Kurzfassung

Pulse wave transit time (PWTT) is a flow-based non-invasive monitoring parameter which consists out of the two parts pre-ejection period (PEP) and vessel transit time (VTT). The respiratory variation of PEP (ΔPEP) has been shown to be a predictor of fluid responsiveness (1). For assessing blood pressure, PEP+VTT=PWTT has been found more suitable than PEP alone (2). Thus, PWTT or the respiratory variation of PWTT (ΔPWTT) might be a predictor of fluid responsiveness.
Whilst PWTT can be assessed...Pulse wave transit time (PWTT) is a flow-based non-invasive monitoring parameter which consists out of the two parts pre-ejection period (PEP) and vessel transit time (VTT). The respiratory variation of PEP (ΔPEP) has been shown to be a predictor of fluid responsiveness (1). For assessing blood pressure, PEP+VTT=PWTT has been found more suitable than PEP alone (2). Thus, PWTT or the respiratory variation of PWTT (ΔPWTT) might be a predictor of fluid responsiveness.
Whilst PWTT can be assessed using a standard monitoring only including ECG and pulsoxymetry, so far it is unknown how to obtain PWTT correctly in a clinical setting. Therefore, this study was conducted to find “best-PWTT” for predicting fluid responsiveness in the perioperative setting compared to ΔPP.
We enrolled 40 patients scheduled for major urological surgery with an expected fluid turnover intraoperatively. In case of hypovolemia a fluid bolus of 7 ml/kg ideal body weight was administered at the discretion of the attending anaesthetist. An increase in stroke volume of 10% as captured by Oesophageal Doppler Monitoring was considered to reflect fluid responsiveness.
The assessment of ΔPP was performed after cannulation of the non-dominant hand by reliable standard monitoring technology.
Beginning of PWTT was detected by either R-wave in the ECG, or Q-wave in the ECG. End of PWTT was detected by pulse oximetry either at the finger, or the ear lobe. PWTT measurements were either corrected by Bazett’s formula (3), or were left uncorrected. PWTT was analyzed either as monitored, or the respiratory variation of PWTT (ΔPWTT) was analyzed. ROC curves and corresponding AUCs were used to compare the 16 methods of determing PWTT and to compare ΔPWTT and ΔPP, a Wilcoxon test was used to discriminate fluid responders from non-responders.
Various ways to assess PWTT are not created equal: “Best-PWTT” is assessed by the respiratory variation of PWTT (ΔPWTT), with the heart rate corrected by Bazett’s formula, the beginning of PWTT to be detected by the R-wave in ECG, and pulse oximetry attached at the earlobe.
AUC was 0.7164 for ΔPWTT, and 0.6265 for ΔPP, respectively. The Wilcoxon test showed a p-value of 0.014 for ΔPWTT, and 0.008 for ΔPP, respectively. ΔPWTT shows promise as a noninvasive parameter to predict fluid responsiveness.

1) Bendjelid K et al, J Appl Phys 2004;96:337-42. 2) Ahlstrom C et al, J Artif Organs 2005;8:192-7, 3) Bazett HC. Heart 1920;7:353–70.
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