Effects of fluids on microvascular perfusion in patients with severe sepsis

From bench to bedside: A review of the application and potential of microcirculatory assessment by hand-held videomicroscopy

In clinical practice, there is vast knowledge regarding the evaluation of macrocirculatory parameters, such as systemic blood pressure and cardiac output, for the hemodynamic monitoring of patients. However, assessment of the microcirculation has not yet been incorporated into the bedside armamentarium. Hand-held intravital video microscopy enables the direct, noninvasive, evaluation of the sublingual microcirculation at the bedside, offering insights into the status of the systemic microcirculation. It is easily performed and may be employed in several clinical settings, providing immediate results that may help guide patient management. Therefore, the incorporation of hand-held intravital video microscopy into clinical practice may lead to tremendous improvements in the quality of care of critical, unstable patients or offer new data in the evaluation of patients with chronic diseases, especially those with microcirculatory involvement, such as occurs in diabetes.

Management of intra-abdominal infections: recommendations by the Italian council for the optimization of antimicrobial use

Intra-abdominal infections (IAIs) are common surgical emergencies and are an important cause of morbidity and mortality in hospital settings, particularly if poorly managed. The cornerstones of effective IAIs management include early diagnosis, adequate source control, appropriate antimicrobial therapy, and early physiologic stabilization using intravenous fluids and vasopressor agents in critically ill patients. Adequate empiric antimicrobial therapy in patients with IAIs is of paramount importance because inappropriate antimicrobial therapy is associated with poor outcomes. Optimizing antimicrobial prescriptions improves treatment effectiveness, increases patients' safety, and minimizes the risk of opportunistic infections (such as Clostridioides difficile) and antimicrobial resistance selection. The growing emergence of multi-drug resistant organisms has caused an impending crisis with alarming implications, especially regarding Gram-negative bacteria. The Multidisciplinary and Intersociety Italian Council for the Optimization of Antimicrobial Use promoted a consensus conference on the antimicrobial management of IAIs, including emergency medicine specialists, radiologists, surgeons, intensivists, infectious disease specialists, clinical pharmacologists, hospital pharmacists, microbiologists and public health specialists. Relevant clinical questions were constructed by the Organizational Committee in order to investigate the topic. The expert panel produced recommendation statements based on the best scientific evidence from PubMed and EMBASE Library and experts' opinions. The statements were planned and graded according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) hierarchy of evidence. On November 10, 2023, the experts met in Mestre (Italy) to debate the statements. After the approval of the statements, the expert panel met via email and virtual meetings to prepare and revise the definitive document. This document represents the executive summary of the consensus conference and comprises three sections. The first section focuses on the general principles of diagnosis and treatment of IAIs. The second section provides twenty-three evidence-based recommendations for the antimicrobial therapy of IAIs. The third section presents eight clinical diagnostic-therapeutic pathways for the most common IAIs. The document has been endorsed by the Italian Society of Surgery.

Resuscitating the macro- vs. microcirculation in septic shock

PURPOSE OF REVIEW

This review summarizes current literature about the relationships between macro and microcirculation and their practical clinical implications in children with septic shock.

RECENT FINDINGS

Current evidence from experimental and clinical observational studies in children and adults with septic shock reveals that the response to treatment and resuscitation is widely variable. Furthermore, there is a loss of hemodynamic coherence, as resuscitation-induced improvement in macrocirculation (systemic hemodynamic parameters) does not necessarily result in a parallel improvement in the microcirculation. Therefore, patient-tailored monitoring is essential in order to adjust treatment requirements during resuscitation in septic shock. Optimal monitoring must integrate macrocirculation (heart rate, blood pressure, cardiac output, and ultrasound images), microcirculation (videomicroscopy parameters and capillary refill time) and cellular metabolism (lactic acid, central venous blood oxygen saturation, and difference of central venous to arterial carbon dioxide partial pressure).

SUMMARY

There is a dire need for high-quality studies to assess the relationships between macrocirculation, microcirculation and tissue metabolism in children with septic shock. The development of reliable and readily available microcirculation and tissue perfusion biomarkers (other than lactic acid) is also necessary to improve monitoring and treatment adjustment in such patients.

Early high-volume resuscitation with crystalloid solution combined with albumin improves survival of critically ill patients: A retrospective analysis from MIMIC-IV database

BACKGROUND

Volume resuscitation is often required in critically ill patients. However, we have no clear consensus on the choice between crystalloid solution and colloidal solution. This study aimed to explore the effect of albumin administration in massive fluid resuscitation.

METHODS

This was a retrospective cohort study based on the Medical Information Mart for Intensive Care IV (MIMIC-IV) database (2008 and 2019). The prognosis of patients receiving albumin in combination with crystalloids and those receiving crystalloids alone was compared to assess the benefits of albumin in fluid resuscitation.

RESULTS

4426 patients received crystalloids alone (crystalloids group), 692 patients received albumin in combination with crystalloids within the first 24 h of initiation of crystalloids (early albumin combination group), and 382 patients received albumin after the first 24 h (late albumin combination group). Patients in early albumin combination group were more severe than those in Crystalloids group. Nevertheless, we found no statistically significant difference in mortality between the two groups. Multivariate logistic regression analysis using the propensity-score matched cohort showed that the 28-day and 60-day mortality in the early albumin combination group were lower than those in the crystalloids group (odds ratio: 0.64 [95% CI 0.50-0.82; P < 0.001] and 0.71 [95% CI 0.56-0.90; P = 0.004], respectively. Patients in early albumin combination group lived, on average, 1.16 days (95% CI 0.33-2.00; P < 0.01) and 3.3 days (95% CI 1.15-5.44; P < 0.01) longer than the crystalloids group during 28-day follow-up and 60-day follow-up.

CONCLUSION

Administration of albumin within 24 h after the initiation of crystalloids was associated with a lower mortality and a longer restricted mean survival time during 28-day follow-up and 60-day follow-up compared with crystalloid infusion alone. However, administration of albumin 24 h after the initiation of crystalloids was not associated with better prognosis compared to crystalloid infusion alone.

Are We Always Right? Evaluation of the Performance and Knowledge of the Passive Leg Raise Test in Detecting Volume Responsiveness in Critical Care Patients: A National German Survey

Background: In hemodynamically unstable patients, the passive leg raise (PLR) test is recommended for use as a self-fluid challenge for predicting preload responsiveness. However, to interpret the hemodynamic effects and reliability of the PLR, the method of performing it is of the utmost importance. Our aim was to determine the current practice of the correct application and interpretation of the PLR in intensive care patients. Methods: After ethical approval, we designed a cross-sectional online survey with a short user-friendly online questionnaire. Using a random sample of 1903 hospitals in Germany, 182 hospitals with different levels of care were invited via an email containing a link to the questionnaire. The online survey was conducted between December 2021 and January 2022. All critical care physicians from different medical disciplines were surveyed. We evaluated the correct points of concern for the PLR, including indication, contraindication, choice of initial position, how to interpret and apply the changes in cardiac output, and the limitations of the PLR. Results: A total of 292 respondents participated in the online survey, and 283/292 (97%) of the respondents completed the full survey. In addition, 132/283 (47%) were consultants and 119/283 (42%) worked at a university medical center. The question about the performance of the PLR was answered correctly by 72/283 (25%) of the participants. The limitations of the PLR, such as intra-abdominal hypertension, were correctly selected by 150/283 (53%) of the participants. The correct effect size (increase in stroke volume ≥ 10%) was correctly identified by 217/283 (77%) of the participants. Conclusions: Our results suggest a considerable disparity between the contemporary practice of the correct application and interpretation of the PLR and the practice recommendations from recently published data at German ICUs.

Latest developments in early diagnosis and specific treatment of severe influenza infection

Influenza pandemics are unpredictable recurrent events with global health, economic, and social consequences. The objective of this review is to provide an update on the latest developments in early diagnosis and specific treatment of the disease and its complications, particularly with regard to respiratory organ failure. Despite advances in treatment, the rate of mortality in the intensive care unit remains approximately 30%. Therefore, early identification of potentially severe viral pneumonia is extremely important to optimize treatment in these patients. The pathogenesis of influenza virus infection depends on viral virulence and host response. Thus, in some patients, it is associated with an excessive systemic response mediated by an authentic cytokine storm. This process leads to severe primary pneumonia and acute respiratory distress syndrome. Initial prognostication in the emergency department based on comorbidities, vital signs, and biomarkers (e.g., procalcitonin, ferritin, human leukocyte antigen-DR, mid-regional proadrenomedullin, and lactate) is important. Identification of these biomarkers on admission may facilitate clinical decision-making to determine early admission to the hospital or the intensive care unit. These decisions are reached considering pathophysiological circumstances that are associated with a poor prognosis (e.g., bacterial co-infection, hyperinflammation, immune paralysis, severe endothelial damage, organ dysfunction, and septic shock). Moreover, early implementation is important to increase treatment efficacy. Based on a limited level of evidence, all current guidelines recommend using oseltamivir in this setting. The possibility of drug resistance should also be considered. Alternative options include other antiviral drugs and combination therapies with monoclonal antibodies. Importantly, it is not recommended to use corticosteroids in the initial treatment of these patients. Furthermore, the implementation of supportive measures for respiratory failure is essential. Current recommendations are limited, heterogeneous, and not regularly updated. Early intubation and mechanical ventilation is the basic treatment for patients with severe respiratory failure. Prone ventilation should be promptly performed in patients with acute respiratory distress syndrome, while early tracheostomy should be considered in case of planned prolonged mechanical ventilation. Clinical trials on antiviral treatment and respiratory support measures specifically for these patients, as well as specific recommendations for different at-risk populations, are necessary to improve outcomes.

Research progress on microcirculatory disorders in septic shock: A narrative review

Hemodynamic coherence plays a critical role in the outcomes of septic shock. Due to the potential negative consequences of microcirculatory disorders on organ failure and clinical outcomes, the maintenance of a balance between the macrocirculation and microcirculation is a topic of significant research focus. Although physical methods and specialized imaging techniques are used in clinical practice to assess microcirculation, the use of monitoring devices is not widespread. The integration of microcirculation research tools into clinical practice poses a significant challenge for the future. Consequently, this review aims to evaluate the impact of septic shock on the microcirculation, the methods used to monitor the microcirculation and highlight the importance of microcirculation in the treatment of critically ill patients. In addition, it proposes an evaluation framework that integrates microcirculation monitoring with macrocirculatory parameters. The optimal approach should encompass dynamic, multiparametric, individualized, and continuous monitoring of both the macrocirculation and microcirculation, particularly in cases of hemodynamic separation.

Evaluating the relationship between ocular blood flow and systemic organ blood flow in hemorrhagic shock using a rabbit model

This study aimed to investigate the feasibility of utilizing noninvasive ocular blood flow measurements as potential indicators of systemic circulation in rabbits experiencing hemorrhagic shock. Using Laser speckle flowgraphy, ocular blood flow indices, relative flow volume (RFV), and mean blur rate in the choroidal area (MBR-CH) were assessed in New Zealand White rabbits (n = 10) subjected to controlled blood removal and return. Hemodynamic parameters and biochemical markers were monitored alongside ocular circulation during blood removal and return phases. Additionally, correlations between ocular parameters and systemic indices were examined. The results indicated that RFV and MBR-CH exhibited significant correlations with renal and intestinal blood flows, with stronger correlations observed during blood removal. Additionally, ocular blood flow changes closely mirrored systemic dynamics, suggesting their potential as real-time indicators of shock progression and recovery. These findings indicate that ocular blood flow measurements may serve as real-time indicators of the systemic circulation status during hemorrhagic shock, offering potential insights into shock management and guiding tailored interventions. Thus, noninvasive ocular blood flow evaluation holds promise as an innovative tool for assessing systemic circulation dynamics during hemorrhagic shock.

Surviving Sepsis Campaign Research Priorities 2023

OBJECTIVES

To identify research priorities in the management, epidemiology, outcome, and pathophysiology of sepsis and septic shock.

DESIGN

Shortly after publication of the most recent Surviving Sepsis Campaign Guidelines, the Surviving Sepsis Research Committee, a multiprofessional group of 16 international experts representing the European Society of Intensive Care Medicine and the Society of Critical Care Medicine, convened virtually and iteratively developed the article and recommendations, which represents an update from the 2018 Surviving Sepsis Campaign Research Priorities.

METHODS

Each task force member submitted five research questions on any sepsis-related subject. Committee members then independently ranked their top three priorities from the list generated. The highest rated clinical and basic science questions were developed into the current article.

RESULTS

A total of 81 questions were submitted. After merging similar questions, there were 34 clinical and ten basic science research questions submitted for voting. The five top clinical priorities were as follows: 1) what is the best strategy for screening and identification of patients with sepsis, and can predictive modeling assist in real-time recognition of sepsis? 2) what causes organ injury and dysfunction in sepsis, how should it be defined, and how can it be detected? 3) how should fluid resuscitation be individualized initially and beyond? 4) what is the best vasopressor approach for treating the different phases of septic shock? and 5) can a personalized/precision medicine approach identify optimal therapies to improve patient outcomes? The five top basic science priorities were as follows: 1) How can we improve animal models so that they more closely resemble sepsis in humans? 2) What outcome variables maximize correlations between human sepsis and animal models and are therefore most appropriate to use in both? 3) How does sepsis affect the brain, and how do sepsis-induced brain alterations contribute to organ dysfunction? How does sepsis affect interactions between neural, endocrine, and immune systems? 4) How does the microbiome affect sepsis pathobiology? 5) How do genetics and epigenetics influence the development of sepsis, the course of sepsis and the response to treatments for sepsis?

CONCLUSIONS

Knowledge advances in multiple clinical domains have been incorporated in progressive iterations of the Surviving Sepsis Campaign guidelines, allowing for evidence-based recommendations for short- and long-term management of sepsis. However, the strength of existing evidence is modest with significant knowledge gaps and mortality from sepsis remains high. The priorities identified represent a roadmap for research in sepsis and septic shock.

Effect on capillary refill time of volume expansion and increase of the norepinephrine dose in patients with septic shock

BACKGROUND

Capillary refill time (CRT) has been suggested as a variable to follow during the course of septic shock. We systematically investigated the effects on CRT of volume expansion and norepinephrine.

METHODS

In 69 septic shock patients, we recorded mean arterial pressure (MAP), cardiac index (CI), and 5 consecutive CRT measurements (video method, standardized pressure applied on the fingertip) before and after a 500-mL saline infusion in 33 patients and before and after an increase of the norepinephrine dose in 36 different patients. Fluid responders were defined by an increase in CI ≥ 15%, and norepinephrine responders by an increase in MAP ≥ 15%.

RESULTS

The least significant change of CRT was 23%, so that changes in CRT were considered significant if larger than 23%. With volume expansion, CRT remained unchanged on average in patients with baseline CRT < 3 s (n = 7) and in all but one patient with baseline CRT ≥ 3 s in whom fluid increased CI < 15% (n = 13 "fluid non-responders"). In fluid responders with baseline CRT ≥ 3 s (n = 13), CRT decreased in 8 patients and remained unchanged in the others, exhibiting a dissociation between CI and CRT responses. The proportion of patients included > 24 h after starting norepinephrine was higher in patients with such a dissociation than in the other ones (60% vs. 0%, respectively). Norepinephrine did not change CRT significantly (except in one patient) if baseline CRT was ≥ 3 s and the increase in MAP < 15% (n = 6). In norepinephrine responders with prolonged baseline CRT (n = 11), it increased in 4 patients and remained unchanged in the other ones, which exhibited a dissociation between MAP and CRT responses.

CONCLUSIONS

In septic shock patients with prolonged CRT, CRT very rarely improves with treatment when volume expansion increases cardiac output < 15% and increasing norepinephrine increases MAP < 15%. When the effects of fluid infusion on cardiac output and of norepinephrine on MAP are significant, the response of CRT is variable, as it decreases in some patients and remains stable in others which exhibit a dissociation between changes in macrohemodynamic variables and in CRT. In this regard, CRT behaves as a marker of microcirculation.

TRIAL REGISTRATION

ClinicalTrial.gov (NCT04870892). Registered January15, 2021. Ethics committee approval CE SRLF 21-25.

Impact of a cumulative positive fluid balance during the first three ICU days in patients with sepsis: a propensity score-matched cohort study

BACKGROUND

The optimal strategy for fluid management during the first few days of ICU in sepsis patients remains controversial. We aimed to investigate the impact of cumulative fluid balance during the first three days of ICU on the mortality of patients with sepsis.

METHODS

This study analyzed prospectively collected data from the Korean Sepsis Alliance Database, which registered 11,981 sepsis patients from 20 hospitals. We selected three propensity score-matched cohorts consisting of patients with a negative or positive cumulative fluid balance during the first three ICU days: from ICU admission to the first midnight as the D1 cohort, until the second midnight as the D2 cohort, and until the third midnight as the D3 cohort. The propensity score for fluid balance was calculated using covariates including the amount of fluid output during the first three ICU days. The primary outcome was mortality at day 28 in the ICU.

RESULTS

From a total of 11,981 patients, 2516 patients were included for propensity score matching. After matching in a 1:1 ratio, there were 483, 373, and 392 matched pairs of patients assigned to the D1, D2, and D3 cohorts, respectively. In the D1 cohort, there were no significant differences in mortality at day 28 (hazard ratio [HR], 1.17; 95% confidence interval [CI] 0.85-1.60; P = 0.354) between the two groups. The positive fluid groups in both the D2 (HR, 2.13; 95% CI 1.48-3.06; P < 0.001) and D3 (HR, 1.56; 95% CI 1.10-2.22; P = 0.012) cohorts had significantly higher mortality rates than the negative fluid groups.

CONCLUSIONS

In patients with sepsis, a positive fluid balance on the first ICU day was not associated with mortality at day 28. In contrast, cumulative positive fluid balances on the second and third ICU days were associated with higher mortality at day 28.

Transfusion increased skin blood flow when initially low in volume-resuscitated patients without acute bleeding

Background

Alterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation.

Methods

A prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT.

Results

Overall, SBFBT did not significantly change after RBCT [from 79.8 (4.3-479.4) to 83.4 (4.9-561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3-279.3) vs. 136.3 (6.5-479.4) perfusion units; p < 0.01], mixed or central venous oxygen saturation (62.5 ± 9.2 vs. 67.3% ± 12.0%; p < 0.01) and CVP (8.3 ± 5.1 vs. 10.3 ± 5.6 mmHg; p = 0.03) at baseline than non-responders. SBFBT increased in responders [from 41.3 (4.3-279.3) to 93.1 (9.8-561.6) perfusion units; p < 0.01], and decreased in the non-responders [from 136.3 (6.5-479.4) to 80.0 (4.9-540.8) perfusion units; p < 0.01] after RBCT. Pre-transfusion SBFBT was independently associated with a 20% increase in SBFBT after RBCT. Baseline SBFBT had an area under receiver operator characteristic of 0.73 (95% CI, 0.68-0.83) to predict SBFBT increase; A SBFBT of 73.0 perfusion units (PU) had a sensitivity of 71.4% and a specificity of 70.4% to predict SBFBT increase after RBCT. No significant differences in SBFBT were observed after RBCT in different subgroup analyses.

Conclusion

The skin blood flow is globally unaltered by red blood cell transfusions in non-bleeding critically ill patients after initial resuscitation. However, a lower SBFBT at baseline was associated with a relative increase in skin tissue perfusion after RBCT.

Microcirculation-guided resuscitation in sepsis: the next frontier?

Microcirculatory dysfunction plays a key role in the pathogenesis of tissue dysoxia and organ failure in sepsis. Sublingual videomicroscopy techniques enable the real-time non-invasive assessment of microvascular blood flow. Alterations in sublingual microvascular perfusion were detected during sepsis and are associated with poor outcome. More importantly, sublingual videomicroscopy allowed to explore the effects of commonly applied resuscitative treatments in septic shock, such as fluids, vasopressors and inotropes, and showed that the optimization of macro-hemodynamic parameters may not be accompanied by an improvement in microvascular perfusion. This loss of "hemodynamic coherence," i.e., the concordance between the response of the macrocirculation and the microcirculation, advocates for the integration of microvascular monitoring in the management of septic patients. Nonetheless, important barriers remain for a widespread use of sublingual videomicroscopy in the clinical practice. In this review, we discuss the actual limitations of this technique and future developments that may allow an easier and faster evaluation of the microcirculation at the bedside, and propose a role for sublingual microvascular monitoring in guiding and titrating resuscitative therapies in sepsis.

Relationship between the rate of fluid resuscitation and acute kidney injury: A retrospective cohort study

Background

Septic shock is the leading cause of acute kidney injury (AKI) in critically ill patients. The foundation of early septic shock management includes early fluid resuscitation, but the association between fluid resuscitation rates and kidney outcomes remains unclear. This investigation examines the association between fluid resuscitation rate and AKI recovery.

Methods

In the medical intensive care unit of Mayo Clinic Rochester, adult patients with AKI and septic shock were retrospectively studied from January 1, 2006 to May 31, 2018. The surviving sepsis campaign recommends an initial fluid bolus of 30 ml/kg for sepsis resuscitation. The cohort of patients was divided into three groups based on the average fluid resuscitation time (<1 h, 1.1-3 h, >3 h) and the corresponding fluid rate ≥0.5, 0.17-0.49, and <0.17 ml/kg/min, respectively. The primary outcome was the recovery of AKI on day 7. To account for potential confounders, multivariable regression analyses were conducted.

Results

After meeting the eligibility, 597 patients were included in the analysis. The AKI recovery was considerably different among the groups (P = 0.006). Patients in group 1 who received fluid resuscitation faster had a higher rate of AKI recovery (53%) compared to group 2 and group 3 (50% and 37.8%).

Conclusion

In septic shock patients with AKI, a higher fluid resuscitation rate of 30 ml/kg IV fluids within the 1st-h sepsis diagnosis (i.e., >0.50 ml/kg/min) lead to higher AKI recovery compared with slower infusion rates.

The Relation of Calculated Plasma Volume Status to Sublingual Microcirculatory Blood Flow and Organ Injury

BACKGROUND

The calculated plasma volume status (cPVS) was validated as a surrogate of intravascular filling. The aim of this study is to assess the cPVS in relation to sublingual perfusion and organ injury.

METHODS

Pre- and postoperative cPVS were obtained by determining the actual and ideal plasma volume levels in surgical patients. The sublingual microcirculation was assessed using SDF imaging, and we determined the De Backer score, the Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Our primary outcome was the assessment of the distribution of cPVS and its association with intraoperative sublingual microcirculation and postoperative complications.

RESULTS

The median pre- and postoperative cPVS were -7.25% (IQR -14.29--1.88) and -0.4% (IQR -5.43-6.06), respectively (p < 0.001). The mean intraoperative administered fluid volume was 2.5 ± 2.5 L (1.14 L h^-1). No statistically significant correlation was observed between the pre- or postoperative cPVS and sublingual microcirculation variables. Higher preoperative (OR = 1.04, p = 0.098) and postoperative cPVS (OR = 1.057, p = 0.029) were associated with postoperative organ injury and complications (sepsis (30%), anemia (24%), respiratory failure (13%), acute kidney injury (6%), hypotension (6%), stroke (3%)).

CONCLUSIONS

The calculated PVS was associated with an increased risk of organ injury and complications in this cohort.

The future of intensive care: the study of the microcirculation will help to guide our therapies

The goal of hemodynamic resuscitation is to optimize the microcirculation of organs to meet their oxygen and metabolic needs. Clinicians are currently blind to what is happening in the microcirculation of organs, which prevents them from achieving an additional degree of individualization of the hemodynamic resuscitation at tissue level. Indeed, clinicians never know whether optimization of the microcirculation and tissue oxygenation is actually achieved after macrovascular hemodynamic optimization. The challenge for the future is to have noninvasive, easy-to-use equipment that allows reliable assessment and immediate quantitative analysis of the microcirculation at the bedside. There are different methods for assessing the microcirculation at the bedside; all have strengths and challenges. The use of automated analysis and the future possibility of introducing artificial intelligence into analysis software could eliminate observer bias and provide guidance on microvascular-targeted treatment options. In addition, to gain caregiver confidence and support for the need to monitor the microcirculation, it is necessary to demonstrate that incorporating microcirculation analysis into the reasoning guiding hemodynamic resuscitation prevents organ dysfunction and improves the outcome of critically ill patients.

Novelties in the evaluation of microcirculation in septic shock

Microvascular alterations were first described in critically ill patients about 20 years ago. These alterations are characterized by a decrease in vascular density and presence of non-perfused capillaries close to well-perfused vessels. In addition, heterogeneity in microvascular perfusion is a key finding in sepsis. In this narrative review, we report our actual understanding of microvascular alterations, their role in the development of organ dysfunction, and the implications for outcome. Herein, we discuss the state of the potential therapeutic interventions and the potential impact of novel therapies. We also discuss how recent technologic development may affect the evaluation of microvascular perfusion.

Pravastatin Improves Colonic and Hepatic Microcirculatory Oxygenation during Sepsis without Affecting Mitochondrial Function and ROS Production in Rats

Microcirculatory and mitochondrial dysfunction are considered the main mechanisms of septic shock. Studies suggest that statins modulate inflammatory response, microcirculation, and mitochondrial function, possibly through their action on peroxisome proliferator-activated receptor alpha (PPAR-α). The aim of this study was to examine the effects of pravastatin on microcirculation and mitochondrial function in the liver and colon and the role of PPAR-α under septic conditions. This study was performed with the approval of the local animal care and use committee. Forty Wistar rats were randomly divided into 4 groups: sepsis (colon ascendens stent peritonitis, CASP) without treatment as control, sepsis + pravastatin, sepsis + PPAR-α-blocker GW6471, and sepsis + pravastatin + GW6471. Pravastatin (200 µg/kg s.c.) and GW6471 (1 mg/kg) were applied 18 h before CASP-operation. 24 h after initial surgery, a relaparotomy was performed, followed by a 90 min observation period for assessment of microcirculatory oxygenation (μHbO2) of the liver and colon. At the end of the experiments, animals were euthanized, and the colon and liver were harvested. Mitochondrial function was measured in tissue homogenates using oximetry. The ADP/O ratio and respiratory control index (RCI) for complexes I and II were calculated. Reactive oxygen species (ROS) production was assessed using the malondialdehyde (MDA)-Assay. Statistics: two-way analysis of variance (ANOVA) + Tukey’s/Dunnett’s post hoc test for microcirculatory data, Kruskal–Wallis test + Dunn’s post hoc test for all other data. In control septic animals µHbO2 in liver and colon deteriorated over time (µHbO2: −9.8 ± 7.5%* and −7.6 ± 3.3%* vs. baseline, respectively), whereas after pravastatin and pravastatin + GW6471 treatment μHbO2 remained constant (liver: µHbO2 pravastatin: −4.21 ± 11.7%, pravastatin + GW6471: −0.08 ± 10.3%; colon: µHbO2 pravastatin: −0.13 ± 7.6%, pravastatin + GW6471: −3.00 ± 11.24%). In both organs, RCI and ADP/O were similar across all groups. The MDA concentration remained unchanged in all groups. Therefore, we conclude that under septic conditions pravastatin improves microcirculation in the colon and liver, and this seems independent of PPAR-α and without affecting mitochondrial function.

Blood gas analysis as a surrogate for microhemodynamic monitoring in sepsis

BACKGROUND

Emergency patients with sepsis or septic shock are at high risk of death. Despite increasing attention to microhemodynamics, the clinical use of advanced microcirculatory assessment is limited due to its shortcomings. Since blood gas analysis is a widely used technique reflecting global oxygen supply and consumption, it may serve as a surrogate for microcirculation monitoring in septic treatment.

METHODS

We performed a search using PubMed, Web of Science, and Google scholar. The studies and reviews that were most relevant to septic microcirculatory dysfunctions and blood gas parameters were identified and included.

RESULTS

Based on the pathophysiology of oxygen metabolism, the included articles provided a general overview of employing blood gas analysis and its derived set of indicators for microhemodynamic monitoring in septic care. Notwithstanding flaws, several parameters are linked to changes in the microcirculation. A comprehensive interpretation of blood gas parameters can be used in order to achieve hemodynamic optimization in septic patients.

CONCLUSION

Blood gas analysis in combination with clinical performance is a reliable alternative for microcirculatory assessments. A deep understanding of oxygen metabolism in septic settings may help emergency physicians to better use blood gas analysis in the evaluation and treatment of sepsis and septic shock.

Early human albumin administration is associated with reduced mortality in septic shock patients with acute respiratory distress syndrome: A retrospective study from the MIMIC-III database

Background: Sepsis-induced acute respiratory distress syndrome (ARDS) was associated with higher mortality. It is unclear whether albumin supplementation early in the course of ARDS can affect the prognostic outcomes of septic shock (SS) patients with ARDS. Methods: The MIMIC-III database was employed to identify SS patients with ARDS. The effect of early application (<24 h after ICU admission) of human albumin on 28-day mortality in SS patients with ARDS was explored. The propensity score matching was used to minimize the bias between the non-albumin and early albumin treatment groups. Results: The analysis for all eligible patients who received human albumin showed significantly lower 28-hospital mortality rates than the non-albumin group (37% versus 47%, p = 0.018). After propensity matching, the difference between the two groups also significantly (34.8% versus 48.1%, p = 0.031). Moreover, we found that the relationship between albumin use and reduced 28-day mortality was inconsistent across SOFA score subgroups (P_interaction = 0.004, non-adjustment for multiple testing). Conclusion: Early human albumin administration in SS patients with ARDS was independently associated with a reduction of 28-day mortality. Furthermore, the benefit of human albumin treatment appeared to be more pronounced in patients with a SOFA score of ≤ 10.

Manipulation of Nitric Oxide Levels via a Modified Hydroxyethyl Starch Molecule

INTRODUCTION

Although the improving effect of nitric oxide (NO) donors has experimentally been demonstrated in shock, there are still no NO donor medications clinically available. Thiol-nitrosothiol-hydroxyethyl starch (S-NO-HES) is a novel molecule consisting of NO coupled to a thiolated derivative of hydroxyethyl starch (HES). It was aimed to assess the ability of S-NO-HES to serve as an NO donor under a variety of in vitro simulated physiologic conditions, which might be the first step to qualify this molecule as a novel type of NO donor-fluid.

METHODS

We studied the effect of temperature on NO-releasing properties of S-NO-HES in blood, at 34°C, 37°C, and 41°C. Ascorbic acid (Asc) and amylase were also tested in a medium environment. In addition, we evaluated the activity of S-NO-HES in the isolated aortic ring and Langendorff-perfused heart setup.

RESULTS

The NO release property of S-NO-HES was found at any temperature. Asc led to a significant increase in the production of NO compared to S-NO-HES incubation (P < 0.05). The addition of amylase together with Asc to the medium further increased the release of NO (P < 0.05). S-NO-HES exerted significant vasodilatory effects on phenylephrine precontracted aortic rings that were dose-dependent (P < 0.01). Furthermore, S-NO-HES significantly increased the heart rate and additionally reduced the duration of the cardiac action potential, as indicated by a reduction of QTc-B values (P < 0.01).

CONCLUSIONS

We demonstrated for the first time that the S-NO-HES molecule exhibited its NO-releasing effects. The effectiveness of this new NO donor to substitute NO deficiency under septic conditions or in other indications needs to be studied.

Effects of Fluids on the Sublingual Microcirculation in Sepsis

Sepsis is one of the most common and deadly syndromes faced in Intensive Care settings globally. Recent advances in bedside imaging have defined the changes in the microcirculation in sepsis. One of the most advocated interventions for sepsis is fluid therapy. Whether or not fluid bolus affects the microcirculation in sepsis has not been fully addressed in the literature. This systematic review of the evidence aims to collate studies examining the microcirculatory outcomes after a fluid bolus in patients with sepsis. We will assimilate the evidence for using handheld intra vital microscopes to guide fluid resuscitation and the effect of fluid bolus on the sublingual microcirculation in patients with sepsis and septic shock. We conducted a systematic search of Embase, CENTRAL and Medline (PubMed) using combinations of the terms "microcirculation" AND "fluid" OR "fluid resuscitation" OR "fluid bolus" AND "sepsis" OR "septic shock". We found 3376 potentially relevant studies. Fifteen studies published between 2007 and 2021 fulfilled eligibility criteria to be included in analysis. The total number of participants was 813; we included six randomized controlled trials and nine non-randomized, prospective observational studies. Ninety percent used Sidestream Dark Field microscopy to examine the microcirculation and 50% used Hydroxyethyl Starch as their resuscitation fluid. There were no clear effects of fluid on the microcirculation parameters. There was too much heterogeneity between studies and methodology to perform meta-analysis. Studies identified heterogeneity of affect in the sepsis population, which could mean that current clinical classifications were not able to identify different microcirculation characteristics. Use of microcirculation as a clinical endpoint in sepsis could help to define sepsis phenotypes. More research into the effects of different resuscitation fluids on the microcirculation is needed.

Feasibility study using longitudinal bioelectrical impedance analysis to evaluate body water status during fluid resuscitation in a swine sepsis model

Fluid resuscitation is crucial in the initial management of sepsis; however, little is known about the serial changes and overall distribution of fluids administered into the body. To identify the feasibility of longitudinal bioelectrical impedance analysis during fluid treatment, a preclinical porcine model of Escherichia coli-induced sepsis was used. After sepsis induction, pigs were treated with fluid and vasopressors and monitored for up to 12 h after bacterial infusion or until death. Bipolar electrodes for bioelectrical impedance analysis were attached to the left extremities and measurements were performed every 10 min. Among the 12 subjects, 7 pigs expired during the experiment, and the median survival was 9.5 h. As sepsis progressed with an increase in cumulative fluid balance, R₀ [∝ 1/extracellular water (ECW)] decreased, while R_i [∝ 1/intracellular water (ICW)] and ratio of extracellular water to total body water (ECW/TBW) increased. The phase angle constantly decreased throughout the monitoring period, and all non-survivors died when the phase angle decreased by more than 10%. Among the variables, ΔR₀ and Δphase angle showed moderate negative correlations, and ΔECW/TBW showed a moderate positive correlation with the hourly fluid balance. Compared to survivors, a greater increase in ΔECW/TBW and a decrease in phase angle were observed in non-survivors over time, with an increase in cumulative fluid balance. Differences in ΔECW/TBW and phase angle emerged at 240 min when the difference in cumulative fluid balance between the two groups (survivors vs non-survivors) exceeded 1000 mL. In conclusion, continuous measurements of bioelectrical impedance analysis in a porcine sepsis model are feasible and may reflect changes in the body water profile during fluid resuscitation.

Effects of fluids vs. vasopressors on spinal cord microperfusion in hemorrhagic shock induced ischemia/reperfusion

OBJECTIVE

Spinal cord injury induced by ischemia/reperfusion is a devastating complication of aortic repair. Despite developments for prevention and treatment of spinal cord injury, incidence is still considerably high majorly impacting patient outcome. Microcirculation is paramount for tissue perfusion and oxygen supply and often dissociated from macrohemodynamic parameters used to guide resuscitation. Effects of fluids vs. vasopressors in the setting of hemodynamic resuscitation on spinal cord microperfusion are unknown. Aim of this study was to compare the effects of vasopressor and fluid resuscitation on spinal cord microperfusion in a translational acute pig model of hemorrhagic shock induced ischemia/reperfusion injury.

METHODS

We designed this study as prospective randomized explorative large animal study. We induced hemorrhagic shock in 20 pigs as a model of global ischemia/reperfusion injury. We randomized animals to receive either fluid or vasopressor resuscitation. We measured spinal cord microperfusion using fluorescent microspheres as well as laser-Doppler probes. We monitored and analyzed macrohemodynamic parameters and cerebrospinal fluid pressure.

RESULTS

Spinal cord microperfusion decreased following hemorrhagic shock induced ischemia/reperfusion injury. Both fluids and vasopressors sufficiently restored spinal cord microperfusion. There were no important changes between groups (percentage changes compared to baseline: fluids 14.0 (0.31-27.6) vs. vasopressors 24.3 (8.12-40.4), p = .340). However, cerebrospinal fluid pressure was higher in animals receiving fluid resuscitation (percentage changes compared to baseline: fluids 27.7 (12.6-42.8) vs. vasopressors -5.56 ((-19.8)-8.72), p = .003). Microcirculatory resuscitation was in line with improvements of macrohemodynamic parameters.

CONCLUSIONS

Both, fluids and vasopressors, equally restored spinal cord microperfusion in a porcine acute model of hemorrhagic shock induced ischemia/reperfusion injury. However, significant differences in cerebrospinal fluid pressure following resuscitation were present. Future studies should evaluate these effects in perfusion disruption induced ischemia/reperfusion conditions of microcirculatory deterioration.

Kinetics of capillary refill time after fluid challenge

Background

Capillary refill time (CRT) is a valuable tool for triage and to guide resuscitation. However, little is known about CRT kinetics after fluid infusion.

Methods

We conducted a prospective observational study in a tertiary teaching hospital. First, we analyzed the intra-observer variability of CRT. Next, we monitored fingertip CRT in sepsis patients during volume expansion within the first 24 h of ICU admission. Fingertip CRT was measured every 2 min during 30 min following crystalloid infusion (500 mL over 15 min).

Results

First, the accuracy of repetitive fingertip CRT measurements was evaluated on 40 critically ill patients. Reproducibility was excellent, with an intra-class correlation coefficient of 99.5% (CI 95% [99.3, 99.8]). A CRT variation larger than 0.2 s was considered as significant. Next, variations of CRT during volume expansion were evaluated on 29 septic patients; median SOFA score was 7 [5–9], median SAPS II was 57 [45–72], and ICU mortality rate was 24%. Twenty-three patients were responders as defined by a CRT decrease  > 0.2 s at 30 min after volume expansion, and 6 were non-responders. Among responders, we observed that fingertip CRT quickly improved with a significant decrease at 6–8 min after start of crystalloid infusion, the maximal improvement being observed after 10–12 min (−0.7 [−0.3;−0.9] s) and maintained at 30 min. CRT variations significantly correlated with baseline CRT measurements (R = 0.39, P = 0.05).

Conclusions

CRT quickly improved during volume expansion with a significant decrease 6–8 min after start of fluid infusion and a maximal drop at 10–12 min.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01049-x.

Biomarkers of Glycocalyx Injury and Endothelial Activation are Associated with Clinical Outcomes in Patients with Sepsis: A Systematic Review and Meta-Analysis

OBJECTIVE

Sepsis is one of the main causes of morbidity and mortality worldwide. Microcirculatory impairment, especially damage to the endothelium and glycocalyx, is often not assessed. The objective of this systematic review and meta-analysis was to summarize the available evidence of the risk of unsatisfactory outcomes in patients with sepsis and elevated glycocalyx injury and endothelial activation biomarkers.

DESIGN

A systematic search was carried out on PubMed/MEDLINE, Embase, Cochrane and Google Scholar up to December 31, 2021, including studies in adults and children with sepsis which measured glycocalyx injury and endothelial activation biomarkers within 48 hours of hospital admission. The primary outcome was the risk of mortality from all causes and the secondary outcomes were the risk of developing respiratory failure (RF) and multiple organ dysfunction syndrome (MODS) in patients with elevations of these biomarkers.

MEASUREMENTS AND MAIN RESULTS

A total of 17 studies (3,529 patients) were included: 11 evaluated syndecan-1 (n=2,397) and 6 endocan (n=1,132). Syndecan-1 was higher in the group of patients who died than in those who survived [255 ng/mL (IQR: 139-305) vs. 83 ng/mL (IQR:40-111); p=0.014]. Patients with elevated syndecan-1 had a greater risk of death (OR 2.32; 95% CI 1.89, 3.10: p<0.001), MODS (OR 3.3; 95% CI 1.51, 7.25: p=0.003;), or RF (OR 7.53; 95% CI 1.86-30.45: p=0.005). Endocan was higher in patients who died [3.1 ng/mL (IQR 2.3, 3.7) vs. 1.62 ng/mL (IQR 1.2, 5.7); OR 9.53; 95% CI 3.34, 27.3; p<0.001], who had MODS (OR 8.33; 95% CI 2.07, 33.58; p=0.003) and who had RF (OR 9.66; 95% CI 2.26, 43.95; p=0.002).

CONCLUSION

Patients with sepsis and abnormal glycocalyx injury and endothelial activation biomarkers have a greater risk of developing respiratory failure, multiple organ failure, and death. Microcirculatory impairment should be routinely evaluated in patients with sepsis, using biomarkers to stratify risk groups.

Endothelial Activation and Microcirculatory Disorders in Sepsis

The vascular endothelium is crucial for the maintenance of vascular homeostasis. Moreover, in sepsis, endothelial cells can acquire new properties and actively participate in the host's response. If endothelial activation is mostly necessary and efficient in eliminating a pathogen, an exaggerated and maladaptive reaction leads to severe microcirculatory damage. The microcirculatory disorders in sepsis are well known to be associated with poor outcome. Better recognition of microcirculatory alteration is therefore essential to identify patients with the worse outcomes and to guide therapeutic interventions. In this review, we will discuss the main features of endothelial activation and dysfunction in sepsis, its assessment at the bedside, and the main advances in microcirculatory resuscitation.

Pathophysiology, mechanisms, and managements of tissue hypoxia

Oxygen is needed to generate aerobic adenosine triphosphate and energy that is required to support vital cellular functions. Oxygen delivery (DO₂) to the tissues is determined by convective and diffusive processes. The ability of the body to adjust oxygen extraction (ERO₂) in response to changes in DO₂ is crucial to maintain constant tissue oxygen consumption (VO₂). The capability to increase ERO₂ is the result of the regulation of the circulation and the effects of the simultaneous activation of both central and local factors. The endothelium plays a crucial role in matching tissue oxygen supply to demand in situations of acute drop in tissue oxygenation. Tissue oxygenation is adequate when tissue oxygen demand is met. When DO₂ is severely compromised, a critical DO₂ value is reached below which VO₂ falls and becomes dependent on DO₂, resulting in tissue hypoxia. The different mechanisms of tissue hypoxia are circulatory, anaemic, and hypoxic, characterised by a diminished DO₂ but preserved capacity of increasing ERO₂. Cytopathic hypoxia is another mechanism of tissue hypoxia that is due to impairment in mitochondrial respiration that can be observed in septic conditions with normal overall DO₂. Sepsis induces microcirculatory alterations with decreased functional capillary density, increased number of stopped-flow capillaries, and marked heterogeneity between the areas with large intercapillary distance, resulting in impairment of the tissue to extract oxygen and to satisfy the increased tissue oxygen demand, leading to the development of tissue hypoxia. Different therapeutic approaches exist to increase DO₂ and improve microcirculation, such as fluid therapy, transfusion, vasopressors, inotropes, and vasodilators. However, the effects of these agents on microcirculation are quite variable.

Advances in Microcirculatory Assessment: A Game Changer in Sepsis Management or the Latest Fad?!

Gupta R, Ray S. Advances in Microcirculatory Assessment: A Game Changer in Sepsis Management or the Latest Fad? Indian J Crit Care Med 2022;26(3):261–263.

Microcirculation during surgery

Throughout the long history of surgery, there has been great advancement in the hemodynamic management of surgical patients. Traditionally, hemodynamic management has focused on macrocirculatory monitoring and intervention to maintain appropriate oxygen delivery. However, even after optimization of macro-hemodynamic parameters, microcirculatory dysfunction, which is related to higher postoperative complications, occurs in some patients. Although the clinical significance of microcirculatory dysfunction has been well reported, little is known about interventions to recover microcirculation and prevent microcirculatory dysfunction. This may be at least partly caused by the fact that the feasibility of monitoring tools to evaluate microcirculation is still insufficient for use in routine clinical practice. However, considering recent advancements in these research fields, with more popular use of microcirculation monitoring and more clinical trials, clinicians may better understand and manage microcirculation in surgical patients in the future. In this review, we describe currently available methods for microcirculatory evaluation. The current knowledge on the clinical relevance of microcirculatory alterations has been summarized based on previous studies in various clinical settings. In the latter part, pharmacological and clinical interventions to improve or restore microcirculation are also presented.

[The role of the microcirculation in the pathogenesis of organ dysfunction]

The microcirculation includes all blood and lymph vessels with a diameter < 100 µm. Microcirculatory dysfunction is common in critically ill patients and is closely associated with both the severity of (multi-)organ dysfunction and mortality. The nature and extent of microcirculatory dysfunction differ depending on the underlying disease and are most pronounced in patients with systemic inflammation (e. g. sepsis), specific infections (e. g. malaria, dengue) or thrombocytopenia-associated multiple organ failure. This manuscript provides an overview of the pathophysiology, monitoring and therapy of microcirculatory dysfunction in the critically ill patient.

The Microcirculatory Response to Endotoxemia and Resuscitation Is a Marker of Regional Renal Perfusion, Renal Metabolic Stress, and Tubular Injury

Aims: We sought to investigate the relationship between macrohemodynamic resuscitation and microcirculatory parameters with the response of microcirculatory flow, tissue-specific parameters of metabolic stress and injury. We hypothesized that early resuscitation based on macrohemodynamic parameters does not prevent the development of organ dysfunction in a porcine model of endotoxemic shock, and that sublingual microcirculatory parameters are associated with markers of tissue metabolic stress and injury. Results: Both resuscitation groups had significant increases in creatinine and neutrophil gelatinase-associated lipocalin as compared with baseline. Neither the macrovascular response to endotoxemia or resuscitation, nor group allocation predicted the development of acute kidney injury (AKI). Only a microvascular flow index (MFI) <2.5 was associated with the development of renal tubular injury and AKI, and with increased renal, liver, peritoneal, and sublingual lactate/pyruvate (L/P) ratio and lactate. Among systemic parameters, only partial pressure of carbon dioxide (PCO₂) gap >6 and P(a-v)CO₂/C(v-a)O₂ >1.8 were associated with increased organ L/P ratio and AKI. Innovation and Conclusion: Our findings demonstrate that targeting macrohemodynamics to guide resuscitation during endotoxemic shock failed to predict tissue metabolic stress and the response of the microvasculature to resuscitation, and was unsuccessful in preventing tubular injury and AKI. Mechanistically, our data suggest that loss of hemodynamic coherence and decoupling of microvascular flow from tissue metabolic demand during endotoxemia may explain the lack of association between macrohemodynamics and perfusion goals. Finally, we demonstrate that MFI, PCO₂ gap, and P(v-a)CO₂/C(a-v)O₂ ratio outperformed macrohemodynamic parameters at predicting the development of renal metabolic stress and tubular injury, and therefore, that these indices merit further validation as promising resuscitation targets. Antioxid. Redox Signal. 35, 1407-1425.

[Fluid management in shock patients : New targets in the initial phase of shock]

BACKGROUND

Early i.v. fluid administration is a cornerstone in modern therapy of shock, especially in septic shock. However, there is much uncertainty concerning the amount and rate of fluid and which goals and measures could guide fluid management. Administering the optimal fluid volume is important because fluid overload can lead to severe negative consequences like organ failure and worsening of patient's outcome.

AIM

This review aims to describe the importance of fluid therapy and discuss possible strategies in fluid management as well as possible measurements and goals to guide such therapy.

RECENT FINDINGS

There is no single measurement to guide fluid management alone. It is important to assess fluid responsiveness, which together with multiple other parameters can be used to repeatedly assess optimal fluid management. However, it has also not been shown that assessing fluid responsiveness can improve outcome.

CONCLUSIONS

After the initial resuscitation, further fluid administration should be determined by individual patient factors and measures of fluid responsiveness. A more restrictive fluid management with early vasopressor administration seems to be increasingly used in modern fluid management. However many questions regarding optimal fluid management remain to be solved.

Is the Sympathetic System Detrimental in the Setting of Septic Shock, with Antihypertensive Agents as a Counterintuitive Approach? A Clinical Proposition

Mortality in the setting of septic shock varies between 20% and 100%. Refractory septic shock leads to early circulatory failure and carries the worst prognosis. The pathophysiology is poorly understood despite studies of the microcirculatory defects and the immuno-paralysis. The acute circulatory distress is treated with volume expansion, administration of vasopressors (usually noradrenaline: NA), and inotropes. Ventilation and anti-infectious strategy shall not be discussed here. When circulation is considered, the literature is segregated between interventions directed to the systemic circulation vs. interventions directed to the micro-circulation. Our thesis is that, after stabilization of the acute cardioventilatory distress, the prolonged sympathetic hyperactivity is detrimental in the setting of septic shock. Our hypothesis is that the sympathetic hyperactivity observed in septic shock being normalized towards baseline activity will improve the microcirculation by recoupling the capillaries and the systemic circulation. Therefore, counterintuitively, antihypertensive agents such as beta-blockers or alpha-2 adrenergic agonists (clonidine, dexmedetomidine) are useful. They would reduce the noradrenaline requirements. Adjuncts (vitamins, steroids, NO donors/inhibitors, etc.) proposed to normalize the sepsis-evoked vasodilation are not reviewed. This itemized approach (systemic vs. microcirculation) requires physiological and epidemiological studies to look for reduced mortality.

Changes in central venous-to-arterial carbon dioxide tension induced by fluid bolus in critically ill patients

BACKGROUND

In this prospective observational study, we evaluated the effects of fluid bolus (FB) on venous-to-arterial carbon dioxide tension (PvaCO2) in 42 adult critically ill patients with pre-infusion PvaCO2 > 6 mmHg.

RESULTS

FB caused a decrease in PvaCO2, from 8.7 [7.6-10.9] mmHg to 6.9 [5.8-8.6] mmHg (p < 0.01). PvaCO2 decreased independently of pre-infusion cardiac index and PvaCO2 changes during FB were not correlated with changes in central venous oxygen saturation (ScvO2) whatever pre-infusion CI. Pre-infusion levels of PvaCO2 were inversely correlated with decreases in PvaCO2 during FB and a pre-infusion PvaCO2 value < 7.7 mmHg could exclude a decrease in PvaCO2 during FB (AUC: 0.79, 95%CI 0.64-0.93; Sensitivity, 91%; Specificity, 55%; p < 0.01).

CONCLUSIONS

Fluid bolus decreased abnormal PvaCO2 levels independently of pre-infusion CI. Low baseline PvaCO2 values suggest that a positive response to FB is unlikely.

Recent advances in the pharmacological management of sepsis-associated acute kidney injury

INTRODUCTION

Acute kidney injury is a common occurrence in patients with sepsis and portends a high mortality as well as increased morbidity with numerous sequelae including the development of chronic kidney disease. Currently, there are no specific therapies that either prevent AKI or hasten its recovery. Thus, clinicians typically rely on management of the underlying infection, optimization of hemodynamic parameters as well as avoidance of nephrotoxins to maximize outcomes.

AREAS COVERED

Recent advances in understanding the mechanisms of sepsis as well as how these pathways may interact to lead to acute kidney injury have opened the door to the development of new, targeted therapies. This review focuses on the operative pathways in sepsis that have been identified as critical in leading to acute kidney injury and associated therapeutic agents that target these pathways.

EXPERT OPINION

Despite increased understanding of the pathogenesis of sepsis, development of effective therapeutics to decrease the incidence of AKI have lagged. This is likely due to the complex pathophysiology with overlapping pathways and need for multiple therapies guided by specific biomarkers. Biomarkers that detail operative pathways may be able to guide the institution of more specific therapies with the hope for improved outcomes.

Hemodynamic Monitoring in Sepsis-A Conceptual Framework of Macro- and Microcirculatory Alterations

Circulatory failure in sepsis is common and places a considerable burden on healthcare systems. It is associated with an increased likelihood of mortality, and timely recognition is a prerequisite to ensure optimum results. While there is consensus that aggressive source control, adequate antimicrobial therapy and hemodynamic management constitute crucial determinants of outcome, discussion remains about the best way to achieve each of these core principles. Sound cardiovascular support rests on tailored fluid resuscitation and vasopressor therapy. To this end, an overarching framework to improve cardiovascular dynamics has been a recurring theme in modern critical care. The object of this review is to examine the nature of one such framework that acknowledges the growing importance of adaptive hemodynamic support combining macro- and microhemodynamic variables to produce adequate tissue perfusion.

The Relevance of Fluid and Blood Management Using Microcirculatory Parameters in Children Undergoing Craniofacial Surgery

ABSTRACT

Perioperative management of bleeding in children can be challenging. Microvascular imaging techniques have allowed evaluating the effect of blood transfusion on the microcirculation, but little is known about these effects in children. We aimed to investigate the effects of blood management using macro- and micro-hemodynamic parameters measurement in children undergoing craniofacial surgery. This is a prospective observational repeated measurement study including fourteen children. The indications for blood transfusion were changes of hemoglobin/hematocrit (Hct) levels, the presence of signs of altered tissue perfusion and impaired microcirculation images. Total and perfused vessel densities, proportion of perfused vessels, microvascular flow index, and systemic parameters (hemoglobin, Hct, lactate, mixed venous oxygen saturation, K+, heart rate, mean arterial blood pressure) were evaluated baseline (T1), at the end of the surgical bleeding (T2) and end of the operation (T3). Four patients did not need a blood transfusion. In the other 10 patients who received a blood transfusion, capillary perfusion was higher at T3 (13[9-16]) when compared with the values of at T2 (11[8-12]) (P < 0.05) but only 6 patients reached their baseline values. Although blood transfusions increased Hct values (17 ± 2.4 [T2]-19 ± 2.8 [T3]) (P < 0.05), there was no correlation between microvascular changes and systemic hemodynamic parameters (P > 0.05). The sublingual microcirculation could change by blood transfusion but there was not any correlation between microcirculation changes, hemodynamic, and tissue perfusion parameters even with Hct values. The indication, guidance, and timing of fluid and blood therapy may be assessed by bedside microvascular analysis in combination with standard hemodynamic and biochemical monitoring for intraoperative bleeding in children.

Time of dissociation between microcirculation, macrocirculation, and lactate levels in a rabbit model of early endotoxemic shock

Background

The relationship between macrocirculation and microcirculation remains controversial. The loss of coherence between microcirculation and macrocirculation has already been found in late-stage sepsis shock. The objective of this study was to determine the earliest possible time of detecting the loss of coherence between microcirculation and macrocirculation in early-stage endotoxemic shock.

Methods

We randomized 24 female New Zealand white rabbits into two groups: endotoxemic shock group (n = 14) and control group (n = 10). Rabbits in the endotoxemic shock group were equipped with arterial and venous catheters and received an intravenous infusion of Escherichia coli lipopolysaccharide (LPS, 2 mg/kg over 10 min). Rabbits in the control group received the same dose of saline infusion. Microcirculatory perfusion parameters were assessed in the sublingual mucosa using sidestream dark-field video microscopy. Systemic hemodynamics and blood lactate levels were measured at baseline and over a 120-min period.

Results

Ninety minutes after completing LPS infusion, all animals in the endotoxemic shock group developed a hypodynamic septic condition, characterized by low cardiac output and increased systemic vascular resistance; 120 min after completing LPS infusion, the mean arterial pressure decreased by 25% (P = 0.01), confirming ongoing endotoxemic shock. However, significant decreases in sublingual microcirculatory parameters of small vessels (microvascular flow index, perfused vessel density, and proportion of small perfused vessels) were observed 30 min after completing LPS infusion (P = 0.01, for all), and threshold decreases of 30% were found 60 min after completing LPS infusion (P = 0.001, for all) in the endotoxemic shock group. Lactate levels significantly increased to more than 2 mm/L at 90 min and more than 4 mm/L at 120 min in the endotoxemic shock group (P = 0.02 and P = 0.01, respectively).

Conclusions

Changes in microcirculatory perfusion precede changes in macrocirculation and lactate levels in a rabbit model of endotoxemia shock. Microcirculation, macrocirculation, and oxygen metabolism are distinct in early-stage endotoxic shock.

Fluid Therapy and the Microcirculation in Health and Critical Illness

Fluid selection and administration during shock is typically guided by consideration of macrovascular abnormalities and resuscitative targets (perfusion parameters, heart rate, blood pressure, cardiac output). However, the microcirculatory unit (comprised of arterioles, true capillaries, and venules) is vital for the effective delivery of oxygen and nutrients to cells and removal of waste products from the tissue beds. Given that the microcirculation is subject to both systemic and local control, there is potential for functional changes and impacts on tissue perfusion that are not reflected by macrocirculatory parameters. This chapter will present an overview of the structure, function and regulation of the microcirculation and endothelial surface layer in health and shock states such as trauma, hemorrhage and sepsis. This will set the stage for consideration of how these microcirculatory characteristics, and the potential disconnect between micro- and macrovascular perfusion, may affect decisions related to acute fluid therapy (fluid type, amount, and rate) and monitoring of resuscitative efforts. Available evidence for the impact of various fluids and resuscitative strategies on the microcirculation will also be reviewed.

The use of pulse pressure variation for predicting impairment of microcirculatory blood flow

Dynamic parameters of preload have been widely recommended to guide fluid therapy based on the principle of fluid responsiveness and with regard to cardiac output. An equally important aspect is however to also avoid volume-overload. This accounts particularly when capillary leakage is present and volume-overload will promote impairment of microcirculatory blood flow. The aim of this study was to evaluate, whether an impairment of intestinal microcirculation caused by volume-load potentially can be predicted using pulse pressure variation in an experimental model of ischemia/reperfusion injury. The study was designed as a prospective explorative large animal pilot study. The study was performed in 8 anesthetized domestic pigs (German landrace). Ischemia/reperfusion was induced during aortic surgery. 6 h after ischemia/reperfusion-injury measurements were performed during 4 consecutive volume-loading-steps, each consisting of 6 ml kg⁻¹ bodyweight⁻¹. Mean microcirculatory blood flow (mean Flux) of the ileum was measured using direct laser-speckle-contrast-imaging. Receiver operating characteristic analysis was performed to determine the ability of pulse pressure variation to predict a decrease in microcirculation. A reduction of ≥ 10% mean Flux was considered a relevant decrease. After ischemia–reperfusion, volume-loading-steps led to a significant increase of cardiac output as well as mean arterial pressure, while pulse pressure variation and mean Flux were significantly reduced (Pairwise comparison ischemia/reperfusion-injury vs. volume loading step no. 4): cardiac output (l min⁻¹) 1.68 (1.02–2.35) versus 2.84 (2.15–3.53), p = 0.002, mean arterial pressure (mmHg) 29.89 (21.65–38.12) versus 52.34 (43.55–61.14), p < 0.001, pulse pressure variation (%) 24.84 (17.45–32.22) versus 9.59 (1.68–17.49), p = 0.004, mean Flux (p.u.) 414.95 (295.18–534.72) versus 327.21 (206.95–447.48), p = 0.006. Receiver operating characteristic analysis revealed an area under the curve of 0.88 (CI 95% 0.73–1.00; p value < 0.001) for pulse pressure variation for predicting a decrease of microcirculatory blood flow. The results of our study show that pulse pressure variation does have the potential to predict decreases of intestinal microcirculatory blood flow due to volume-load after ischemia/reperfusion-injury. This should encourage further translational research and might help to prevent microcirculatory impairment due to excessive fluid resuscitation and to guide fluid therapy in the future.

Microcirculatory Response to Changes in Venoarterial Extracorporeal Membrane Oxygenation Pump Flow: A Prospective Observational Study

Background: Venoarterial extracorporeal membrane oxygenation (VA-ECMO) pump flow is crucial for maintaining organ perfusion in patients with cardiogenic shock, but VA-ECMO pump flow optimization remains as a clinical challenge. This study aimed to investigate the response of sublingual microcirculation to changes in VA-ECMO pump flow.

Methods: Sublingual microcirculation was measured before and after changing VA-ECMO pump flow according to the treatment plan of ECMO team within 24 h and at 24-48 h after VA-ECMO placement. In clinical events of increasing VA-ECMO pump flow, those events with increased perfused vessel density (PVD) were grouped into group A, and the others were grouped into group B. In clinical events of decreasing VA-ECMO pump flow, those events with increased PVD were grouped into group C, and the others were grouped into group D.

Results: Increased PVD was observed in 60% (95% CI, 38.5–81.5%) of the events with increasing VA-ECMO pump flow. The probability of increasing PVD after increasing VA-ECMO pump flow were higher in the events with a PVD < 15 mm/mm² at baseline than those with a PVD ≥ 15 mm/mm² [100% (95% CI, 54.1–100%) vs. 42.9% (95% CI, 17.7–71.1%), P = 0.042]. Other microcirculatory and hemodynamic parameters at baseline did not differ significantly between group A and B or between group C and D.

Conclusion: This study revealed contradictory and non-contradictory responses of sublingual microcirculation to changes in VA-ECMO pump flow. Tandem measurements of microcirculation before and after changing VA-ECMO pump flow may help to ensure a good microcirculation.

The Surviving Sepsis Campaign: Fluid Resuscitation and Vasopressor Therapy Research Priorities in Adult Patients

OBJECTIVE

Expand upon the priorities of fluid resuscitation and vasopressor therapy research priorities identified by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

DATA SOURCES

Original article, literature search.

STUDY SELECTION

Several members of the original task force with expertise specific to the area of fluid resuscitation and vasopressor therapy.

DATA EXTRACTION

None.

DATA SYNTHESIS

None.

CONCLUSION

In the second of a series of manuscripts subsequent to the original article, members with expertise in the subjects expound upon the three identified priorities related to fluid resuscitation and vasopressor therapies. This analysis summarizes what is known and what were identified as ongoing and future research.

Early combination of albumin with crystalloids administration might be beneficial for the survival of septic patients: a retrospective analysis from MIMIC-IV database

Background

Fluid therapy is a cornerstone in the treatment of sepsis. Recently, the guidelines have recommended the combined administration that using crystalloids plus albumin for septic patients, but the optimal timing for albumin combined is still unclear. The objective of this study was to investigate the association of timing of albumin combined with 28-day mortality in patients with sepsis.

Methods

We involved septic patients from the Medical Information Mart for Intensive Care (MIMIC)-IV database, and these patients were categorized into crystalloids group (crystalloids alone) and early combination group (crystalloids combined albumin at 0–24 h). The primary outcome was 28-day mortality. We used propensity score matching (PSM) to adjust confounding and restricted mean survival time (RMST) analysis was conducted to quantify the beneficial effect on survival due to the combination group.

Results

We categorized 6597 and 920 patients in the “crystalloids alone” and “early combination”, respectively. After PSM, compared to the crystalloids group, the combination group was associated with the increased survival among 28-day (increased survival: 3.39 days, 95% CI 2.53–4.25; P < 0.001) after ICU admission. Patients who received albumin combination at the first 24-h was associated with prolonged LOS in ICU (10.72 days vs. 8.24 days; P < 0.001) but lower risk of 28-day mortality (12.5% vs 16.4%, P = 0.003) than those received crystalloids alone.

Conclusion

In septic patients, receiving albumin combined within the first 24-h after crystalloids administration was associated with an increment of survival in 28 days.

Septic shock: a microcirculation disease

PURPOSE OF REVIEW

The aim of this study was to discuss the implication of microvascular dysfunction in septic shock.

RECENT FINDINGS

Resuscitation of sepsis has focused on systemic haemodynamics and, more recently, on peripheral perfusion indices. However, central microvascular perfusion is altered in sepsis and these alterations often persist despite normalization of various macro haemodynamic resuscitative goals. Endothelial dysfunction is a key element in sepsis pathophysiology. It is responsible for the sepsis-induced hypotension. In addition, endothelial dysfunction is also implicated involved in the activation of inflammation and coagulation processes leading to amplification of the septic response and development of organ dysfunction. It also promotes an increase in permeability, mostly at venular side, and impairs microvascular perfusion and hence tissue oxygenation.Microvascular alterations are characterized by heterogeneity in blood flow distribution, with adequately perfused areas in close vicinity to not perfused areas, thus characterizing the distributive nature of septic shock. Such microvascular alterations have profound implications, as these are associated with organ dysfunction and unfavourable outcomes. Also, the response to therapy is highly variable and cannot be predicted by systemic hemodynamic assessment and hence cannot be detected by classical haemodynamic tools.

SUMMARY

Microcirculation is a key element in the pathophysiology of sepsis. Even if microcirculation-targeted therapy is not yet ready for the prime time, understanding the processes implicated in microvascular dysfunction is important to prevent chasing systemic hemodynamic variables when this does not contribute to improve tissue perfusion.

The surviving sepsis campaign: fluid resuscitation and vasopressor therapy research priorities in adult patients

Objective

To expand upon the priorities of fluid resuscitation and vasopressor therapy research priorities identified by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data Sources

Original paper and literature search.

Study Selection

Several members of the original task force with expertise specific to the area of fluid resuscitation and vasopressor therapy.

Data Extraction

None.

Data Synthesis

None.

Conclusion

In the second of a series of manuscripts subsequent to the original paper, members with expertise in the subjects expound upon the three identified priorities related to fluid resuscitation and vasopressor therapies. This analysis summarizes what is known and what were identified as ongoing and future research.

Incoherence between Systemic Hemodynamic and Microcirculatory Response to Fluid Challenge in Critically Ill Patients

Background: The aim of the study was to assess the coherence between systemic hemodynamic and microcirculatory response to a fluid challenge (FC) in critically ill patients. Methods: We prospectively collected data in patients requiring a FC whilst cardiac index (CI) and microcirculation were monitored. The sublingual microcirculation was assessed using the incident dark field (IDF) CytoCam device (Braedius Medical, Huizen, The Netherlands). The proportion of small perfused vessels (PPV) was calculated. Fluid responders were defined by at least a 10% increase in CI during FC. Responders according to changes in microcirculation were defined by at least 10% increase in PPV at the end of FC. Cohen’s kappa coefficient was measured to assess the agreement to categorize patients as “responders” to FC according to CI and PPV. Results: A total of 41 FC were performed in 38 patients, after a median time of 1 (0–1) days after ICU admission. Most of the fluid challenges (39/41, 95%) were performed using crystalloids and the median total amount of fluid was 500 (500–500) mL. The main reasons for fluid challenge were oliguria (n = 22) and hypotension (n = 10). After FC, CI significantly increased in 24 (58%) cases; a total of 19 (46%) FCs resulted in an increase in PPV. Both CI and PPV increased in 13 responders and neither in 11; the coefficient of agreement was only 0.21. We found no correlation between absolute changes in CI and PPV after fluid challenge. Conclusions: The results of this heterogenous population of critically ill patients suggest incoherence in fluid responsiveness between systemic and microvascular hemodynamics; larger cohort prospective studies with adequate a priori sample size calculations are needed to confirm these findings.