title: Cooling gradients and formation of gaseous microemboli with cardiopulmonary bypass: an echocardiographic study.
abstract: BACKGROUND
  Previous studies demonstrated gas emboli formation during rewarming from hypothermia on cardiopulmonary bypass when the temperature gradient exceeded a critical threshold. It also has been suggested that formation of arterial gas emboli may occur during cooling on cardiopulmonary bypass when cooled oxygenated blood exiting the heat exchanger is warmed on mixture with the patient's blood. The purpose of this study was to determine under what circumstances gas emboli formation would occur during cooling on cardio-pulmonary bypass.
  
  
  METHODS
  Eight anesthetized mongreal dogs were placed on cardiopulmonary bypass using a roller pump, membrane oxygenator, and arterial line filter. For emboli detection, we positioned a transesophageal echocardiographic probe at the aortic arch distal to the aortic cannula and Doppler probes at the common carotid artery and the arterial line. Cooling gradients between normothermic blood and cooled arterial perfusate of 5 degrees, 10 degrees, 15 degrees, 20 degrees, and 0 degree C (isothermal controls) were investigated. In addition to preestablished temperature gradients, we investigated the effect of rapid cooling (maximal flow through the heat exchanger at a water bath temperature of 4 degrees C) after the initiation of normothermic cardiopulmonary bypass.
  
  
  RESULTS
  Minimal gas emboli were detected at the aortic arch at gradients of 10 degrees C or greater. The incidence of emboli was related directly to the magnitude of the temperature gradient (p < 0.01). No emboli were detected at the carotid artery. During rapid cooling, no emboli were observed either at the aorta or at the carotid artery.
  
  
  CONCLUSIONS
  Cooling gradients of 10 degrees C or greater may be associated with gas emboli formation, but they may be of limited clinical significance because no emboli were detected distal to the aortic arch. During the application of rapid cooling, no emboli formation was observed.
authors.affiliation: Department of Anesthesiology, University of Texas-Houston Medical School 77030, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Geissler
authors.forename: S J
authors.initials: SJ
authors.lastname: Allen
authors.forename: U
authors.initials: U
authors.lastname: Mehlhorn
authors.forename: K L
authors.initials: KL
authors.lastname: Davis
authors.forename: E R
authors.initials: ER
authors.lastname: de Vivie
authors.forename: M
authors.initials: M
authors.lastname: Kurusz
authors.forename: B D
authors.initials: BD
authors.lastname: Butler
mesh_terms: D000818:Animals; D002315:Cardiopulmonary Bypass; D004285:Dogs; D004452:Echocardiography; D004618:Embolism, Air / Q000000981:diagnostic imaging / Q000209:etiology*; D005260:Female; D007036:Hypothermia, Induced; D008297:Male