Evaluation of sublingual and gut mucosal microcirculation in sepsis: a quantitative analysis. Crit Care Med. 2009;37:2875-2881. [PMID: 19770750 DOI: 10.1097/ccm.0b013e3181b029c1]

Changes in the sublingual microcirculation during major abdominal surgery and post-operative morbidity

BACKGROUND

Little is known about perioperative microcirculatory changes during major abdominal surgery, and the main objectives of this study were to evaluate perioperative microcirculatory alterations in this setting, and if changes in microcirculatory parameters are associated with post-operative morbidity and/or with changes in parameters reflecting oxygen delivery.

METHODS

Patients scheduled for major abdominal surgery with an estimated Portsmouth Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (P-POSSUM) score of > 30 and operation time > 3 h were eligible for inclusion. Perioperative microcirculatory alterations were evaluated in the sublingual mucosa using Sidestream Dark Field (SDF) imaging. Perfused vessel density (PVD), vessel perfusion [microvascular flow index (MFI)], and flow heterogeneity [heterogeneity index (HI)] were analysed. Central venous oxygen saturation (ScvO2) and lactate were measured simultaneously. During a 30-day follow-up period, post-operative complications were registered according to predefined criteria.

RESULTS

Forty-two patients with a median P-POSSUM of 33 were included in the study. MFI was higher during anaesthesia than pre- and post-anaesthesia. PVD and HI did not change during the observation period. Lactate and ScvO2 increased during surgery. Perioperative lactate and ScvO2 values were not correlated with microcirculatory parameters. Complications occurred in 16 patients. No differences in microcirculatory parameters were detected between patients with and without complications.

CONCLUSIONS

Perioperative changes in the sublingual microcirculatory parameters measured with the SDF-imaging technique appear to be minor, and no association with outcome after major abdominal surgery could be demonstrated. Changes in ScvO2 and serum lactate do not reflect sublingual microcirculatory alterations in this setting.

Fluid management in the critically ill child

Fluid management has a major impact on the duration, severity and outcome of critical illness. The overall strategy for the acutely ill child should be biphasic. Aggressive volume expansion to support tissue oxygen delivery as part of early goal-directed resuscitation algorithms for shock--especially septic shock--has been associated with dramatic improvements in outcome. Recent data suggest that the cost-benefit of aggressive fluid resuscitation may be more complex than previously thought, and may depend on case-mix and the availability of intensive care. After the resuscitation phase, critically ill children tend to retain free water while having reduced insensible losses. Fluid regimens that limit or avoid positive fluid balance are associated with a reduced length of hospital stay and fewer complications. Identifying the point at which patients change from the 'early shock' pattern to the later 'chronic critical illness' pattern remains a major challenge. Very little data are available on the choice of fluids, and most of the information that is available arises from studies of critically ill adults. There is therefore an urgent need for high-quality trials of both resuscitation and maintenance fluid regimens in critically ill children.

Hypothermia improves oral and gastric mucosal microvascular oxygenation during hemorrhagic shock in dogs

Hypothermia is known to improve tissue function in different organs during physiological and pathological conditions. The aim of this study was to evaluate the effects of hypothermia on oral and gastric mucosal microvascular oxygenation (μHbO₂) and perfusion (μflow) under physiological and hemorrhagic conditions. Five dogs were repeatedly anesthetized. All animals underwent each experimental protocol (randomized cross-over design): hypothermia (34°C), hypothermia during hemorrhage, normothermia, and normothermia during hemorrhage. Microcirculatory and hemodynamic variables were recorded. Systemic (DO₂) and oral mucosal (μDO₂) oxygen delivery were calculated. Hypothermia increased oral μHbO₂ with no effect on gastric μHbO₂. Hemorrhage reduced oral and gastric μHbO₂ during normothermia (−36 ± 4% and −27 ± 7%); however, this effect was attenuated during additional hypothermia (−15 ± 5% and −11 ± 5%). The improved μHbO₂ might be based on an attenuated reduction in μflow during hemorrhage and additional hypothermia (−51 ± 21 aU) compared to hemorrhage and normothermia (−106 ± 19 aU). μDO₂ was accordingly attenuated under hypothermia during hemorrhage whereas DO₂ did not change. Thus, in this study hypothermia alone improves oral μHbO₂ and attenuates the effects of hemorrhage on oral and gastric μHbO₂. This effect seems to be mediated by an increased μDO₂ on the basis of increased μflow.

Sublingual microcirculation in patients with intra-abdominal hypertension: a pilot study in 15 critically ill patients

PURPOSE

The purpose of the study is to clarify whether increased intra-abdominal pressure (IAP) is associated with sublingual microcirculatory alterations in intensive care patients.

METHODS

Fifteen adult, mechanically ventilated patients were included if their IAP was at least 12 mm Hg for at least 12 hours within the first 3 days after admission to the intensive care unit. Sublingual sidestream dark field (SDF) images were recorded twice a day for 7 days.

RESULTS

Median (interquartile range) IAP at inclusion was 14.5 (12.5-16.0) mm Hg. The total vascular density of small vessels at the sublingual area was 13.1 (10.6-14.3) per square millimeter at baseline; the proportion of perfused vessels, 78.9% (69.6%-86.2%); and perfused vessels density, 12.4 (10.8-13.8) per square millimeter. The calculated indices suggested relatively good blood flow in the capillaries, with a De Backer score of 9.0 (8.3-10.2) and a microvascular blood flow of 3.0 (2.9-3.0). Blood flow heterogeneity index was 0.3 (0.1-0.5) at study entry. Despite that IAP, vasopressors dose, and arterial lactate decreased significantly over time, no significant changes were observed in sublingual microvascular density or blood flow. Weak correlations of microvascular blood flow (positive) and heterogeneity index (negative) were detected with both mean arterial pressure and abdominal perfusion pressure.

CONCLUSIONS

Neither grade I or II intra-abdominal hypertension (IAP from 12 to 18 mm Hg) is associated with significant changes of sublingual microcirculation in intensive care patients. Correlation analysis indicates better microvascular blood flow at higher mean arterial pressure and abdominal perfusion pressure levels.

Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the various mechanisms that are potentially involved in their development and the implications of these alterations. Endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability are the main mechanisms involved in the development of these alterations. Microcirculatory alterations increase the diffusion distance for oxygen and, due to the heterogeneity of microcirculatory perfusion in sepsis, may promote development of areas of tissue hypoxia in close vicinity to well-oxygenated zones. The severity of microvascular alterations is associated with organ dysfunction and mortality. At this stage, therapies to specifically target the microcirculation are still being investigated.

Hypercapnia counteracts captopril-induced depression of gastric mucosal oxygenation

Hypercapnia (HC) increases systemic oxygen delivery (DO2) and gastric mucosal oxygenation. However, it activates the renin-angiotensin-aldosterone system (RAAS), which conversely reduces mesenteric perfusion. The aims of this study were to evaluate the effect of RAAS inhibition during normocapnia and HC on oral and gastric mucosal oxygenation (μHbO2) and to assess the effect of blood pressure under these circumstances. Five dogs were repeatedly anesthetized to study the effects of ACE inhibition (ACE-I; 5 mg/kg captopril, followed by 0.25 mg/kg per h) on μHbO2 (reflectance spectrophotometry) and hemodynamic variables during normocapnia (end-tidal CO2=35 mmHg) and HC (end-expiratory carbon dioxide (etCO2)=70 mmHg). In the control group, the dogs were subjected to HC alone. To exclude the effects of reduced blood pressure, in one group, blood pressure was maintained at baseline values via titrated phenylephrine (PHE) infusion during HC and additional captopril infusion. ACE-I strongly reduced gastric μHbO2 from 72±2 to 65±2% and mean arterial pressure (MAP) from 64±2 to 48±4 mmHg, while DO2 remained unchanged. This effect was counteracted in the presence of HC, which increased gastric μHbO2 from 73±3 to 79±6% and DO2 from 15±2 to 22±4 ml/kg per min during ACE-I without differences during HC alone. However, MAP decreased similar to that observed during ACE-I alone from 66±3 to 47±5 mmHg, while left ventricular contractility (dPmax) increased from 492±63 to 758±119 mmHg/s. Titrated infusion of PHE had no additional effects on μHbO2. In summary, our data suggest that RAAS inhibition reduces gastric mucosal oxygenation in healthy dogs. HC not only abolishes this effect, but also increases μHbO2, DO2, and dPmax. The increase in μHbO2 during ACE-I under HC is in accordance with our results independent of blood pressure.

Microcirculation and its relation to continuous subcutaneous glucose sensor accuracy in cardiac surgery patients in the intensive care unit

OBJECTIVE

Continuous glucose monitoring could be helpful for glucose regulation in critically ill patients; however, its accuracy is uncertain and might be influenced by microcirculation. We investigated the microcirculation and its relation to the accuracy of 2 continuous glucose monitoring devices in patients after cardiac surgery.

METHODS

The present prospective, observational study included 60 patients admitted for cardiac surgery. Two continuous glucose monitoring devices (Guardian Real-Time and FreeStyle Navigator) were placed before surgery. The relative absolute deviation between continuous glucose monitoring and the arterial reference glucose was calculated to assess the accuracy. Microcirculation was measured using the microvascular flow index, perfused vessel density, and proportion of perfused vessels using sublingual sidestream dark-field imaging, and tissue oxygenation using near-infrared spectroscopy. The associations were assessed using a linear mixed-effects model for repeated measures.

RESULTS

The median relative absolute deviation of the Navigator was 11% (interquartile range, 8%-16%) and of the Guardian was 14% (interquartile range, 11%-18%; P = .05). Tissue oxygenation significantly increased during the intensive care unit admission (maximum 91.2% [3.9] after 6 hours) and decreased thereafter, stabilizing after 20 hours. A decrease in perfused vessel density accompanied the increase in tissue oxygenation. Microcirculatory variables were not associated with sensor accuracy. A lower peripheral temperature (Navigator, b = -0.008, P = .003; Guardian, b = -0.006, P = .048), and for the Navigator, also a higher Acute Physiology and Chronic Health Evaluation IV predicted mortality (b = 0.017, P < .001) and age (b = 0.002, P = .037) were associated with decreased sensor accuracy.

CONCLUSIONS

The results of the present study have shown acceptable accuracy for both sensors in patients after cardiac surgery. The microcirculation was impaired to a limited extent compared with that in patients with sepsis and healthy controls. This impairment was not related to sensor accuracy but the peripheral temperature for both sensors and patient age and Acute Physiology and Chronic Health Evaluation IV predicted mortality for the Navigator were.

Sublingual microcirculation is impaired in post-cardiac arrest patients

AIM

We hypothesized that microcirculatory dysfunction, similar to that seen in sepsis, occurs in post-cardiac arrest patients and that better microcirculatory flow will be associated with improved outcome. We also assessed the association between microcirculatory dysfunction and inflammatory markers in the post-cardiac arrest state.

METHODS

We prospectively evaluated the sublingual microcirculation in post-cardiac arrest patients, severe sepsis/septic shock patients, and healthy control patients using Sidestream Darkfield microscopy. Microcirculatory flow was assessed using the microcirculation flow index (MFI) at 6 and 24h in the cardiac arrest patients, and within 6h of emergency department admission in the sepsis and control patients.

RESULTS

We evaluated 30 post-cardiac arrest patients, 16 severe sepsis/septic shock patients, and 9 healthy control patients. Sublingual microcirculatory blood flow was significantly impaired in post-cardiac arrest patients at 6h (MFI 2.6 [IQR: 2-2.9]) and 24h (2.7 [IQR: 2.3-2.9]) compared to controls (3.0 [IQR: 2.9-3.0]; p<0.01 and 0.02, respectively). After adjustment for initial APACHE II score, post-cardiac arrest patients had significantly lower MFI at 6-h compared to sepsis patients (p<0.03). In the post-cardiac arrest group, patients with good neurologic outcome had better microcirculatory blood flow as compared to patients with poor neurologic outcome (2.9 [IQR: 2.4-3.0] vs. 2.6 [IQR: 1.9-2.8]; p<0.03). There was a trend toward higher median MFI at 24h in survivors vs. non-survivors (2.8 [IQR: 2.4-3.0] vs. 2.6 [IQR: 2.1-2.8] respectively; p<0.09). We found a negative correlation between MFI-6 and vascular endothelial growth factor (VEGF) (r=-0.49, p=0.038). However, after Bonferroni adjustment for multiple comparisons, this correlation was statistically non-significant.

CONCLUSION

Microcirculatory dysfunction occurs early in post-cardiac arrest patients. Better microcirculatory function at 24h may be associated with good neurologic outcome.

Confocal laser endomicroscopy reliably detects sepsis-related and treatment-associated changes in intestinal mucosal microcirculation

BACKGROUND

Microcirculatory alterations play a central role in the pathophysiology of sepsis. We investigated probe-based confocal laser endomicroscopy (pCLE) to assess alterations in mucosal microcirculatory perfusion in vivo in a porcine model of septic shock and in patients fulfilling consensus criteria for severe sepsis.

METHODS

Septic shock was induced using a faecal peritonitis model in anaesthetized, mechanically ventilated pigs. Mucosal microcirculation was assessed using pCLE in the stomach, duodenum, terminal ileum, and rectum. Duodenal microcirculation was further evaluated in 10 patients with severe sepsis and in 8 healthy controls to quantify capillary diameter, capillary length, and functional capillary density (FCD).

RESULTS

In the animal model, FCD was markedly decreased in duodenal (P<0.001), ileal (P<0.001), gastric (P<0.001), and rectal mucosa (P<0.005) 4 h after induction of sepsis. After volume therapy, FCD partially recovered to 90.0% (duodenum), 94.4% (ileum), 95.4% (gastric), and 97% (rectum) of baseline values, indicating decoupling of microvascular and macrovascular flow. In septic patients, the mean capillary diameter (P<0.01) and FCD (P<0.05) in duodenal mucosa were decreased compared with healthy controls.

CONCLUSIONS

pCLE reliably detected and quantified microcirculatory alterations in the gastrointestinal mucosa in a porcine model of sepsis and in patients with severe sepsis. Our data suggest that pCLE is a promising tool to assess the efficacy of therapeutic interventions on mucosal microcirculation in real-time, even in the clinical context.

Microcirculatory alterations in patients with severe sepsis: impact of time of assessment and relationship with outcome

OBJECTIVES

Sepsis induces microvascular alterations that may play an important role in the development of organ dysfunction. However, the relationship of these alterations to systemic variables and outcome is still not well defined. We investigated which factors may influence microcirculatory alterations in patients with severe sepsis and whether these are independently associated with mortality.

DESIGN

Analysis of prospectively collected data from previously published studies by our group.

SETTING

A 36-bed, medicosurgical university hospital Department of Intensive Care.

PATIENTS

A total of 252 patients with severe sepsis in whom the sublingual microcirculation was visualized using orthogonal polarization spectral or sidestream darkfield imaging techniques.

MEASUREMENTS AND MAIN RESULTS

Microcirculatory measurements were obtained either early, within 24h of the onset of severe sepsis (n = 204), or later, after 48h (n = 48). When multiple measurements were obtained, only the first was considered. Although global hemodynamic variables were relatively preserved (mean arterial pressure 70 [65-77] mm Hg, cardiac index 3.3 [2.7-4.0] L/min.m, and SvO2 68.3 [62.8-74.7]%), microvascular variables were markedly altered (proportion of perfused small vessels 65 [50-74]%, microvascular flow index 2.15 [1.80-2.60], and heterogeneity of proportion of perfused small vessels 35 [20-50]%). Among microcirculatory variables, proportion of perfused small vessels was the strongest predictor of outcome (receiver operating characteristic curve area 0.818 [0.766-0.871], p < 0.001). Survival rates decreased markedly with severity of alterations in the proportion of perfused small vessels (70% and 75% in the two upper proportion of perfused small vessel quartiles compared with 3% and 44% in the two lower quartiles, p < 0.0001). Multivariable analysis identified proportion of perfused small vessels and sequential organ failure assessment score as independent predictors of outcome. Microcirculatory alterations were less severe in the later than in the earlier (proportion of perfused small vessels, 74 [57-82]% vs. 63 [48-71]%, p = 0.004) phase of sepsis. In multivariable analysis focused on the early period of sepsis, proportion of perfused small vessels and lactate were independent predictors of outcome.

CONCLUSIONS

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

Administration of tetrahydrobiopterin improves the microcirculation and outcome in an ovine model of septic shock

OBJECTIVE

Supplementation with tetrahydrobiopterin, a nitric oxide synthase cofactor, may reduce microvascular endothelial dysfunction in severe sepsis. We studied whether tetrahydrobiopterin administration exerts beneficial effects in an ovine septic shock model.

DESIGN

Randomized animal study.

SETTING

University hospital animal research laboratory.

SUBJECTS

Fourteen adult female sheep.

INTERVENTIONS

Fecal peritonitis was induced, and the sheep were randomized to receive tetrahydrobiopterin (n=7), given intravenously as 20 mg/kg boluses at 4 and 12 hrs after sepsis induction, or placebo (n=7). All animals were fluid resuscitated. The experiment was continued until death or for a maximum of 30 hrs.

MEASUREMENTS AND MAIN RESULTS

In addition to standard hemodynamic assessment, the sublingual microcirculation was evaluated using sidestream dark-field videomicroscopy. The first bolus of tetrahydrobiopterin blunted the increase in heart rate and cardiac index seen in the control group without affecting mean arterial pressure, and the second bolus of tetrahydrobiopterin prevented the decreases in cardiac index and mean arterial pressure. The reduction in mixed venous blood oxygen saturation and the increase in blood lactate seen in the control group were also delayed. Tetrahydrobiopterin significantly attenuated the deterioration in perfused small vessel proportion and density, microvascular flow index, and the increase in microvascular heterogeneity observed in the control group. Tetrahydrobiopterin was associated with better preserved lung compliance and PaO2/FIO2 ratio, which were associated with a lower lung wet/dry weight ratio at the end of the study. Median survival time was significantly prolonged in the tetrahydrobiopterin group (25.0 vs. 17.8 hrs, p<.01).

CONCLUSION

In this clinically relevant model of sepsis, tetrahydrobiopterin supplementation attenuated the impairment in sublingual microvascular perfusion and permeability, which was accompanied by better preserved gas exchange, renal flow and urine output, and prolonged survival.

Microcirculatory alterations in the critically ill

Disturbed regional oxygenation is believed to contribute to organ dysfunction, organ failure, and death. Recent techniques such as orthogonal polarization spectral/sidestream darkfield imaging and near infrared spectroscopy have provided insight into the microcirculatory alterations present in critically ill patients. Using these techniques, persistent microcirculatory alterations have been shown to be associated with a worse prognosis, notably in patients with septic shock, irrespective of systemic hemodynamic variables. Data on the effects of therapeutic interventions on the microcirculation are also being gathered and may help in developing strategies that can influence regional oxygenation and cellular metabolism, and thereby prevent or reverse organ failure. Whether monitoring the microcirculation can be used to guide therapy remains unclear and requires further study, and this is an exciting field of ongoing research.

Pulsatile versus nonpulsatile flow during cardiopulmonary bypass: microcirculatory and systemic effects

BACKGROUND

Controversy exists regarding the optimal perfusion modality during cardiopulmonary bypass (CPB). Here we compare the effects of pulsatile versus nonpulsatile perfusion on microvascular blood flow during and after CPB.

METHODS

High-risk cardiac surgical patients were randomly assigned to have pulsatile (n=10) or nonpulsatile (n=10) flow during CPB. The sublingual microcirculation was assessed using orthogonal polarization spectral imaging. Hemodynamic and microvascular variables were obtained after anesthesia (baseline), during CPB, and post-CPB.

RESULTS

Compared with baseline, a normal microcirculatory blood flow pattern was accomplished at all time points under pulsatile flow conditions. Peaking 24 hours postoperatively, a higher proportion of normally perfused microvessels occurred under pulsatile versus nonpulsatile flow (56.0%±3.9% vs 33.3%±4.1%; p<0.05). Concurrently, pulsatility resulted in a reduction in the prevalence of pathologic hyper-dynamically perfused vessels (6.0%±3.4% vs 19.6%±8.8%; p<0.05). Leukocyte adherence decreased relative to the nonpulsatile group both during and after CPB. Furthermore, peak lactate levels were reduced under pulsatile flow conditions postoperatively.

CONCLUSIONS

Pulsatile perfusion is superior to nonpulsatile perfusion at preserving the microcirculation, which may reflect attenuation of the systemic inflammatory response during CPB. We suggest the implementation of pulsatile flow can better optimize microvascular perfusion, and may lead to improved patient outcomes in high-risk cardiac surgical procedures requiring prolonged CPB time.

Physiology and pathophysiology of splanchnic hypoperfusion and intestinal injury during exercise: strategies for evaluation and prevention

Physical exercise places high demands on the adaptive capacity of the human body. Strenuous physical performance increases the blood supply to active muscles, cardiopulmonary system, and skin to meet the altered demands for oxygen and nutrients. The redistribution of blood flow, necessary for such an increased blood supply to the periphery, significantly reduces blood flow to the gut, leading to hypoperfusion and gastrointestinal (GI) compromise. A compromised GI system can have a negative impact on exercise performance and subsequent postexercise recovery due to abdominal distress and impairments in the uptake of fluid, electrolytes, and nutrients. In addition, strenuous physical exercise leads to loss of epithelial integrity, which may give rise to increased intestinal permeability with bacterial translocation and inflammation. Ultimately, these effects can deteriorate postexercise recovery and disrupt exercise training routine. This review provides an overview on the recent advances in our understanding of GI physiology and pathophysiology in relation to strenuous exercise. Various approaches to determine the impact of exercise on the individual athlete's GI tract are discussed. In addition, we elaborate on several promising components that could be exploited for preventive interventions.

From bench to bedside

Because the microcirculation has emerged as an important reanimation target, appropriate methods to monitor the microcirculatory function are crucial. Several teams have now succeeded in crossing this bridge from bench to bedside, but the choice of the tissues of interest remains a debate. The potential accessible vascular beds that doctors could use in reanimation strategies and the relationship of these beds to more relevant microcirculatory ones are important issues to address.

Microvascular response to red blood cell transfusion in trauma patients

Trauma patients are often transfused allogeneic red blood cells (RBCs) in an effort to augment tissue oxygen delivery. However, the effect of RBC transfusion on microvascular perfusion in this patient population is not well understood. To this end, we investigated the effect of RBC transfusion on sublingual microvascular perfusion in trauma patients. Sublingual microcirculation was imaged at bedside with a sidestream dark-field illumination microscope before and after transfusion of one RBC unit in hemodynamically stable, anemic trauma patients. The perfused proportion of capillaries (PPC) before and after transfusion was determined, and the percent change in capillary perfusion following transfusion (ΔPPC) calculated. Sublingual microcirculation was observed in 30 patients. Mean age was 47 (SD, 21) years, mean Injury Severity Score was 29 (SD, 16), and mean pretransfusion hemoglobin was 7.5 (SD, 0.9) g/dL. No patients had a mean arterial pressure of less than 65 mmHg (mean, 89 [SD, 17] mmHg) or lactate of greater than 2.5 mmol/L (mean, 1.1 [SD, 0.3] mmol/L). Following transfusion, ΔPPC ranged from +68% to -36% and was found to inversely correlate significantly with pretransfusion PPC (Spearman r = -0.63, P = 0.0002). Pretransfusion PPC may be selectively deranged in otherwise stable trauma patients. Patients with relatively altered baseline PPC tend to demonstrate improvement in perfusion following transfusion, whereas those with relatively normal perfusion at baseline tend to demonstrate either no change or, in fact, a decline in PPC. Bedside sublingual imaging may have the potential to detect subtle perfusion defects and ultimately inform clinical decision making with respect to transfusion.

Quantitative assessment of the microcirculation in healthy volunteers and in patients with septic shock

OBJECTIVE

The microcirculation of septic patients has been characterized only semiquantitatively. Our goal was to characterize the sublingual microcirculation in healthy volunteers and patients with septic shock quantitatively. Our hypotheses were that 1) hyperdynamic blood flow is absent in septic shock; 2) nonsurvivors show more severe alterations than survivors; and 3) quantitative and semiquantitative microcirculatory parameters have a similar performance.

DESIGN

Prospective, observational study.

SETTING

Teaching intensive care unit in a university-affiliated hospital.

SUBJECTS

Twenty-five normal volunteers and 25 patients with septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The sublingual microcirculation was evaluated by means of sidestream dark field imaging. Semiquantitative and quantitative microcirculatory parameters were determined through the use of applied software. Septic patients showed decreased perfused capillary density (13.2±4.4 mm/mm² vs. 16.6±1.6 mm/mm²), proportion of perfused capillaries (0.78±0.23 vs. 1.00±0.01), microvascular flow index (2.15±0.61 vs. 2.97±0.03), and red blood cell velocity (830±183 µm/sec vs. 1332±187 µm/sec) along with increased heterogeneity flow index (1.64±1.14 vs. 0.25±0.19) compared with controls. No differences were found in total capillary density (16.9±2.2 vs. 16.7±1.6). Only 4% of capillaries analyzed showed red blood cell velocities>75th percentile of the velocities of the normal volunteers. The nonsurvivors exhibited decreased perfused capillary density, proportion of perfused capillaries, and microvascular flow index along with increased heterogeneity flow index compared with the survivors. The correlations between microvascular flow index and proportion of perfused capillaries, total capillary density and number of grid-crossing capillaries, and red blood cell velocities and microvascular flow index gave high R values (0.92, 0.65, and 0.52, respectively; p<.0001 for all).

CONCLUSIONS

The main characteristics of sublingual microcirculation in patients with septic shock are hypoperfusion and increased flow heterogeneity. Hyperdynamic microvascular blood flow was not found. Nonsurvivors showed more severe alterations than survivors. Quantitative and semiquantitative microcirculatory variables displayed similar behaviors.

Citrulline a more suitable substrate than arginine to restore NO production and the microcirculation during endotoxemia

Background

Impaired microcirculation during endotoxemia correlates with a disturbed arginine-nitric oxide (NO) metabolism and is associated with deteriorating organ function. Improving the organ perfusion in endotoxemia, as often seen in patients with severe infection or systemic inflammatory response syndrome (SIRS) is, therefore, an important therapeutic target. We hypothesized that supplementation of the arginine precursor citrulline rather than arginine would specifically increase eNOS-induced intracellular NO production and thereby improve the microcirculation during endotoxemia.

Methodology/Principal Findings

To study the effects of L-Citrulline and L-Arginine supplementation on jejunal microcirculation, intracellular arginine availability and NO production in a non-lethal prolonged endotoxemia model in mice. C57/Bl6 mice received an 18 hrs intravenous infusion of endotoxin (LPS, 0.4 µg•g bodyweight⁻¹•h⁻¹), combined with either L-Citrulline (6.25 mg•h-1), L-Arginine (6.25 mg•h⁻¹), or L-Alanine (isonitrogenous control; 12.5 mg•h⁻¹) during the last 6 hrs. The control group received an 18 hrs sterile saline infusion combined with L-Alanine or L-Citrulline during the last 6 hrs. The microcirculation was evaluated at the end of the infusion period using sidestream dark-field imaging of jejunal villi. Plasma and jejunal tissue amino-acid concentrations were measured by HPLC, NO tissue concentrations by electron-spin resonance spectroscopy and NOS protein concentrations using Western blot.

Conclusion/Significance

L-Citrulline supplementation during endotoxemia positively influenced the intestinal microvascular perfusion compared to L-Arginine-supplemented and control endotoxemic mice. L-Citrulline supplementation increased plasma and tissue concentrations of arginine and citrulline, and restored intracellular NO production in the intestine. L-Arginine supplementation did not increase the intracellular arginine availability. Jejunal tissues in the L-Citrulline-supplemented group showed, compared to the endotoxemic and L-Arginine-supplemented endotoxemic group, an increase in degree of phosphorylation of eNOS (Ser 1177) and a decrease in iNOS protein level. In conclusion, L-Citrulline supplementation during endotoxemia and not L-Arginine reduced intestinal microcirculatory dysfunction and increased intracellular NO production, likely via increased intracellular citrulline and arginine availability.

Early course of microcirculatory perfusion in eye and digestive tract during hypodynamic sepsis

INTRODUCTION

The aim of the study was to evaluate and compare the microcirculatory perfusion during experimental sepsis in different potentially available parts of the body, such as sublingual mucosa, conjunctiva of the eye, and mucosa of jejunum and rectum.

METHODS

Pigs were randomly assigned to sepsis (n = 9) and sham (n = 4) groups. The sepsis group received a fixed dose of live Escherichia coli infusion over a 1-hour period (1.8 × 10(9)/kg colony-forming units). Animals were observed 5 hours after the start of E. coli infusion. In addition to systemic hemodynamic assessment, we performed conjunctival, sublingual, jejunal, and rectal evaluation of microcirculation by using Sidestream Dark Field (SDF) videomicroscopy at the same time points: at baseline, and at 3 and 5 hours after the start of live E. coli infusion. Assessment of microcirculatory parameters of convective oxygen transport (microvascular flow index (MFI) and proportion of perfused vessels (PPV)), and diffusion distance (perfused vessel density (PVD) and total vessel density (TVD)) was done by using a semiquantitative method.

RESULTS

Infusion of E. coli resulted in a hypodynamic state of sepsis associated with low cardiac output and increased systemic vascular resistance despite fluid administration. Significant decreases in MFI and PPV of small vessels were observed in sublingual, conjunctival, jejunal, and rectal locations 3 and 5 hours after the start of E. coli infusion in comparison with baseline variables. Correlation between sublingual and conjunctival (r = 0.80; P = 0.036), sublingual and jejunal (r = 0.80; P = 0.044), and sublingual and rectal (r = 0.79; P = 0.03) MFI was observed 3 hours after onset of sepsis. However, this strong correlation between the sublingual and other regions disappeared 5 hours after the start of E. coli infusion. Overall, the sublingual mucosa exhibited the most-pronounced alterations of microcirculatory flow in comparison with conjunctival, jejunal, and rectal microvasculature (P < 0.05).

CONCLUSIONS

In this pig model, a time-dependent correlation exists between sublingual and microvascular beds during the course of a hypodynamic state of sepsis.

Pulsatile flow during cardiopulmonary bypass preserves postoperative microcirculatory perfusion irrespective of systemic hemodynamics

The onset of nonpulsatile cardiopulmonary bypass is known to deteriorate microcirculatory perfusion, but it has never been investigated whether this may be prevented by restoration of pulsatility during extracorporeal circulation. We therefore investigated the distinct effects of nonpulsatile and pulsatile flow on microcirculatory perfusion during on-pump cardiac surgery. Patients undergoing coronary artery bypass graft surgery were randomized into a nonpulsatile (n = 17) or pulsatile (n = 16) cardiopulmonary bypass group. Sublingual mucosal microvascular perfusion was measured at distinct perioperative time intervals using sidestream dark field imaging, and quantified as the level of perfused small vessel density and microvascular flow index (vessel diameter < 20 μm). Microcirculation measurements were paralleled by hemodynamic and free hemoglobin analyses. The pulse wave during pulsatile bypass estimated 58 ± 17% of the baseline blood pressure waveform. The observed reduction in perfused vessel density during aorta cross-clamping was only restored in the pulsatile flow group and increased from 15.5 ± 2.4 to 20.3 ± 3.7 mm/mm(2) upon intensive care admission (P < 0.01). The median postoperative microvascular flow index was higher in the pulsatile group [2.6 (2.5-2.9)] than in the nonpulsatile group [2.1 (1.7-2.5); P = 0.001]. Pulsatile flow was not associated with augmentation of free hemoglobin production and was paralleled by improved oxygen consumption from 70 ± 14 to 82 ± 16 ml·min(-1)·m(-2) (P = 0.01) at the end of aortic cross-clamping. In conclusion, pulsatile cardiopulmonary bypass preserves microcirculatory perfusion throughout the early postoperative period, irrespective of systemic hemodynamics. This observation is paralleled by an increase in oxygen consumption during pulsatile flow, which may hint toward decreased microcirculatory heterogeneity during extracorporeal circulation and preservation of microcirculatory perfusion throughout the perioperative period.

Changes in the sublingual microcirculation and endothelial adhesion molecules during the course of severe meningococcal disease treated in the paediatric intensive care unit

PURPOSE

The sublingual microcirculation can be visualised in real time using sidestream dark-field (SDF) imaging. Endothelial activation mediated through adhesion molecules may alter flow patterns in the microcirculation. We studied sublingual microcirculatory disturbances in children with meningococcal disease (MCD) and simultaneously measured plasma levels of adhesion molecules.

METHOD

Twenty children admitted to the paediatric intensive care unit (PICU) with MCD were studied. Forty healthy children were controls. The sublingual microcirculation was assessed at admission and at timed intervals until extubation. The microvascular flow index (MFI), capillary density (CD), proportion of perfused vessels (PPV) and perfused vessel density (PVD) were measured using SDF imaging. Plasma intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin and P-selectin were measured at admission and at timed intervals during the course of PICU treatment.

RESULTS

Significant reductions in MFI, CD, PPV and PVD were found in children with MCD compared with controls (p < 0.005). These differences had resolved prior to extubation. Initial MFI values predicted the duration of mechanical ventilation, irrespective of the stage of illness at the time of presentation to PICU. There were negative correlations between the ICAM-1, VCAM-1 and E-selectin levels and the microcirculatory MFI and PPV values at the time of admission to PICU (p < 0.005).

CONCLUSIONS

Microcirculatory dysfunction is present in children with severe MCD with improvement alongside clinical recovery. Microcirculatory dysfunction correlated with markers of endothelial activation. Sublingual SDF imaging is feasible in children ventilated on PICU for severe sepsis and may prove useful in studies assessing illness severity and therapy.

Microcirculatory alterations: potential mechanisms and implications for therapy

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the characteristics of these alterations, the various mechanisms potentially involved, and the implications for therapy. Sepsis-induced microvascular alterations are characterized by a decrease in capillary density with an increased number of stopped-flow and intermittent-flow capillaries, in close vicinity to well-perfused capillaries. Accordingly, the surface available for exchange is decreased but also is highly heterogeneous. Multiple mechanisms may contribute to these alterations, including endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability. Given the heterogeneous nature of these alterations and the mechanisms potentially involved, classical hemodynamic interventions, such as fluids, red blood cell transfusions, vasopressors, and inotropic agents, have only a limited impact, and the microcirculatory changes often persist after resuscitation. Nevertheless, fluids seem to improve the microcirculation in the early phase of sepsis and dobutamine also can improve the microcirculation, although the magnitude of this effect varies considerably among patients. Finally, maintaining a sufficient perfusion pressure seems to positively influence the microcirculation; however, which mean arterial pressure levels should be targeted remains controversial. Some trials using vasodilating agents, especially nitroglycerin, showed promising initial results but they were challenged in other trials, so it is difficult to recommend the use of these agents in current practice. Other agents can markedly improve the microcirculation, including activated protein C and antithrombin, vitamin C, or steroids. In conclusion, microcirculatory alterations may play an important role in the development of sepsis-related organ dysfunction. At this stage, therapies to target microcirculation specifically are still being investigated.

Changes in Microvascular Blood Flow during Coupled Plasma Filtration and Adsorption

A 51-year-old man with septic shock underwent three consecutive sessions of coupled plasma filtration-adsorption each lasting 12 hours. Sublingual microvascular perfusion was assessed using the orthogonal polarisation spectral imaging technique at three different times: immediate pre-coupled plasma filtration-adsorption phase, two hours following commencement and two hours after its termination. The video images of the sublingual microcirculation were analysed by an investigator blinded to the time of image acquisition. The De Backer's score was calculated. During the coupled plasma filtration-adsorption, the number of perfused vessels increased compared with the pre-coupled plasma filtration-adsorption period, but decreased again after its termination. It is arguable that the elimination of septic mediators during the procedure could account for the observed variations.

Sublingual microcirculatory changes during high-volume hemofiltration in hyperdynamic septic shock patients

INTRODUCTION

Previous studies have suggested that high volume hemofiltration (HVHF) may contribute to revert hypotension in severe hyperdynamic septic shock patients. However, arterial pressure stabilization occurs due to an increase in systemic vascular resistance, which could eventually compromise microcirculatory blood flow and perfusion. The goal of this study was to determine if HVHF deteriorates sublingual microcirculation in severe hyperdynamic septic shock patients.

METHODS

This was a prospective, non-randomized study at a 16-bed, medical-surgical intensive care unit of a university hospital. We included 12 severe hyperdynamic septic shock patients (norepinephrine requirements > 0.3 μg/kg/min and cardiac index > 3.0 L/min/m2) who underwent a 12-hour HVHF as a rescue therapy according to a predefined algorithm. Sublingual microcirculation (Microscan for NTSC, Microvision Medical), systemic hemodynamics and perfusion parameters were assessed at baseline, at 12 hours of HVHF, and 6 hours after stopping HVHF.

RESULTS

Microcirculatory flow index increased after 12 hours of HVHF and this increase persisted 6 hours after stopping HVHF. A similar trend was observed for the proportion of perfused microvessels. The increase in microcirculatory blood flow was inversely correlated with baseline levels. There was no significant change in microvascular density or heterogeneity during or after HVHF. Mean arterial pressure and systemic vascular resistance increased while lactate levels decreased after the 12-hour HVHF.

CONCLUSIONS

The use of HVHF as a rescue therapy in patients with severe hyperdynamic septic shock does not deteriorate sublingual microcirculatory blood flow despite the increase in systemic vascular resistance.

Withdrawing intra-aortic balloon pump support paradoxically improves microvascular flow

INTRODUCTION

The Intra-Aortic Balloon Pump (IABP) is frequently used to mechanically support the heart. There is evidence that IABP improves microvascular flow during cardiogenic shock but its influence on the human microcirculation in patients deemed ready for discontinuing IABP support has not yet been studied. Therefore we used sidestream dark field imaging (SDF) to test our hypothesis that human microcirculation remains unaltered with or without IABP support in patients clinically ready for discontinuation of mechanical support.

METHODS

We studied 15 ICU patients on IABP therapy. Measurements were performed after the clinical decision was made to remove the balloon catheter. We recorded global hemodynamic parameters and performed venous oximetry during maximal IABP support (1:1) and 10 minutes after temporarily stopping the IABP therapy. At both time points, we also recorded video clips of the sublingual microcirculation. From these we determined indices of microvascular perfusion including perfused vessel density (PVD) and microvascular flow index (MFI).

RESULTS

Ceasing IABP support lowered mean arterial pressure (74 ± 8 to 71 ± 10 mmHg; P = 0.048) and increased diastolic pressure (43 ± 10 to 53 ± 9 mmHg; P = 0.0002). However, at the level of the microcirculation we found an increase of PVD of small vessels <20 μm (5.47 ± 1.76 to 6.63 ± 1.90; P = 0.0039). PVD for vessels >20 μm and MFI for both small and large vessels were unaltered. During the procedure global oxygenation parameters (ScvO2/SvO2) remained unchanged.

CONCLUSIONS

In patients deemed ready for discontinuing IABP support according to current practice, SDF imaging showed an increase of microcirculatory flow of small vessels after ceasing IABP therapy. This observation may indicate that IABP impairs microvascular perfusion in recovered patients, although this warrants confirmation.

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

PURPOSE

To assess sublingual microcirculatory changes following passive leg raising (PLR) and volume expansion (VE) in septic patients.

METHODS

This prospective study was conducted in two university hospital intensive care units and included 25 mechanically ventilated patients with severe sepsis or septic shock who were eligible for VE in the first 24 h of their admission. Pulse pressure variation (ΔPP), cardiac output (CO) and sublingual microcirculation indices were assessed at five consecutive steps: (1) semi-recumbent position (Baseline 1), (2) during PLR manoeuvre (PLR), (3) after returning to semi-recumbent position (Baseline 2), (4) at the time when VE induced the same degree of preload responsiveness as PLR (VE(∆PP = PLR)) and (5) at the end of VE (VE(END)). At each step, five sublingual microcirculation sequences were acquired using sidestream darkfield imaging to assess functional capillary density (FCD), microcirculatory flow index (MFI), proportion of perfused vessels (PPV) and flow heterogeneity index (FHI).

RESULTS

The PLR, VE(∆PP = PLR) and VE(END) induced a significant increase in CO and a significant decrease in ΔPP compared to Baseline 1 and Baseline 2 values. Both PLR and VE induced significant increases in FCD, MFI and PPV and a significant decrease in FHI compared to Baseline 1 and Baseline 2 values.

CONCLUSIONS

In preload responsive severe septic patients examined within the first 24 h of their admission, both PLR and VE improved sublingual microcirculatory perfusion. At the level of volume infusion used in this study, these changes in sublingual microcirculation were not explained by changes in rheologic factors or changes in arterial pressure.

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

PURPOSE

To assess sublingual microcirculatory changes following passive leg raising (PLR) and volume expansion (VE) in septic patients.

METHODS

This prospective study was conducted in two university hospital intensive care units and included 25 mechanically ventilated patients with severe sepsis or septic shock who were eligible for VE in the first 24 h of their admission. Pulse pressure variation (ΔPP), cardiac output (CO) and sublingual microcirculation indices were assessed at five consecutive steps: (1) semi-recumbent position (Baseline 1), (2) during PLR manoeuvre (PLR), (3) after returning to semi-recumbent position (Baseline 2), (4) at the time when VE induced the same degree of preload responsiveness as PLR (VE(∆PP = PLR)) and (5) at the end of VE (VE(END)). At each step, five sublingual microcirculation sequences were acquired using sidestream darkfield imaging to assess functional capillary density (FCD), microcirculatory flow index (MFI), proportion of perfused vessels (PPV) and flow heterogeneity index (FHI).

RESULTS

The PLR, VE(∆PP = PLR) and VE(END) induced a significant increase in CO and a significant decrease in ΔPP compared to Baseline 1 and Baseline 2 values. Both PLR and VE induced significant increases in FCD, MFI and PPV and a significant decrease in FHI compared to Baseline 1 and Baseline 2 values.

CONCLUSIONS

In preload responsive severe septic patients examined within the first 24 h of their admission, both PLR and VE improved sublingual microcirculatory perfusion. At the level of volume infusion used in this study, these changes in sublingual microcirculation were not explained by changes in rheologic factors or changes in arterial pressure.

Cerebral microcirculation is impaired during sepsis: an experimental study

Introduction

Pathophysiology of brain dysfunction due to sepsis remains poorly understood. Cerebral microcirculatory alterations may play a role; however, experimental data are scarce. This study sought to investigate whether the cerebral microcirculation is altered in a clinically relevant animal model of septic shock.

Methods

Fifteen anesthetized, invasively monitored, and mechanically ventilated female sheep were allocated to a sham procedure (n = 5) or sepsis (n = 10), in which peritonitis was induced by intra-abdominal injection of autologous faeces. Animals were observed until spontaneous death or for a maximum of 20 hours. In addition to global hemodynamic assessment, the microcirculation of the cerebral cortex was evaluated using Sidestream Dark-Field (SDF) videomicroscopy at baseline, 6 hours, 12 hours and at shock onset. At least five images of 20 seconds each from separate areas were recorded at each time point and stored under a random number to be analyzed, using a semi-quantitative method, by an investigator blinded to time and condition.

Results

All septic animals developed a hyperdynamic state associated with organ dysfunction and, ultimately, septic shock. In the septic animals, there was a progressive decrease in cerebral total perfused vessel density (from 5.9 ± 0.9 at baseline to 4.8 ± 0.7 n/mm at shock onset, P = 0.009), functional capillary density (from 2.8 ± 0.4 to 2.1 ± 0.7 n/mm, P = 0.049), the proportion of small perfused vessels (from 95 ± 3 to 85 ± 8%, P = 0.02), and the total number of perfused capillaries (from 22.7 ± 2.7 to 17.5 ± 5.2 n/mm, P = 0.04). There were no significant changes in microcirculatory flow index over time. In sham animals, the cerebral microcirculation was unaltered during the study period.

Conclusions

In this model of peritonitis, the cerebral microcirculation was impaired during sepsis, with a significant reduction in perfused small vessels at the onset of septic shock. These alterations may play a role in the pathogenesis of septic encephalopathy.