VALIDITY AND REPRODUCIBILITY OF TRANSIT-TIME FLOWMETRY

A new intraoperative method for blood flow measurement, ultrasonic tra nsit-time flowmetry, was validated regarding its variation and error o f measurement. Both common iliac arteries of five piglets were dissect ed under inhalation anaesthesia. Three probes, calibrated by the manuf acturer, were used. Variability was evaluated by repeated measurements from the native artery and under exsanguination controlled with a wit hdrawal pump. The errors of measurement were calculated by comparing t he flow with the exsanguinated volume by time. For each vessel 34-36 s eparate exsanguinations were carried out, with flow ranging from 10 to 500 ml/min. The coefficients of variation for the two 5 mm probes mea sured from the native artery were 3.8 % and 4.2 %, and 4.5 % for the 3 mm probe. With the use of the withdrawal pump the coefficients were 2 .5 %, 2.2 % and 2.1 %, respectively. The two 5 mm probes showed a mean error of measurement of 0.7 % (95 % confidence interval (CI) was -10. 4 to 13.25) and -11.4 % (95 % CI -20.6 to -1.1), while the error for t he 3 mm probe was 3.4 % (95 % CI -18.1 to 14.0). The small variation o f all probes indicated a good reproducibility. With accurate calibrati on of the probes, ultrasonic transit-time flowmetry appears to be a va lid and adequate method for clinical use.