Introduction: Microvascular alterations may play an important role in the development of organ failure in critically ill patients and especially in sepsis. Recent advances in technology have allowed visualization of the microcirculation, but several scoring systems have been used so it is sometimes difficult to compare studies. This paper reports the results of a round table conference that was organized in Amsterdam in November 2006 in order to achieve consensus on image acquisition and analysis. Methods: The participants convened to discuss the various aspects of image acquisition and the different scores, and a consensus statement was drafted using the Delphi methodology. Results: The participants identified the following five key points for optimal image acquisition: five sites per organ, avoidance of pressure artifacts, elimination of secretions, adequate focus and contrast adjustment, and recording quality. The scores that can be used to describe numerically the microcirculatory images consist of the following: a measure of vessel density (total and perfused vessel density; two indices of perfusion of the vessels (proportion of perfused vessels and microcirculatory flow index); and a heterogeneity index. In addition, this information should be provided for all vessels and for small vessels (mostly capillaries) identified as smaller than 20 μm. Venular perfusion should be reported as a quality control index, because venules should always be perfused in the absence of pressure artifact. It is anticipated that although this information is currently obtained manually, it is likely that image analysis software will ease analysis in the future. Conclusion: We proposed that scoring of the microcirculation should include an index of vascular density, assessment of capillary perfusion and a heterogeneity index.

Infection with COVID-19, the disease caused by SARS-CoV-2, commonly results in asymptomatic or mild disease.¹ Nevertheless, the number of infected patients progressing to acute hypoxemic respiratory failure might become substantially high during pandemic circumstances, thus challenging health care system capacities.^2,3

Rationale: A recent randomized controlled trial showed that a peripheral perfusion–guided resuscitation strategy was associated with lower mortality and less organ dysfunction when compared with lactate-guided resuscitation strategy in patients with septic shock, but the difference in the primary outcome, 28-day mortality, did not reach the proposed statistical significance threshold (P = 0.06). We tested different analytic methods to aid in the interpretation of these results. Objectives: To reassess the results of the ANDROMEDA-SHOCK trial using both Bayesian and frequentist frameworks. Methods: All patients recruited in ANDROMEDA-SHOCK were included. Both a post hoc Bayesian analysis and a mixed logistic regression analysis were performed. The Bayesian analysis included four different priors (optimistic, neutral, null, and pessimistic) for mortality endpoints. The probability of having a Sequential Organ Failure Assessment in the lowest quartile at 72 hours was assessed using Bayesian networks. Measurements and Main Results: In the Bayesian analysis, the posterior probability that a peripheral perfusion–targeted resuscitation strategy is superior to lactate-targeted resuscitation at 28 days was above 90% for all priors; the probability of benefit at 90 days was above 90% for all but the pessimistic prior. Using an optimistic prior, posterior median odds ratios were 0.61 (95% credible interval, 0.41–0.90) and 0.68 (95% credible interval, 0.47–1.01) for 28-day and 90-day mortality, respectively. The comparable frequentist odds ratios for 28-day and 90-day mortality were 0.61 (95% confidence interval [CI], 0.38–0.92) and 0.70 (95% CI, 0.45–1.08), respectively. The odds that that patients in the peripheral perfusion–targeted resuscitation arm had Sequential Organ Failure Assessment scores in the lower quartile at 72 hours was 1.55 (95% CI, 1.02–2.37). Conclusions: Peripheral perfusion–targeted resuscitation may result in lower mortality and faster resolution of organ dysfunction when compared with a lactate-targeted resuscitation strategy.

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the characteristics of these alterations, the various mechanisms potentially involved, and the implications for therapy. Sepsis-induced microvascular alterations are characterized by a decrease in capillary density with an increased number of stopped-flow and intermittent-flow capillaries, in close vicinity to well-perfused capillaries. Accordingly, the surface available for exchange is decreased but also is highly heterogeneous. Multiple mechanisms may contribute to these alterations, including endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability. Given the heterogeneous nature of these alterations and the mechanisms potentially involved, classical hemodynamic interventions, such as fluids, red blood cell transfusions, vasopressors, and inotropic agents, have only a limited impact, and the microcirculatory changes often persist after resuscitation. Nevertheless, fluids seem to improve the microcirculation in the early phase of sepsis and dobutamine also can improve the microcirculation, although the magnitude of this effect varies considerably among patients. Finally, maintaining a sufficient perfusion pressure seems to positively influence the microcirculation; however, which mean arterial pressure levels should be targeted remains controversial. Some trials using vasodilating agents, especially nitroglycerin, showed promising initial results but they were challenged in other trials, so it is difficult to recommend the use of these agents in current practice. Other agents can markedly improve the microcirculation, including activated protein C and antithrombin, vitamin C, or steroids. In conclusion, microcirculatory alterations may play an important role in the development of sepsis-related organ dysfunction. At this stage, therapies to target microcirculation specifically are still being investigated.

Purpose Septic shock has been associated with microvascular alterations and these in turn with the development of organ dysfunction. Despite advances in video microscopic techniques, evaluation of microcirculation at the bedside is still limited. Venous-to-arterial carbon dioxide difference (Pv-aCO₂) may be increased even when venous O₂ saturation (SvO₂) and cardiac output look normal, which could suggests microvascular derangements. We sought to evaluate whether Pv-aCO₂ can reflect the adequacy of microvascular perfusion during the early stages of resuscitation of septic shock. Methods Prospective observational study including 75 patients with septic shock in a 60-bed mixed ICU. Arterial and mixed-venous blood gases and hemodynamic variables were obtained at catheter insertion (T0) and 6 h after (T6). Using a sidestream dark-field device, we simultaneously acquired sublingual microcirculatory images for blinded semiquantitative analysis. Pv-aCO₂ was defined as the difference between mixed-venous and arterial CO₂ partial pressures. Results Progressively lower percentages of small perfused vessels (PPV), lower functional capillary density, and higher heterogeneity of microvascular blood flow were observed at higher Pv-aCO₂ values at both T0 and T6. Pv-aCO₂ was significantly correlated to PPV (T0: coefficient −5.35, 95 % CI −6.41 to −4.29, p < 0.001; T6: coefficient, −3.49, 95 % CI −4.43 to −2.55, p < 0.001) and changes in Pv-aCO₂ between T0 and T6 were significantly related to changes in PPV (R ² = 0.42, p < 0.001). Absolute values and changes in Pv-aCO₂ were not related to global hemodynamic variables. Good agreement between venous-to-arterial CO₂ and PPV was maintained even after corrections for the Haldane effect. Conclusions During early phases of resuscitation of septic shock, Pv-aCO₂ could reflect the adequacy of microvascular blood flow.

Background: Optimal timing for the start of vasopressors (VP) in septic shock has not been widely studied since it is assumed that fluids must be administered in advance. We sought to evaluate whether a very early start of VP, even without completing the initial fluid loading, might impact clinical outcomes in septic shock. Methods: A total of 337 patients with sepsis requiring VP support for at least 6 h were initially selected from a prospectively collected database in a 90-bed mixed-ICU during a 24-month period. They were classified into very-early (VE-VPs) or delayed vasopressor start (D-VPs) categories according to whether norepinephrine was initiated or not within/before the next hour of the first resuscitative fluid load. Then, VE-VPs (n = 93) patients were 1:1 propensity matched to D-VPs (n = 93) based on age; source of admission (emergency room, general wards, intensive care unit); chronic and acute comorbidities; and lactate, heart rate, systolic, and diastolic pressure at vasopressor start. A risk-adjusted Cox proportional hazard model was fitted to assess the association between VE-VPs and day 28 mortality. Finally, a sensitivity analysis was performed also including those patients requiring VP support for less than 6 h. Results: Patients subjected to VE-VPs received significantly less resuscitation fluids at vasopressor starting (0[0–510] vs. 1500[650–2300] mL, p < 0.001) and during the first 8 h of resuscitation (1100[500–1900] vs. 2600[1600–3800] mL, p < 0.001), with no significant increase in acute renal failure and/or renal replacement therapy requirements. VE-VPs was related with significant lower net fluid balances 8 and 24 h after VPs. VE-VPs was also associated with a significant reduction in the risk of death compared to D-VPs (HR 0.31, CI95% 0.17–0.57, p < 0.001) at day 28. Such association was maintained after including patients receiving vasopressors for < 6 h. Conclusion: A very early start of vasopressor support seems to be safe, might limit the amount of fluids to resuscitate septic shock, and could lead to better clinical outcomes.