DE-AIRING THE HEART AFTER CARDIAC SURGERY 

After completing the repair and as the cardiac chambers are closed or as CABG is being completed, the heart must be freed of as much air as possible before it begins to eject into the systemic circulation. Clinical studies have demonstrated a correlation between the number of gaseous microemboli and the severity of neuropsychological impairment after surgical procedures employing CPB. Thus, special maneuvers are necessary to avoid air embolism, as has clearly been demonstrated by intraoperative echocardiography.

 The exact steps and sequences and the time of de-airing may vary, but the principles are well established: 

■ The heart is filled with fluid (blood or electrolyte solution) before closing to minimize air entrapment.

■ The heart must be reperfused and beating.

■ Residual air is aspirated from the heart before allowing it to eject.

■ The lungs are intermittently ventilated to express air from the pulmonary veins.

■ Continuous suction is applied on a needle vent or catheter in the ascending aorta as the heart commences ejecting blood to retrieve any air that may have remained in the heart or pulmonary veins (alternatively, a freely bleeding stab wound may be used)

One technique can be illustrated with the procedure for aortic valve replacement:

1. As the suture line for aortic closure is being completed, suction on the left atrial vent is discontinued, and flow is reduced to allow the heart to fill with blood. If blood is not freely escaping from the most anterior portion of the aortotomy before completing this suture line, fluid (saline or Ringer’s lactate) is injected into the opened aorta with a syringe. The suture line is completed. A needle vent connected to tubing from the pump-oxygenator is inserted into the ascending aorta. The anesthesiologist gently inflates the lungs to remove air from the pulmonary veins into the left atrium; vigorous inflation is inadvisable because when the lungs collapse, air can be drawn into the left ventricle through the still-opened aorta.

2. With a large-bore needle connected to a 20-mL syringe or to tubing from the pump-oxygenator, the left atrium is aspirated through its dome beneath the aorta. Air is almost invariably obtained. Aspiration is combined with gentle ventilation on two or three occasions until no further air appears. The left atrial appendage is inverted to evacuate air.

3. The heart is gently pulled forward and to the right, and needle aspiration of the left ventricular cavity is performed through the front of the left ventricular apex. This is a simple and effective way of removing the pocket of air that is almost always present at this site. The maneuver can be repeated several times.

4. The operating table is tilted, with the patient’s head down.

5. Perfusion flow rate is temporarily reduced as the aortic clamp is slowly released. Blood and air are gently aspirated from the needle vent in the ascending aorta. Left ventricular overdistention must be prevented.

6. The left atrial vent is removed while the lungs are gently inflated, and the central venous pressure is slowly increased to evacuate any residual air. The purse-string suture is secured. The heart is electrically defibrillated if not already beating. The left ventricle is shaken with the left hand several times.

7. Central venous pressure is slowly raised by the perfusionist. The heart begins to eject. Air may then appear in the aortic vent suction line. When the central venous pressure has been elevated to 10 mmHg and the heart has ejected for several minutes, CPB flow is slowly reduced. The ventricle is again shaken, and CPB is discontinued.

8. The table is leveled. Suction on the aortic needle is reduced and then discontinued, the needle is removed, and the stitch is tied. These maneuvers should not be hurried. The longer the aortic needle vent is in use, the better, and it should not be removed until the heart has been ejecting well for some time.

Transesophageal twodimensional echocardiography (TEE) is commonly used to monitor removal of air from the heart before CPB is discontinued. TEE enables the operating team to identify the presence of even small amounts of intracardiac and intraaortic air.

Flooding the operative field with carbon dioxide is used for displacing air from the cardiac chambers. Its use was first reported by Nichols and colleagues in 1988. The theoretical value of this technique is that carbon dioxide will displace air from the operative field because it is a heavier gas and because carbon dioxide emboli, if they occur, are better tolerated than air emboli.