A nurse is caring for a client receiving hemodialysis when the client suddenly develops chest pain, dyspnea, and restlessness. The client's blood pressure drops from 140/90 mmHg to 90/60 mmHg, and heart rate increases from 78 bpm to 120 bpm. What is the nurse's priority action?

Turn off the blood pump. This halts the active forcing of air into the patient's venous circulation under pressure from the compromised circuit.

Clamp the venous and arterial lines or the catheter hub. This physically occludes the direct conduit to the central circulation, preventing further air entrainment even after the pump is stopped. Do not disconnect the lines initially to avoid an open portal for air.

Place the patient in the left lateral decubitus (Durant's maneuver) and Trendelenburg position (head down) to trap air in the right atrium and prevent it from entering the pulmonary artery. Note: Trendelenburg alone is contraindicated as it may trap air in the right ventricle.

Apply 100% oxygen via a non-rebreather mask. This helps reduce the size of the air embolus by promoting nitrogen washout and improves tissue oxygenation.

Call the healthcare provider immediately after the initial life-saving measures. Anticipate the need for fluid resuscitation, vasopressors, and possible transfer to a critical care setting.