This study investigates the correlation between the radial resistance index (RRI), measured via ultrasound at the anatomical snuffbox, and the systemic vascular resistance index (SVRI), determined by pulmonary artery catheter (PAC), in patients post-cardiac surgery. PAC remains the gold standard for assessing hemodynamic variables like cardiac index (CI) and SVRI, crucial for managing critically ill patients. However, ultrasound offers a non-invasive, accessible alternative for bedside monitoring. RRI, derived from Doppler ultrasound, has been proposed as a potential estimator of SVRI. This cross-sectional study included 35 hemodynamic measurements from post-operative cardiac surgery patients monitored with PAC. Ultrasound RRI measurements were performed by trained senior residents and validated by an experienced intensive care physician.
Results showed a low correlation (r = 0.37) between RRI and SVRI. The mean SVRI was 1967.47 dyn·s·m²/cm5, and the average RRI was 0.94. Patients with RRI > 1.1 had slightly higher mean SVRI than those with RRI ≤ 1.1, but the difference was not statistically significant (p = 0.62). Inter-rater consistency for RRI measurements was high, with an intraclass correlation coefficient of 0.88. Bland-Altman analysis confirmed agreement between evaluators. Despite the promising theoretical basis, the findings suggest that RRI is not a reliable surrogate for SVRI in post-cardiac surgery patients.
In conclusion, while ultrasound is a valuable tool for hemodynamic assessment, its application for estimating SVRI using RRI in this context is limited. Further studies are needed to refine ultrasound-based methods for systemic vascular resistance estimation.
