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Ann Thorac Surg 1997;64:1527
© 1997 The Society of Thoracic Surgeons
Cardiothoracic Surgery, 1110 Broad Ave Suite 800, Gulfport, Ms 39501
To the Editor:
In the recent article by Cochran and associates [1] about the use of perfluorocarbon emulsion in cardiopulmonary bypass prime to reduce neurologic injury, the authors state that macroscopic air emulsion is rare and list mechanisms whereby it can be introduced during cardiopulmonary bypass. They report that perfluorocarbon can reduce neurologic injury after massive air embolism during cardiopulmonary bypass.
Although massive air embolism is rare, it is reasonable to assume that the introduction of macroscopic bubbles is a common occurrence during cardiopulmonary bypass. According to the laws of Boyle and Henry regarding gas solubility, the solubility of a gas in a liquid is directly proportional to the pressure applied to the medium and inversely proportional to its temperature. Because most patients on cardiopulmonary bypass are cooled, either actively or passively, it is reasonable to assume that the gaseous components of air dissolve in the blood then come out of solution with rewarming.
More than 15 years ago I participated in two neurosurgical operations for removal of giant cerebral aneurysms using deep hypothermia and circulatory arrest. My role was instituting and supervising partial bypass by way of femorofemoral cannulation. After commencement of rewarming the surface vessels of the brain in the still open head wound were seen to be filled with thousands of tiny bubbles, obviously not introduced with cannulation. Despite this occurrence, both patients awoke immediately after the operations.
Doppler studies in scuba divers demonstrate that intravascular bubble formation is present after any significant dive to depth while breathing compressed air. Because oxygen and carbon dioxide are rapidly assimilated into tissue, it is assumed that these are nitrogen. Despite this bubble formation, development of the "bends" is uncommon.
Recently, I was able to extubate a 72-year-old, diabetic woman the morning after quadruple coronary artery bypass grafting, but she remained somnolent and barely able to answer "yes" or "no" in response to questions. When she exhibited even more central nervous system depression the second postoperative day, she was referred for hyperbaric treatment. After 15 minutes in 2 atmospheres of pressure, the patient was able to recite the phone numbers of her children. Two hours after the session, she had relapsed into her previous state but recovered completely after another treatment the next day. Attempts to duplicate this phenomenon in two subsequent patients, both with different clinical presentations, have failed to achieve such dramatic improvement.
Cochran and associates' studies with perfluorocarbon, as reported, were directed toward the treatment of massive air embolus. Because I believe it is likely that nitrogen bubbles occur with every period of cardiopulmonary bypass in which systemic rewarming is necessary, and that they might account for some of the "postpump syndrome," the use of perfluorocarbon might have wide application during cardiopulmonary bypass.
References
Division of Cardiothoracic Surgery, University of Washington Medical Center, 1959 Ne Pacific St, Box 356310, Seattle, Wa 98195-6310
To the Editor:
We appreciate the opportunity to respond to the letter by Dr Dye regarding our article. As pointed out in the article and by Dr Dye's discussion, we did design this experimental model to address the efficacy of preventing injury in massive macroscopic air embolism. However, like Dr Dye, we believe that neurologic injury and dysfunction secondary to microemboli is as important, and far more common, than macroemboli in the post–cardiopulmonary bypass patient population. We also share Dr Dye's concern that nitrogen bubbles may occur during all periods of cardiopulmonary bypass, secondary to systemic rewarming. As such, we are of a like mind with Dr Dye in the conclusion that the use of perfluorocarbons may have a much greater role in routine cardiopulmonary bypass than outlined in our article in which a massive air embolism was the mechanism. We have performed and are in the process of analyzing further studies delineating the role of perfluorocarbon emulsion as a prophylactic measure, and have also examined the dose effect. In addition, at the present time clinical trials are underway for the establishment of the safety of this modality in cardiopulmonary bypass patients.
We appreciate the opportunity to respond to Dr Dye's comments and share his hopes that perfluorocarbons may have a much wider utilization in cardiopulmonary bypass in the future for the prevention of both major and minor neurologic injuries.
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