Significance of Gaseous Microemboli in the Cerebral Circulation During Cardiopulmonary Bypass in Dogs

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Abstract

Background.

Gaseous microemboli during cardiac surgery may damage the brain by reducing cerebral blood flow (CBF). We examined whether the incidence of gaseous microemboli during 150-minute hypothermic (28°C) cardiopulmonary bypass (CPB) adversely affects CBF (radioactive microspheres).

Methods and Results.

Thirty anesthetized dogs were placed on CPB using bubble oxygenators with 50% O2 (n=10) or 100% O2 (n=10) to produce a wide range in the number of gaseous microemboli or membrane oxygenators with 50% O2 (n=10) to avoid microemboli. The number of carotid artery microemboli occurring in a 1-minute interval was counted using a 5-MHz Doppler probe every 15 minutes for the duration of CPB, which lasted 258±5 minutes. With bubbled 100% O2, the number of microemboli averaged 4.1±1.7 emboli per minute on normothermic bypass and increased with cooling to 18.3±4.9 emboli per minute (P<.001). With bubbled 50% O2, the microemboli number was greater on normothermic bypass (19.8±9.8 emboli per minute,P=.0653 compared with bubbled 100% O2) and increased with cooling (100.3±18.7 emboli per minute,P<.001) to a greater extent than with bubbled 100% O2 (P<.001). In contrast, with membrane 50% O2, the emboli number was small (0.6±0.1 emboli per minute) and did not change with CPB temperature. CBF values were not reduced after termination of CPB, even when compared with prebypass values, being 48.3±7.5 mL/min per 100 g (bubbled 50% O2), 49.6±4.1 mL/min per 100 g (bubble 100% O2), and 44.5±2.8 mL/min per 100 g (membrane 50% O2,P=.7581). Similarly, regional perfusion to the cerebellum, hippocampus, and caudal brainstem was not adversely affected by microemboli. After CPB, cortical biopsies demonstrated no difference among groups with respect to lactate (P=.1753), energy charge (P=.5179), and brain water content (P=.939). Retinal histopathology indicated no differences among groups.

Conclusions.

These results indicate that (1) the incidence of gaseous microemboli during hypothermia increases when a bubble oxygenator is used, and (2) global CBF and regional brain perfusion are not adversely affected by numerous gaseous microemboli. (Circulation.1993;88[part 2]:319–329.)

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