A new review examines the effects of vasoactive medications on the microcirculation in septic shock to synthesise current knowledge and identify gaps in evidence. Sepsis remains a leading cause of inpatient mortality, with rates approaching 30%, and although management strategies focus on restoring macrohaemodynamic parameters such as mean arterial pressure (MAP) and cardiac output (CO), these do not necessarily translate into improved tissue perfusion. This disconnect, termed “loss of haemodynamic coherence,” reflects the uncoupling of systemic haemodynamics from microcirculatory function.
Microcirculation, comprising arterioles, capillaries, and venules, plays a central role in oxygen delivery at the cellular level and is significantly impaired in septic shock due to endothelial dysfunction, inflammation, and vasodilation. Various techniques are used to assess microcirculation, including sublingual microscopy, laser Doppler flowmetry (LDF), near-infrared spectroscopy (NIRS), and gastric tonometry, though each has methodological limitations.
The authors conducted a comprehensive search to identify 33 studies involving adult patients with septic shock who received vasoactive medications and underwent microcirculatory assessment. These included 11 randomised controlled trials and 22 non-randomised studies, with considerable heterogeneity in design, definitions of sepsis, and measurement techniques. Mortality across studies was high, with a median of 56%.
A key finding was that studies enrolling patients early in septic shock (within 24 hours) were more likely to demonstrate significant improvements in microcirculation and greater concordance with changes in cardiac index. However, overall alignment between macrohaemodynamic improvements and microcirculatory changes occurred in only 39% of cases, highlighting the frequent dissociation between systemic and microvascular responses.
Eight different microcirculatory measurement techniques were identified, with sidestream dark field (SDF) imaging emerging as the most commonly used in recent years. Among assessed parameters, perfused vessel density (PVD) showed the highest rate of improvement following interventions. Despite technological advances, no single method reliably reflects microcirculation across all organ systems, and sublingual measurements may not correlate with intra-abdominal perfusion.
The effects of individual vasoactive agents were variable and context dependent. Norepinephrine, the first-line vasopressor in septic shock, was associated with improved microcirculation in early stages, particularly when assessed using NIRS, and did not appear to impair perfusion even at higher MAP targets.
Vasopressin demonstrated mixed effects: while it improved sublingual microcirculation in some studies, it was associated with impaired gastric perfusion, as indicated by worsening carbon dioxide gaps. Its benefit may partly arise from reducing norepinephrine requirements or through vasodilatory mechanisms mediated by V2 receptors. Similarly, terlipressin showed improvements in some settings, particularly when administered as a bolus, though results were inconsistent.
Phenylephrine showed either comparable or slightly worse effects on gastric perfusion relative to norepinephrine. Among vasodilators and inotropes, dobutamine was the most extensively studied. It frequently improved gastric microcirculation, even in the absence of changes in cardiac index, suggesting a direct microvascular effect. However, results were inconsistent across studies and did not demonstrate clear improvements in clinical outcomes.
Epinephrine produced conflicting findings, with some studies indicating improved gastric perfusion and others showing no difference or even detrimental effects, particularly in hyperdynamic states. Levosimendan, in contrast, showed more consistent benefits, improving both myocardial function and microcirculatory parameters, especially in patients with septic cardiomyopathy.
The review also evaluated whether increasing MAP targets improves microcirculation. Most studies found no significant benefit when MAP was raised above 65 mm Hg, despite increases in cardiac index. Some improvements were observed in select subgroups, such as patients with pre-existing hypertension, but overall evidence does not support routinely targeting higher MAP levels for microcirculatory benefit.
The authors conclude that although vasoactive medications can influence microcirculation, their effects are inconsistent and highly context dependent. A clearer understanding requires standardised research methodologies, improved bedside monitoring tools, and study designs that account for the timing and heterogeneity of septic shock. Future research should focus on differentiating early versus late sepsis, identifying responders to specific therapies, and linking microcirculatory improvements to meaningful clinical outcomes.
Source: Critical Care Medicine
Image Credit: iStock
