Air Embolus

"Never open a beating heart" is an axiom referring to the left heart when the aorta is unclamped (i.e. one may still open the right atrium for repair of an ASD or tricuspid valve repair since this is on the right side of the heart). Opening the left atrium is much more dire than opening the left ventricle because of the vacuum effect of the atrium sucking in air. The most common cause of air embolism is inattention by the perfusionist to the oxygenator blood level. If the blood level falls below a certain critical level air will be sucked into the pump. Fortunately, the pumps now in use will automatically shut off when air is sensed. Another cause is an unexpected resumption of heartbeat while the heart is open and the cross-clamp is off. Reversal of left ventricular vent suction, such as air pumped directly into the left ventricle, is another cause. Opening a low pressure right superior pulmonary vein while off bypass, with the cross-clamp off and the heart beating may result in air being aspirated into the left heart. Detachment of the oxygenator during perfusion may result in air embolus. Faulty technique during circulatory arrest, in which air is left in the aorta, may result in air embolus.

In case gross air embolism occurs, the following emergency maneuvers are undertaken. The pump is immediately shut off and a clamp is placed on the arterial line. The arterial line is disconnected from the arterial cannula and placed onto a cannula in the superior vena cava. The patient, meanwhile, is placed in Trendelenburg as the anesthesiologist massages the carotid arteries retrograde. Flow through the superior vena cave is instituted at 2 l/min for 2 minutes and blood is retrogradely flushed through the superior vena cava through the brain, down the carotid arteries and back out through the arterial cannula into the peri-cardial sac which is then sucked up with the pump sucker to be returned to the pump circuit. Mannitol and pentobarbital should be given. If an air embolus does occur, the patient should be cooled to afford some cerebral protection. The patient should also be ventilated with 100% FIO2 to facilitate the resorption of nitrogen. Hyperbaric oxygen can be used postoperatively to increase oxygen delivery and increase solubility of gas emboli.

The largest source of fragment microembolization in cardiopulmonary bypass is field aspirated pump sucker blood, since this causes trauma of the blood components and sends back unwanted debris. Arterial filters are therefore used in the cardiopulmonary bypass circuit. Arterial filters usually have a pore size of 40 microns and filter gaseous as well as particulate emboli from the blood before it is returned to the patient.

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