Both passive leg raising and intravascular volume expansion improve sublingual microcirculatory perfusion in severe sepsis and septic shock patients

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.

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.

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.

Serum vascular endothelial growth factor affects tissue fluid accumulation and is associated with deteriorating tissue perfusion and oxygenation in severe sepsis: a prospective observational study

BACKGROUND

Positive fluid balance and tissue fluid accumulation are associated with adverse outcomes in sepsis. Vascular endothelial growth factor (VEGF) increases in sepsis, promotes vascular permeability, and may affect tissue fluid accumulation and oxygenation. We used near-infrared spectroscopy (NIRS) to estimate tissue hemoglobin (Hb) oxygenation and water (H₂O) levels to investigate their relationship with serum VEGF levels.

MATERIAL AND METHODS

New-onset severe sepsis patients admitted to the intensive care unit were enrolled. Relative tissue concentrations of oxy-Hb ([HbO₂]), deoxy-Hb ([HbR]), total Hb ([HbT]), and H₂O ([H₂O]) were estimated by near-infrared spectroscopy (NIRS) for three consecutive days and serum VEGF levels were measured. Comparisons between oliguric and non-oliguric patients were conducted and the correlations between variables were analyzed.

RESULTS

Among 75 eligible patients, compared with non-oliguric patients, oliguric patients were administrated more intravascular fluids (median [IQR], 1926.00 [1348.50-3092.00] mL/day vs. 1069.00 [722.00-1486.75] mL/day, p < 0.001) and had more positive daily net intake and output (mean [SD], 1,235.06 [1303.14] mL/day vs. 313.17 [744.75] mL/day, p = 0.012), lower [HbO₂] and [HbT] over the three-day measurement (analyzed by GEE p = 0.01 and 0.043, respectively) and significantly higher [H₂O] on the third day than on the first two days (analyzed by GEE p = 0.034 and 0.018, respectively). Overall, serum VEGF levels were significantly negatively correlated with [HbO₂] and [HbT] (rho = - 0.246 and - 0.266, p = 0.042 and 0.027, respectively) but positively correlated with [H₂O] (rho = 0.449, p < 0.001). Subgroup analysis revealed a significant correlation between serum VEGF and [H2O] in oliguric patients (rho = 0.532, p = 0.003). Multiple regression analysis determined the independent effect of serum VEGF on [H₂O] (standardized coefficient = 0.281, p = 0.038).

CONCLUSIONS

In severe sepsis, oliguria relates to higher positive fluid balance, lower tissue perfusion and oxygenation, and progressive tissue fluid accumulation. Elevated serum VEGF is associated with worsening tissue perfusion and oxygenation and independently affects tissue fluid accumulation.

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.

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.

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.

Bedside determination of microcirculatory oxygen delivery and uptake: a prospective observational clinical study for proof of principle

Assessment of microcirculatory functional capacity is considered to be of prime importance for therapy guidance and outcome prediction in critically ill intensive care patients. Here, we show determination of skin microcirculatory oxygen delivery and consumption rates to be a feasible approach at the patient’s bedside. Real time laser-doppler flowmetry (LDF) and white light spectrophotometry (WLS) were used for assessment of thenar skin microperfusion, regional Hb and postcapillary venous oxygen saturation before and after forearm ischemia. Adapted Fick’s principle equations allowed for calculation of microcirculatory oxygen delivery and uptake. Patient groups with expected different microcirculatory status were compared [control (n = 20), sepsis-1/2 definition criteria identified SIRS (n = 10) and septic shock patients (n = 20), and the latter group further classified according to sepsis-3 definition criteria in sepsis (n = 10) and septic shock (n = 10)], respectively. In otherwise healthy controls, microcirculatory oxygen delivery and uptake approximately doubled after ischemia with maximum values (mDO2max and mVO2max) significantly lower in SIRS or septic patient groups, respectively. Scatter plots of mVO2max and mDO2max values defined a region of unphysiological low values not observed in control but in critically ill patients with the percentage of dots within this region being highest in septic shock patients. LDF and WLS combined with vasoocclusive testing reveals significant differences in microcirculatory oxygen delivery and uptake capacity between control and critically ill patients. As a clinically feasible technique for bedside determination of microcirculatory oxygen delivery and uptake, LDF and WLS combined with vasoocclusive testing holds promise for monitoring of disease progression and/or guidance of therapy at the microcirculatory level to be tested in further clinical trials.

ClinicalTrials.gov: NCT01530932.

Ten answers to key questions for fluid management in intensive care

This review focuses on fluid management of critically ill patients. The topic is addressed based on 10 single questions with simplified answers that provide clinicians with the basic information needed at the point of care in treating patients in the Intensive Care Unit. The review has didactic purposes and may serve both as an update on fluid management and as an introduction to the subject for novices in critical care. There is an urgent need to increase awareness regarding the potential risks associated with fluid overload. Clinicians should be mindful not only of the indications for administering fluid loads and of the type of fluids administered, but also of the importance to set safety limits. Lastly, it is important to implement proactive strategies seeking to establish negative fluid balance as soon as the clinical conditions are considered to be stable and the risk of deterioration is low.

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.

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.

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.

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.

Monitoring Microcirculation: Utility and Barriers - A Point-of-View Review

Microcirculation is a particular organ of the cardiovascular system. The goal of this narrative review is a critical reappraisal of the present knowledge of microcirculation monitoring, mainly focused on the videomicroscopic evaluation of sublingual microcirculation in critically ill patients. We discuss the technological developments in handheld videomicroscopy, which have resulted in adequate tools for the bedside monitoring of microcirculation. By means of these techniques, a large body of evidence has been acquired about the role of microcirculation in the pathophysiological mechanisms of shock, especially septic shock. We review the characteristics of sublingual microcirculation in septic shock, which mainly consist in a decrease in the perfused vascular density secondary to a reduction in the proportion of perfused vessels along with a high heterogeneity in perfusion. Even in patients with high cardiac output, red blood cell velocity is decreased. Thus, hyperdynamic flow is absent in the septic microcirculation. We also discuss the dissociation between microcirculation and systemic hemodynamics, particularly after shock resuscitation, and the different behavior among microvascular beds. In addition, we briefly comment the effects of some treatments on microcirculation. Despite the fact that sublingual microcirculation arises as a valuable goal for the resuscitation in critically ill patients, significant barriers remain present for its clinical application. Most of them are related to difficulties in video acquisition and analysis. We comprehensively analyzed these shortcomings. Unfortunately, a simpler approach, such as the central venous minus arterial PCO₂ difference, is a misleading surrogate for sublingual microcirculation. As conclusion, the monitoring of sublingual microcirculation is an appealing method for monitoring critically ill patients. Nevertheless, the lack of controlled studies showing benefits in terms of outcome, as well as technical limitations for its clinical implementation, render this technique mainly as a research tool.

Ten answers to key questions for fluid management in intensive care

This review focuses on fluid management of critically ill patients. The topic is addressed based on 10 single questions with simplified answers that provide clinicians with the basic information needed at the point of care in treating patients in the Intensive Care Unit. The review has didactic purposes and may serve both as an update on fluid management and as an introduction to the subject for novices in critical care. There is an urgent need to increase awareness regarding the potential risks associated with fluid overload. Clinicians should be mindful not only of the indications for administering fluid loads and of the type of fluids administered, but also of the importance to set safety limits. Lastly, it is important to implement proactive strategies seeking to establish negative fluid balance as soon as the clinical conditions are considered to be stable and the risk of deterioration is low.

Posture and Time Arrangement Influence Shank Circumference Reduction When Performing Leg Raising Exercise

This study recruited nine young women who performed a leg raising exercise under six test combinations of three holding postures (lying supine, placing the shanks on a yoga ball, and elevating the legs at 60° against the wall) and two time arrangements (continuous vs. intermittent) for a period of 15 min. The intermittent arrangement included an additional 1-min rest set in the middle of the 15 min test. The participants' shank circumference (SC) reductions and discomfort ratings were measured after each test combination was performed. Results indicated that the most efficient method for SC reduction was the yoga ball (5.4 mm), followed by the supine lying posture (4.6 mm) and wall-supported leg raising (3.1 mm). A significant interaction of posture × time arrangement (p < 0.01) implied that the yoga ball method combined with a 1-min rest produced the greatest SC reduction (6.7 mm). Our results also showed that participants experienced the greatest discomfort (score: 4.96) when performing wall-supported leg raising, compared with both lying supine (score: 1.34) and the yoga ball (score: 1.32). This study suggests that the effectiveness of leg raising as conventionally practiced for eliminating leg fatigue or swelling requires further consideration.

Assessment of sublingual microcirculation in critically ill patients: consensus and debate

The main concern in shock and resuscitation is whether the microcirculation can carry adequate oxygen to the tissues and remove waste. Identification of an intact coherence between macro- and microcirculation during states of shock and resuscitation shows a functioning regulatory mechanism. However, loss of hemodynamic coherence between the macro and microcirculation can be encountered frequently in sepsis, cardiogenic shock, or any hemodynamically compromised patient. This loss of hemodynamic coherence results in an improvement in macrohemodynamic parameters following resuscitation without a parallel improvement in microcirculation resulting in tissue hypoxia and tissue compromise. Hand-held vital microscopes (HVMs) can visualize the microcirculation and help to diagnose the nature of microcirculatory shock. Although treatment with the sole aim of recruiting the microcirculation is as yet not realized, interventions can be tailored to the needs of the patient while monitoring sublingual microcirculation. With the help of the newly introduced software, called MicroTools, we believe sublingual microcirculation monitoring and diagnosis will be an essential point-of-care tool in managing shock patients.

Microvascular Dysfunction in the Critically Ill

Microvascular dysfunction is a frequent complication of many chronic and acute conditions, especially in the critically ill. Moreover, the severity of microvascular alterations is associated with development of organ dysfunction and poor outcome. The complexities and heterogeneity of critical illness, especially in the elderly patient, requires more mechanistically oriented clinical trials that monitor the effectiveness of existing therapies and of those to come. Recent advances in the ability to obtain physiologically based assessments of microcirculatory function at the bedside will make microcirculatory-guided resuscitation a point of care reality.

Capillary refill time variation induced by passive leg raising predicts capillary refill time response to volume expansion

BACKGROUND

A peripheral perfusion-targeted resuscitation during early septic shock has shown encouraging results. Capillary refill time, which has a prognostic value, was used. Adding accuracy and predictability on capillary refill time (CRT) measurement, if feasible, would benefit to peripheral perfusion-targeted resuscitation. We assessed whether a reduction of capillary refill time during passive leg raising (ΔCRT-PLR) predicted volume-induced peripheral perfusion improvement defined as a significant decrease of capillary refill time following volume expansion.

METHODS

Thirty-four patients with acute circulatory failure were selected. Haemodynamic variables, metabolic variables (PCO2gap), and four capillary refill time measurements were recorded before and during a passive leg raising test and after a 500-mL volume expansion over 20 min. Receiver operating characteristic curves were built, and areas under the curves were calculated (ROCAUC). Confidence intervals (CI) were performed using a bootstrap analysis. We recorded mortality at day 90.

RESULTS

The least significant change in the capillary refill time was 25% [95% CI, 18-30]. We defined CRT responders as patients showing a reduction of at least 25% of capillary refill time after volume expansion. A decrease of 27% in ΔCRT-PLR predicted peripheral perfusion improvement with a sensitivity of 87% [95% CI, 73-100] and a specificity of 100% [95% CI, 74-100]. The ROCAUC of ΔCRT-PLR was 0.94 [95% CI, 0.87-1.0]. The ROCAUC of baseline capillary refill time was 0.73 [95% CI, 0.54-0.90] and of baseline PCO2gap was 0.79 [0.61-0.93]. Capillary refill time was significantly longer in non-survivors than in survivors at day 90.

CONCLUSION

ΔCRT-PLR predicted peripheral perfusion response following volume expansion. This simple low-cost and non-invasive diagnostic method could be used in peripheral perfusion-targeted resuscitation protocols.

TRIAL REGISTRATION

CPP Lyon Sud-Est II ANSM: 2014-A01034-43 Clinicaltrial.gov, NCT02248025 , registered 13th of September 2014.

Colloids and the Microcirculation

Colloid solutions have been advocated for use in treating hypovolemia due to their expected effect on improving intravascular retention compared with crystalloid solutions. Because the ultimate desired effect of fluid resuscitation is the improvement of microcirculatory perfusion and tissue oxygenation, it is of interest to study the effects of colloids and crystalloids at the level of microcirculation under conditions of shock and fluid resuscitation, and to explore the potential benefits of using colloids in terms of recruiting the microcirculation under conditions of hypovolemia. This article reviews the physiochemical properties of the various types of colloid solutions (eg, gelatin, dextrans, hydroxyethyl starches, and albumin) and the effects that they have under various conditions of hypovolemia in experimental and clinical scenarios.

Minimizing catecholamines and optimizing perfusion

Catecholamines are used to increase cardiac output and blood pressure, aiming ultimately at restoring/improving tissue perfusion. While intuitive in its concept, this approach nevertheless implies to be effective that regional organ perfusion would increase in parallel to cardiac output or perfusion pressure and that the catecholamine does not have negative effects on the microcirculation. Inotropic agents may be considered in some conditions, but it requires prior optimization of cardiac preload. Alternative approaches would be either to minimize exposure to vasopressors, tolerating hypotension and trying to prioritize perfusion but this may be valid as long as perfusion of the organ is preserved, or to combine moderate doses of vasopressors to vasodilatory agents, especially if these are predominantly acting on the microcirculation. In this review, we will discuss the pros and cons of the use of catecholamines and alternative agents for improving tissue perfusion in septic shock.

Influence of systemic hemodynamics on microcirculation during sepsis

PURPOSE

During sepsis, improvement of hemodynamic may not be related to improvement of microcirculation. The aim of this study was to investigate influence of systemic circulation on microcirculation in septic ICU patients.

METHODS

This is a prospective cohort study of septic ICU patients. Microcirculation was investigated with Near infrared spectrometry (NIRS) measuring tissue oxygen saturation (StO₂). StO₂ desaturation (desStO₂) and resaturation (resStO₂) slopes were determined. Analyses were made at baseline and after fluid challenges.

RESULTS

Seventy-two patients were included. One hundred and sixty measures were performed at baseline. StO₂ was 77.8% [72.4-85.0] and resStO₂ was 87.3%/min [57.8-141.7]. Univariate analysis showed an association between resStO₂ and diastolic arterial pressure (DAP) (p = .001), and norepinephrine dose (p = .033). In multivariate linear regression, there was an association between resStO₂ and DAP (β = 1.85 (0.64 to 3.08), p = .004)_. Fluid challenges (n = 60) increased CO, and resStO₂ (all p < .001). In multivariate analysis, variation of stroke volume was associated with variation of resStO₂ (p = .004) after fluid challenge. There was no association between CVP and resStO₂.

CONCLUSIONS

DAP was the only independent determinant of resStO2 in septic patients. Fluid challenges may improve microcirculation. CVP did not influence resStO₂.

Preload Dependence Is Associated with Reduced Sublingual Microcirculation during Major Abdominal Surgery

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Dynamic indices, such as pulse pressure variation, detect preload dependence and are used to predict fluid responsiveness. The behavior of sublingual microcirculation during preload dependence is unknown during major abdominal surgery. The purpose of this study was to test the hypothesis that during abdominal surgery, microvascular perfusion is impaired during preload dependence and recovers after fluid administration.

Methods

This prospective observational study included patients having major abdominal surgery. Pulse pressure variation was used to identify preload dependence. A fluid challenge was performed when pulse pressure variation was greater than 13%. Macrocirculation variables (mean arterial pressure, heart rate, stroke volume index, and pulse pressure variation) and sublingual microcirculation variables (perfused vessel density, microvascular flow index, proportion of perfused vessels, and flow heterogeneity index) were recorded every 10 min.

Results

In 17 patients, who contributed 32 preload dependence episodes, the occurrence of preload dependence during major abdominal surgery was associated with a decrease in mean arterial pressure (72 ± 9 vs. 83 ± 15 mmHg [mean ± SD]; P = 0.016) and stroke volume index (36 ± 8 vs. 43 ± 8 ml/m2; P &lt; 0.001) with a concomitant decrease in microvascular flow index (median [interquartile range], 2.33 [1.81, 2.75] vs. 2.84 [2.56, 2.88]; P = 0.009) and perfused vessel density (14.9 [12.0, 16.4] vs. 16.1 mm/mm2 [14.7, 21.4], P = 0.009), while heterogeneity index was increased from 0.2 (0.2, 0.4) to 0.5 (0.4, 0.7; P = 0.001). After fluid challenge, all microvascular parameters and the stroke volume index improved, while mean arterial pressure and heart rate remained unchanged.

Conclusions

Preload dependence was associated with reduced sublingual microcirculation during major abdominal surgery. Fluid administration successfully restored microvascular perfusion.

Relationship between Microcirculatory Perfusion and Arterial Elastance: A Pilot Study

Background

Arterial elastance (Ea) represents the total afterload imposed on the left ventricle, and it is largely influenced by systemic vascular resistance (SVR). Although one can expect that Ea is influenced by peripheral endothelial function, no data are available to support it in patients. The aim of this study was to investigate the relationship between Ea, SVR, and microvascular perfusion in critically ill patients undergoing the fluid challenge (FC).

Methods

A prospective study in patients receiving a fluid challenge. A pulse wave analysis system (MostCare, Vygon, France) was used to estimate Ea and an incident dark field (IDF) handheld device (Braedius Medical BV, The Netherlands) to evaluate the sublingual microcirculation. Microvascular perfusion was assessed using the proportion of small-perfused vessels (PPV). Relative changes in each variable were calculated before and after FC; fluid responsiveness was defined as an increase in the cardiac index by at least 10% from baseline.

Results

We studied 20 patients requiring a fluid challenge (n=10 for hypotension; n=5 for oliguria; n=3 for lactate values greater than 2 mmol/l; n=2 for tachycardia), including 12 fluid responders. There was a strong correlation between Ea and SVR (r² = 0.75; p < 0.001) and only a weak correlation between Ea and PPV at baseline (r² = 0.22; p=0.04). Ea decreased from 1.4 [1.2–1.6] to 1.2 [1.1–1.4] mmHg/mL (p=0.01), SVR from 1207 [1006–1373] to 1073 [997–1202] dyn ∗ s/cm⁵ (p=0.06), and PPV from 56 [51–64] % to 59 [47–73] % (p=0.25) after fluid challenge. Changes in Ea were significantly correlated with changes in SVR, but not with changes in PPV.

Conclusions

The correlation between Ea and indexes of microvascular perfusion in the sublingual region is weak. The impact of microcirculatory perfusion on the arterial load is probably limited.

Exploration de la perfusion tissulaire microcirculatoire au cours du choc septique

Au cours des infections graves, les travaux chez l’animal et chez l’homme ont mis en évidence une altération de la perfusion microcirculatoire à l’origine des défaillances viscérales et potentiellement du décès. La sévérité des anomalies microcirculatoires ainsi que leur persistance sont des facteurs prédictifs de mortalité indépendamment du débit cardiaque ou de la pression artérielle. Il est donc indispensable de développer des outils permettant d’évaluer la perfusion microcirculatoire au lit du malade. De nombreux travaux au cours du sepsis suggèrent que l’analyse de la perfusion cutanée au travers de sa température (et/ou du gradient), du temps de recoloration cutané, de l’étendue des marbrures et de l’indice de perfusion périphérique constitue un outil simple qui permet au réanimateur une évaluation rapide des anomalies microcirculatoires.

Volume Based Resuscitation and Intestinal Microcirculation after Ischaemia/Reperfusion Injury: Results of an Exploratory Aortic Clamping Study in Pigs

OBJECTIVES

In the presence of ischaemia/reperfusion (I/R) induced endothelial injury, volume administration may not correlate with increased microcirculation. The aim of this study was to evaluate intestinal microcirculation after standardised sequential volume loading in an animal model of I/R injury following supracoeliac aortic clamping.

METHODS

This was a prospective exploratory pilot animal study. Intestinal I/R injury was induced in eight pigs during experimental thoraco-abdominal aortic repair. After 6 h of I/R, microcirculatory blood flow (mFlux, measured in the ileum using direct laser speckle contrast imaging) and macrohaemodynamic parameters (using trans-cardiopulmonary thermodilution) were measured and measurements were repeated after each of four sequential volume loading steps (VLS1 - 4). Each load was administered over 5 min followed by another 5 min for equilibration.

RESULTS

All animals survived until after VLS4. After 6 h of I/R cardiac output (CO) (p < .001) and mFlux (p < .001) had both decreased. CO increased again after VLS1 (p < .001) and VLS2 (p = .036), whereas mFlux did not change. In contrast, mFlux further decreased after VLS3 (p < .01) and VLS4 (p < .001), whereas CO did not change anymore. Extravascular lung water continued to increase after VLS2 (p = .046) and VLS4 (p = .049).

CONCLUSIONS

I/R leads to impaired intestinal microcirculation, which was not restored by volume administration in spite of improved CO. In contrast, further volume administration exceeding preload reserves was associated with additional decreases in the intestinal microcirculation. The potentially negative effect of excessive volume resuscitation after I/R injury should encourage further translational research.

Lactate and microcirculation as suitable targets for hemodynamic optimization in resuscitation of circulatory shock

PURPOSE OF REVIEW

A discussion of recent research exploring the feasibility of perfusion-guided resuscitation of acute circulatory failure with a focus on lactate and microcirculation.

RECENT FINDINGS

Upon diagnosis of shock, hyperlactemia is associated with poor outcome and, under appropriate clinical circumstances, may reflect inadequate tissue perfusion. Persistent hyperlactemia despite resuscitation is even more strongly correlated with morbidity and mortality. Importantly, there is minimal coherence between lactate trends and static hemodynamic measures such as blood pressure, especially after the initial, hypovolemic phase of shock. During this early period, lactate guided-resuscitation is effective and possibly superior to hemodynamic-guided resuscitation. Similar to hyperlactemia, impaired microcirculation is ubiquitous in shock and is evident even in the setting of hemodynamic compensation (i.e., occult shock). Moreover, persistent microcirculatory derangement is associated with poor outcome and may reflect ongoing shock and/or long-lasting damage. Although the wait continues for a microcirculation-guided resuscitation trial, there is progress toward this goal.

SUMMARY

Although questions remain, a multimodal perfusion-based approach to resuscitation is emerging with lactate and microcirculation as core measures. In this model, hyperlactemia and microcirculatory derangement support the diagnosis of shock, may help guide resuscitation during the initial period, and may reflect resuscitation efficacy and iatrogenic harm (e.g., fluid overload).

Monitoring microcirculation in critical illness

PURPOSE OF REVIEW

Critical illness includes a wide range of conditions from sepsis to high-risk surgery. All these diseases are characterized by reduced tissue oxygenation. Macrohemodynamic parameters may be corrected by fluids and/or vasoactive compounds; however, the microcirculation and its tissues may be damaged and remain hypoperfused. An evaluation of microcirculation may enable more physiologically based approaches for understanding the pathogenesis, diagnosis, and treatment of critically ill patients.

RECENT FINDINGS

Microcirculation plays a pivotal role in delivering oxygen to the cells and maintains tissue perfusion. Negative results of several studies, based on conventional hemodynamic resuscitation procedures to achieve organ perfusion and decrease morbidity and mortality following conditions of septic shock and other cardiovascular compromise, have highlighted the need to monitor microcirculation. The loss of hemodynamic coherence between the macrocirculation and microcirculation, wherein improvement of hemodynamic variables of the systemic circulation does not cause a parallel improvement of microcirculatory perfusion and oxygenation of the essential organ systems, may explain why these studies have failed.

SUMMARY

Critical illness is usually accompanied by abnormalities in microcirculation and tissue hypoxia. Direct monitoring of sublingual microcirculation using hand-held microscopy may provide a more physiological approach. Evaluating the coherence between macrocirculation and microcirculation in response to therapy seems to be essential in evaluating the efficacy of therapeutic interventions.

Vasodilators in Septic Shock Resuscitation: A Clinical Perspective

Microcirculatory abnormalities have been shown to be frequent in patients with septic shock despite "normalization" of systemic hemodynamics. Several studies have explored the impact of vasodilator therapy (prostacyclin, inhaled nitric oxide, topic acetylcholine, and nitroglycerin) on microcirculation and tissue perfusion, with contradictory findings.In this narrative review, we briefly present the pathophysiological aspects of microcirculatory dysfunction, and depict the evidence supporting the use of vasodilators and other therapeutic interventions (fluid administration, blood transfusion, vasopressors, and dobutamine) aiming to improve the microcirculatory flow in septic shock patients.

Detailing the cardiovascular profile in shock patients

Evaluation of the cardiovascular profile of critically ill patients is one of the most important actions performed in critically ill patients. It allows recognition that the patient is in shock and characterization of the type of circulatory failure. This step is crucial to initiate supportive interventions and to cure the cause responsible for the development of shock. Evaluation of tissue perfusion allows identification of the patient insufficiently resuscitated and also to trigger therapeutic interventions. Monitoring tissue perfusion can be achieved by lactate, venoarterial gradients in PCO₂, and central venous or mixed venous oxygen saturation. Ultimately, monitoring the microcirculation may help not only to identify alterations in tissue perfusion but also to identify the type of alterations: diffuse decrease in microvascular perfusion versus heterogeneity in the alterations, as in sepsis, with well perfused areas in close vicinity to poorly perfused areas. Regarding supportive therapy, a step-by-step approach is suggested, with fluid optimization followed by vasoactive support to preserve perfusion pressure and global and regional blood flows. The different variables should be integrated into decision and management pathways, and therapies adapted accordingly.

Evaluation of microvascular endothelial function in patients with infective endocarditis using laser speckle contrast imaging and skin video-capillaroscopy: research proposal of a case control prospective study

OBJECTIVE

Infective endocarditis is a severe condition with high in-hospital and 5-year mortality. There is increasing incidence of infective endocarditis, which may be related to healthcare and changes in prophylaxis recommendations regarding oral procedures. Few studies have evaluated the microcirculation in patients with infective endocarditis, and so far, none have utilized laser-based technology or evaluated functional capillary density. The aim of the study is to evaluate the changes in the systemic microvascular bed of patients with both acute and subacute endocarditis. This is a cohort study that will include adult patients with confirmed active infective endocarditis according to the modified Duke criteria who were admitted to our center for treatment. A control group of sex- and age-matched healthy volunteers will be included. Functional capillary density, which is defined as the number of spontaneously perfused capillaries per square millimeter of skin, will be assessed by video-microscopy with an epi-illuminated fiber optic microscope. Capillary recruitment will be evaluated using post-occlusive reactive hyperemia. Microvascular flow will be evaluated in the forearm using a laser speckle contrast imaging system for the noninvasive and continuous measurement of cutaneous microvascular perfusion changes. Laser speckle contrast imaging will be used in combination with skin iontophoresis of acetylcholine, an endothelium-dependent vasodilator, or sodium nitroprusside (endothelium independent) to test microvascular reactivity.

RESULTS

The present study will contribute to the investigation of microcirculatory changes in infective endocarditis and possibly lead to an earlier diagnosis of the condition and/or determination of its severity and complications. Trial registration ClinicalTrials.gov ID: NCT02940340.

Not Bad: Passive Leg Raising in Cardiopulmonary Resuscitation-A New Modeling Study

Aim: To evaluate, using a simulated haemodynamic circulation model, whether passive leg raising (PLR) is able to improve the effect during cardiopulmonary resuscitation (CPR); to expose the possible reasons why PLR works or not. Materials and Methods: We adapted a circulatory model for CPR with PLR. First we compared cardiac output (CO), coronary perfusion pressure (CPP), blood flow to heart (Q_heart), and blood flow to neck and brain (Q_head) of standard chest compression-only CPR with and without PLR; second we simulated the effects of PLR in different situations, by varying the thoracic pump factor (TPF) from 0 to 1; third we simulated the effects when the legs are lifted to the different heights. Finally, we compared our results with those obtained from a published clinical study. Results: According to the simulation model, (1) When TPF is in the interval (0,1), CPP, CO, Q_heart, and Q_head are improved with PLR, among them with half-thoracic/half-cardiac pump effect (TPF is 0.5), CPP, CO, Q_head, and Q_heart increase the most (by 14, 14, 15, and 17%). (2) When TPF is 1 (pure thoracic pump, with an emphysema or extremely thick thorax), PLR has almost no effect on CPP, CO, and Q_heart (-1, 2, and 0%), whereas Q_head is increased by 9%; (3) Regardless of whether there is a cardiac or thoracic pump effect, PLR is able to increase Q_head by 9-15%. (4) When the legs are lifted to 30° to the ground, the volume transferred from legs to upper body is 36% of the initial volume in legs; when the legs are lifted to 45°, the volume transferred is 43%; when the legs are lifted to 60°, the volume transferred is 47%; when the legs are lifted to 90°, the volume transferred is 50%. Conclusion: Generally PLR is able to achieve improved cerebral perfusion and coronary perfusion. In some extreme situations, it has no effect on cardiac output and coronary perfusion, but still improves cerebral perfusion. PLR could be a beneficial supplement to CPR, and it is not necessary to lift the legs too high above the ground.