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 (280C) cardiopulmonary bypass (CPB) adversely affects CBF (radioactive microspheres).Methods and Results
Thirty anesthetized dogs were placed on CPB using bubble oxygenators with 50%o 02 (n= 10) or 100%o 02 (n=10) to produce a wide range in the number of gaseous microemboli or membrane oxygenators with 50% 02 (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%O 02 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%o 02, the microemboli number was greater on normothermic bypass (19.8±9.8 emboli per minute, P=.0653 compared with bubbled 100%o 02) and increased with cooling (100.3±18.7 emboli per minute, P<.001) to a greater extent than with bubbled 100% °02 (P<.001). In contrast, with membrane 50o 02, 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% 0°2), 49.6±4.1 mLlmin per 100 g (bubble 100%o 02), and 44.5±2.8 mlmin per 100 g (membrane 50% 02, 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.