Non-invasive ultrasound defines snuffbox artery RI and PI reference ranges in healthy volunteers versus ICU patients with septic shock or hypertension.

BackgroundSystemic vascular resistance is conventionally assessed using invasive methods; the snuffbox artery resistance index (RI) is a superior non-invasive predictor of lactate clearance in septic shock patients to the perfusion index. However, the normal reference ranges of the snuffbox artery RI and pulsatility index (PI) remain undefined, with inconsistent RI data in healthy populations due to non-standardized measurements.ObjectiveThis study aimed to establish the normal reference ranges for the snuffbox artery RI and PI in healthy volunteers and to compare these hemodynamic parameters between healthy volunteers and intensive care unit (ICU) patients to evaluate their clinical utility in assessing peripheral microcirculation.DesignThis was a single-center prospective observational cohort study.SettingThis study was conducted at a 4,900-bed tertiary care hospital with a 215-bed closed ICU in China.ParticipantsA total of 91 healthy volunteers—stratified by history of hypertension and age—and 55 ICU patients—classified by shock status—were included in the study from February to November 2024.InterventionsNo interventional measures were implemented; all data were collected through a non-invasive ultrasound and clinical record review.Measurements and main resultsUltrasound parameters and vital signs were measured under standardized conditions. The normal RI and PI ranges in healthy volunteers were 0.72–0.75 and 1.93–2.03, respectively. Significant differences in the RI and end-diastolic flow velocity (EDV) were found between healthy volunteers and ICU patients (all p