Systemic microvascular shunting through hyperdynamic capillaries after acute physiological disturbances following cardiopulmonary bypass

Optimization of cardiopulmonary bypass prime fluid to preserve microcirculatory perfusion during on-pump coronary artery bypass graft surgery: PRIME study protocol for a double-blind randomized trial

BACKGROUND

Acute microcirculatory perfusion disturbances and organ edema are important factors leading to organ dysfunction during cardiac surgery with cardiopulmonary bypass (CPB). Priming of the CPB system with crystalloid or colloid fluids, which inevitably leads to hemodilution, could contribute to this effect. However, there is yet no optimal evidence-based strategy for this type of priming. Hence, we will investigate different priming strategies to reduce hemodilution and preserve microcirculatory perfusion.

METHODS

The PRIME study is a single-center double-blind randomized trial. Patients undergoing elective coronary artery bypass graft surgery with CPB will be randomized into three groups of prime fluid strategy: (1) gelofusine with crystalloid, (2) albumin with crystalloid, or (3) crystalloid and retrograde autologous priming. We aim to include 30 patients, 10 patients in each arm. The primary outcome is the change in microcirculatory perfusion. Secondary outcomes include colloid oncotic pressure; albumin; hematocrit; electrolytes; fluid balance and requirements; transfusion rates; and endothelial-, glycocalyx-, inflammatory- and renal injury markers. Sublingual microcirculatory perfusion will be measured using non-invasive sidestream dark field video microscopy. Microcirculatory and blood measurements will be performed at five consecutive time points during surgery up to 24 h after admission to the intensive care unit.

DISCUSSION

PRIME is the first study to assess the effect of different prime fluid strategies on microcirculatory perfusion in cardiac surgery with CPB. If the results suggest that a specific crystalloid or colloid prime fluid strategy better preserves microcirculatory perfusion during on-pump cardiac surgery, the current study may help to find the optimal pump priming in cardiac surgery.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05647057. Registered on 04/25/2023.

CLINICALTRIALS

gov PRS: Record Summary NCT05647057, all items can be found in the protocol.

Microcirculatory Alterations in Cardiac Surgery: A Comprehensive Guide

Microcirculation is essential for cellular life and its functions. It comprises a complex network of capillaries, arterioles, and venules, which distributes oxygenated blood across and within organs based on regional metabolic demands. Because previous research indicated that organ function is linked to microcirculatory function, it is crucial to maintain sufficient and effective microcirculatory function during major surgery. Impaired microcirculation can lead to inadequate tissue perfusion, potentially resulting in perioperative complications and an unfavorable outcome. Indeed, changes in microcirculation in cardiovascular disease and cardiac surgery have a direct correlation with prolonged stays in the postoperative intensive care unit and high mortality rates within 30 days. Additionally, cardiopulmonary bypass, a regularly employed method in cardiac surgery, has been proven to induce microcirculatory malfunction and, thus, lead to postoperative multiple organ dysfunction. As global hemodynamic parameters can remain stable or improve, whereas microcirculation is still compromised, tracking microcirculatory variables could lead to the development of targeted microcirculatory treatment within hemodynamic management. Therefore, it is necessary to enhance the use of microcirculatory monitoring in the medical domain to assist physicians in the therapeutic management of patients undergoing cardiac surgery. This potentially can lead to better hemodynamic management and outcomes. This review article concentrates on the use of handheld video microscopes for real-time microcirculatory assessment of cardiac surgery patients in the immediate and early postoperative period. Emphasis is placed on integrating microcirculatory monitoring with conventional hemodynamic monitoring in the therapeutic management of patients undergoing cardiac surgery.

Preoperative endothelial dysfunction for the prediction of acute kidney injury after cardiac surgery using cardiopulmonary bypass: a pilot study based on a second analysis of the MONS study

BACKGROUND

Up to 42% of patients develop acute kidney injury (AKI) after cardiac surgery. The aim of this study was to describe the relationship between preoperative microcirculatory function and postoperative AKI after cardiac surgery using cardiopulmonary bypass (CPB).

METHODS

The prospective observational cohort MONS enrolled 60 patients scheduled for valvular (n = 30, 50%) or coronary (n = 30, 50%) surgery using CPB. Preoperative microcirculation was assessed during preoperative consultation from January 2019 to April 2019 at the University Hospital of Angers, France, using endothelium-dependent and endothelium-independent reactivity tests on the forearm (iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively). Skin blood flow was measured by laser speckle contrast imaging. The primary endpoint was the occurrence of AKI according to the KDIGO classification during the hospital stay.

RESULTS

Forty-three (71.7%) patients developed AKI during the in-hospital follow-up, and 15 (25%) were classified as KDIGO stage 1, 20 (33%) KDIGO stage 2, and 8 (13%) KDIGO stage 3. Regarding preoperative microcirculation, a higher peak amplitude of vasodilation in response to iontophoresis of ACh was found in patients with postoperative occurrence of AKI (35 [20-49] vs 23 [9-44] LSPU, p = 0.04). Iontophoresis of SNP was not significantly different according to AKI occurrence (34 [22-49] vs 36 [20-50] LSPU, p = 0.95). In a multivariable model, the preoperative peak amplitude at iontophoresis of ACh was independently associated with postoperative AKI (OR 1.045 [1.001-1.092], p = 0.045).

CONCLUSIONS

The preoperative peak amplitude of endothelium-dependent vasodilation is independently associated with the postoperative occurrence of AKI.

TRIAL REGISTRATION

Clinical-Trials.gov, NCT03631797. Registered 15 August 2018, https://clinicaltrials.gov/ct2/show/NCT03631797.

Association between lactic acidosis and multiple organ dysfunction syndrome after cardiopulmonary bypass

Background

The relationship between hyperlactatemia and prognosis after cardiopulmonary bypass (CPB) is controversial, and some studies ignore the presence of lactic acidosis in patients with severe hyperlactacemia. This study explored the association between lactic acidosis (LA) and the occurrence of multiple organ dysfunction syndrome (MODS) after cardiopulmonary bypass.

Methods

This study was a post hoc analysis of patients who underwent cardiac surgery between February 2017 and August 2018 and participated in a prospective study at Taizhou Hospital. The data were collected at: ICU admission (H0), and 4, 8, 12, 24, and 48 h after admission. Blood lactate levels gradually increased after CPB, peaking at H8 and then gradually decreasing. The patients were grouped as LA, hyperlactatemia (HL), and normal control (NC) based on blood test results 8 h after ICU admission. Basic preoperative, perioperative, and postoperative conditions were compared between the three groups, as well as postoperative perfusion and oxygen metabolism indexes.

Results

There were 22 (19%), 73 (64%), and 19 (17%) patients in the LA, HL, and NC groups, respectively. APACHE II (24h) and SOFA (24h) scores were the highest in the LA group (P < 0.05). ICU stay duration was the longest for the LA group (48.5 (42.5, 50) h), compared with the HL (27 (22, 48) h) and NC (27 (25, 46) h) groups (P = 0.012). The LA group had the highest incidence of MODS (36%), compared with the HL (14%) and NC (5%) groups (P = 0.015). In the LA group, the oxygen extraction ratio (O2ER) was lower (21.5 (17.05, 32.8)%) than in the HL (31.3 (24.8, 37.6)%) and the NC group (31.3 (29.0, 35.4) %) (P = 0.018). In the univariable analyses, patient age (OR = 1.054, 95% CI [1.003-1.109], P = 0.038), the LA group (vs. the NC group, (OR = 10.286, 95% CI [1.148-92.185], P = 0.037), and ΔPCO2 at H8 (OR = 1.197, 95% CI [1.022-1.401], P = 0.025) were risk factor of MODS after CPB.

Conclusions

We speculated that there was correlation between lactic acidosis and MODS after CPB. In addition, LA should be monitored intensively after CPB.

The microcirculation in perioperative medicine: a narrative review

The microcirculation describes the network of the smallest vessels in our cardiovascular system. On a microcirculatory level, oxygen delivery is determined by the flow of oxygen-carrying red blood cells in a given single capillary (capillary red blood cell flow) and the density of the capillary network in a given tissue volume (capillary vessel density). Handheld vital videomicroscopy enables visualisation of the capillary bed on the surface of organs and tissues but currently is only used for research. Measurements are generally possible on all organ surfaces but are most often performed in the sublingual area. In patients presenting for elective surgery, the sublingual microcirculation is usually intact and functional. Induction of general anaesthesia slightly decreases capillary red blood cell flow and increases capillary vessel density. During elective, even major, noncardiac surgery, the sublingual microcirculation is preserved and remains functional, presumably because elective noncardiac surgery is scheduled trauma and haemodynamic alterations are immediately treated by anaesthesiologists, usually restoring the macrocirculation before the microcirculation is substantially impaired. Additionally, surgery is regional trauma and thus likely causes regional, rather than systemic, impairment of the microcirculation. Whether or not the sublingual microcirculation is impaired after noncardiac surgery remains a subject of ongoing research. Similarly, it remains unclear if cardiac surgery, especially with cardiopulmonary bypass, impairs the sublingual microcirculation. The effects of therapeutic interventions specifically targeting the microcirculation remain to be elucidated and tested. Future research should focus on further improving microcirculation monitoring methods and investigating how regional microcirculation monitoring can inform clinical decision-making and treatment.

Sublingual Microcirculation in Temporary Mechanical Circulatory Support: A Current State of Knowledge

Cardiogenic shock causes hypoperfusion within the microcirculation, leading to impaired oxygen delivery, cell death, and progression of multiple organ failure. Mechanical circulatory support (MCS) is the last line of treatment for cardiac failure. The goal of MCS is to ensure end-organ perfusion by maintaining perfusion pressure and total blood flow. However, machine-blood interactions and the nonobvious translation of global macrohemodynamics into the microcirculation suggest that the use of MCS may not necessarily be associated with improved capillary flow. With the use of hand-held vital microscopes, it is possible to assess the microcirculation at the bedside. The paucity of literature on the use of microcirculatory assessment suggests the need for an in-depth look into microcirculatory assessment within the context of MCS. The purpose of this review is to discuss the possible interactions between MCS and microcirculation, as well as to describe the research conducted in this area. Regarding sublingual microcirculation, 3 types of MCS will be discussed: venoarterial extracorporeal membrane oxygenation, intra-aortic balloon counterpulsation, and microaxial flow pumps (Impella).

Symptom progression following on-pump versus off-pump coronary artery bypass graft surgery in patients with peripheral arterial disease

OBJECTIVE

This study aims to examine whether cardiac surgery leads to symptom progression in the early postoperative period in patients with the peripheral arterial disease (PAD) and evaluate the difference between on-pump (OPCAB) and off-pump (ONCAB) coronary artery bypass graft surgery with regard to the symptom progression.

METHODS

This retrospective study included one hundred consecutive adult patients with PAD at Fontaine stage 2b (pain-free walking distance less than 100 m) undergoing ONCAB and one hundred consecutive adult patients with PAD at Fontaine stage 2b (pain-free walking distance less than 100 m) undergoing OPCAB. Symptom progression was defined as the development of ischemic rest pain (Fontaine stage 3).

RESULTS

In the first week after surgery, 12 patients in the OPCAB group and 53 patients in the ONCAB group had postoperative symptom progression (p < 0.001). Rest pain resolved in most of these patients on the 15th postoperative day. At the end of the second month, rest pain resolved in all patients. Logistic regression analysis revealed that cardiac surgery with CPB, ABI < 0.5, postoperative nadir hct levels ≤ 25%, and intraoperative tissue hypoxia were independently associated with postoperative symptom progression.

CONCLUSIONS

In summary, we found that cardiac surgery may lead to symptom progression in patients with severe claudication in the early postoperative period. Our results suggest that OPCAB may lead to lower rates of symptom progression compared to ONCAB.

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.

Topical nitroglycerin to detect reversible microcirculatory dysfunction in patients with circulatory shock after cardiovascular surgery: an observational study

Persistent abnormalities in microcirculatory function are associated with poor clinical outcomes in patients with circulatory shock. We sought to identify patients with acutely reversible microcirculatory dysfunction using a low-dose topical nitroglycerin solution and handheld videomicroscopy during circulatory shock after cardiac surgery. Forty subjects were enrolled for the study, including 20 preoperative control and 20 post-operative patients with shock. To test whether microcirculatory dysfunction is acutely reversible during shock, the sublingual microcirculation was imaged with incident dark field microscopy before and after the application of 0.1 mL of a 1% nitroglycerin solution (1 mg/mL). Compared to the control group, patients with shock had a higher microcirculation heterogeneity index (MHI 0.33 vs. 0.12, p < 0.001) and a lower microvascular flow index (MFI 2.57 vs. 2.91, p < 0.001), total vessel density (TVD 22.47 vs. 25.90 mm/mm2, p = 0.005), proportion of perfused vessels (PPV 90.76 vs. 95.89%, p < 0.001) and perfused vessel density (PVD 20.44 vs. 24.81 mm/mm2, p < 0.001). After the nitroglycerin challenge, patients with shock had an increase in MFI (2.57 vs. 2.97, p < 0.001), TVD (22.47 vs. 27.51 mm/mm2, p < 0.009), PPV (90.76 vs. 95.91%, p < 0.001), PVD (20.44 vs. 26.41 mm/mm2, p < 0.001), venular RBC velocity (402.2 vs. 693.9 µm/s, p < 0.0004), and a decrease in MHI (0.33 vs. 0.04, p < 0.001. Thirteen of 20 patients showed a pharmacodynamic response, defined as an increase in PVD > 1.8 SD from shock baseline. Hemodynamics and vasoactive doses did not change during the 30-min study period. Our findings suggest a topical nitroglycerin challenge with handheld videomicroscopy can safely assess for localized recruitment of the microcirculatory blood flow in patients with circulatory shock and may be a useful test to identify nitroglycerin responsiveness.

Protocol for the MicroRESUS study: The impact of circulatory shock and resuscitation on microcirculatory function and mitochondrial respiration after cardiovascular surgery

Background

Despite current resuscitation strategies, circulatory shock and organ injury after cardiac surgery occur in 25–40% of patients. Goal-directed resuscitation after cardiac surgery has generated significant interest, but clinical practice to normalize hemodynamic variables including mean arterial pressure, cardiac filling pressures, and cardiac output may not reverse microcirculation abnormalities and do not address cellular dysoxia. Recent advances in technology have made it possible to measure critical components of oxygen delivery and oxygen utilization systems in live human tissues and blood cells. The MicroRESUS study will be the first study to measure microcirculatory and mitochondrial function in patients with circulatory shock and link these findings with clinical outcomes.

Methods and analysis

This will be a prospective, observational study that includes patients undergoing elective cardiovascular surgery with cardiopulmonary bypass (CPB). Microcirculation will be quantified with sublingual incident dark field videomicroscopy. Mitochondrial respiration will be measured by performing a substrate–uncoupler–inhibitor titration protocol with high resolution respirometry on peripheral blood mononuclear cells at baseline and serial timepoints during resuscitation and at recovery as a possible liquid biomarker. Plasma samples will be preserved for future analysis to examine endothelial injury and other mechanisms of microcirculatory dysfunction. Thirty-day ventilator and vasopressor-free days (VVFDs) will be measured as a primary outcome, along with sequential organ failure assessment scores, and other clinical parameters to determine if changes in microcirculation and mitochondrial respiration are more strongly associated with clinical outcomes compared to traditional resuscitation targets.

Discussion

This will be the first prospective study to examine both microcirculatory and mitochondrial function in human patients with circulatory shock undergoing cardiac bypass and address a key mechanistic knowledge gap in the cardiovascular literature. The results of this study will direct future research efforts and therapeutic development for patients with shock.

Hemodynamic evaluation of a new pulsatile blood pump during low flow cardiopulmonary bypass support

BACKGROUND

The VentriFlo^® True Pulse Pump (VentriFlo, Inc, Pelham, NH, USA) is a new pulsatile blood pump intended for use during short-term circulatory support. The purpose of this study was to evaluate the feasibility of the VentriFlo and compare it to a conventional centrifugal pump (ROTAFLOW, Getinge, Gothenberg, Sweden) in acute pig experiments.

METHODS

Pigs (40-45 kg) were supported by cardiopulmonary bypass (CPB) with the VentriFlo (n = 9) or ROTAFLOW (n = 5) for 6 h. Both VentriFlo and ROTAFLOW circuits utilized standard CPB components. We evaluated hemodynamics, blood chemistry, gas analysis, plasma hemoglobin, and microcirculation at the groin skin with computer-assisted video microscopy (Optilia, Sollentuna, Sweden).

RESULTS

Pigs were successfully supported by CPB for 6 h without any pump-related complications in either group. The VentriFlo delivered an average stroke volume of 29.2 ± 4.8 ml. VentriFlo delivered significantly higher pulse pressure (29.1 ± 7.2 mm Hg vs. 4.4 ± 7.0 mm Hg, p < 0.01) as measured in the carotid artery, with mean aortic pressure and pump flow comparable with those in ROTAFLOW. In blood gas analysis, arterial pH was significantly lower after five hours support in the VentriFlo group (7.30 ± 0.07 vs. 7.43 ± 0.03, p = 0.001). There was no significant difference in plasma hemoglobin level in both groups after six hours of CPB support. In microcirculatory assessment, VentriFlo tended to keep normal capillary flow, but it was not statistically significant.

CONCLUSIONS

VentriFlo-supported pigs showed comparable hemodynamic parameters with significantly higher pulse pressure compared to ROTAFLOW without hemolysis.

Low Microcirculatory Perfused Vessel Density and High Heterogeneity are Associated With Increased Intensity and Duration of Lactic Acidosis After Cardiac Surgery with Cardiopulmonary Bypass

INTRODUCTION

Lactic acidosis after cardiac surgery with cardiopulmonary bypass is common and associated with an increase in postoperative morbidity and mortality. A number of potential causes for an elevated lactate after cardiopulmonary bypass include cellular hypoxia, impaired tissue perfusion, ischemic-reperfusion injury, aerobic glycolysis, catecholamine infusions, and systemic inflammatory response after exposure to the artificial cardiopulmonary bypass circuit. Our goal was to examine the relationship between early abnormalities in microcirculatory convective blood flow and diffusive capacity and lactate kinetics during early resuscitation in the intensive care unit. We hypothesized that patients with impaired microcirculation after cardiac surgery would have a more severe postoperative hyperlactatemia, represented by the lactate time-integral of an arterial blood lactate concentration greater than 2.0 mmol/L.

METHODS

We measured sublingual microcirculation using incident darkfield video microscopy in 50 subjects on intensive care unit admission after cardiac surgery. Serial measurements of systemic hemodynamics, blood gas, lactate, and catecholamine infusions were recorded each hour for the first 6 h after surgery. Lactate area under the curve (AUC) was calculated over the first 6 h. The lactate AUC was compared between subjects with normal and low perfused vessel density (PVD < 18 mm/mm2), high microcirculatory heterogeneity index (MHI > 0.4), and low vessel-by-vessel microvascular flow index (MFIv < 2.6).

RESULTS

Thirteen (26%) patients had a low postoperative PVD, 20 patients (40%) had a high MHI, and 26 (52%) patients had a low MFIv. Patients with low perfused vessel density had higher lactate AUC compared with subjects with a normal PVD (22.3 [9.4-31.0] vs. 2.6 [0-8.8]; P < 0.0001). Patients with high microcirculatory heterogeneity had a higher lactate AUC compared with those with a normal MHI (2.5 [0.1-8.2] vs. 13.1 [3.7-31.1]; P < 0.001). We did not find a difference in lactate AUC when comparing high and low MFIv.

CONCLUSION

Low perfused vessel density and high microcirculatory heterogeneity are associated with an increased intensity and duration of lactic acidosis after cardiac surgery with cardiopulmonary bypass.

Effect of the oXiris membrane on microcirculation after cardiac surgery under cardiopulmonary bypass: study protocol for a randomised controlled trial (OXICARD Study)

INTRODUCTION

Cytokine storm and endotoxin release during cardiac surgery with cardiopulmonary bypass (CPB) have been related to vasoplegic shock and organ dysfunction. We hypothesised that early (during CPB) cytokine adsorption with oXiris membrane for patients at high risk of inflammatory syndrome following cardiac surgery may improve microcirculation, endothelial function and outcomes.

METHODS AND ANALYSIS

The Oxicard trial is a prospective, monocentric trial, randomising 70 patients scheduled for cardiac surgery. The inclusion criterion is patients aged more than 18 years old undergoing elective cardiac surgery under CPB with an expected CPB time >90 min (double valve replacement or valve replacement plus coronary arterial bypass graft). Patients will be allocated to the intervention group (n=35) or the control group (n=35). In the intervention group, oXiris membrane will be used on the Prismaflex device (Baxter) at blood pump flow of 450 mL/min during cardiac surgery under CPB. In the control group, cardiac surgery under CPB will be conducted as usual without oXiris membrane. An intention-to-treat analysis will be performed. The primary endpoint will be the microcirculatory flow index measured by sublingual microcirculation device at day 1 following cardiac surgery. The secondary endpoints will be other microcirculation variables at CPB end, 6 hours after CPB, at day 1 and at day 2. We also aim to evaluate the occurrence of major cardiovascular and cerebral events (eg, myocardial infarction, stroke, ischaemic mesenteric, resuscitated cardiac arrest, acute kidney injury) within the first 30 days. Cumulative catecholamine use, intensive care unit length of stay, endothelium glycocalyx shedding parameters (syndecan-1, heparan-sulfate and hyaluronic acid), inflammatory cytokines (tumour necrosis factor (TNF) alpha, interleukin 1 (IL1) beta, IL 10, IL 6, lipopolysaccharide, endothelin) and endothelial permeability biomarkers (angiopoietin 1, angiopoietin 2, Tie2 soluble receptor and Vascular Endothelial Growth Factor (VEGF) will also be evaluated.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Institutional Review Board of the University Hospital of Amiens (registration number ID RDB: 2019-A02437-50 in February 2020). Results of the study will be disseminated via peer-reviewed publications and presentations at national and international conferences.

TRIAL REGISTRATION NUMBER

NCT04201119.

Preoperative endothelial dysfunction in cutaneous microcirculation is associated with postoperative organ injury after cardiac surgery using extracorporeal circulation: a prospective cohort study

Background

Cardiac surgery is known to induce acute endothelial dysfunction, which may be central to the pathophysiology of postoperative complications. Preoperative endothelial dysfunction could also be implicated in the pathophysiology of postoperative complications after cardiac surgery. However, the relationship between preoperative endothelial function and postoperative outcomes remains unknown. The primary objective was to describe the relationship between a preoperative microcirculatory dysfunction identified by iontophoresis of acetylcholine (ACh), and postoperative organ injury in patients scheduled for cardiac surgery using cardiopulmonary bypass (CPB).

Methods

Sixty patients undergoing elective cardiac surgery using CPB were included in the analysis of a prospective, observational, single-center cohort study conducted from January to April 2019. Preoperative microcirculation was assessed with reactivity tests on the forearm (iontophoresis of ACh and nitroprusside). Skin blood flow was measured by laser speckle contrast imaging. Postoperative organ injury, the primary outcome, was defined as a Sequential Organ Failure Assessment score (SOFA) 48 h after surgery greater than 3.

Results

Organ injury at 48 h occurred in 29 cases (48.3%). Patients with postoperative organ injury (SOFA score > 3 at 48 h) had a longer time to reach the peak of preoperative iontophoresis of acetylcholine (133 s [104–156] vs 98 s [76–139] than patients without, P = 0.016), whereas endothelium-independent vasodilation to nitroprusside was similar in both groups. Beyond the proposed threshold of 105 s for time to reach the peak of preoperative endothelium-dependent vasodilation, three times more patients presented organ dysfunction at 48 h (76% vs 24% below or equal 105 s). In multivariable model, the time to reach the peak during iontophoresis of acetylcholine was an independent predictor of postoperative organ injury (odds ratio = 4.81, 95% confidence interval [1.16–19.94]; P = 0.030).

Conclusions

Patients who postoperatively developed organ injury (SOFA score > 3 at 48 h) had preoperatively a longer time to reach the peak of endothelium-dependent vasodilation.

Trial registration Clinical-Trials.gov, NCT03631797. Registered 15 August 2018, https://clinicaltrials.gov/ct2/show/NCT03631797

Central venous-to-arterial CO2 difference is a poor tool to predict adverse outcomes after cardiac surgery: a retrospective study

PURPOSE

The venous-to-arterial carbon dioxide partial pressure difference (CO₂ gap) has been reported to be a sensitive indicator of cardiac output adequacy. We aimed to assess whether the CO₂ gap can predict postoperative adverse outcomes after cardiac surgery.

METHODS

A retrospective study was conducted of 5,151 patients from our departmental database who underwent cardiac surgery from 1 January 2008 to 31 December 2018. Lactate level (mmol·L^-1), central venous oxygen saturation (ScVO₂) (%), and the venous-to-arterial carbon dioxide difference (CO₂ gap) were measured at intensive care unit (ICU) admission and on days 1 and 2 after cardiac surgery. The following postoperative adverse outcomes were collected: ICU mortality, hemopericardium or tamponade, resuscitated cardiac arrest, acute kidney injury, major bleeding, acute hepatic failure, mesenteric ischemia, and pneumonia. The primary outcome was the presence of at least one postoperative adverse outcome. Logistic regression was used to assess the association between ScVO₂, lactate, and the CO₂ gap with adverse outcomes. Their diagnostic performance was compared using a receiver operating characteristic (ROC) curve.

RESULTS

There were 1,933 patients (38%) with an adverse outcome. Cardiopulmonary bypass (CPB) parameters were similar between groups. The CO₂ gap was slightly higher for the "adverse outcomes" group than for the "no adverse outcomes" group. Arterial lactate at admission, day 1, and day 2 was also slightly higher in patients with adverse outcomes. Central venous oxygen saturation was not significantly different between patients with and without adverse outcomes. The area under the ROC curve to predict outcomes after CPB for the CO₂ gap at admission, day 1, and day 2 were 0.52, 0.55, and 0.53, respectively.

CONCLUSION

After cardiac surgery with CPB, the CO₂ gap at ICU admission, day 1, and day 2 was associated with postoperative adverse outcomes but showed poor diagnostic performance.

Severe Impairment of Microcirculatory Perfused Vessel Density Is Associated With Postoperative Lactate and Acute Organ Injury After Cardiac Surgery

OBJECTIVE

Resuscitation after cardiac surgery needs to address multiple pathophysiological processes that are associated with significant morbidity and mortality. Functional microcirculatory derangements despite normal systemic hemodynamics have been previously described but must be tied to clinical outcomes. The authors hypothesized that microcirculatory dysfunction after cardiac surgery would include impaired capillary blood flow and impaired diffusive capacity and that subjects with the lowest quartile of perfused vessel density would have an increased postoperative lactate level and acute organ injury scores.

DESIGN

Prospective, observational study.

SETTING

A single, tertiary university cardiovascular surgical intensive care unit.

PARTICIPANTS

25 adults undergoing elective cardiac surgery requiring cardiopulmonary bypass.

INTERVENTION

Sublingual microcirculation was imaged using incident dark field microscopy before and 2 to 4 hours after surgery in the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

Compared with baseline measurements, postoperative vessel-by-vessel microvascular flow index (2.9 [2.8-2.9] v 2.5 [2.4-2.7], p < 0.0001) and perfused vessel density were significantly impaired (20.7 [19.3-22.9] v 16.3 [12.8-17.9], p < 0.0001). The lowest quartile of perfused vessel density (<12.8 mm/mm2) was associated with a significantly increased postoperative lactate level (6.0 ± 2.9 v 1.8 ± 1.2, p < 0.05), peak lactate level (7.6 ± 2.8 v 2.8 ± 1.5, p = 0.03), and sequential organ failure assessment (SOFA) score at 24 and 48 hours.

CONCLUSION

In patients undergoing cardiac surgery, there was a significant decrease in postoperative microcirculatory convective blood flow and diffusive capacity during early postoperative resuscitation. Severely impaired perfused vessel density, represented by the lowest quartile of distribution, is significantly related to hyperlactatemia and early organ injury.

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

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

Microcirculatory perfusion disturbances following cardiopulmonary bypass: a systematic review

Background

Microcirculatory perfusion disturbances are associated with increased morbidity and mortality in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). Technological advancements made it possible to monitor sublingual microcirculatory perfusion over time. The goal of this review is to provide an overview of the course of alterations in sublingual microcirculatory perfusion following CPB. The secondary goal is to identify which parameter of sublingual microcirculatory perfusion is most profoundly affected by CPB.

Methods

PubMed and Embase databases were systematically searched according to PRISMA guidelines and as registered in PROSPERO. Studies that reported sublingual microcirculatory perfusion measurements before and after onset of CPB in adult patients undergoing cardiac surgery were included. The primary outcome was sublingual microcirculatory perfusion, represented by functional capillary density (FCD), perfused vessel density (PVD), total vessel density (TVD), proportion of perfused vessels (PPV), and microvascular flow index (MFI).

Results

The search identified 277 studies, of which 19 fulfilled all eligibility criteria. Initiation of CPB had a profound effect on FCD, PVD, or PPV. Seventeen studies (89%) reported one or more of these parameters, and in 11 of those studies (65%), there was a significant decrease in these parameters during cardiac surgery; the other 6 studies (35%) reported no effect. In 29% of the studies, FCD, PVD, or PPV normalized by the end of cardiac surgery, and in 24% percent of the studies, this effect lasted at least 24 h. There was no clear effect of CPB on TVD and a mixed effect on MFI.

Conclusion

CPB during cardiac surgery impaired sublingual microcirculatory perfusion as reflected by reduced FCD, PVD, and PPV. Four studies reported this effect at least 24 h after surgery. Further research is warranted to conclude on the duration of CPB-induced microcirculatory perfusion disturbances and the relationship with clinical outcome.

Trial registration

PROSPERO, CRD42019127798

Relevance of Microvascular Flow Assessments in Critically Ill Neonates and Children: A Systematic Review

OBJECTIVES

Resolution of impaired microvascular flow may lag the normalization of macrocirculatory variables. The significance of microcirculatory dysfunction in critically ill children and neonates is unknown, but microcirculatory variables can be measured using Doppler or videomicroscopy imaging techniques. We outline the current understanding of the role of the microcirculation in critical illness, review methods for its assessment, and perform a systematic review of how it has been monitored in critically ill neonates and children.

DESIGN

Systematic review (PROSPERO CRD42019117993).

SETTING

Not applicable.

SUBJECTS

Not applicable.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

We systematically searched MEDLINE, EMBASE, PubMed, and Web of Science. We included studies of critically ill patients 0 to 18 years old investigating microcirculatory blood flow. Two reviewers analyzed abstracts and articles. Results were qualitatively analyzed due to study heterogeneity. A total of 2,559 abstracts met search criteria, of which 94 underwent full-text review. Of those, 36 met inclusion criteria. Seven studies investigated microcirculatory changes in critically ill children. Twenty studies investigated the microcirculatory changes in neonates with variable diagnoses compared with a diverse set of clinical endpoints. Nine studies assessed the effects of age, sex, and birth weight on microvascular flow in neonates. Across all studies, microcirculatory dysfunction was associated with poor outcomes and may not correlate with observed macrovascular function.

CONCLUSIONS

Assessment of microvascular flow in critically ill children and neonates is possible, although significant challenges remain. In many such patients, microvascular blood flow is disrupted despite medical management targeting normalized macrovascular variables. Future studies are needed to define normal pediatric microvascular flow variables and to assess the impact of patient and treatment factors on its function.

Prospective, observational study of carbon dioxide gaps and free energy change and their association with fluid therapy following cardiac surgery

Background Venoarterial carbon dioxide pressure (p_v-a CO₂ ) and content (C_v-a CO₂ ) differences, including the ratio to arteriovenous oxygen content difference (C_a-v O₂ ), and free energy changes (-∆∆G_a-v ) may reflect tissue hypoperfusion. The associations with changes in cardiac output (CO) or oxygen consumption (VO₂ ) following fluid bolus administration were investigated. Methods Single-centre, observational study of 89 adult post-operative cardiac surgical patients admitted to ICU. The p_v-a CO₂ , C_v-a CO₂ and their ratios to C_a-v O₂ as well as the -∆∆G_a-v were determined before and after a 250-500 mL fluid bolus using arterial, central venous and mixed venous blood gas analyses. Responses associated with changes ≥ or <15% in CO or oxygen consumption (VO₂ ) were compared. Results In 234 boluses, the mixed venous to arterial p_v-a CO₂ and its ratio to C_a-v O₂ were independently associated with an increase in CO; odds ratio 1.3 (95% CI 1.1-1.5) and 1.7 (95% CI 1.5-1.9) respectively, P < .001) and VO₂ ; odds ratio 2.1 (95% CI 1.3-3.1), P < .001 for C_a-v O₂ . No measures of p_v-a CO₂ , C_v-a CO₂ or related ratios to the C_a-v O₂ were associated with an increase in CO ≥15% following a single volume bolus. The mixed venous and central venous C_v-a CO₂ to C_a-v O₂ ratios were different for the first bolus episode only; mean differences 0.81 (95% CI 0.13-1.5), P = .02 and 0.44 (95% CI 0.06-0.82), P = .02, respectively, for increased VO₂  ≥ 15%. The -∆∆G_a-v did not change. Conclusion The venoarterial carbon dioxide gradients and related calculations to assess the adequacy of tissue perfusion before a fluid bolus were not associated with subsequent increases in CO of oxygen consumption. Editorial Comment In some shock conditions, regional tissue hypoperfusion can be obvious and arterio-venous differences for CO₂ or O₂ may reflect this. This is not always the case; sometimes there are A-V differences or even a high lactate level without any obvious regional tissue hypoperfusion. Fluid therapy is a cornerstone in shock resuscitation treatment, but determining optimal fluid therapy is challenging, particularly as fluid overload may be detrimental. Fluid challenges are used as an "ex juvantebus" method to dose fluid therapy, but it is not clear if a positive response reflects a state of hypoperfusion or the existence of a cardiac reserve. Still, a better understanding on how to target and guide fluid therapy is welcome, and studies digging into the problem are needed. Here, invasively monitored post-operative cardiac surgery patients are assessed as a model to investigate if carbon dioxide gaps and free energy charge may be useful in detecting possible tissue hypoperfusion.

Central venous-to-arterial PCO2 difference, arteriovenous oxygen content and outcome after adult cardiac surgery with cardiopulmonary bypass: A prospective observational study

BACKGROUND

Rapid identification and treatment of tissue hypoxia reaching anaerobiosis (dysoxia) may reduce organ failure and the occurrence of major postoperative complications (MPC) after cardiac surgery. The predictive ability of PCO2-based dysoxia biomarkers, central venous-to-arterial PCO2 difference (ΔPCO2) and ΔPCO2 to arteriovenous oxygen content difference ratio, is poorly studied in this setting.

OBJECTIVES

We evaluated the ability of PCO2-based tissue dysoxia biomarkers, blood lactate concentration and central venous oxygen saturation measured 2 h after admission to the ICU as predictors of MPC.

DESIGN

A prospective, observational cohort study.

SETTING

Single-centre, academic hospital cardiovascular ICU.

PATIENTS

We included adult patients undergoing cardiac surgery with cardiopulmonary bypass and measured dysoxia biomarkers at ICU admission, and after 2, 6 and 24 h.

MAIN OUTCOME MEASURES

The primary endpoint was MPC, a composite of cardiac and noncardiac MPC evaluated in the 48 h following surgery. After univariate analysis of MPC covariates including dysoxia biomarkers measured at 2 h, multivariate logistic regression analyses were performed to identify the association of these biomarkers with MPC for confounders. Areas under the receiver operating characteristic curves were determined for biomarkers which remained independently associated with MPC.

RESULTS

MPC occurred in 56.5% of the 308 patients analysed. ΔPCO2, blood lactate concentration and central venous oxygen saturation measured at 2 h, but not ΔPCO2 to arteriovenous oxygen content difference ratio, were significantly associated with MPC. However, only ΔPCO2 was independently associated with MPC after multivariate analysis. The areas under the receiver operating characteristic curves of ΔPCO2 measured at 2 h for MPC prediction was 0.64 (95% CI 0.57 to 0.70, P < 0.001).

CONCLUSION

After cardiac surgery with cardiopulmonary bypass, ΔPCO2 measured 2 h after ICU admission was the only dysoxia biomarker independently associated with MPC, but with limited performance.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03107572.

Venous-to-arterial pCO2 difference in high-risk surgical patients

Alteration of tissue perfusion is a main contributor to organ dysfunction in high-risk surgical patients. The difference between venous carbon dioxide and arterial carbon dioxide pressure (pCO₂ gap) has been described as a parameter reflecting tissue hypoperfusion in critically ill patients who are insufficiently resuscitated. The pCO₂ gap/CavO₂ ratio has also been described as an indicator of the respiratory quotient, thus the relationship between DO₂ and VO₂. Most of the knowledge about the pCO₂ gap and the pCO₂ gap/CavO₂ ratio has come from studies in the literature on animal models or intensive care unit (ICU) patients. To date, publications pertaining to the operative setting are sparse. In the present review, we will first discuss the physiological background of the pCO₂ gap and CO₂-O₂ derived parameters used in the operating room. Few studies have focused on the clinical relevance of the pCO₂ gap in high-risk non-cardiac surgical patients. Prospective observational studies with a small sample size and retrospective studies have shown that the pCO₂ gap may be a useful complementary tool to identify patients who remain insufficiently optimized hemodynamically. In a few studies, a high pCO₂ gap was associated with postoperative complications following non-cardiac high-risk surgery. Results of observational studies conducted in patients undergoing cardiac surgery are contradictory. We focused on the divergence between non-cardiac surgery, cardiac surgery, and septic critically ill patients. When analyzing the literature, we can find some explanations for the discrepancies in the published results between cardiac and non-cardiac surgery. Finally, we will discuss the clinical utility of the pCO₂ gap in high-risk surgical patients.

Increased admission central venous-arterial CO2 difference predicts ICU-mortality in adult cardiac surgery patients

BACKGROUND

Invasive procedures such as cardiac surgery are associated with perioperative dysfunction of macrocirculation and/or microcirculation and organ failures. Maintenance or resuscitation of an adequate macrocirculation and/or microcirculation is thus crucial in patients after cardiac surgery. We investigated the prognostic power of early central venous-arterial carbon dioxide pressure difference (delta-pCO2) after cardiac surgery.

METHODS

Retrospective analysis of data from 1,019 cardiac surgery patients treated in the ICU of a tertiary medical care academic center. Clinical outcomes and laboratory measures including metabolic indices and calculated delta-pCO₂ were assessed. Receiver operating characteristic (ROC) curves were generated and sensitivity / specificity analysis was performed. Univariate and multivariate regression models were analyzed.

RESULTS

The area under the ROC curve for delta-pCO₂ to predict ICU mortality was 0.72 (sensitivity 65% / specificity 76%) with an optimal delta-pCO₂ cut-off value of 8.6 mmHg. In multivariate regression, delta-pCO₂ was associated with increased ICU mortality (HR 3.72, 95%-CI 1.3-10.66, p = 0.02). After adjustment for typical confounders, delta-pCO₂ remained as independent predictor of ICU mortality after cardiac surgery.

CONCLUSIONS

In a retrospective data analysis in a large sample of adult post cardiac surgery patients treated in the ICU, we observed that admission central venous-arterial delta-pCO₂ independently predicts ICU mortality. Delta-pCO₂ might thus contribute risk stratification in ICU patients after cardiac surgery.

Postoperative microcirculatory perfusion and endothelial glycocalyx shedding following cardiac surgery with cardiopulmonary bypass

We investigated microcirculatory perfusion disturbances following cardiopulmonary bypass in the early postoperative period and whether the course of these disturbances mirrored restoration of endothelial glycocalyx integrity. We performed sublingual sidestream dark field imaging of the microcirculation during the first three postoperative days in patients who had undergone on‐pump coronary artery bypass graft surgery. We calculated the perfused vessel density, proportion of perfused vessels and perfused boundary region. Plasma was obtained to measure heparan sulphate and syndecan‐1 levels as glycocalyx shedding markers. We recruited 17 patients; the mean (SD) duration of non‐pulsatile cardiopulmonary bypass was 103 (18) min, following which 491 (29) ml autologous blood was transfused through cell salvage. Cardiopulmonary bypass immediately decreased both microcirculatory perfused vessel density; 11 (3) vs. 16 (4) mm.mm⁻², p = 0.052 and the proportion of perfused vessels; 92 (5) vs. 69 (9) %, p < 0.0001. The proportion of perfused vessels did not increase after transfusion of autologous salvaged blood following cardiopulmonary bypass; 72 (7) %, p = 0.19 or during the first three postoperative days; 71 (5) %, p < 0.0001. The perfused boundary region increased after cardiopulmonary bypass; 2.2 (0.3) vs. 1.9 (0.3) μm, p = 0.037 and during the first three postoperative days; 2.4 (0.3) vs. 1.9 (0.3) μm, p = 0.003. Increased plasma heparan sulphate levels were inversely associated with the proportion of perfused vessels during cardiopulmonary bypass; R = −0.49, p = 0.02. Plasma syndecan‐1 levels were inversely associated with the proportion of perfused vessels during the entire study period; R = −0.51, p < 0.0001. Our study shows that cardiopulmonary bypass‐induced acute microcirculatory perfusion disturbances persist in the first three postoperative days, and are associated with prolonged endothelial glycocalyx shedding. This suggests prolonged impairment and delayed recovery of both microcirculatory perfusion and function after on‐pump cardiac surgery.

The ratios of central venous to arterial carbon dioxide content and tension to arteriovenous oxygen content are not associated with overall anaerobic metabolism in postoperative cardiac surgery patients

Background

The aim of the present study was to evaluate the ability of the ratios of central venous to arterial carbon dioxide content and tension to arteriovenous oxygen content to predict an increase in oxygen consumption (VO₂) upon fluid challenge (FC).

Methods and results

110 patients admitted to cardiothoracic ICU and in whom the physician had decided to perform an FC (with 500 ml of Ringer's lactate solution) were included. The arterial pressure, cardiac index (Ci), and arterial and venous blood gas levels were measured before and after FC. VO₂ and CO₂-O₂ derived variables were calculated. VO₂ responders were defined as patients showing more than a 15% increase in VO₂. Of the 92 FC responders, 43 (46%) were VO₂ responders. At baseline, pCO₂ gap, C(a-v)O₂ were lower in VO₂ responders than in VO₂ non-responders, and central venous oxygen saturation (ScvO₂) was higher in VO₂ responders. FC was associated with an increase in MAP, SV, and CI in both groups. With regard to ScvO_2, FC was associated with an increase in VO₂ non-responders and a decrease in VO₂ responders. FC was associated with a decrease in pvCO₂ and pCO₂ gap in VO₂ non-responders only. The pCO₂ gap/C(a-v)O₂ ratio and C(a-v)CO₂ content /C(a-v)O₂ content ratio did not change with FC. The CO₂ gap content/C(a-v)O₂ content ratio and the C(a-v)CO₂ content /C(a-v)O₂ content ratio did not predict fluid-induced VO₂ changes (area under the curve (AUC) [95% confidence interval (CI)] = 0.52 [0.39‒0.64] and 0.53 [0.4–0.65], respectively; p = 0.757 and 0.71, respectively). ScvO₂ predicted an increase of more than 15% in the VO₂ (AUC [95%CI] = 0.67 [0.55‒0.78]; p<0.0001).

Conclusions

Our results showed that the ratios of central venous to arterial carbon dioxide content and tension to arteriovenous oxygen content were not predictive of VO₂ changes following fluid challenge in postoperative cardiac surgery patients.

Sublingual microcirculatory alterations in cirrhotic patients

OBJECTIVE

To assess sublingual microcirculation in cirrhotic patients and its relationship to spider angiomas, complications, and outcome.

METHODS

Thirty-one cirrhotic patients were prospectively compared to 31 matched controls. Sublingual microcirculation was evaluated by videomicroscopy. We specifically looked for capillaries with increased RBCV, which was defined as a velocity higher than the percentile 100th of controls.

RESULTS

Compared to controls, cirrhotic patients showed decreased total and PVD (14.4 ± 2.2 vs 16.0 ± 1.3 and 14.1 ± 2.3 vs 15.9 ± 1.6 mm/mm² , respectively, P < .001 for both) and increased HFI (0.64 ± 0.39 vs 0.36 ± 0.21, P = .001). They also exhibited high RBCV in 2% of the microvessels (P < .0001). Patients with MELD score ≥10 had higher RBCV than patients with score <10 (1414 ± 290 vs 1206 ± 239 μm/s, P < .05). Patients with spider angiomas showed lower vascular densities. Microcirculation did not differ between survivors and nonsurvivors.

CONCLUSIONS

Cirrhosis is associated with microcirculatory alterations that can be easily monitored in the sublingual mucosa. Alterations included decreased density and PPV and hyperdynamic microvessels. The most striking finding, however, was the microvascular heterogeneity. Patients with spider angiomas had more severe alterations. Larger studies should clarify the relationship between microcirculatory abnormalities and outcome.

Identification and quantification of human microcirculatory leukocytes using handheld video microscopes at the bedside

Leukocyte recruitment and adhesion to the endothelium are hallmarks of systemic inflammation that manifest in a wide range of diseases. At present, no method is available to directly measure leukocyte kinetics at the bedside. In this study, we validate a new method to identify and quantify microcirculatory leukocytes observed by handheld vital microscopy (HVM) using space-time diagram (STD) analysis. Video clips ( n = 59) containing one capillary-postcapillary venule unit where leukocytes could be observed emanating from a capillary into a venule in cardiac surgery patients ( n = 20) were included. STD analysis and manual counting were used to quantify the number of leukocytes (total, rolling, and nonrolling). Pearson's correlation and Bland-Altman analysis were used to determine agreement between the STDs and manual counting. For reproducibility, intra- and interobserver coefficients of variation (CVs) were assessed. Leukocyte (rolling and nonrolling) and red blood cell velocities were assessed. The STDs and manual counting procedures for the quantification of rolling leukocytes showed good agreement ( r = 0.8197, P < 0.0001), with a Bland-Altman analysis mean difference of -0.0 (-6.56; 6.56). The overall intraobserver CV for the STD method was 1.5%. The overall interobserver CVs for the STD and the manual method were 5.6% and 9.4%, respectively. The nonrolling velocity was significantly higher than the rolling velocity (812 ± 519 µm/s vs. 201 ± 149 µm/s, P = 0.001). STD results agreed with the manual counting procedure results, had a better reproducibility, and could assess the leukocyte velocity. STD analysis using bedside HVM imaging presented a new methodology for quantifying leukocyte kinetics and functions in the microcirculation. NEW & NOTEWORTHY In this study, we introduce space-time diagram analysis of sublingual microcirculation imaging using handheld vital microscopy to identify and quantify the presence and kinetics of human microcirculatory leukocytes. We validated the methodology by choosing anatomical units consisting of a capillary connected to a venule, which allowed precise identification of leukocytes.

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

Severity of hyperoxia as a risk factor in patients undergoing on-pump cardiac surgery

Background.

Hyperoxia has long been perceived as a desirable or at least an inevitable part of cardiopulmonary bypass. Recent evidence suggest that it might have multiple detrimental effects on patient homeostasis. The aim of the study was to identify the determinants of supra-physiological values of partial oxygen pressure during on-pump cardiac surgery and to assess the impact of hyperoxia on clinical outcomes.

Materials and methods.

Retrospective data analysis of the institutional research database was performed to evaluate the effects of hyperoxia in patients undergoing elective cardiac surgery with cardiopulmonary bypass, 246 patients were included in the final analysis. Patients were divided in three groups: mild hyperoxia (MHO, PaO₂ 100–199 mmHg), moderate hyperoxia (MdHO, PaO₂ 200–299 mmHg), and severe hyperoxia (SHO, PaO₂ >300 mmHg). Postoperative complications and outcomes were defined according to standardised criteria of the Society of Thoracic Surgeons.

Results.

The extent of hyperoxia was more immense in patients with a lower body mass index (p = 0.001) and of female sex (p = 0.005). A significant link between severe hyperoxia and a higher incidence of infectious complications (p – 0.044), an increased length of hospital stay (p – 0.044) and extended duration of mechanical ventilation (p < 0.001) was confirmed.

Conclusions.

Severe hyperoxia is associated with an increased incidence of postoperative infectious complications, prolonged mechanical ventilation, and increased hospital stay.

Four-Dimensional Microvascular Analysis Reveals That Regenerative Angiogenesis in Ischemic Muscle Produces a Flawed Microcirculation

Rationale:

Angiogenesis occurs after ischemic injury to skeletal muscle, and enhancing this response has been a therapeutic goal. However, to appropriately deliver oxygen, a precisely organized and exquisitely responsive microcirculation must form. Whether these network attributes exist in a regenerated microcirculation is unknown, and methodologies for answering this have been lacking.

Objective:

To develop 4-dimensional methodologies for elucidating microarchitecture and function of the reconstructed microcirculation in skeletal muscle.

Methods and Results:

We established a model of complete microcirculatory regeneration after ischemia-induced obliteration in the mouse extensor digitorum longus muscle. Dynamic imaging of red blood cells revealed the regeneration of an extensive network of flowing neo-microvessels, which after 14 days structurally resembled that of uninjured muscle. However, the skeletal muscle remained hypoxic. Red blood cell transit analysis revealed slow and stalled flow in the regenerated capillaries and extensive arteriolar-venular shunting. Furthermore, spatial heterogeneity in capillary red cell transit was highly constrained, and red blood cell oxygen saturation was low and inappropriately variable. These abnormalities persisted to 120 days after injury. To determine whether the regenerated microcirculation could regulate flow, the muscle was subjected to local hypoxia using an oxygen-permeable membrane. Hypoxia promptly increased red cell velocity and flux in control capillaries, but in neocapillaries, the response was blunted. Three-dimensional confocal imaging revealed that neoarterioles were aberrantly covered by smooth muscle cells, with increased interprocess spacing and haphazard actin microfilament bundles.

Conclusions:

Despite robust neovascularization, the microcirculation formed by regenerative angiogenesis in skeletal muscle is profoundly flawed in both structure and function, with no evidence for normalizing over time. This network-level dysfunction must be recognized and overcome to advance regenerative approaches for ischemic disease.

Similar Microcirculatory Alterations in Patients with Normodynamic and Hyperdynamic Septic Shock

RATIONALE

In normodynamic septic shock, the quantitative assessment of sublingual microcirculation has shown decreases in perfused vascular density and red blood cell velocity. However, no studies have been performed in hyperdynamic septic shock.

OBJECTIVES

To characterize the microcirculatory patterns and rule out the presence of fast red blood cell velocity in patients with hyperdynamic septic shock.

METHODS

We prospectively evaluated the sublingual microcirculation in healthy volunteers (n = 20) and in patients with hyperdynamic (n = 20) and normodynamic (n = 20) septic shock. Hyperdynamic septic shock was defined by a cardiac index >4.0 L/min/m(2). The microcirculation was assessed with sidestream dark field imaging and AVA 3.0 software.

MEASUREMENTS AND MAIN RESULTS

There were no differences in perfused vascular density, proportion of perfused vessels, or microvascular flow index between patients with hyperdynamic and normodynamic septic shock, but these variables were reduced compared with those of healthy volunteers, A similar pattern was observed in red blood cell velocity (912 ± 291, 968 ± 204, and 1303 ± 120 μm/s, respectively; P < 0.0001) and its coefficient of variation. In both types of septic shock, no microvessel had a red blood cell velocity higher than the 100th percentile value for healthy volunteers.

CONCLUSIONS

Patients with hyperdynamic septic shock showed microcirculatory alterations similar to those of patients with normal cardiac output. Both groups of patients had reduced perfused vascular density and red blood cell velocity and increased flow heterogeneity compared with that of healthy subjects. Fast red blood cell velocity was not found, even in patients with high cardiac output. These results support the conclusion that microcirculatory function is frequently dissociated from systemic hemodynamic derangements in septic shock.

Regulation of blood flow and volume exchange across the microcirculation

Oxygen delivery to cells is the basic prerequisite of life. Within the human body, an ingenious oxygen delivery system, comprising steps of convection and diffusion from the upper airways via the lungs and the cardiovascular system to the microvascular area, bridges the gap between oxygen in the outside airspace and the interstitial space around the cells. However, the complexity of this evolutionary development makes us prone to pathophysiological problems. While those problems related to respiration and macrohemodynamics have already been successfully addressed by modern medicine, the pathophysiology of the microcirculation is still often a closed book in daily practice. Nevertheless, here as well, profound physiological understanding is the only key to rational therapeutic decisions. The prime guarantor of tissue oxygenation is tissue blood flow. Therefore, on the premise of intact macrohemodynamics, the microcirculation has three major responsibilities: 1) providing access for oxygenated blood to the tissues and appropriate return of volume; 2) maintaining global tissue flood flow, even in the face of changes in central blood pressure; and 3) linking local blood flow to local metabolic needs. It is an intriguing concept of nature to do this mainly by local regulatory mechanisms, impacting primarily on flow resistance, be this via endothelial or direct smooth muscle actions. The final goal of microvascular blood flow per unit of time is to ensure the needed exchange of substances between tissue and blood compartments. The two principle means of accomplishing this are diffusion and filtration. While simple diffusion is the quantitatively most important form of capillary exchange activity for the respiratory gases, water flux across the blood-brain barrier is facilitated via preformed specialized channels, the aquaporines. Beyond that, the vascular barrier is practically nowhere completely tight for water, with paracellular filtration giving rise to generally low but permanent fluid flux outwards into the interstitial space at the microvascular high pressure segment. At the more leaky venular aspect, both filtration and diffusion allow for bidirectional passage of water, nutrients, and waste products. We are just beginning to appreciate that a major factor for maintaining tissue fluid homeostasis appears to be the integrity of the endothelial glycocalyx.

Microcirculatory changes during cardiac surgery with cardiopulmonary bypass

OBJECTIVE

To evaluate microcirculation in intermediate and high mortality risk patients undergoing cardiac surgery (CS) with cardiopulmonary bypass (CPB).

PATIENTS AND METHODS

The study included 22 patients with a Euroscore >3. Using the Videomicroscopy Side Stream Dark Field system, and evaluation was made of, capillary density, proportion of perfused capillaries, density of perfused capillaries, microcirculatory flow index (MFI), and heterogeneity flow index. Three to five video sequences were recorded: after induction of anaesthesia (T1), at the beginning of the CPB (T2), before finalising CPB (T3), at the end of the surgery, and before the patient was transferred to Intensive Care Unit (T4). Mean arterial pressure decreased, while the blood lactate increased significantly, when comparing the initial and final values (P<.05). MFI increased significantly in T3 and T4 (P<.05) with regards to the initial values. When the patients with and without postoperative complications were compared, significant differences were found in, Euroscore, left ventricular ejection fraction, and MFI in T3.

CONCLUSIONS

in patients with intermediate/high preoperative risk, CS and CBP can involve an increase in MFI and blood lactate at the end of the study. These alterations suggest the possibility of a functional microcirculatory shunt at tissue perfusion level, secondary to the surgical injury and the CPB. Further investigation is needed to have a better understanding of the mechanisms involved.

Impaired microcirculatory perfusion in a rat model of cardiopulmonary bypass: the role of hemodilution

Although hemodilution is attributed as the main cause of microcirculatory impairment during cardiopulmonary bypass (CPB), this relationship has never been investigated. We investigated the distinct effects of hemodilution with or without CPB on microvascular perfusion and subsequent renal tissue injury in a rat model. Male Wistar rats (375–425 g) were anesthetized, prepared for cremaster muscle intravital microscopy, and subjected to CPB ( n = 9), hemodilution alone ( n = 9), or a sham procedure ( n = 6). Microcirculatory recordings were performed at multiple time points and analyzed for perfusion characteristics. Kidney and lung tissue were investigated for mRNA expression for genes regulating inflammation and endothelial adhesion molecule expression. Renal injury was assessed with immunohistochemistry. Hematocrit levels dropped to 0.24 ± 0.03 l/l and 0.22 ± 0.02 l/l after onset of hemodilution with or without CPB. Microcirculatory perfusion remained unaltered in sham rats. Hemodilution alone induced a 13% decrease in perfused capillaries, after which recovery was observed. Onset of CPB reduced the perfused capillaries by 40% (9.2 ± 0.9 to 5.5 ± 1.5 perfused capillaries per microscope field; P < 0.001), and this reduction persisted throughout the experiment. Endothelial and inflammatory activation and renal histological injury were increased after CPB compared with hemodilution or sham procedure. Hemodilution leads to minor and transient disturbances in microcirculatory perfusion, which cannot fully explain impaired microcirculation following cardiopulmonary bypass. CPB led to increased renal injury and endothelial adhesion molecule expression in the kidney and lung compared with hemodilution. Our findings suggest that microcirculatory impairment during CPB may play a role in the development of kidney injury.

What is microcirculatory shock?

PURPOSE OF REVIEW

Microcirculatory shock is a condition defined by the presence of tissue hypoperfusion despite the normalization of systemic and regional blood flow. In this article, we discuss the characteristics of the microcirculation in septic shock, the main form of microcirculatory shock, along with its interaction with systemic hemodynamics, and the response to different therapies.

RECENT FINDINGS

In septic shock, microcirculatory abnormalities are common, and more severe in nonsurvivors. In addition, the microcirculation shows a behavior that is frequently dissociated from that of systemic hemodynamics. Therefore, microcirculatory alterations may persist despite correction of systemic hemodynamic variables. Sublingual and intestinal microcirculation might also display divergent behaviors. Moreover, microvascular alterations may improve in response to hemodynamic resuscitation, but the response might depend on the underlying microcirculatory alterations. Particularly, the response to fluids seems to be related to both its basal state and the magnitude of the increase in cardiac output.

SUMMARY

The optimal treatment of microcirculatory shock might require monitoring and therapeutic goals targeted on the microcirculation, more than in systemic variables. The clinical benefits of this approach should be demonstrated in clinical trials.

Cardiovascular effects of hyperoxia during and after cardiac surgery

During and after cardiac surgery with cardiopulmonary bypass, high concentrations of oxygen are routinely administered, with the intention of preventing cellular hypoxia. We systematically reviewed the literature addressing the effects of arterial hyperoxia. Extensive evidence from pre-clinical experiments and clinical studies in other patient groups suggests predominant harm, caused by oxidative stress, vasoconstriction, perfusion heterogeneity and myocardial injury. Whether these alterations are temporary and benign, or actually affect clinical outcome, remains to be demonstrated. In nine clinical cardiac surgical studies in low-risk patients, higher oxygen targets tended to compromise cardiovascular function, but did not affect clinical outcome. No data about potential beneficial effects of hyperoxia, such as reduction of gas micro-emboli or post-cardiac surgery infections, were reported. Current evidence is insufficient to specify optimal oxygen targets. Nevertheless, the safety of supraphysiological oxygen suppletion is unproven. Randomised studies with a variety of oxygen targets and inclusion of high-risk patients are needed to identify optimal oxygen targets during and after cardiac surgery.

Effects of early hemodynamic resuscitation on left ventricular performance and microcirculatory function during endotoxic shock

Background

Microcirculation and macrohemodynamics are severely compromised during septic shock. However, the relationship between these two compartments needs to be further investigated. We hypothesized that early resuscitation restores left ventricular (LV) performance and microcirculatory function but fails to prevent metabolic disorders. We studied the effects of an early resuscitation protocol (ERP) on LV pressure/volume loops-derived parameters, sublingual microcirculation, and metabolic alterations during endotoxic shock.

Methods

Twenty-five pigs were randomized into three groups: LPS group: Escherichia coli lipopolysaccharide (LPS); ERP group: LPS + ERP based on volume expansion, dobutamine, and noradrenaline infusion; Sham group. LV pressure/volume-derived parameters, systemic hemodynamics, sublingual microcirculation, and metabolic profile were assessed at baseline and after completing the resuscitation protocol.

Results

LPS significantly decreased LV end-diastolic volume, myocardial contractility, stroke work, and cardiac index (CI). Early resuscitation preserved preload, and myocardial contractility, increased CI and heart rate (p < .05). LPS severely diminished sublingual microvascular flow index (MFI), perfused vascular density (PVD), and the proportion of perfused vessels (PPV), while increased the heterogeneity flow index (HFI) (p < .05). Despite MFI was relatively preserved, MVD, PVD, and HFI were significantly impaired after resuscitation (p < .05). The macro- and microcirculatory changes were associated with increased lactic acidosis and mixed venous O₂ saturation when compared to baseline values (p < .05). The scatter plot between mean arterial pressure (MAP) and MFI showed a biphasic relationship, suggesting that the values were within the limits of microvascular autoregulation when MAP was above 71 ± 6 mm Hg (R² = 0.63).

Conclusions

Early hemodynamic resuscitation was effective to restore macrohemodynamia and myocardial contractility. Despite MAP and MFI were relatively preserved, the persistent microvascular dysfunction could explain metabolic disorders. The relationship between micro- and systemic hemodynamia and their impact on cellular function and metabolism needs to be further studied during endotoxic shock.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-015-0049-y) contains supplementary material, which is available to authorized users.