Finger and forehead photoplethysmography-derived pulse-pressure variation and the benefits of baseline correction

Abstract

To non-invasively predict fluid responsiveness, respiration-induced pulse amplitude variation (PAV) in the photoplethysmographic (PPG) signal has been proposed as an alternative to pulse pressure variation (PPV) in the arterial blood pressure (ABP) signal. However, it is still unclear how the performance of the PPG-derived PAV is site-dependent during surgery. The aim of this study is to compare finger- and forehead-PPG derived PAV in their ability to approach the value and trend of ABP-derived PPV. Furthermore, this study investigates four potential confounding factors, (1) baseline variation, (2) PPV, (3) ratio of respiration and heart rate, and (4) perfusion index, which might affect the agreement between PPV and PAV. In this work, ABP, finger PPG, and forehead PPG were continuously recorded in 29 patients undergoing major surgery in the operating room. A total of 91.2 h data were used for analysis, from which PAV and PPV were calculated and compared. We analyzed the impact of the four factors using a multiple linear regression (MLR) analysis. The results show that compared with the ABP-derived PPV, finger-derived PAV had an agreement of 3.2 ± 5.1%, whereas forehead-PAV had an agreement of 12.0 ± 9.1%. From the MLR analysis, we found that baseline variation was a factor significantly affecting the agreement between PPV and PAV. After correcting for respiration-induced baseline variation, the agreements for finger- and forehead-derived PAV were improved to reach an agreement of - 1.2 ± 3.8% and 3.3 ± 4.8%, respectively. To conclude, finger-derived PAV showed better agreement with ABP-derived PPV compared to forehead-derived PAV. Baseline variation was a factor that significantly affected the agreement between PPV and PAV. By correcting for the baseline variation, improved agreements were obtained for both the finger and forehead, and the difference between these two agreements was diminished. The tracking abilities for both finger- and forehead-derived PAV still warrant improvement for wide use in clinical practice. Overall, our results show that baseline-corrected finger- and forehead-derived PAV may provide a non-invasive alternative for PPV.

Keywords: Fluid responsiveness; Major surgery; Photoplethysmography; Pulse pressure variation; Site dependency; Volume status.

Fig. 1

The diagram of signal selection process

Fig. 2

An example of baseline correction. The segment length is approximately one ventilation cycle (5 s). The original extrema are denoted by OPA (original pulse amplitude), while the corrected extrema are denoted by CPA (corrected pulse amplitude)

Fig. 3

Bland–Altman plot of PPG-derived PAV versus ABP-derived PPV for the data points of all patients aggregated. a Finger-derived PAV versus PPV. b Forehead-derived PAV versus PPV. The solid line corresponds to the bias (mean difference) and the dotted lines correspond to the limits of agreement (1.96 × SD of difference)

Fig. 4

Bland–Altman plot of PPG-derived PAV versus ABP-derived PPV. a Finger-derived PAV versus PPV. b Forehead-derived PAV versus PPV. The solid line corresponds to the bias (mean difference) and the dotted lines correspond to the limits of agreement (1.96 × SD of the difference)

Fig. 5

An example of how baseline correction helps improve the agreement between PAV and PPV. a ABP, finger PPG, and forehead PPG signals. b ABP-derived PPV, finger-derived PAV, baseline-corrected finger-derived PAV. c ABP-derived PPV, forehead-derived PAV, baseline-corrected forehead-derived PAV

Fig. 6

An example of the behavior of PAV in comparison to PPV in the episodes with fast hemodynamic changes. a ABP, finger PPG, and forehead PPG signals. b ABP-derived PPV, finger-derived PAV, baseline-corrected finger-derived PAV. c ABP-derived PPV, forehead-derived PAV, baseline-corrected forehead-derived PAV