TRANSCRANIAL DOPPLER MONITORING DURING CAROTID ENDARTERECTOMY - IS ITAPPROPRIATE FOR SELECTING PATIENTS IN NEED OF A SHUNT

Purpose: This report summarizes our experience in evaluating a series of 168 patients who underwent a total of 175 carotid endarterectomy pr ocedures under local anesthesia. Patients were monitored by stump pres sure (SP) measurement and transcranial Doppler scanning (TCD). The nee d for shunting was compared between SP/TCD flow velocity reduction and the awake response (gold standard). Methods: The study cohort represe nted 56% of all the carotid patients treated during the study period. Clamping ischemia was defined as the appearance of focal deficit (foca l ischemia) or unconsciousness (global deficit) on carotid clamping. I n the case of clamping ischemia, a shunt was inserted. To define the o ptimal value of SP and TCD flow velocity that is able to discriminate patients with clamping ischemia, a receiver operator characteristic (R OC) curve was constructed. Sensitivity and specificity tests, together with negative and positive predictive values (NPV and PPV), were calc ulated. Cutoff values were defined as the ROC curve values that correl ated the highest sensitivity with the highest specificity for both SP and TCD. Results: Clamping ischemia was present in 18 procedures (10%) in which a shunt was used. No perioperative deaths were recorded. Maj or perioperative morbidity occurred in one patient (0.6%). Two nondisa bling strokes were also recorded (1.8% overall rate of neurologic morb idity). Cutoff values for both SP and TCD, using the ROC curve, were l ess than or equal to 50 mm Hg and greater than or equal to 70% flow ve locity reduction from baseline, respectively. SP values of less than o r equal to 50 mm Hg or less showed a sensitivity of 100%, a specificit y of 83%, a PPV of 40%, and an NPV of 100%. TCD flow monitoring (great er than or equal to 70% flow reduction) revealed a lower sensitivity ( 83%) but a greater ability to avoid false positive results (96% specif icity), resulting in increased PPV (71%) and NPV (98%). Combining SP a nd TCD failed to provide better results in terms of specificity (81%) and PPV (38%). Conclusions: SP measurement using a 50 mm Hg cutoff app ears to be a reliable predictor of clamping ischemia but requires the use of a shunt in 17% of the patients who would otherwise not require this procedure. In contrast, TCD has a greater specificity but is asso ciated with a lower sensitivity, with 17% false negative results. In o ur experience, both SP and TCD show limitations, as they overestimate or underestimate carotid endarterectomy procedures in need of a shunt. We believe that sensitivity is more important than specificity in car otid endarterectomy, and thus conclude that TCD flow velocity measurem ent is not an optimal method for detecting clamping ischemia.