title: Residual air in the venous cannula increases cerebral embolization at the onset of cardiopulmonary bypass.
abstract: OBJECTIVE
  When the right atrium (RA) cannula is connected to the venous return line of the cardiopulmonary bypass (CPB) circuit, air is often introduced. Air in the venous cannula may increase cerebral air embolization at initiation of CPB despite the arterial line filter. We measured the volume of air present in the venous cannula after cannulation of the RA. Transcranial Doppler quantified emboli as high-intensity transient-signals (HITS) in both middle-cerebral arteries (MCA) at the beginning of CPB.
  
  
  METHODS
  After RA cannulation, the air column in the venous line was measured and the total volume calculated using the known lumen diameter. CPB onset was defined as the instant when the CPB machine started moving the patient's blood from the RA into the venous reservoir. Starting from CPB onset, HITS were counted: (a) until completion of the first minute on CPB (1-min count) and (b) until aortic cross clamping (pre-clamping count).
  
  
  RESULTS
  We studied 135 patients during coronary artery bypass surgery operated on by 10 cardiac surgeons. HITS during onset of CPB were detected in 95% of patients. Median counts were 10 HITS (25th, 75th percentiles: 3, 26) at 1-min and 21 HITS (8, 51) during pre-clamping. A significant correlation was found between the volume of air in the venous cannula and the HITS counts (r=0.524, p<0.0001). Absence of retained air was associated with lower HITS counts [3 HITS (1, 11)] compared with any amount of air [13 HITS (4, 29), p=0.002)]. The volume of air in the venous cannula, the MCA mean blood flow velocity and the pre-clamping time were the only independent predictors of the pre-clamping HITS counts (p<0.001).
  
  
  CONCLUSIONS
  Air in the venous cannula can result in HITS in the MCA. Minimizing the volume of air introduced into the venous cannula after cannulation of the RA can decrease cerebral air embolization at the beginning of CPB.
authors.affiliation: Department of Surgery, Division of Cardiac Surgery, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario, Canada K1Y 4W7. Rrodriguez@Ottawaheart.ca
authors.forename: Rosendo A
authors.initials: RA
authors.lastname: Rodriguez
authors.forename: Fraser
authors.initials: F
authors.lastname: Rubens
authors.forename: Dean
authors.initials: D
authors.lastname: Belway
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Nathan
mesh_terms: D000368:Aged; D001831:Body Temperature; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D002404:Catheterization / Q000009:adverse effects; D001026:Coronary Artery Bypass; D003327:Coronary Disease / Q000000981:diagnostic imaging / Q000601:surgery; D004618:Embolism, Air / Q000000981:diagnostic imaging / Q000209:etiology*; D006801:Humans; D020766:Intracranial Embolism / Q000000981:diagnostic imaging / Q000209:etiology*; D007431:Intraoperative Complications / Q000000981:diagnostic imaging / Q000209:etiology*; D016014:Linear Models; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging; D009305:Nasopharynx / Q000502:physiology; D012044:Regression Analysis; D017585:Ultrasonography, Doppler, Transcranial