenario.