Changes in pulse pressure following fluid loading: a comparison between aortic root (non-invasive tonometry) and femoral artery (invasive recordings)

To document the relationship between stroke volume (SV) and pulse pressure (PP) recorded at the femoral and aortic sites during volume expansion (VE) in patients in shock. We hypothesized that non-invasively estimated aortic PP would exhibit the same ability as PP recorded invasively at the femoral level to track SV changes. Included in this prospective study were 56 ICU patients needing VE. Femoral PP (indwelling catheter), aortic PP (tonometry) and cardiac output (thermodilution) were recorded before and after VE. Responders were defined as patients who showed an increase in SV of a parts per thousand yen15% after VE. Of the 56 included patients in shock, 39 (age 57 +/- A 14 years, SAPS II 46 +/- A 18) completed the study. At both sites, PP increased after VE in responders (n = 17, mean SV increase 30 +/- A 15%) but not in non-responders. In the overall population, there was a positive relationship between VE-induced changes in SV and in PP at the femoral (r = 0.60, p < 0.001) and aortic (r = 0.52, p < 0.001) sites. Increases in femoral PP of a parts per thousand yen9% indicated SV increases of a parts per thousand yen15% with 82% sensitivity and 95% specificity. Increases in aortic PP of a parts per thousand yen4.5% indicated SV increases of a parts per thousand yen15% with 76% sensitivity and 82% specificity. Areas under the ROC curves indicated that aortic PP was not different from femoral PP for tracking changes in SV. The ability of non-invasively estimated aortic PP to track fluid response was the same as that of invasively recorded femoral PP. This may have implications for non-invasive haemodynamic monitoring.