Non-invasive measurements of pulse pressure variation and stroke volume variation in anesthetized patients using the Nexfin blood pressure monitor

Abstract

Nexfin beat-to-beat arterial blood pressure monitoring enables continuous assessment of hemodynamic indices like cardiac index (CI), pulse pressure variation (PPV) and stroke volume variation (SVV) in the perioperative setting. In this study we investigated whether Nexfin adequately reflects alterations in these hemodynamic parameters during a provoked fluid shift in anesthetized and mechanically ventilated patients. The study included 54 patients undergoing non-thoracic surgery with positive pressure mechanical ventilation. The provoked fluid shift comprised 15° Trendelenburg positioning, and fluid responsiveness was defined as a concomitant increase in stroke volume (SV) >10 %. Nexfin blood pressure measurements were performed during supine steady state, Trendelenburg and supine repositioning. Hemodynamic parameters included arterial blood pressure (MAP), CI, PPV and SVV. Trendelenburg positioning did not affect MAP or CI, but induced a decrease in PPV and SVV by 3.3 ± 2.8 and 3.4 ± 2.7 %, respectively. PPV and SVV returned back to baseline values after repositioning of the patient to baseline. Bland-Altman analysis of SVV and PPV showed a bias of -0.3 ± 3.0 % with limits of agreement ranging from -5.6 to 6.2 %. The SVV was more superior in predicting fluid responsiveness (AUC 0.728) than the PVV (AUC 0.636), respectively. The median bias between PPV and SVV was different for patients younger [-1.5 % (-3 to 0)] or older [+2 % (0-4.75)] than 55 years (P < 0.001), while there were no gender differences in the bias between PPV and SVV. The Nexfin monitor adequately reflects alterations in PPV and SVV during a provoked fluid shift, but the level of agreement between PPV and SVV was low. The SVV tended to be superior over PPV or Eadyn in predicting fluid responsiveness in our population.

Keywords: Anesthesia; Blood pressure; Cardiac output; Fluid challenge; Hemodynamic; Non-invasive monitoring.

Fig. 1

Changes in mean arterial pressure (MAP; a), heart rate b, pulse pressure variation (PPV; c), stroke volume variation (SVV; d), stroke volume e and cardiac index (CI; f) during Trendelenburg (TB) and reversal to neutral supine position. Data represent mean ± SD

Fig. 2

Receiver operating characteristic (ROC) curves to assess the predictive value of the steady state stroke volume variation (a; SVV; straight line; AUC 0.728 CI 0.551–0.906) and pulse pressure variation (PPV; dotted line; AUC 0.636 CI 0.462–0.811) to predict fluid responsiveness defined as an increase in stroke volume of 10 % or more upon Trendelenburg positioning. b and c show the ROC curves for PPV and SVV in patients with an Ea_dyn <0.89 or Ea_dyn >0.89, respectively. AUC = area under the curve with 95 % confidence intervals (CI)

Fig. 3

The difference between PPV and SVV as revealed by Bland–Altman analysis was categorized for age (<55 or ≥55 years; a), gender (b) and body mass index (<25 or ≥25 kg/m²; c). Data represent mean ± standard deviation. P values are shown in the figure panels

Fig. 4

Dynamic arterial elastance (Ea_dyn) expressed as the ratio between pulse pressure variation and stroke volume variation for patients younger (n = 22) or older (n = 21) than 55 years. Supine = repositioning to supine state. Data represent mean ± standard deviation P < 0.001 (repeated measures analysis) for changes in dynamic arterial elastance over time between groups