Effects of Anisodamine on Sublingual Microcirculation and Vascular Waterfall Phenomenon in Patients With Septic Shock (ANISO-MICRO)

Septic shock is characterized by profound circulatory dysfunction involving both the macrocirculation and the microcirculation. Although conventional resuscitation targets such as mean arterial pressure, cardiac output, and serum lactate are widely used, microcirculatory alterations may persist despite apparent stabilization of systemic hemodynamics. Direct evaluation of sublingual microcirculation may therefore provide additional physiological information in patients with septic shock.

Anisodamine is a non-specific muscarinic cholinoceptor antagonist that has been used in China as an adjunctive therapy in septic shock. Previous clinical studies suggest that anisodamine may improve microcirculatory perfusion, reduce lactate levels, and decrease vasopressor requirements in selected patients with septic shock. However, its immediate effects on directly visualized sublingual microcirculation and vascular-waterfall physiology remain insufficiently characterized.

The vascular-waterfall phenomenon refers to the concept that tissue perfusion is influenced not only by arterial and venous pressures but also by the relationship between upstream pressure, critical closing pressure, and mean systemic filling pressure. In septic shock, changes in vascular tone, vasopressor exposure, vascular closing pressure, and stressed blood volume may alter the effective pressure gradient for tissue perfusion. Evaluation of vascular-waterfall variables together with direct sublingual microcirculatory imaging may provide mechanistic insight into the physiological effects of anisodamine beyond conventional macrocirculatory variables.

This is a prospective, multicenter, single-arm, open-label, interventional pilot physiological study conducted in adult intensive care unit patients with septic shock. Patients will be screened after initial hemodynamic optimization. Eligible patients must have septic shock according to Sepsis-3 criteria, ongoing norepinephrine support, invasive mechanical ventilation, and PiCCO-based hemodynamic monitoring before anisodamine initiation. Patients with contraindications to anisodamine, major conditions interfering with sublingual microcirculatory imaging, severe uncontrolled arrhythmia, or expected death or withdrawal of life-sustaining treatment within 24 hours will be excluded.

After informed consent is obtained, baseline measurements will be performed immediately before anisodamine administration. Anisodamine will be given as an intravenous loading dose of 0.5 mg/kg within 3 minutes, with a minimum dose of 20 mg and a maximum dose of 40 mg, followed by continuous intravenous infusion at 0.02-0.1 mg/kg/hour. The total daily dose will not exceed 200 mg. The maintenance dose may be adjusted by the treating physician according to the patient's microcirculatory status, serum lactate level, capillary refill time, hemodynamics, and adverse effects. Dose reduction, temporary interruption, or discontinuation will be permitted for safety reasons, including clinically significant hypotension, tachycardia, new-onset or worsening arrhythmia, prolonged QT interval, myocardial ischemia, mental status changes, urinary retention, ileus, or other clinically significant adverse events.

Study assessments will be performed at baseline, 3 hours, and 6 hours after initiation of anisodamine. Sublingual microcirculatory imaging will be used to assess microvascular flow index, perfused vessel density, proportion of perfused vessels, and microcirculatory heterogeneity index. Vascular-waterfall related variables will include estimated critical closing pressure, estimated mean systemic filling pressure, and the Pcc-Pmsf gradient. Systemic hemodynamic and perfusion variables, including heart rate, mean arterial pressure, cardiac index, norepinephrine dose, arterial lactate, urine output, capillary refill time, and PiCCO-derived variables, will also be recorded.

Approximately 20 patients will be enrolled to assess feasibility and generate preliminary estimates of physiological changes after anisodamine administration. The main analyses will describe changes from baseline in sublingual microcirculatory and vascular-waterfall parameters over the 6-hour observation period. Safety events, especially tachycardia and arrhythmias, will be summarized descriptively to inform the design of subsequent controlled studies.