Neuropsychological deficits as a function of the heart-lung machine used in open-heart surgery: two lungs compared

Hearn, Richard Simon Fairfax (1986) Neuropsychological deficits as a function of the heart-lung machine used in open-heart surgery: two lungs compared. Masters thesis, Memorial University of Newfoundland.

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Abstract

Psychiatric and neurological symptoms, as well as neuropsychological test decrements, frequently occur after open-heart operations, and are seen much more commonly than after other types of surgery. A working hypothesis is that microbubbles of air escape from the heart-lung machine and enter the patient's bloodstream. These microbubbles, it is hypothesized, proceed to blood vessels in the brain, there causing blockages and then mental disturbances. 'Lungs' have accordingly been designed to minimize release of microbubbles. In the present study, two differently designed 'lungs' were compared with regard to patients' postoperative performances on eight neuropsychological tests. One of these, the membrane, is a newer model of more sophisticated technical design than the other, the bubbler. -- Forty-one coronary bypass patients were divided into two groups matched for age, sex, education, and scores on the WAIS-R Vocabulary and the Conceptual Levels Analogy Tests. Testing took place one week preoperatively and at one and six weeks postoperatively. Multiple Analyses of Variance were performed on raw scores and on residuals remaining when effects of covariates were removed. Covariates comprised the matching variables, State and Trait Anxiety, Beck Depression, time on the heart-lung machine and total length of intraoperative periods of low blood pressure. -- Postoperatively, the bubbler group scored significantly higher on two measures of new learning derived from the Rey Auditory Verbal Learning Test. The measures of new learning were the only ones to indicate robust group differences. These findings confirm those of some earlier authors in pinpointing new learning as a sensitive index of postsurgical organic impairment. They also suggest that the bubbler, though of less sophisticated design than the membrane oxygenator, is the safer of the two devices when used with an appropriate filter.

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