INTERPRETATION OF EMBOLIC PHENOMENA DURING CAROTID ENDARTERECTOMY

Background and Purpose Air and particulate emboli are a major source o f morbidity during carotid endarterectomy (CEA); however, amplitude ov erload and poor time resolution have restricted the ability of transcr anial Doppler ultrasound to differentiate between the two. Methods We have now overcome these two limitations by (1) rerouting embolic signa ls away from the audio frequency amplifier to avoid amplitude overload and (2) substituting the Wigner distribution function for the fast Fo urier transform to improve time and frequency resolution. Thus, we can now accurately determine embolic duration and embolic velocity, the p roduct of which is the sample volume length (SVL). This measurement re presents the physical distance over which an embolic signal can be det ected. The underlying hypothesis was that air reflected more ultrasoun d and would therefore be detected over a greater SVL.Results The media n SVL (interquartile range) for 75 in vitro air emboli was 1.97 cm (ra nge, 1.70 to 2.35) compared detected during the dissection phase of CE A. Off-line analysis on an additional 560 embolic signals detected dur ing different phases of CEA suggested that 46 of 143 (32%) of emboli i mmediately after shunt insertion were particulate, as were 19 of 33 (5 8%) occurring during shunting, 28 of 78 (36%) after restoration of flo w in the external carotid artery, 23 of 251 (9%) after restoration of flow in the internal carotid artery, and 55 of 55 (100%) of those embo li detected during the early recovery phase. Conclusions This developm ent provides objective physical criteria upon which embolus characteri zation (particulate/aire) can be based. This could have major implicat ions for future patient monitoring with respect to modification of sur gical technique and pharmacological intervention.