Ability of the PulseCO Algorithm to Assess Changes in Stroke Volume Induced by Changes in Vascular Tone

Vasoconstriction during anesthesia can influence stroke volume (SV) by preload modulation, making accurate SV monitoring essential to guide vasopressor therapy. Since gold standard methods like pulmonary artery catheterization and lithium dilution provide only intermittent estimates, continuous and less invasive arterial pulse contour analysis systems are increasingly used. However, their accuracy under altered vascular tone remains uncertain. We aimed to evaluate the PulseCO algorithm's (SV-P) ability to detect clinically relevant changes in SV index (SVI) during manipulation of vascular tone, using lithium dilution with the LiDCO method (CI-Li) as reference, and to assess how absolute systemic vascular resistance index (SVRI) levels influenced agreement between methods.

In this prospective observational study, adult patients undergoing general anesthesia were monitored using continuous SV-P and intermittent CI-Li at three predefined time points: (1) supine baseline after anesthetic induction, (2) after head-up tilt (HUT), and (3) during phenylephrine infusion in HUT. Agreement in SVI changes was assessed by directional concordance, absolute changes and Bland-Altman analysis, and the impact of vascular load was further explored by examining SVRI. A ≥ 10% change in SVI was defined as clinically relevant.

A total of 19 patients were included. Directional concordance between the two methods was 100% in both interventions. The SV-P registered SVI changes ≥ 10% in all patients during both interventions, while lithium dilution registered this in 16 and 18 patients, respectively. The SV-P consistently overestimated SVI changes compared with CI-Li, with a non-significant mean difference of -1.6 mL/m² (95% CI: -4.2 to 1.1, p = 0.28) from baseline to HUT, and a significant overestimation during phenylephrine infusion with a mean difference of 4.9 mL/m² (95% CI: 2.5 to 7.4, p = 0.001). Relative discrepancies between SV-P and CI-Li appeared to increase with higher SVRI.

The arterial pulse wave-based algorithm detected clinically relevant changes in SVI with 100% sensitivity and showed a 100% concordance with lithium dilution in the direction of change. However, it generally overestimated absolute SVI changes, and most markedly so during phenylephrine administration. Relative discrepancies in absolute SVI values appeared to increase with higher SVRI, highlighting that vascular load affects agreement.

This study compares the performance of one device's pulse contour-based estimates for stroke volume to estimates of stroke volume, same device, based on dilution-based cardiac output and observed heart rate. This was also tracked during anesthesia interventions expected to alter peripheral vascular tone. These 2 methods for stroke volume (index) estimation agreed in direction of change with the clinical interventions, while pulse contour analysis appeared to overestimate changes in stroke volume compared to the flow-based estimates.