Characterization of Sublingual Microvascular Tortuosity in Steady-State Physiology and Septic Shock

<b>Background:</b> The characteristics of hemodynamic coherence in healthy states and disease remain unknown. Capillary tortuosity is a morphologic variant of microcirculatory vessels, but its effects have generally not been considered in the assessment of tissue perfusion and oxygenation. We investigated the role of sublingual capillary tortuosity in the hemodynamic coherence of anesthetized adult individuals with steady-state physiology (ASA 1) and patients with septic shock requiring emergency abdominal surgery (ASA 4E and 5E). <b>Methods:</b> Sublingual macro and microcirculatory variables, oxygen transport, metabolic parameters, and the capillary tortuosity score (CTS) were assessed. <b>Results:</b> Mean (SD) CTS was 0.55 (0.76) and 3.31 (0.86) in the steady-state and septic shock group, respectively (<i>p</i> < 0.001). In patients with septic shock, CTS was significantly associated with alveolar-to-arterial oxygen gradient (r = 0.658, <i>p</i> = 0.015) and oxygen debt (r = -0.769, <i>p</i> = 0.002). Significant differences were also observed in Consensus Proportion of Perfused Vessels (PPV; <i>p</i> < 0.001), Consensus PPV (small) (<i>p</i> < 0.001), Microvascular Flow Index (<i>p</i> < 0.001), vessel diameter (<i>p</i> < 0.001) and length (<i>p</i> < 0.001), wall shear stress (<i>p</i> < 0.001), lactate (<i>p</i> < 0.001), oxygen extraction ratio (<i>p</i> = 0.001), arterial oxygen content (<i>p</i> < 0.001), venous oxygen content (<i>p</i> < 0.001), oxygen delivery (<i>p</i> < 0.001), oxygen consumption (<i>p</i> < 0.001), and oxygen debt (<i>p</i> = 0.002) between the two groups. <b>Conclusions:</b> Sublingual tortuosity was essentially absent in individuals with steady-state physiology. In contrast, it was significantly increased and associated with Alveolar-to-arterial oxygen gradient and oxygen debt in critically ill patients with septic shock.