Using ventilation-induced aortic pressure and flow variation to diagnose preload responsiveness

Excerpt

The recent literature has documented that both arterial pulse pressure [1] and left ventricular stroke volume variations [2] induced by positive-pressure ventilation are sensitive and specific markers of preload responsiveness. The greater the degree of flow or pressure variation over the course of the respiratory cycle for a fixed tidal volume, the more likely the subject is to increase their cardiac output in response to a volume challenge and the greater that increase may be. Slama et al. [3] report in this issue that in a rabbit model of graded hemorrhage measures of aortic flow variation during positive-pressure ventilation cardiac output will increase in response to volume expansion. Furthermore, aortic flow variation was more sensitive than aortic pulse pressure variation in describing this effect further into the hemorrhagic state, presumably because arterial tone also increased. Since measures of descending aortic flow, using an esophageal Doppler probe, can be made easily and continuously without the need for complex echocardiographic techniques, this observation is clinically relevant. These concepts have been previously commented upon in this journal [4] and elsewhere [5]; however, the overarching principals of this clinical tool have not been previously described. In retrospect, the above observations may seem intuitively obvious based on simple principles of heart–lung interactions [6] and initial clinical observations [7]. Still, there are several important caveats and limitations to this approach that need to be considered before the clinician proceeds to monitoring arterial pulse pressure or stroke volume variation during ventilation as a routine assessment of preload responsiveness. …