Critical care ultrasound evaluation of snuffbox artery vascular tension: a prospective observational study between healthy volunteers and intensive care unit patients

Background Systemic 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. Objective This 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. Design This was a single-center prospective observational cohort study. Setting This study was conducted at a 4,900-bed tertiary care hospital with a 215-bed closed ICU in China. Participants A 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. Interventions No interventional measures were implemented; all data were collected through a non-invasive ultrasound and clinical record review. Measurements and main results Ultrasound 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 < 0.001), with no differences in the peak systolic flow velocity (PSV) or PI. EDV was associated with 28-day mortality in patients ( p < 0.05). Volunteers had significant post-exercise EDV changes, and hypertension/age had no effect on their vascular tension parameters. After excluding 5 patients, the remaining 50 shock and non-shock ICU patients showed no significant differences in all snuffbox artery parameters. Conclusion This study established standardized normal reference ranges for the snuffbox artery RI and PI in healthy adults and found significant RI and EDV differences between ICU patients and healthy volunteers. EDV may serve as a potential prognostic indicator, and alterations in diastolic flow may reflect early peripheral vascular tension changes. The lack of parameter differences between shock and non-shock ICU patients reveals the physiological limitations of the snuffbox artery RI as a surrogate for systemic vascular resistance.