title: Significance of gaseous microemboli in the cerebral circulation during cardiopulmonary bypass in dogs.
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 degrees C) cardiopulmonary bypass (CPB) adversely affects CBF (radioactive microspheres).
  
  
  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.
authors.affiliation: Department of Anesthesiology, University of Texas Medical Branch, Galveston 77555-0591.
authors.forename: W E
authors.initials: WE
authors.lastname: Johnston
authors.forename: D A
authors.initials: DA
authors.lastname: Stump
authors.forename: D S
authors.initials: DS
authors.lastname: DeWitt
authors.forename: J
authors.initials: J
authors.lastname: Vinten-Johansen
authors.forename: W K
authors.initials: WK
authors.lastname: O'Steen
authors.forename: R L
authors.initials: RL
authors.lastname: James
authors.forename: D S
authors.initials: DS
authors.lastname: Prough
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002315:Cardiopulmonary Bypass; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004285:Dogs; D004618:Embolism, Air / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D007036:Hypothermia, Induced; D015994:Incidence; D002542:Intracranial Embolism and Thrombosis / Q000209:etiology* / Q000503:physiopathology; D008297:Male; D010106:Oxygenators; D010107:Oxygenators, Membrane; D013997:Time Factors