Unilateral Vs. bilateral ultrasound in the monitoring of cerebral microemboli

We used bilateral transcranial Doppler to monitor the number of microemboli c events (ME) in the left acid right middle cerebral arteries of 29 patient s during cardiac surgery that required extracorporeal circulation, Based on a previously published study, we hypothesized that the commonly used metho d of doubling unilateral ME counts to obtain an estimated bihemispheric loa d would result in significant errors of estimation. In our sample, estimate d bihemispheric counts were inaccurate by an average of 18% (range 0-80%), Despite this large range of error, calculation of Cronbach's alpha revealed that actual error due to unreliability (4%) was small relative to the larg e variation in ME counts across subjects in this patient series. These find ings suggest that unilateral monitoring is sufficient when the goal is to c haracterize a given subject's ME load within the context of the other subje cts in the sample. However, when precise ME counts are required, bilateral monitoring is essential. (C) 2001 World Federation for Ultrasound in Medici ne & Biology.