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Department of Anesthesiology, University of Florida, College of Medicine, Gainesville, Florida
To the Editor:
We would like to commend Schmitt et al. (1) for their careful prospective study of venous air embolism (VAE) during release of positive end-expiratory pressure and repositioning of patients undergoing surgery in the sitting position. Their finding that intraoperative VAE was followed by a pattern of recurrent VAE during both positive end-expiratory pressure release and repositioning suggests that only some of the air entrained intraoperatively manifests as intraoperative VAE. Other air entrained during surgery appears to move in the circulation during both positive end-expiratory pressure release and changes in patient position. An additional consideration is that air may be entrained postoperatively upon removal of head pins, provided the pin site is above the heart.
We believe that these observations can be extrapolated to form one of the etiologies of unexpected, sudden postoperative cardiovascular collapse. For example, entrainment of air is a known risk during a number of other surgical procedures, such as spinal instrumentation, hepatic surgery, and hip and shoulder arthroplasty. Movement of previously entrained air may occur at the end of these cases while changing ventilation or while moving the patient from either prone or lateral decubitus positions to the supine position. Furthermore, the study of Schmitt et al. underscores the unique and rapid diagnostic help offered by transesophageal echocardiography performed during such events and reminds us to keep a delayed manifestation of VAE in our differential at all times, even when it is not clinically suspected or apparent intraoperatively.
Reference
Université de Montréal, Montréal, Canada Friedrich-Alexander University Erlangen, Erlangen, Germany
In Response:
We thank Drs. Seubert and Gravenstein for their appreciation of our findings and their comments. We can only agree with their comment that movement of previously entrained air entering the circulation during other surgery at risk for air embolism (such as hip arthroplasty), at the end of surgery, or after surgery due to changing ventilation patterns (such as positive end-expiratory pressure release), or change of patient positions can severely impair the patient’s hemodynamic stability. Intraoperative transesophageal echocardiography (TEE) is not only the most sensitive monitor of venous air embolism, but also the most useful monitor to visualize directly the cardiac performance. It is this double function of TEE, the recognition of venous air embolism in the heart and the possibility to observe to what degree the cardiac function is affected, which makes TEE so useful in our daily practice.
We can only hope that the increasing perception of how frequent venous air embolism really is and that it can occur with so many different types of surgery will lead us to further advance the distribution of TEE devices and to train not only cardiac anesthesiologists in this immensely important technique.
The essential message of our investigation is to use TEE in all surgery at risk for venous air embolism and to continue TEE monitoring after surgery until the patient is in the supine position and positive end-expiratory pressure has been released to ensure that sudden hemodynamic problems due to reoccurrence of air in the circulation are not missed.
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