A Comparison of the Vasotrac with Invasive Arterial Blood Pressure Monitoring

To the Editor: We read with great interest the article by Cua et al. (1). They evaluated the compliance of Vasotrac (Medwave, Arden Hills, MN) with invasive arterial monitoring in pediatric patients. The research design and statistical analysis were sound. However, some readers may misunderstand that the two measurements have the same target. Invasive blood pressure measurement and noninvasive blood pressure measurement have intrinsic differences because they measure different quantities. Invasive blood pressure has more value because it records the sum of the lateral pressure (measured by noninvasive blood pressure) and the converted kinetic energy. The pressure converted from blood flow could be more than 15 mm Hg depending on the blood density and velocity (2). Furthermore, invasive blood pressure using fluid-filled catheters can distort the original pressure waveforms. They may result in phase delay and an overestimation of pressure. If the exact invasive blood pressure value is needed as in Cua et al.'s study, the micromanometer-tipped catheter should be used or correction of the results by fluid-filled catheters should be performed (3). It is more reasonable to consider the correctness of invasive blood pressure value and the original differences between invasive blood pressure and noninvasive blood pressure for the compatibility of two measurements. Wonsik Ahn, MD Chul Woo Jung, MD Department of Anesthesiology Seoul National University Hospital Seoul, South Korea [email protected]