Lukasz R Nowak, M. Sklodowska-Curie Memorial Institute of Oncology Kraków Branch
24 November 2014
The results obtained by the authors are very promising and a possibility of employing such a small fluid volume for testing the fluid responsiveness is very attractive. Nonetheless I have some doubts about the methodology of echocardiographic measurements employed by the authors. The doubts arose for the first time when I looked at the Figure 1. of the article. It's title: "Photo of an echocardiographic Doppler flow velocity measurement from the level of the aortic annulus from the parasternal long-axis window" immediately raises concerns - it is not possible to measure aortic flow from the parasternal long axis (PLAX) window due to the beam non-alignement with flow direction (such measurements are performed from the apical window as the authors stated elsewhere in the article). And in fact the figure depicts some M-mode measurements of left ventricle (LV). But this raises some additional problems: the view is slanted and does not correspond to the standard PLAX view as defined by echocardiography textbooks and guidelines. The measurement axis is not perpendicular to the walls. The obtained values of LVIDd and LVIDs are erroneous. It is especially concerning given the fact that the authors used them to calculate volumes, which involves raising the results of measurements to the third power thus multiplying the error. Inability of obtaining the correct PLAX view in mechanically ventillated patients is quite common, but in such situation one should refrain from measuring standard distances. Moreover the authors used a non specified method of converting LVID to volumes - "calculated by internal software". All those methods (Teichholtz, cubed etc) are fairly inaccurate, and rely very much on correct measurements and many geometrical assumptions, and probably should be used with extreme caution in critical care patients. Another questions that ensues is where was the VTI measured - the standard practice is to measure LVOT diameter (in PLAX) and flow (apical directly upstream from the aortic valve, at the level the LVOT diameter was taken), and not as described by by the authors - aortic diameter at the level of annulus and "aortic blood flow" and VTI from apical 5 chamber view.
Critical Care
Methodology of echocardiographic measurements.
24 November 2014
The results obtained by the authors are very promising and a possibility of employing such a small fluid volume for testing the fluid responsiveness is very attractive. Nonetheless I have some doubts about the methodology of echocardiographic measurements employed by the authors. The doubts arose for the first time when I looked at the Figure 1. of the article. It's title: "Photo of an echocardiographic Doppler flow velocity measurement from the level of the aortic annulus from the parasternal long-axis window" immediately raises concerns - it is not possible to measure aortic flow from the parasternal long axis (PLAX) window due to the beam non-alignement with flow direction (such measurements are performed from the apical window as the authors stated elsewhere in the article). And in fact the figure depicts some M-mode measurements of left ventricle (LV). But this raises some additional problems: the view is slanted and does not correspond to the standard PLAX view as defined by echocardiography textbooks and guidelines. The measurement axis is not perpendicular to the walls. The obtained values of LVIDd and LVIDs are erroneous. It is especially concerning given the fact that the authors used them to calculate volumes, which involves raising the results of measurements to the third power thus multiplying the error. Inability of obtaining the correct PLAX view in mechanically ventillated patients is quite common, but in such situation one should refrain from measuring standard distances. Moreover the authors used a non specified method of converting LVID to volumes - "calculated by internal software". All those methods (Teichholtz, cubed etc) are fairly inaccurate, and rely very much on correct measurements and many geometrical assumptions, and probably should be used with extreme caution in critical care patients. Another questions that ensues is where was the VTI measured - the standard practice is to measure LVOT diameter (in PLAX) and flow (apical directly upstream from the aortic valve, at the level the LVOT diameter was taken), and not as described by by the authors - aortic diameter at the level of annulus and "aortic blood flow" and VTI from apical 5 chamber view.Competing interests
None.