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Centre for Anaesthesia, University College London, London, United Kingdom (Grocott, Mythen) Department of Anesthesiology, Duke University Medical Center, Durham, NC, gan00001{at}mc.duke.edu (Gan)
In Response:
We welcome the letter by Reuter and Goetz.
The respondents’ assertion that we did not differentiate between assessing "static" preload parameters (presumably they mean variables) and assessing "fluid responsiveness" is inaccurate. We clearly state, "There is no evidence to support the concept that use of static measurements of intravascular pressure achieves the goal of avoiding tissue under perfusion" (column 1, page 1101) and that "Information may be gained by observing the response of CVP and/or PAOP to a fluid challenge...This approach has been shown to improve outcome when compared with ‘routine practice’" (column 1, page 1102), and then detail five reports of fluid responsiveness (fluid challenge against stroke volume measured using Esophageal Doppler Velocimetry) being used to guide fluid therapy in randomized controlled trials (column 2, page 1102) (1).
We agree with the respondents’ assertion that other technologies such as transesophageal echocardiography and transcardiopulmonary thermodilution can be used to derive volumetric variables and that there is some preliminary data to suggest that these values can effectively predict fluid responsiveness in patients. However we note that there are, as yet, no studies that have used these techniques to guide fluid therapy and thereby improve clinical outcomes.
Similarly, we agree (and discussed in some detail in our review) that systolic pressure variation (SPV) and stroke volume variation (SVV) have been demonstrated to be good predictors of preload responsiveness. This is an exciting area, but we would caution against overinterpreting the limited available data and have three particular concerns. First, this is a new area and the six studies listed by our respondents include only 111 patients, with no more than 30 in any study. Second, it is still unclear whether these variables are superior to other, more established, measures in predicting fluid responsiveness. For example, three studies comparing the value of pulmonary artery occlusion pressure (PAOP) and SVV/SPV for predicting the response to a fluid challenge produced conflicting results. Bennett-Guerrero et al. (2) compared PAOP and SPV in surgical patients and found PAOP to predict volume responsiveness more effectively. Tavernier et al. (3) compared PAOP with SPV in patients with sepsis and found SPV to be superior in predictive ability. Reuter and Goetz (4) compared the predictive value of PAOP and SVV and found them to be equivalent for patients with a left ventricular ejection fraction >50% but that SVV was better in patients with a left ventricular ejection fraction <35%. Third, our paper addressed the question of clinical outcomes and perioperative fluid management and we are not aware of any data evaluating the effect of fluid administration guided by SVV/SPV variation on clinical outcomes. This is in contrast to the large number of randomized controlled trials of esophageal Doppler velocimetry guided stroke volume maximization demonstrating improved outcomes in perioperative patients (5-10).
It is interesting to speculate on the results that might be obtained in a comparison between a technique predicting fluid responsiveness and an approach using fluid challenge titrated against stroke volume measurement until there is no increase in stroke volume. The latter approach would be expected to result in the administration of one additional fluid bolus (typically 200 to 250 mL) over the former. The difference in fluids administered between intervention and control groups in the esophageal Doppler velocimetry guided studies is typically approximately 500 mL in favor of the intervention group. Using a technique to predict volume responsiveness might be expected to diminish this difference to 250-300 mL, which might dilute the benefit observed in the intervention groups in these studies.
We eagerly await the results of studies assessing the effect of these approaches on clinically relevant outcomes.
References
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