Exploring Macro-to-Microcirculatory Coupling Through the Vasopressor Test in Septic Shock Patients

Background: Macrohemodynamic optimization does not always ensure adequate microcirculatory perfusion in patients with septic shock. The vasopressor test (VPT), a controlled and transitory increase in the mean arterial pressure (MAP), has been proposed to assess the functional coherence between systemic circulation and microvascular flow. However, the physiological determinants of capillary refill time (CRT) in response to VPT remain poorly understood. Objectives: 1) To evaluate macro-to-microcirculatory coupling during VPT in patients with septic shock using CRT as a dynamic marker of perfusion, 2) to explore the association between CRT and splanchnic perfusion indices, and 3) to identify baseline hemodynamic predictors of CRT response. Methods: This prospective multicenter study enrolled 32 patients with septic shock, persistent hypoperfusion, and fluid-unresponsive status. Hemodynamic, echocardiographic, and perfusion-related variables were recorded at baseline (MAP 65 mmHg) and during VPT (MAP 85 mmHg). We correlated changes in CRT with those instroke volume (SV), and coupling patterns were identified based on the slope of the ΔCRT/ΔSV relationship. Splanchnic perfusion was assessed by Doppler-derived resistive indices. The statistical models included logistic regression and linear mixed-effects analyses. Results: The CRT response to VPT was heterogeneous. Patients with macro-to-microcirculatory coupling were more likely to show CRT improvement, whereas patients without coupling showed no perfusion benefit. No correlation was found between CRT and splanchnic resistive indices. A normal mean systemic filling pressure (Pmsf) was independently associated with CRT improvement. Mixed models confirmed a significant inverse association between changes in SV and CRT. Conclusions: The CRT response to VPT may identify patients with preserved macro-to-microcirculatory coupling. The lack of association with splanchnic resistive indices emphasizes the need for multimodal monitoring strategies. Finally, the baseline Pmsf may be a powerful predictor of CRT responsiveness during a vasopressors test.