Fluid Resuscitation Guided by Sublingual Partial Pressure of Carbon Dioxide During Hemorrhagic Shock in a Porcine Model

Real-Time Measurements of Oral Mucosal Carbon Dioxide (POMCO2) Reveals an Inverse Correlation With Blood Pressure in a Porcine Model of Coagulopathic Junctional Hemorrhage

INTRODUCTION

Shock states that occur during, for example, profound hemorrhage can cause global tissue hypoperfusion leading to organ failure. There is an unmet need for a reliable marker of tissue perfusion during hemorrhage that can be followed longitudinally. Herein, we investigated whether longitudinal POMCO2 tracks changes in hemodynamics in a swine model of coagulopathic uncontrolled junctional hemorrhage.

MATERIALS AND METHODS

Female Yorkshire-crossbreed swine (n = 7, 68.1 ± 0.7 kg) were anesthetized and instrumented for continuous measurement of mean arterial pressure (MAP). Coagulopathy was induced by the exchange of 50 to 60% of blood volume with 6% Hetastarch over 30 minutes to target a hematocrit of <15%. A 4.5-mm arteriotomy was made in the right common femoral artery with 30 seconds of free bleeding. POMCO2 was continuously measured from baseline through hemodilution, hemorrhage, and a subsequent 3-h intensive care unit period. Rotational thromboelastometry and blood gases were measured.

RESULTS

POMCO2 and MAP showed no significant changes during the hemodilution phase of the experiment, which produced coagulopathy evidenced by prolonged clot formation times. However, POMCO2 increased because of the uncontrolled hemorrhage by 11.3 ± 3.1 mmHg and was inversely correlated with the drop (17.9 ± 5.9 mmHg) in MAP (Y = -0.4122*X + 2.649, P = .02, r2 = 0.686). In contrast, lactate did not significantly correlate with the changes in MAP (P = .35) or POMCO2 (P = .37).

CONCLUSIONS

Despite the logical appeal of measuring noninvasive tissue CO2 measurement as a surrogate for gastrointestinal perfusion, prior studies have only reported snapshots of this readout. The present investigation shows real-time longitudinal measurement of POMCO2 to confirm that MAP inversely correlates to POMCO2 in the face of coagulopathy. The simplicity of measuring POMCO2 in real time can provide an additional practical option for military or civilian medics to monitor trends in hypoperfusion during hemorrhagic shock.

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

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

Establishment of a swine model of traumatic cardiac arrest induced by haemorrhage and ventricular fibrillation

OBJECTIVE

To establish and evaluate a swine model of traumatic cardiac arrest (TCA) induced by haemorrhage and ventricular fibrillation.

METHODS

Thirteen male pigs were divided into a sham group (n = 5) and TCA group (n = 8). Animals in the sham-operated group underwent intubation and monitoring but not haemorrhage and resuscitation, while animals in the TCA group underwent 40% blood volume haemorrhage over 20 min followed by 5 min of ventricular fibrillation and 5 min of cardiopulmonary resuscitation with fluid resuscitation.

RESULTS

Restoration of spontaneous circulation was achieved in seven of eight animals in the TCA group. After resuscitation, the heart rate was significantly increased while the mean arterial pressure and ejection fraction were significantly decreased in the TCA group. The TCA group had significant cardiac and neurological injuries post-resuscitation and had higher serum creatinine and blood lactic acid levels and lower PaO₂ than the sham group. Animals in the TCA group also exhibited significantly higher apoptotic indices and caspase-3 protein levels in the heart, brain and kidney than the sham group.

CONCLUSION

Animals in this swine model of TCA exhibited high rates of successful resuscitation, significant vital organ injury and prolonged survival. The model is suitable for use in further TCA research.

Imaging of the Intestinal Microcirculation during Acute and Chronic Inflammation

Because of its unique microvascular anatomy, the intestine is particularly vulnerable to microcirculatory disturbances. During inflammation, pathological changes in blood flow, vessel integrity and capillary density result in impaired tissue oxygenation. In severe cases, these changes can progress to multiorgan failure and possibly death. Microcirculation may be evaluated in superficial tissues in patients using video microscopy devices, but these techniques do not allow the assessment of intestinal microcirculation. The gold standard for the experimental evaluation of intestinal microcirculation is intravital microscopy, a technique that allows for the in vivo examination of many pathophysiological processes including leukocyte-endothelial interactions and capillary blood flow. This review provides an overview of changes in the intestinal microcirculation in various acute and chronic inflammatory conditions. Acute conditions discussed include local infections, severe acute pancreatitis, necrotizing enterocolitis and sepsis. Inflammatory bowel disease and irritable bowel syndrome are included as examples of chronic conditions of the intestine.

The Effects of the Duration of Aortic Balloon Occlusion on Outcomes of Traumatic Cardiac Arrest in a Porcine Model

Aortic balloon occlusion (ABO) facilitates the success of cardiopulmonary resuscitation (CPR) in non-traumatic cardiac arrest, and is also effective in controlling traumatic hemorrhage; however, a prolonged occlusion results in irreversible organ injury and death. In this study, we investigated the effects of ABO on CPR outcomes and its optimal duration for post-resuscitation organ protection in a porcine model of traumatic cardiac arrest (TCA).Twenty-seven male domestic pigs weighing 33 ± 4 kg were utilized. Forty percent of estimated blood volume was removed within 20 min. The animals were then subjected to 5 min of untreated ventricular fibrillation and 5 min of CPR. Coincident with the start of CPR, the animals were randomized to receive either 30-min ABO (n = 7), 60-min ABO (n = 8) or control (n = 12). Meanwhile, fluid resuscitation was initiated by the infusion of normal saline with 1.5 times of hemorrhage volume in 1 h, and finished by the reinfusion of 50% of the shed blood in another 1 h. The resuscitated animals were monitored for 6 h and observed for an additional 18 h.During CPR, coronary perfusion pressure was significantly increased followed by a higher rate of resuscitation success in the 30 and 60-min ABO groups compared with the control group. However, post-resuscitation cardiac, neurologic dysfunction, and injuries were significantly milder accompanied with less renal and intestinal injuries in the 30-min ABO group than in the other two groups.In conclusion, ABO augmented the efficacy of CPR after TCA, and furthermore a 30-min ABO improved post-resuscitation cardiac and neurologic outcomes without exacerbating the injuries of kidney and intestine.

Efficacy of a Temporary Hemostatic Device in a Swine Model of Closed, Lethal Liver Injury

INTRODUCTION

Solid abdominal organ hemorrhage remains one of the leading causes of death both on the battlefield of modern warfare and in the civilian setting. A novel, temporary hemostatic device combining CELOX and direct intra-abdominal physical compression was invented to control closed SAOH during transport to a medical treatment facility.

MATERIALS AND METHODS

A swine model of closed, lethal liver injury was established to determine hemostasis. The animals were randomly divided into group A (extra-abdominal compression), group B (gauze packing), group C (intra-abdominal compression), group D (CELOX coverage), and group E (intra-abdominal compression and CELOX coverage) with six swines per group. Survival time (ST), blood loss (BL), vital signs, pathologic examination, and CT-scan were monitored to further observe the effectiveness of the device.

RESULTS

Group E had an average 30-minute extension in ST (74.3 ± 15.4 minutes versus 44.0 ± 13.8 minutes, p = 0.026) with less BL (46.0 ± 13.0 versus 70.8 ± 8.2 g/kg, p = 0.018), and maintained mean arterial pressure≥70 mmHg and cardiac output ≥ 3.5 L/minute for a longer time. No significant differences were observed in ST and BL of groups B and E, and there were no marked differences in ST and BL of groups A, C, and D. No CELOX clots were noted in the spleen, pancreas, lungs, heart, kidneys, or the adjacent large vessels in groups D and E. Compared to group A, the CT-scan showed better hepatic hemorrhage control in group E.

CONCLUSIONS

The device, which combined 20 g of CELOX particles and 20 pieces of CELOX (8 g) sponge tablets with 50-mmHg intra-abdominal compression for 10 minutes, prolonged the ST by an average of 30 minutes with less BL. It was not markedly different from the full four quadrants gauze packing of liver in hemostatic effect, with no CELOX clot formation in other organs.

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.

Resuscitation incoherence and dynamic circulation-perfusion coupling in circulatory shock

OBJECTIVE

Poor tissue perfusion/cellular hypoxia may persist despite restoration of the macrocirculation (Macro). This article reviewed the literatures of coherence between hemodynamics and tissue perfusion in circulatory shock.

DATA SOURCES

We retrieved information from the PubMed database up to January 2018 using various search terms or/and their combinations, including resuscitation, circulatory shock, septic shock, tissue perfusion, hemodynamic coherence, and microcirculation (Micro).

STUDY SELECTION

The data from peer-reviewed journals printed in English on the relationships of tissue perfusion, shock, and resuscitation were included.

RESULTS

A binary (coherence/incoherence, coupled/uncoupled, or associated/disassociated) mode is used to describe resuscitation coherence. The phenomenon of resuscitation incoherence (RI) has gained great attention. However, the RI concept requires a more practical, systematic, and comprehensive framework for use in clinical practice. Moreover, we introduce a conceptual framework of RI to evaluate the interrelationship of the Macro, Micro, and cell. The RI is divided into four types (Type 1: Macro-Micro incoherence + impaired cell; Type 2: Macro-Micro incoherence + normal cell; Type 3: Micro-Cell incoherence + normal Micro; and Type 4: both Macro-Micro and Micro-cell incoherence). Furthermore, we propose the concept of dynamic circulation-perfusion coupling to evaluate the relationship of circulation and tissue perfusion during circulatory shock.

CONCLUSIONS

The concept of RI and dynamic circulation-perfusion coupling should be considered in the management of circulatory shock. Moreover, these concepts require further studies in clinical practice.

Differences in capillary recruitment between cardiac surgery and septic patients after fluid resuscitation

BACKGROUND

Clinical evaluation of the effects of fluid therapy remains cumbersome and strategies are based on the assumption that normalization of macrohemodynamic variables will result in parallel improvement in organ perfusion. Recently, we and others suggested the use of direct in-vivo observation of the microcirculation to evaluate the effects of fluid therapy.

METHODS

A single-centre observational study, using in-vivo microscopy to assess total vessel density (TVD) in two subsets of ICU patients.

RESULTS

After fluid resuscitation TVD showed no difference between sepsis patients (N = 47) and cardiac surgery patients (N = 52): 18.4[16.8-20.8] vs 18.7[16.8-20.9] mm/mm², p = 0.59. In cardiac surgery patients there was a significant correlation between the amount of fluids administered and TVD, with an optimum in the third quartile. However, such correlation was absent in septic patients.

CONCLUSIONS

TVD after fluid administration is not different between 2 subtypes of intensive care patients. However, only in septic patients we observed a lack of coherence between the amount of fluids administered and TVD. Further research is needed to determine if TVD may serve as potential endpoint for fluid administration.

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 Cytocam video microscope. A new method for visualising the microcirculation using Incident Dark Field technology

We report a new microcirculatory assessment device, the Braedius Cytocam, an Incident Dark Field (IDF) video microscope, and compare it with a precursor device utilising side stream dark field (SDF) imaging.

METHODS

Time matched measurements were made with both devices from the sublingual microcirculation of pigs subjected to traumatic injury and hemorrhagic shock at baseline and during a shock phase. Images were analysed for vessel density, microcirculatory flow and image quality.

RESULTS

There were no differences in density or flow data recorded from the two devices at baseline [TVD IDF 14.2 ± 2.4/TVD SDF 13.2 ± 2.0, p 0.17] [MFI IDF 3 (2.8-3.0)/MFI SDF 3 (2.9-3.0), p 0.36] or during the shock state [TVD IDF 11.64 ± 3.3/TVD SDF 11.4 ± 4.0 p = 0.98] [MFI IDF 1.9 (0.6-2.7)/MFI SDF 1.7 (0.3-2.6) p 0.55]. Bland and Altman analysis showed no evidence of significant bias. Vessel contrast was significantly better with the IDF device for both capillaries [17.1 ± 3.9 (IDF) v 3.4 ± 3.6 (SDF), p = 0.0006] and venules [36.1 ± 11.4 (IDF) v 26.4 ± 7.1 (SDF) p 0.014]

CONCLUSION

The Braedius Cytocam showed comparable vessel detection to a precursor device during both baseline and low flow (shock) states.

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.

Microcirculatory perfusion shows wide inter-individual variation and is important in determining shock reversal during resuscitation in a porcine experimental model of complex traumatic hemorrhagic shock

Background

Traumatic hemorrhagic shock (THS) is a leading cause of preventable death following severe traumatic injury. Resuscitation of THS is typically targeted at blood pressure, but the effects of such a strategy on systemic and microcirculatory flow remains unclear. Failure to restore microcirculatory perfusion has been shown to lead to poor outcomes in experimental and clinical studies. Systemic and microcirculatory variables were examined in a porcine model of complex THS, in order to investigate inter-individual variations in flow and the effect of microcirculatory perfusion on reversal of the shock state.

Methods

Baseline standard microcirculatory variables were obtained for 22 large white pigs using sublingual incident dark field (IDF) video-microscopy. All animals were subjected to a standardised hind-limb injury followed by a controlled haemorrhage of approximately 35 % of blood volume (shock phase). This was followed by 60 min of fluid resuscitation with either 0.9 % saline or component blood products and a target SBP of 80 mmHg (early resuscitation phase). All animals were then given blood products to a target SBP of 110 mmHg for 120 min (mid-resuscitation phase), and a further 100 min (late resuscitation phase). IDF readings were obtained at the midpoint of each of these phases. Cardiac output was measured using a pulmonary artery catheter. Animals were divided into above average (A) and below average (B) perfused vessel density (PVD) groups based on the lowest recorded PVD measurement taken during the shock and early resuscitation phases.

Results

There was minimal inter-individual variation in blood pressure but wide variation of both systemic and microcirculatory flow variables during resuscitation. During shock and early resuscitation, group A (n = 10) had a mean PVD of 10.5 (SD ± 2.5) mm/mm² and group B (n = 12) 5.5 (SD ± 4.1) mm/mm². During the later resuscitation phases, group A maintained a significantly higher PVD than group B. Group A initially had a higher cardiac output, but the difference between the groups narrowed as resuscitation progressed. At the end of resuscitation, group A had significantly lower plasma lactate, higher lactate clearance, lower standard base deficit and smaller mixed venous-arterial CO₂ gradient. There was no significant difference in blood pressure between the two groups at any stage.

Conclusion

There was a wide variation in both macro- and microcirculatory flow variables in this pressure-targeted experimental model of THS resuscitation. Early changes in microvascular perfusion appear to be key determinants in the reversal of the shock state during resuscitation. Microcirculatory flow parameters may be more reliable markers of physiological insult than pressure-based parameters and are potential targets for goal-directed resuscitation.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-016-0088-z) contains supplementary material, which is available to authorized users.

Recent Advances of Mucosal Capnometry and the Perspectives of Gastrointestinal Monitoring in the Critically Ill. A Pilot Study

Mucosal capnometry involves the monitoring of partial pressure of carbon dioxide (PCO2) in mucous membranes. Different techniques have been developed and applied for this purpose, including sublingual or buccal sensors, or special gastrointestinal tonometric devices. The primary use of these procedures is to detect compensated shock in critically ill patients or patients undergoing major surgery. Compensatory mechanisms, in the early phases of shock, lead to the redistribution of blood flow towards the vital organs, within ostensibly typical macro-haemodynamic parameters. Unfortunately, this may result in microcirculatory disturbances, which can play a pivotal role in the development of organ failure. In such circumstances mucosal capnometry monitoring, at different gastrointestinal sites, can provide a sensitive method for the early diagnosis of shock. The special PCO2 monitoring methods assess the severity of ischaemia and help to define the necessary therapeutic interventions and testing of these monitors have justified their prognostic value. Gastrointestinal mucosal capnometry monitoring also helps in determining the severity of ischaemia and is a useful adjunctive in the diagnosis of occlusive splanchnic arterial diseases. The supplementary functional information increases the diagnostic accuracy of radiological techniques, assists in creating individualized treatment plans, and helps in follow-up the results of interventions. The results of a pilot study focusing on the interrelation of splanchnic perfusion and gastrointestinal function are given and discussed concerning recent advances in mucosal capnometry.

To use or not to use hydroxyethyl starch in intraoperative care: are we ready to answer the 'Gretchen question'?

PURPOSE OF REVIEW

The decision of the European Medicines Agency (EMA) against the use of hydroxyethyl starch (HES)-based volume replacement solutions in critically ill patients has led to a general uncertainty when dealing with HES-based solutions, even though HES-containing solutions can still be used for the treatment of hypovolaemia caused by acute (sudden) blood loss. This review discusses current evidence of the intraoperative use of HES-based solutions.

RECENT FINDINGS

HES solutions are often criticized for possible side-effects on the kidney, the coagulation system or tissue storage. Relevant differences exist between modern 6% HES 130/0.4 and older generation of starches. Because of pathophysiological differences between elective surgery and critical illness, the evidence on renal injury and coagulation impairment with HES administration cannot be generalized. Current data suggest that there is no clinically relevant impact of 6% HES 130/0.4 administration on perioperative renal function and coagulation. Over-resuscitation is a frequent problem associated with adverse outcomes. Due to the higher volume effect, fluid overload with HES is probably more harmful than with crystalloids, whereas goal-directed use of HES may be able to reduce intraoperative fluid accumulation and overload.

SUMMARY

The use of 6% HES 130/0.4 in elective surgery patients is associated with reduced fluid accumulation and no clinically relevant difference in bleeding or the rate of acute kidney injury as compared with crystalloid use alone. Current data do not allow a conclusion on mortality. As they provide no benefit, older starch preparations should not be used.

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.

Monitoring Microcirculatory Blood Flow with a New Sublingual Tonometer in a Porcine Model of Hemorrhagic Shock

Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60-180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = -0.65, p < 0.0001), CPR (r = -0.64, p < 0.0001), central venous oxygen saturation (r = -0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.

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.

Clinical classification of tissue perfusion based on the central venous oxygen saturation and the peripheral perfusion index

Introduction

We investigated whether combining the peripheral perfusion index (PI) and central venous oxygen saturation(ScvO₂) would identify subsets of patients for assessing the tissue perfusion and predicting outcome during the resuscitation in critically ill patients.

Methods

A total of 202 patients with central venous catheters for resuscitation were enrolled in this prospective observational study. The arterial, central venous blood gas and the PI were measured simultaneously at the enrollment (T0) and 8 h (T8) after early resuscitation. Based on the distribution of the PI in healthy population, a cutoff of PI ≥1.4 was defined as a normal PI. Moreover, the critical value of PI was defined as the best cutoff value related to the mortality in the study population. The PI impairment stratification is defined as follows: a normal PI(≥1.4), mild PI impairment (critical value < PI < 1.4) and critical PI impairment (PI ≤ critical value).

Results

The PI at T8 was with the greatest AUC for prediction the 30-day mortality and PI is an independent risk factor for 30-day mortality. Moreover, a cutoff of PI < 0.6 is related to poor outcomes following resuscitation. So, based on cutoffs of ScvO₂ (70 %) and critical PI (0.6) at T8, we assigned the patients to four categories: group 1 (PI ≤ 0.6 on ScvO₂ < 70 %), group 2 (PI ≤ 0.6 on ScvO₂ ≥ 70 %), group 3 (PI > 0.6 on ScvO₂ < 70 %), and group 4 (PI > 0.6 on ScvO₂ ≥ 70 %). The combination of low ScvO₂(<70 %) and PI(≤0.6) was associated with the lowest survival rates at 30 days [log rank (Mantel–Cox) = 87.518, p < 0.0001]. The sub-group patients who had high ScvO₂(>80 %) at T8 were with low mortality and high PI. Moreover, the normal PI (≥1.4) did not show a better outcome than mild impaired PI (0.6-1.4) patients who had a normalized ScvO₂(>70 %) after resuscitation. The PI was correlated with the lactate, P(v-a)CO₂, and ScvO₂ in all the measurements (n = 404). These relationships are strengthened with abnormal PI (PI < 1.4) but not with normal PI (PI ≥ 1.4).

Conclusion

Complementing ScvO₂ assessment with PI can better identify endpoints of resuscitation and adverse outcomes. Pursuing a normalized PI (≥1.4) may not result in better outcomes for a mild impaired PI after ScvO₂ is normalized.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1057-8) contains supplementary material, which is available to authorized users.

Investigation of noninvasive muscle pH and oxygen saturation during uncontrolled hemorrhage and resuscitation in swine

This study evaluated noninvasively determined muscle pH (pHm) and muscle oxygen saturation (SmO2) in a swine shock model that used uncontrolled hemorrhage and restricted volume resuscitation. Anesthetized 40-kg female swine underwent hemorrhage until 24 mL/kg of blood was removed (n = 26), followed by transection of the spleen, causing uncontrolled hemorrhage throughout the remainder of the protocol. After 15 min, 15 mL/kg of resuscitation fluid (Hextend, fresh-frozen plasma or platelets) was given for 30 min. Arterial and venous blood gases were measured at baseline, shock, end of resuscitation, and end of the study (death or 5 h), along with lactate and base excess. In addition, seven animals underwent a sham procedure. Spectra were collected continuously from the posterior thigh using a prototype CareGuide 1100 Oximeter, and pHm and SmO2 were calculated from the spectra. A two-factor analysis of variance with repeated measures followed by Tukey post hoc comparisons was used to compare experimental factors. It was shown that, for both pH and SO2, venous and muscle values were similar to each other at the end of the resuscitation period and at the end of the study for both surviving and nonsurviving animals. pH and SO2, venous and muscle, significantly declined as a result of bleeding, but lactate and base excess did not show significant changes during this period. Noninvasive pHm and SmO2 tracked the adequacy of resuscitation in real time, indicating at the time all of the fluid was delivered, which animals would live and which would die. The results of this swine study indicate that further evaluation on trauma patients is warranted.

Evolution of fluid therapy

The human organism consists of evolutionary conserved mechanisms to prevent death from hypovolaemia. Intravenous fluid therapy to support these mechanisms had first been published about 180 years ago. The present review depicts the evolution of fluid therapy from early, not well-defined solutions up to modern balanced fluids. Notably, evidence accumulates that the most commonly used fluid (i.e. 0.9% saline) has no advantage over balanced solutions, increases the risk of acute kidney injury and should therefore be abandoned. Notably, in published trials, the prognostically important 'golden hours' of shock, where fluid therapy may be essential, have not been adequately addressed. It is therefore unclear whether negative data on colloids in some trials reflect real harm or rather inadequate use. Future studies should focus on optimal protocols for initiation, dosing and discontinuation of fluid therapy in specific disease entities. Moreover, the practice of de-resuscitation after fluid-based haemodynamic stabilization should be further investigated.

The case for 0.9% NaCl: is the undefendable, defensible?

Although 0.9% NaCl solution is by far the most-used fluid for fluid therapy in resuscitation, it is difficult to find a paper advocating its use over other types of crystalloid solutions. Literature on the deleterious effects of 0.9% NaCl has accumulated over the last decade, but critical appraisal of alternative crystalloid solutions is lacking. As such, the literature seems to suggest that 0.9% NaCl should be avoided at all costs, whereas alternative crystalloid solutions can be used without scrutiny. The basis of this negative evaluation of 0.9% NaCl is almost exclusively its effect on acid-base homeostasis, whereas the potentially deleterious effects present in other types of crystalloids are neglected. We have the challenging task of defending the use of 0.9% NaCl and reviewing its positive attributes, while an accompanying paper will argue against the use of 0.9% NaCl. It is challenging because of the large amount of literature, including our own, showing adverse effects of 0.9% NaCl. We will discuss why 0.9% NaCl solution is the most frequently used resuscitation fluid. Although it has some deleterious effects, all fluids share common features of concern. As such the emphasis on fluid resuscitation should be on volume rather than on composition and should be accompanied by a physiological assessment of the impact of fluids. In this paper, we hope to discuss the context within which fluids, specifically 0.9% NaCl, can be given in a safe and effective manner.

New insights into the pathophysiology of cardiogenic shock: the role of the microcirculation

PURPOSE OF REVIEW

The ultimate goal of therapy for cardiogenic shock is to restore microcirculatory function and thereby restore the oxygen supply to sustain cellular function. Therapeutic measures mainly focus on improving pressure-derived macrocirculatory parameters. However, it is increasingly clear that to achieve significant progress in treatment, microcirculatory physiopathological mechanisms must be considered.

RECENT FINDINGS

Microcirculatory function deteriorated during cardiogenic shock and improved after treatment. Postcardiogenic shock microcirculatory disturbances, both myocardial and peripheral, were a prognostic factor for the long-term outcome. Hypothermia, whether pharmacologically or physically induced, improved postresuscitation myocardial and cerebral function, an effect associated with improved postresuscitation microcirculation. The impact of cardiogenic shock on cerebral and myocardial microcirculation could be evaluated with MRI. In severe heart failure, pharmacological interventions improved microcirculation. An assessment of the microcirculation was often performed using handheld video microscopy for direct observation of the sublingual microcirculation, which proved to be useful for evaluating the effects of interventions during cardiogenic shock. A large multicenter study on critically ill patients is now being conducted using this technique.

SUMMARY

Cardiogenic shock induces microcirculatory disorders that can be monitored and influenced in various manners, both pharmacologically and physically. In addition to global hemodynamic optimization, interventions must also ameliorate the microcirculation.