Effects of vasopressor dose on microcirculation despite preserved macrohemodynamic targets in septic shock: a prospective observational study.

BACKGROUND: Septic shock may be complicated by hemodynamic incoherence, in which macrohemodynamic targets are achieved despite persistent microcirculatory alterations. Whether norepinephrine requirement is associated with dynamic microvascular reactivity after initial resuscitation, and whether central venous oxygen saturation (ScvO2) reflects this microvascular reserve, remains uncertain. METHODS: This prospective observational study included 30 mechanically ventilated adults with septic shock receiving vasopressor therapy. Thenar near-infrared spectroscopy (NIRS) vascular occlusion testing (VOT) was performed after initial hemodynamic resuscitation, once mean arterial pressure (MAP) ≥65 mmHg had been achieved with vasopressor support. Norepinephrine-equivalent dose was analyzed primarily as a continuous variable. Secondary exploratory group comparisons used a 0.5 μg/kg/min threshold. Primary microvascular outcomes were tissue oxygen saturation (StO2) recovery slope and StO2 hyperemia area under the curve (AUC). Correlation, linear regression, and exploratory receiver operating characteristic analyses for 28-day mortality were performed. RESULTS: Despite similar MAP and ScvO2 between dose groups, the High Dose group had lower StO2 recovery slope and StO2 hyperemia AUC. Norepinephrine-equivalent dose was inversely associated with StO2 recovery slope (rho = -0.728; Holm-adjusted p < 0.001), and this association persisted after separate adjustment for severity, oxygen transport, and metabolic variables. ScvO2 was not associated with dynamic VOT-derived indices after correction for multiple comparisons. StO2 hyperemia AUC and recovery slope showed exploratory prognostic signal for 28-day mortality. CONCLUSION: Higher norepinephrine-equivalent dose was associated with lower dynamic microvascular reactivity despite preserved MAP and ScvO2. Preserved ScvO2 did not track dynamic VOT-derived microvascular reserve. TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov (NCT07312071). The study procedures performed in this study were approved by the local ethical committee.