First, a number of parameters have been used to evaluate shunt function by Doppler ultrasound. Many of these parameters, particularly the velocity calculation, can vary with the equipment used and are operator-dependent. For example, the MPFV measured in a given patient is dependent on the type of ultrasound machine used and its calibration, as well as the skill and technique of the sonographer. Second, the venographic findings to which ultrasound is compared vary among investigators. Owens' results differ from those reported previously for ultrasound detection of TIPS dysfunction.
More recent reports show a downward trend in accuracy for sonography that is perhaps more realistic.
Are the poor sonographic results reported by Owens et al. Several aspects of their results are worth noting and may have led to the low ultrasound accuracy. First, the authors report a very high rate of malfunction among the shunts studied. This rate of dysfunction is considerably higher than the rate we have reported. Perhaps the high rate of shunt dysfunction in the study by Owens et al. contributed to an increased rate of ascites, which impaired the sonographer's ability to image the shunts on ultrasound.