Case 4

The most likely diagnosis is air embolism with pump head airlock. The mechanism: during the central line exchange, air entered the venous system through the open catheter hub or introducer sheath. Because the drainage cannula is also in the right internal jugular vein with its tip nearby, the negative pressure on the pre-pump side of the circuit actively entrained air from the venous system into the ECMO circuit through the drainage cannula. A massive amount of air entering the centrifugal pump head deprimed it, causing airlock—a complete loss of blood flow. The distinctive sound heard was air passing through the pump head, which is often the first clue.

Answer: B. The correct first step is to clamp the return tubing close to the patient. This isolates the patient from the ECMO circuit and prevents any air remaining in the circuit from being pushed into the patient’s venous system. 

Increasing pump speed (A) will not overcome airlock and may worsen the situation by pushing air further through the circuit. A fluid bolus (C) does not address the immediate emergency. Turning off the pump and waiting (D) delays critical intervention and does not protect the patient from air embolization.

The complete algorithm: 

(1) Clamp the return tubing close to the patient to isolate the circuit. 

(2) Call for help—enough people are needed to manage both the patient and the ECMO circuit simultaneously. 

(3) Provide respiratory and cardiac support via conventional methods (ACLS if the patient has arrested). 

(4) De-air the circuit. If de-airing is not achievable, a circuit exchange will be needed. 

(5) Simultaneously, identify and address the source of air embolism—in this case, the central line procedure. 

(6) Once the circuit is de-aired and the source of air is eliminated, restore ECMO support.

Multiple preventive strategies should have been employed: 

(1) All central line lumens should be properly protected with needleless connection hubs to prevent air entrainment. 

(2) The procedure should have been performed with the patient in the Trendelenburg position to reduce air entrainment risk. 

(3) Wet swabs should be used to cover the puncture site during the exchange. 

(4) If feasible, ECMO blood flow should be temporarily reduced during the procedure to reduce the negative pressure at the drainage cannula, decreasing the suction force that draws air into the circuit. 

(5) The team should have been aware that the drainage cannula and CVC are in the same vessel, making air entrainment particularly high-risk when the CVC tip is near the drainage 

Answer: C. Membrane lung clot deposition does not cause air entrainment. Clot on the membrane lung causes obstruction to blood flow, impaired gas exchange, and hemolysis/coagulopathy, but it does not introduce air into the circuit. 

All other choices are recognized sources: circuit breach on the pre-pump side (A) allows atmospheric air to enter due to negative pressure; central line mismanagement near the drainage cannula (B) allows air to enter the venous system and be drawn into the circuit; and dislodged multistage drainage cannulas (D) can have proximal holes migrate extravascularly, allowing air entrainment.