The microcirculation in humans can be evaluated directly by videomicroscopy (OPS/SDF) or indirectly by vascular occlusion tests. Of note, direct videomicroscopic visualization evaluates the actual state of the microcirculation, whereas the vascular occlusion test evaluates microvascular reserve.

Microcirculatory alterations are stronger predictors of outcome than global hemodynamic variables.

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.

IMPORTANCEThe effect of high-flow oxygen therapy vs conventional oxygen therapy has not been established in the setting of severe COVID-19.OBJECTIVE To determine the effect of high-flow oxygen therapy through a nasal cannula compared with conventional oxygen therapy on need for endotracheal intubation and clinical recovery in severe COVID-19. DESIGN, SETTING, AND PARTICIPANTSRandomized, open-label clinical trial conducted in emergency and intensive care units in 3 hospitals in Colombia. A total of 220 adults with respiratory distress and a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen of less than 200 due to COVID-19 were randomized from August 2020 to January 2021, with last follow-up on February 10, 2021.INTERVENTIONS Patients were randomly assigned to receive high-flow oxygen through a nasal cannula (n = 109) or conventional oxygen therapy (n = 111). MAIN OUTCOMES AND MEASURESThe co-primary outcomes were need for intubation and time to clinical recovery until day 28 as assessed by a 7-category ordinal scale (range, 1-7, with higher scores indicating a worse condition). Effects of treatments were calculated with a Cox proportional hazards model adjusted for hypoxemia severity, age, and comorbidities. RESULTS Among 220 randomized patients, 199 were included in the analysis (median age, 60 years; n = 65 women [32.7%]). Intubation occurred in 34 (34.3%) randomized to high-flow oxygen therapy and in 51 (51.0%) randomized to conventional oxygen therapy (hazard ratio, 0.62; 95% CI, 0.39-0.96; P = .03). The median time to clinical recovery within 28 days was 11 (IQR, 9-14) days in patients randomized to high-flow oxygen therapy vs 14 (IQR,(11)(12)(13)(14)(15)(16)(17)(18)(19) days in those randomized to conventional oxygen therapy (hazard ratio, 1.39; 95% CI, 1.00-1.92; P = .047). Suspected bacterial pneumonia occurred in 13 patients (13.1%) randomized to high-flow oxygen and in 17 (17.0%) of those randomized to conventional oxygen therapy, while bacteremia was detected in 7 (7.1%) vs 11 (11.0%), respectively.CONCLUSIONS AND RELEVANCE Among patients with severe COVID-19, use of high-flow oxygen through a nasal cannula significantly decreased need for mechanical ventilation support and time to clinical recovery compared with conventional low-flow oxygen therapy.

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BackgroundThe decision of when to stop septic shock resuscitation is a critical but yet a relatively unexplored aspect of care. This is especially relevant since the risks of over-resuscitation with fluid overload or inotropes have been highlighted in recent years. A recent guideline has proposed normalization of central venous oxygen saturation and/or lactate as therapeutic end-points, assuming that these variables are equivalent or interchangeable. However, since the physiological determinants of both are totally different, it is legitimate to challenge the rationale of this proposal. We designed this study to gain more insights into the most appropriate resuscitation goal from a dynamic point of view. Our objective was to compare the normalization rates of these and other potential perfusion-related targets in a cohort of septic shock survivors.MethodsWe designed a prospective, observational clinical study. One hundred and four septic shock patients with hyperlactatemia were included and followed until hospital discharge. The 84 hospital-survivors were kept for final analysis. A multimodal perfusion assessment was performed at baseline, 2, 6, and 24 h of ICU treatment.ResultsSome variables such as central venous oxygen saturation, central venous-arterial pCO2 gradient, and capillary refill time were already normal in more than 70% of survivors at 6 h. Lactate presented a much slower normalization rate decreasing significantly at 6 h compared to that of baseline (4.0 [3.0 to 4.9] vs. 2.7 [2.2 to 3.9] mmol/L; p < 0.01) but with only 52% of patients achieving normality at 24 h. Sublingual microcirculatory variables exhibited the slowest recovery rate with persistent derangements still present in almost 80% of patients at 24 h.ConclusionsPerfusion-related variables exhibit very different normalization rates in septic shock survivors, most of them exhibiting a biphasic response with an initial rapid improvement, followed by a much slower trend thereafter. This fact should be taken into account to determine the most appropriate criteria to stop resuscitation opportunely and avoid the risk of over-resuscitation.

This literature search demonstrates that relatively few of the randomized controlled trials conducted in intensive care units and using mortality as a primary outcome show a beneficial impact of the intervention on the survival of critically ill patients. Methodological limitations of some of the randomized controlled trials may have prevented positive results. Other forms of evidence and end points other than mortality need to be considered when evaluating interventions in critically ill patients.

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 veryearly (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 riskadjusted 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.