Ultrasound detection of micro-emboli in the middle cerebral artery during cardiopulmonary bypass surgery

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Abstract
The occurrence of neurological sequelae following cardiopulmonary bypass(CBP) surgery has stimulated interest in refining the techniques ofextracorporeal circulation. Air micro-emboli originating from theoxygenator have been postulated as one source of cerebral damage. Sincecontroversy still exists regarding the merits of bubble versus membraneoxygenators, this has prompted investigators to devise methods to determinethe amount of micro-emboli produced during CPB. In this study, 27 patientsundergoing CPB surgery for coronary artery disease (21) or valvereplacement (6) were examined. The surgical and anaesthetic techniques werestandardised in all patients except for the type of oxygenator used. Abubble oxygenator was used in 17 patients (Bentley Bio-10, William Harveyor Dideco) and a membrane oxygenator with a 25 microns filter in theremaining 10 patients (Bentley BOS CM50). Transcranial pulsed Dopplerultrasound was used to obtain blood velocity signals from the middlecerebral artery throughout CPB. A flow disturbance index (FDI) was definedwhich provided a representative index of the number of micro-emboli passingthe ultrasound transducer. The FDI indicated the presence of gaseousmicro-emboli during insertion of the aortic cannula in 22 of the 27patients. In the 17 patients with a bubble oxygenator, the FDI ranged from4-39. In the 10 patients with a membrane oxygenator, the FDI was always 0.Variation of gas flow rates in 3 patients with bubble oxygenators showed achange in the FDI from 4 +/- 4 at a flow rate of 2 l/min to 17 +/- 9 at 5l/min.(ABSTRACT TRUNCATED AT 250 WORDS)

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