Effects of Dexmedetomidine on Sublingual Microcirculation and Vascular Waterfall Phenomenon in Patients With Septic Shock

This prospective, multicenter, single-arm, open-label interventional pilot study aims to evaluate the short-term physiological effects of intravenous dexmedetomidine on sublingual microcirculation and vascular-waterfall parameters in adult patients with septic shock. Eligible patients will have septic shock according to Sepsis-3 criteria, require norepinephrine support after adequate fluid resuscitation, receive invasive mechanical ventilation, and have PiCCO-based hemodynamic monitoring available before dexmedetomidine initiation. After baseline assessment, participants will receive intravenous dexmedetomidine according to the study protocol. Dexmedetomidine will be administered as a continuous intravenous infusion at 0.2-0.7 µg/kg/hour without a loading dose. The infusion rate may be adjusted according to the target sedation level, hemodynamic status, and adverse effects. Sublingual microcirculatory variables, including microvascular flow index, perfused vessel density, proportion of perfused vessels, and heterogeneity index, as well as vascular-waterfall parameters, including estimated critical closing pressure, estimated mean systemic filling pressure, and the Pcc-Pmsf gradient, will be measured at baseline, 3 hours, and 6 hours after initiation of dexmedetomidine. Systemic hemodynamic, perfusion, vasopressor, PiCCO-derived, sedation-related, and safety outcomes will also be collected. The primary objective is to characterize immediate changes in sublingual microcirculation and vascular-waterfall physiology after dexmedetomidine administration and to provide preliminary data for future controlled studies.