Intraoperative echocardiographic study of air embolism during cardiac operations.

Background: Central nervous system damage remains a feared complication after heart operations. Air embolism (AE) is one of several possible causes of central nervous system damage. In previous studies, intraoperative transesophageal echocardiography (ITEE) has been used to detect AE, but identification of the periods of risk and the origin of AE is lacking.

Methods: Two groups of patients undergoing elective heart operations were studied with ITEE. Group I consisted of 15 patients undergoing true "open heart" operations, either aortic or mitral valve. Group II consisted of 15 patients undergoing coronary artery bypass grafting.

Results: In group I (valve operation), ITEE detected AE in all patients, particularly in the period between the release of the aortic cross-clamp and the termination of cardiopulmonary bypass. Furthermore, 12 of the 15 patients had new episodes of AE up to 28 minutes after termination of cardiopulmonary bypass. In the majority of cases, ITEE clearly demonstrated that the air originated in the lung veins and was not air retained in the heart. In group II (coronary artery bypass grafting) episodes of AE were only seen in the period between cross-clamp removal and the termination of cardiopulmonary bypass, and only in half of the patients.

Conclusions: Careful standard cardiac deairing did not prevent AE caused by the delayed release of air trapped in the lung vessels. Routine use of ITEE is recommended to assess the thoroughness of deairing procedures. This will help eliminate AE or at least lead to an increased awareness of the problem of retained air. Minimizing AE during open heart operations should contribute to a reduction in central nervous system damage and improvement of intellectual function after heart operations.