Microcirculation follows macrocirculation in heart and gut in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation in pigs

Shenfu injection alleviate gut ischemia/reperfusion injury after severe hemorrhagic shock through improving intestinal microcirculation in rats

Background

Shenfu (SF) injection, a traditional Chinese medication, would improve microcirculation in cardiogenic shock and infectious shock. This study was aimed to explore the therapeutic potential of the SF injection in gut ischemia-reperfusion (I/R) injury after severe hemorrhagic shock (SHS) and resuscitation. Furthermore, we also investigated the optimal adm？ inistration timing.

Methods

Twenty-four male SD rats were randomly divided into four groups: Sham group (sham, n = 6), Control group (n = 6), SF injection group (SF, n = 6), and Delayed Shenfu injection administration group (SF-delay, n = 6). In SHS and resuscitation model, rats were induced by blood draw to a mean arterial pressure (MAP) of 40 ± 5 mmHg within 1 h and then maintained for 40 min; HR, MAP 'were recorded, microcirculation index [De Backer score, perfused small vessel density (PSVD), total vessel density (TVD), microcirculation flow index score (MFI), flow heterogeneity index (HI)] were analyzed. The blood gas index was detected, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), diamine oxidase (DAO), malondialdehyde (MDA) were measured by ELISA; ZO-1, and claudin-1 were measured by Western blotting. In addition, hematoxylin-eosin (HE) and periodic acid schiff (PAS) staining pathological sections of the intestinal mucosal tissues were also performed.

Results

SF injection increased the MAP, relieved the metabolic acidosis degree associated with the hypoperfusion, and improved the intestinal microcirculatory density and perfusion quality after I/R injury. The expression of DAO, MDA in intestinal tissue, and plasma IL-6, TNF-α significantly decreased in the SF injection group compared to the control group. The concentration of ZO-1 and claudin-1 is also higher in the SF injection group. In addition, the HE and PAS staining results also showed that SF injection could decrease mucosal damage and maintain the structure. In the SF-delay group, the degree of intestinal tissue damage was intermediate between that of the control group and SF injection group.

Conclusions

SF injection protect the intestine from I/R injury induced by SHS and resuscitation, the mechanism of which might be through improving intestinal microcirculation, reducing the excessive release of inflammatory factors and increasing intestinal mucosal permeability. Furthermore, the protection effect is more pronounced if administration during the initial resuscitation phase.

Microcirculation and Mitochondria: The Critical Unit

Critical illness is often accompanied by a hemodynamic imbalance between macrocirculation and microcirculation, as well as mitochondrial dysfunction. Microcirculatory disorders lead to abnormalities in the supply of oxygen to tissue cells, while mitochondrial dysfunction leads to abnormal energy metabolism and impaired tissue oxygen utilization, making these conditions important pathogenic factors of critical illness. At the same time, there is a close relationship between the microcirculation and mitochondria. We introduce here the concept of a "critical unit", with two core components: microcirculation, which mainly comprises the microvascular network and endothelial cells, especially the endothelial glycocalyx; and mitochondria, which are mainly involved in energy metabolism but perform other non-negligible functions. This review also introduces several techniques and devices that can be utilized for the real-time synchronous monitoring of the microcirculation and mitochondria, and thus critical unit monitoring. Finally, we put forward the concepts and strategies of critical unit-guided treatment.

Characteristics of sublingual microcirculatory changes during the early postoperative period following cardiopulmonary bypass-assisted cardiac surgery-a prospective cohort study

BACKGROUND

Persistent microcirculatory dysfunction associated with increased morbidity and mortality. Interventions in the early resuscitation can be tailored to the changes of microcirculation and patient's need. However, there is usually an uncoupling of macrocirculatory and microcirculatory hemodynamics during resuscitation. Current research on the patterns of microcirculatory changes and recovery after cardiopulmonary bypass (CPB)-assisted cardiac surgery is limited. This study aimed to analyze changes in the microcirculatory parameters after CPB and their correlation with macrocirculation and to explore the characteristics of microcirculatory changes following CPB-assisted cardiac surgery.

METHODS

Between December 2018 and January 2019, 24 adult patients with indwelling pulmonary artery catheters after elective cardiac surgery using CPB were enrolled in this study. Both microcirculatory and macrocirculatory parameters were collected at 0, 6, 16, and 24 hours after admission to the intensive care unit (ICU). Video images of sublingual microcirculation were analyzed to obtain the microcirculatory parameters, including total vascular density (TVD), perfused small vessel density (PSVD), the proportion of perfused small vessels (PPV), microvascular flow index (MFI), and flow heterogeneity index (HI). The characteristics of microcirculatory parameter change following cardiac surgery and the correlation between microcirculatory parameters and macroscopic hemodynamic indicators, oxygen metabolic indicators, and carbon dioxide partial pressure difference (PCO2gap) were analyzed.

RESULTS

There were significant differences in the changes of TVD (P=0.012) and PSVD (P=0.005) during the first 24 hours postoperatively in patients who underwent CPB-assisted cardiac surgery. The microcirculatory density parameters (TVD: r=-0.5059, P=0.0456; PVD: r=-0.5499, P=0.0273) were correlated with oxygen delivery index (DO2I) at 24 hours after surgery. The microcirculatory flow parameters (PPV: r=0.4370, P=0.0327; MFI: r=0.6496, P=0.0006; and HI: r=-0.5350, P=0.0071) had a strong correlation with PCO2gap at 0 hour after surgery.

CONCLUSIONS

TVD and PSVD might be two most sensitive indicators affected by CPB-assisted cardiac surgery. There was no consistency between microcirculation and macrocirculation until 24 hours following cardiac surgery, meaning the improvement of systemic hemodynamic indicators does not guarantee correspondently improvement in microcirculation. Early controlled oxygen supply after CPB-assisted cardiac surgery may be conducive to the resuscitation of patients to a certain extent.

Remote Ischemic Preconditioning Attenuates Hepatic Ischemia/Reperfusion Injury after Hemorrhagic Shock by Increasing Autophagy

Fluid resuscitation after hemorrhagic shock is a model of systemic ischemia/reperfusion injury (SI/RI), and the liver is one of the main target organs. Ischemic preconditioning (IPC) can reduce hepatic ischemia-reperfusion injury (I/RI) via autophagy. However, whether remote ischemic preconditioning (RIPC) can alleviate the liver injury that is secondary to hemorrhagic shock and the role of autophagy in this process remain unclear. Thus, we constructed a hemorrhagic shock model in rats with or without RIPC to monitor mean arterial pressure (MAP) and investigate liver secondary injury levels via serum aminotransferase, ultrasound, HE staining and TUNEL fluorescence staining. We also detected levels of serum inflammatory factors including tumor necrosis factor-alpha (TNF-α) and interleukin 1β (IL-1β) by enzyme-linked immunosorbent assay (ELLSA), observed autophagosomes by Transmission electron microscopy (TEM), and analyzed LC3, Beclin-1, p62 protein expression levels by immunohistochemical (IHC) and western blot (WB). We found that RIPC increased blood pressure adaptability, decreased lactate (Lac) and aminotransferase levels, and delayed the decrease in liver density. Levels of inflammatory factors TNF-α, IL-1β and apoptosis were attenuated, autophagosomes was increased in the RIPC group compared with controls. IHC and WB both revealed increased LC3 and Beclin-1 but decreased p62 protein expression levels in the RIPC group. Together, our data suggest that RIPC-activated autophagy could play a protective role against secondary liver injury following hemorrhagic shock.

Unmasking the Hypovolemic Shock Continuum: The Compensatory Reserve

Hypovolemic shock exists as a spectrum, with its early stages characterized by subtle pathophysiologic tissue insults and its late stages defined by multi-system organ dysfunction. The importance of timely detection of shock is well known, as early interventions improve mortality, while delays render these same interventions ineffective. However, detection is limited by the monitors, parameters, and vital signs that are traditionally used in the intensive care unit (ICU). Many parameters change minimally during the early stages, and when they finally become abnormal, hypovolemic shock has already occurred. The compensatory reserve (CR) is a parameter that represents a new paradigm for assessing physiologic status, as it comprises the sum total of compensatory mechanisms that maintain adequate perfusion to vital organs during hypovolemia. When these mechanisms are overwhelmed, hemodynamic instability and circulatory collapse will follow. Previous studies involving CR measurements demonstrated their utility in detecting central blood volume loss before hemodynamic parameters and vital signs changed. Measurements of the CR have also been used in clinical studies involving patients with traumatic injuries or bleeding, and the results from these studies have been promising. Moreover, these measurements can be made at the bedside, and they provide a real-time assessment of hemodynamic stability. Given the need for rapid diagnostics when treating critically ill patients, CR measurements would complement parameters that are currently being used. Consequently, the purpose of this article is to introduce a conceptual framework where the CR represents a new approach to monitoring critically ill patients. Within this framework, we present evidence to support the notion that the use of the CR could potentially improve the outcomes of ICU patients by alerting intensivists to impending hypovolemic shock before its onset.

Effects of Fluids on the Macro- and Microcirculations

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2018. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2018. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

The coherence of macrocirculation, microcirculation, and tissue metabolic response during nontraumatic hemorrhagic shock in swine

Hemorrhagic shock is clinically observed as changes in macrocirculatory indices, while its main pathological constituent is cellular asphyxia due to microcirculatory alterations. The coherence between macro‐ and microcirculatory changes in different shock states has been questioned. This also applies to the hemorrhagic shock. Most studies, as well as clinical situations, of hemorrhagic shock include a “second hit” by tissue trauma. It is therefore unclear to what extent the hemorrhage itself contributes to this lack of circulatory coherence. Nine pigs in general anesthesia were exposed to a controlled withdrawal of 50% of their blood volume over 30 min, and then retransfusion over 20 min after 70 min of hypovolemia. We collected macrocirculatory variables, microcirculatory blood flow measurement by the fluorescent microspheres technique, as well as global microcirculatory patency by calculation of Pv‐aCO₂, and tissue metabolism measurement by the use of microdialysis. The hemorrhage led to anticipated changes in macrocirculatory variables with a coherent change in microcirculatory and metabolic variables. In the late hemorrhagic phase, the animals' variables generally improved, probably through recruitment of venous blood reservoirs. After retransfusion, all variables were normalized and remained same throughout the study period. We find in our nontraumatic model consistent coherence between changes in macrocirculatory indices, microcirculatory blood flow, and tissue metabolic response during hemorrhagic shock and retransfusion. This indicates that severe, but brief, hemorrhage with minimal tissue injury is in itself not sufficient to cause lack of coherence between macro‐ and microcirculation.

Effect of RBC Transfusion on Sublingual Microcirculation in Hemorrhagic Shock Patients: A Pilot Study

OBJECTIVES

The effects of RBC transfusion on microvascular perfusion are not well documented. We investigated the effect of RBC transfusion on sublingual microcirculation in hemorrhagic shock patients.

DESIGN

Prospective, preliminary observational study.

SETTINGS

A 28-bed, surgical ICU in a university hospital.

PATIENTS

Fifteen hemorrhagic shock patients requiring RBC transfusion.

INTERVENTION

Transfusion of one unit of RBCs.

MEASUREMENTS AND MAIN RESULTS

The sublingual microcirculation was assessed with a Sidestream Dark Field imaging device before and after RBC transfusion. After transfusion of one unit of RBC, hemoglobin concentration increased from 8.5 g/dL (7.6-9.5 g/dL) to 9.6 g/dL (9.1-10.3 g/dL) g/dL (p = 0.02) but no effect on macrocirculatory parameters (arterial pressure, cardiac index, heart rate, and pulse pressure variations) was observed. Transfusion of RBC significantly increased microcirculatory flow index (from 2.3 [1.6-2.5] to 2.7 [2.6-2.9]; p < 0.003), the proportion of perfused vessels (from 79% [57-88%] to 92% [88-97%]; p < 0.004), and the functional capillary density (from 21 [19-22] to 24 [22-26] mm/mm; p = 0.003). Transfusion of RBC significantly decreased the flow heterogeneity index (from 0.51 [0.34-0.62] to 0.16 [0.04-0.29]; p < 0.001). No correlations were observed between other macrovascular parameters and microvascular changes after transfusion. The change in microvascular perfusion after transfusion correlated negatively with baseline microvascular perfusion.

CONCLUSIONS

RBC transfusion improves sublingual microcirculation independently of macrocirculation and the hemoglobin level in hemorrhagic shock patients. The change in microvascular perfusion after transfusion correlated negatively with baseline microvascular perfusion. Evaluation of microcirculation perfusion is critical for optimization of microvascular perfusion and to define which patients can benefit from RBC transfusion during cardiovascular resuscitation.

Systemic and microcirculatory effects of blood transfusion in experimental hemorrhagic shock

Background

The microvascular reperfusion injury after retransfusion has not been completely characterized. Specifically, the question of heterogeneity among different microvascular beds needs to be addressed. In addition, the identification of anaerobic metabolism is elusive. The venoarterial PCO₂ to arteriovenous oxygen content difference ratio (P_v-aCO₂/C_a-vO₂) might be a surrogate for respiratory quotient, but this has not been validated. Therefore, our goal was to characterize sublingual and intestinal (mucosal and serosal) microvascular injury after blood resuscitation in hemorrhagic shock and its relation with O₂ and CO₂ metabolism.

Methods

Anesthetized and mechanically ventilated sheep were assigned to stepwise bleeding and blood retransfusion (n = 10) and sham (n = 7) groups. We performed analysis of expired gases, arterial and mixed venous blood gases, and intestinal and sublingual videomicroscopy.

Results

In the bleeding group during the last step of hemorrhage, and compared to the sham group, there were decreases in oxygen consumption (3.7 [2.8–4.6] vs. 6.8 [5.8–8.0] mL min⁻¹ kg⁻¹, P < 0.001) and increases in respiratory quotient (0.96 [0.91–1.06] vs. 0.72 [0.69–0.77], P < 0.001). Retransfusion normalized these variables. The P_v-aCO₂/C_a-vO₂ increased in the last step of bleeding (2.4 [2.0–2.8] vs. 1.1 [1.0–1.3], P < 0.001) and remained elevated after retransfusion, compared to the sham group (1.8 [1.5–2.0] vs. 1.1 [0.9–1.3], P < 0.001). P_v-aCO₂/C_a-vO₂ had a weak correlation with respiratory quotient (Spearman R = 0.42, P < 0.001). All the intestinal and sublingual microcirculatory variables were affected during hemorrhage and improved after retransfusion. The recovery was only complete for intestinal red blood cell velocity and sublingual total and perfused vascular densities.

Conclusions

Although there were some minor differences, intestinal and sublingual microcirculation behaved similarly. Therefore, sublingual mucosa might be an adequate window to track intestinal microvascular reperfusion injury. Additionally, P_v-aCO₂/C_a-vO₂ was poorly correlated with respiratory quotient, and its physiologic behavior was different. Thus, it might be a misleading surrogate for anaerobic metabolism.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-017-0136-3) contains supplementary material, which is available to authorized users.

Haemodynamic coherence - The relevance of fluid therapy

The ultimate goal of fluid therapy is to improve the oxygenation of cells by improving the cardiac output, thus improving microcirculation by optimizing macrocirculation. This haemodynamic coherence is often altered in patients with haemorrhagic shock and sepsis. The loss of haemodynamic coherence is associated with adverse outcomes. It may be influenced by the mechanisms of the underlying disease and properties of different fluids used for resuscitation in these critically ill patients. Monitoring microcirculation and haemodynamic coherence may be an additional tool to predict the response to fluid administration. In addition, microcirculatory analysis may support the clinician in his decision to not administer fluids when microcirculatory blood flow is preserved. In future, the indication, guidance and termination of fluid therapy may be assessed by bedside microvascular analysis in combination with standard haemodynamic monitoring.

Lactate levels and hemodynamic coherence in acute circulatory failure

In this review, the relationship between changes in macrohemodynamics during the development and treatment of acute circulatory failure is discussed in the context of coherence with microcirculation and changes in lactate. In models of circulatory failure, coherence between changes in macrocirculatory and microcirculatory perfusion and coherence with subsequent changes in lactate levels are more or less preserved. However, in patients, particularly those with septic shock, these relationships are much less clear. As many factors influence the effect of circulatory failure and infection on microcirculation and on lactate levels, this should not be surprising. Resuscitation should therefore aim at adequate tissue perfusion where systemic hemodynamics, microcirculatory perfusion parameters, and lactate levels should be used in their relevant context. This results in treating the individual patient as an n = 1 experiment.

Microcirculatory alterations during haemorrhagic shock and after resuscitation in a paediatric animal model

BACKGROUND

Haemorrhagic shock is frequent in paediatric trauma patients and after cardiac surgery, especially after cardiopulmonary bypass. It has demonstrated to be related to bad outcome.

OBJECTIVES

To evaluate changes on microcirculatory parameters during haemorrhagic shock and resuscitation in a paediatric animal model. To determine correlation between microcirculatory parameters and other variables routinely used in the monitoring of haemorrhagic shock.

METHODS

Experimental study on 17 Maryland pigs. Thirty minutes after haemorrhagic shock induction by controlled bleed animals were randomly assigned to three treatment groups receiving 0.9% normal saline, 5% albumin with 3% hypertonic saline, or 5% albumin with 3% hypertonic saline plus a bolus of terlipressin. Changes on microcirculation (perfused vessel density (PVD), microvascular blood flow (MFI) and heterogeneity index (HI)) were evaluated and compared with changes on macrocirculation and tisular perfusion parameters.

RESULTS

Shock altered microcirculation: PVD decreased from 13.5 to 12.3 mm mm(-2) (p=0.05), MFI decreased from 2.7 to 1.9 (p<0.001) and HI increased from 0.2 to 0.5 (p<0.001). After treatment, microcirculatory parameters returned to baseline (PVD 13.6 mm mm(-2) (p<0.05), MFI 2.6 (p<0.001) and HI 0.3 (p<0.05)). Microcirculatory parameters showed moderate correlation with other parameters of tissue perfusion. There were no differences between treatments.

CONCLUSIONS

Haemorrhagic shock causes important microcirculatory alterations, which are reversed after treatment. Microcirculation should be assessed during haemorrhagic shock providing additional information to guide resuscitation.

Microcirculatory and mitochondrial hypoxia in sepsis, shock, and resuscitation

After shock, persistent oxygen extraction deficit despite the apparent adequate recovery of systemic hemodynamic and oxygen-derived variables has been a source of uncertainty and controversy. Dysfunction of oxygen transport pathways during intensive care underlies the sequelae that lead to organ failure, and the limitations of techniques used to measure tissue oxygenation in vivo have contributed to the lack of progress in this area. Novel techniques have provided detailed quantitative insight into the determinants of microcirculatory and mitochondrial oxygenation. These techniques, which are based on the oxygen-dependent quenching of phosphorescence or delayed luminescence are briefly reviewed. The application of these techniques to animal models of shock and resuscitation revealed the heterogeneous nature of oxygen distributions and the alterations in oxygen distribution in the microcirculation and in mitochondria. These studies identified functional shunting in the microcirculation as an underlying cause of oxygen extraction deficit observed in states of shock and resuscitation. The translation of these concepts to the bedside has been enabled by our development and clinical introduction of hand-held microscopy. This tool facilitates the direct observation of the microcirculation and its alterations at the bedside under the conditions of shock and resuscitation. Studies identified loss of coherence between the macrocirculation and the microcirculation, in which resuscitation successfully restored systemic circulation but did not alleviate microcirculatory perfusion alterations. Various mechanisms responsible for these alterations underlie the loss of hemodynamic coherence during unsuccessful resuscitation procedures. Therapeutic resolution of persistent heterogeneous microcirculatory alterations is expected to improve outcomes in critically ill patients.

Hemodynamic coherence and the rationale for monitoring the microcirculation

This article presents a personal viewpoint of the shortcoming of conventional hemodynamic resuscitation procedures in achieving organ perfusion and tissue oxygenation following conditions of shock and cardiovascular compromise, and why it is important to monitor the microcirculation in such conditions. The article emphasizes that if resuscitation procedures are based on the correction of systemic variables, there must be coherence between the macrocirculation and microcirculation if systemic hemodynamic-driven resuscitation procedures are to be effective in correcting organ perfusion and oxygenation. However, in conditions of inflammation and infection, which often accompany states of shock, vascular regulation and compensatory mechanisms needed to sustain hemodynamic coherence are lost, and the regional circulation and microcirculation remain in shock. We identify four types of microcirculatory alterations underlying the loss of hemodynamic coherence: type 1, heterogeneous microcirculatory flow; type 2, reduced capillary density induced by hemodilution and anemia; type 3, microcirculatory flow reduction caused by vasoconstriction or tamponade; and type 4, tissue edema. These microcirculatory alterations can be observed at the bedside using direct visualization of the sublingual microcirculation with hand-held vital microscopes. Each of these alterations results in oxygen delivery limitation to the tissue cells despite the presence of normalized systemic hemodynamic variables. Based on these concepts, we propose how to optimize the volume of fluid to maximize the oxygen-carrying capacity of the microcirculation to transport oxygen to the tissues.

Remote ischemic preconditioning mitigates myocardial and neurological dysfunction via K(ATP) channel activation in a rat model of hemorrhagic shock

Severe hemorrhagic shock and resuscitation is a state of global body ischemia and reperfusion that causes myocardial and cerebral dysfunction. We investigated whether remote ischemic preconditioning (RIPC) would reduce myocardial and cerebral ischemia and reperfusion injuries after hemorrhagic shock as the result of the K(ATP) channel activation. Twenty-one male rats were randomized into three groups: RIPC, RIPC with K(ATP) channel blocker, and control. Remote ischemic preconditioning was induced by four cycles of 5 min of limb ischemia followed by reperfusion for 5 min. Hemorrhagic shock was induced by removing 50% of the estimated total blood volume during an interval of 1 h. Thirty minutes after the completion of bleeding, the animals were reinfused with shed blood during the ensuing 30 min. The animals were monitored for 2 h and observed for an additional 72 h. Myocardial function was measured by echocardiography, and sublingual microcirculation was measured by a sidestream dark-field imaging device at baseline, 1 h after bleeding, 30 min after the completion of bleeding, 30 min after reinfusion, and hourly intervals thereafter. The survival and neurological function were evaluated at 12, 24, 48, and 72 h after reinfusion. At 2 h after reinfusion, ejection fraction and myocardial performance index were significantly better in the RIPC group than in the control group (P < 0.01). The sublingual microvascular flow index and perfused vessel density were significantly greater after reinfusion in the RIPC group than that in the control group (P < 0.01). The duration of survival was significantly longer, and neurological deficit score was significantly better in the RIPC group than the control animals (P < 0.01). Pretreatment with the K(ATP) channel blocker (glibenclamide) completely abolished the myocardial and cerebral protective effects of RIPC. We demonstrate, for the first time, that after severe hemorrhagic shock and resuscitation, RIPC mitigated myocardial and neurological dysfunction with improved survival by activation of the K(ATP) channel.

Oxygenation measurement by multi-wavelength oxygen-dependent phosphorescence and delayed fluorescence: catchment depth and application in intact heart

Oxygen delivery and metabolism represent key factors for organ function in health and disease. We describe the optical key characteristics of a technique to comprehensively measure oxygen tension (PO(2)) in myocardium, using oxygen-dependent quenching of phosphorescence and delayed fluorescence of porphyrins, by means of Monte Carlo simulations and ex vivo experiments. Oxyphor G2 (microvascular PO(2)) was excited at 442 nm and 632 nm and protoporphyrin IX (mitochondrial PO(2)) at 510 nm. This resulted in catchment depths of 161 (86) µm, 350 (307) µm and 262 (255) µm respectively, as estimated by Monte Carlo simulations and ex vivo experiments (brackets). The feasibility to detect changes in oxygenation within separate anatomical compartments is demonstrated in rat heart in vivo. Schematic of ex vivo measurements.

Microvascular perfusion as a target for fluid resuscitation in experimental circulatory shock

OBJECTIVES

To study regional perfusion during experimental endotoxemic and obstructive shock and compare the effect of initial cardiac output-targeted fluid resuscitation with optimal cardiac output-targeted resuscitation on different peripheral tissues.

DESIGN

Controlled experimental study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Fourteen fasted anesthetized mechanically ventilated domestic pigs.

INTERVENTIONS

Domestic pigs were randomly assigned to the endotoxemic (n = 7) or obstructive shock (n = 7) model. Central and regional perfusion parameters were obtained at baseline, during greater than or equal to 50% reduction of cardiac output (T1), after initial resuscitation to baseline (T2), and after optimization of cardiac output (T3).

MEASUREMENTS AND MAIN RESULTS

Regional perfusion was assessed in the sublingual, intestinal, and muscle vascular beds at the different time points and included visualization of the microcirculation, measurement of tissue oxygenation, and indirect assessments of peripheral skin perfusion. Hypodynamic shock (T1) simultaneously decreased all regional perfusion variables in both models. In the obstructive model, these variables returned to baseline levels at T2 and remained in this range after T3, similar to cardiac output. In the endotoxemic model, however, the different regional perfusion variables were only normalized at T3 associated with the hyperdynamic state at this point. The magnitude of changes over time between the different vascular beds was similar in both models, but the endotoxemic model displayed greater heterogeneity between tissues.

CONCLUSIONS

This study demonstrates that the relationship between the systemic and regional perfusion is dependent on the underlying cause of circulatory shock. Further research will have to demonstrate whether different microvascular perfusion variables can be used as additional resuscitation endpoints.

[Erythrocytes and microvascular tone during acute traumatic haemorrhagic shock]

Haemorrhagic shock remains a leading cause of death in trauma patients. The concept of haematologic damage control is gradually taking place in the management of traumatic haemorrhagic shock. It is based primarily on the early implementation of a quality blood transfusion involving erythrocytes, plasmas and platelets transfusion. Red blood cell transfusion is mainly supported by the oxygen carrier properties of erythrocytes. However, it appears that erythrocytes ability to modulate the bioavailability of nitric oxide (NO) plays a major role in capillary opening and perfusion. Erythrocytes are also actively involved in the processes of hemostasis and coagulation. In this context, it seems difficult to define a threshold of hemoglobin concentration to determine the implementation of a blood transfusion in traumatic haemorrhagic shock.