Monitoring of Conjunctival Microcirculation Reflects Sublingual Microcirculation in Ovine Septic and Hemorrhagic Shock

HEMORRHAGIC SHOCK ASSESSED BY TISSUE MICROCIRCULATORY MONITORING: A NARRATIVE REVIEW

ABSTRACT

Hemorrhagic shock (HS) is a common complication after traumatic injury. Early identification of HS can reduce patients' risk of death. Currently, the identification of HS relies on macrocirculation indicators such as systolic blood pressure and heart rate, which are easily affected by the body's compensatory functions. Recently, the independence of the body's overall macrocirculation from microcirculation has been demonstrated, and microcirculation indicators have been widely used in the evaluation of HS. In this study, we reviewed the progress of research in the literature on the use of microcirculation metrics to monitor shock. We analyzed the strengths and weaknesses of each metric and found that microcirculation monitoring could not only indicate changes in tissue perfusion before changes in macrocirculation occurred but also correct tissue perfusion and cell oxygenation after the macrocirculation index returned to normal following fluid resuscitation, which is conducive to the early prediction and prognosis of HS. However, microcirculation monitoring is greatly affected by individual differences and environmental factors. Therefore, the current limitations of microcirculation assessments mean that they should be incorporated as part of an overall assessment of HS patients. Future research should explore how to better combine microcirculation and macrocirculation monitoring for the early identification and prognosis of HS patients.

Eye signs as a novel risk predictor in pulmonary arterial hypertension associated with systemic lupus erythematosus

OBJECTIVE

To investigate the role of eye signs in predicting poor outcomes in systemic lupus erythematosus (SLE) patients with pulmonary arterial hypertension (PAH).

METHODS

This prospective observational study recruited patients diagnosed with SLE-PAH from Jan. 2021 to Dec. 2021 at the First Affiliated Hospital of Nanchang University; those with other potential causes of PAH were excluded. The evaluation of various parameters, such as N-terminal prohormone of brain natriuretic peptide (NT-proBNP), 6-minute walking distance (6MWD), World Health Organization functional class (WHO-FC), echocardiography, and risk stratification based on the 2015 European Society of Cardiology (ESC)/European Respiratory Society (ERS) Guidelines, was conducted at intervals of every 1-3 months, and a 6-month follow-up period was observed. The primary outcome measure considered improvement if there was a decline in the risk stratification grade at the end point and unimproved if there was no decline. Conjunctival microvascular images were observed and recorded.

RESULTS

A total of 29 SLE-PAH patients were enrolled, comprising 12 in the improved group and 17 in the nonimproved group. All SLE-PAH patients showed various manifestations of eye signs, including vessel twisting, dilation, ischaemic areas, haemorrhages, reticulum deformity, and wound spots. The nonimproved group exhibited significantly lower vessel density (VD) and microvascular flow index (MFI) of conjunctival microvascular images than the improved group. Correlation analysis revealed that VD displayed a negative correlation with the WHO-FC (r = -0.413, p = 0.026) and NT-proBNP (r = -0.472, p = 0.010), as well as a positive correlation with the 6MWD (r = 0.561, p = 0.002). Similarly, MFI exhibited a negative correlation with WHO-FC (r = -0.408, p = 0.028) and NT-proBNP (r = -0.472, p = 0.010) and a positive correlation with 6MWD (r = 0.157, p = 0.004). Multivariate logistic regression analysis indicated that VD (OR 10.11, 95% CI 1.95-52.36), MFI (OR 7.85, 95% CI 1.73-35.67), NT-proBNP, and 6MWD were influential factors in predicting the prognostic improvement of SLE-PAH patients. ROC curve analysis demonstrated that VD, MFI, 6MWD, and NT-proBNP (with respective AUC values of 0.83, 0.83, 0.76, and 0.90, respectively) possessed a sensitivity and specificity of 75 and 100%, as well as 83 and 100%, respectively. Regarding prognostic prediction, VD and MFI exhibited higher sensitivity than 6MWD, whereas MFI displayed higher sensitivity and specificity than NT-proBNP.

CONCLUSION

SLE-PAH can lead to various conjunctival microvascular manifestations in which vascular density and microvascular flow index can be used to assess cardiopulmonary function and predict therapeutic efficacy and prognosis in SLE-PAH patients.

Conjunctival microcirculation in ocular and systemic microvascular disease

The conjunctival microcirculation is an accessible complex network of micro vessels whose quantitative assessment can reveal microvascular haemodynamic properties. Currently, algorithms for the measurement of conjunctival haemodynamics use either manual or semi-automated systems, which may provide insight into overall conjunctival health, as well as in ocular and systemic disease. These algorithms include functional slit-lamp biomicroscopy, laser doppler flowmetry, optical coherence tomography angiography, orthogonal polarized spectral imaging, computer-assisted intravitral microscopy, diffuse reflectance spectroscopy and corneal confocal microscopy. Furthermore, several studies have demonstrated a relationship between conjunctival microcirculatory haemodynamics and many diseases such as dry eye disease, Alzheimer's disease, diabetes, hypertension, sepsis, coronary microvascular disease, and sickle cell anaemia. This review aims to describe conjunctival microcirculation, its characteristics, and techniques for its measurement, as well as the association between conjunctival microcirculation and microvascular abnormalities in disease states.

Retinal blood flow in critical illness and systemic disease: a review

BACKGROUND

Assessment and maintenance of end-organ perfusion are key to resuscitation in critical illness, although there are limited direct methods or proxy measures to assess cerebral perfusion. Novel non-invasive methods of monitoring microcirculation in critically ill patients offer the potential for real-time updates to improve patient outcomes.

MAIN BODY

Parallel mechanisms autoregulate retinal and cerebral microcirculation to maintain blood flow to meet metabolic demands across a range of perfusion pressures. Cerebral blood flow (CBF) is reduced and autoregulation impaired in sepsis, but current methods to image CBF do not reproducibly assess the microcirculation. Peripheral microcirculatory blood flow may be imaged in sublingual and conjunctival mucosa and is impaired in sepsis. Retinal microcirculation can be directly imaged by optical coherence tomography angiography (OCTA) during perfusion-deficit states such as sepsis, and other systemic haemodynamic disturbances such as acute coronary syndrome, and systemic inflammatory conditions such as inflammatory bowel disease.

CONCLUSION

Monitoring microcirculatory flow offers the potential to enhance monitoring in the care of critically ill patients, and imaging retinal blood flow during critical illness offers a potential biomarker for cerebral microcirculatory perfusion.

An adaptive fractal model for sublingual microcirculation

The hemodynamic conditions and partial pressure of oxygen in microcirculation generally indicate the status of tissue perfusion, which provides essential information for the assessment and treatment of critical diseases such as sepsis. The human tongue is known to have abundant microcirculation and is an ideal window to observe the microcirculation. At present, the monitoring of sublingual microcirculation is mostly achieved using handheld vital microscopy (HVM). Microcirculation is organized and works as a network. However, HVM can obtain only limited view of few vessels and is not able to acquire information regarding the entire network. In this work, we proposed a method to construct a mathematical network model of sublingual microcirculation to solve the problems. The proposed method is based on fractal analysis to model and simulate the hemodynamic and functional activities of sublingual microcirculation. Specifically, the HVM technology is used to obtain the partial morphological and hemodynamic data of sublingual microcirculation, and fractal analysis is applied thereafter to establish the hemodynamic model of the network based on the data from few vessels. Further, the adaptive regulation mechanism of microcirculation is introduced to enhance the performance of the model. The model was validated by the experimental data and the results are consistent with the characteristics of microcirculation. The work demonstrates the potential of the proposed method in sublingual microcirculation research and for the further assessment of tissue perfusion.

Superior Survival Outcomes of a Polyethylene Glycol-20k Based Resuscitation Solution in a Preclinical Porcine Model of Lethal Hemorrhagic Shock

OBJECTIVE

To compare early outcomes and 24-hour survival after LVR with the novel polyethylene glycol-20k-based crystalloid (PEG-20k), WB, or hextend in a preclinical model of lethal HS.

BACKGROUND

Posttraumatic HS is a major cause of preventable death. Current resuscitation strategies focus on restoring oxygen-carrying capacity (OCC) and coagulation with blood products. Our lab shows that PEG-20k is an effective non-sanguineous, LVR solution in acute models of HS through mechanisms targeting cell swelling-induced microcirculatory failure.

METHODS

Male pigs underwent splenectomy followed by controlled hemorrhage until lactate reached 7.5-8.5 mmol/L. They were randomized to receive LVR with PEG-20k, WB, or Hextend. Surviving animals were recovered 4 hours post-LVR. Outcomes included 24-hour survival rates, mean arterial pressure, lactate, hemoglobin, and estimated intravascular volume changes.

RESULTS

Twenty-four-hour survival rates were 100%, 16.7%, and 0% in the PEG-20k, WB, and Hextend groups, respectively (P = 0.001). PEG-20k significantly restored mean arterial press, intravascular volume, and capillary perfusion to baseline, compared to other groups. This caused complete lactate clearance despite decreased OCC. Neurological function was normal after next-day recovery in PEG-20k resuscitated pigs.

CONCLUSION

Superior early and 24-hour outcomes were observed with PEG-20k LVR compared to WB and Hextend in a preclinical porcine model of lethal HS, despite decreased OCC from substantial volume-expansion. These findings demonstrate the importance of enhancing microcirculatory perfusion in early resuscitation strategies.

Ocular microvascular changes in patients with sepsis: a prospective observational study

Background

The aim of the study was to detect differences in the conjunctival microcirculation between septic patients and healthy subjects and to evaluate the course of conjunctival and retinal microvasculature in survivors and non-survivors over a 24-h period of time.

Methods

This single-center prospective observational study was performed in mixed ICU in a tertiary teaching hospital. We included patients with sepsis or septic shock within the first 24 h after ICU admission. Conjunctival imaging, using an IDF video microscope, and retinal imaging, using portable digital fundus camera, as well as systemic hemodynamic measurements, were performed at three time points: at baseline, 6 h and 24 h. Baseline conjunctival microcirculatory parameters were compared with healthy controls.

Results

A total of 48 patients were included in the final assessment and analysis. Median APACHE II and SOFA scores were 16[12–21] and 10[7–12], respectively. Forty-four (92%) patients were in septic shock, 48 (100%) required mechanical ventilation. 19 (40%) patients were discharged alive from the intensive care unit. We found significant reductions in all microcirculatory parameters in the conjunctiva when comparing septic and healthy subjects. In addition, we observed a significant lower microvascular flow index (MFI) of small conjunctival vessels during all three time points in non-survivors compared with survivors. However, retinal arteriolar vessels were not different between survivors and non-survivors.

Conclusions

Conjunctival microvascular blood flow was altered in septic patients. In the 24-h observation period conjunctival small vessels had a significantly higher MFI, but no difference in retinal arteriolar diameter in survivors in comparison with non-survivors.

Trial registration NCT04214743, https://www.clinicaltrials.gov. Date of registration: 31 December 2019 – Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04214743

Resuscitation with Hydroxyethyl Starch Maintains Hemodynamic Coherence in Ovine Hemorrhagic Shock

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Fluid resuscitation in hemorrhagic shock aims to restore hemodynamics and repair altered microcirculation. Hemodynamic coherence is the concordant performance of macro- and microcirculation. The present study on fluid therapy in hemorrhagic shock hypothesized that the choice of fluid (0.9% sodium chloride [saline group] or balanced 6% hydroxyethyl starch 130/0.4 [hydroxyethyl starch group]) impacts on hemodynamic coherence.

Methods

After instrumentation, 10 sheep were bled up to 30 ml/kg body weight of blood stopping at a mean arterial pressure of 30 mmHg to establish hemorrhagic shock. To reestablish baseline mean arterial pressure, they received either saline or hydroxyethyl starch (each n = 5). Hemodynamic coherence was assessed by comparison of changes in mean arterial pressure and both perfused vessel density and microvascular flow index.

Results

Bleeding of 23 ml/kg blood [21; 30] (median [25th; 75th percentile]) in the saline group and 24 ml/kg [22; 25] (P = 0.916) in the hydroxyethyl starch group led to hemorrhagic shock. Fluid resuscitation reestablished baseline mean arterial pressure in all sheep of the hydroxyethyl starch group and in one sheep of the saline group. In the saline group 4,980 ml [3,312; 5,700] and in the hydroxyethyl starch group 610 ml [489; 615] of fluid were needed (P = 0.009). In hemorrhagic shock perfused vessel density (saline from 100% to 83% [49; 86]; hydroxyethyl starch from 100% to 74% [61; 80]) and microvascular flow index (saline from 3.1 [2.5; 3.3] to 2.0 [1.6; 2.3]; hydroxyethyl starch from 2.9 [2.9; 3.1] to 2.5 [2.3; 2.7]) decreased in both groups. After resuscitation both variables improved in the hydroxyethyl starch group (perfused vessel density: 125% [120; 147]; microvascular flow index: 3.4 [3.2; 3.5]), whereas in the saline group perfused vessel density further decreased (64% [62; 79]) and microvascular flow index increased less than in the hydroxyethyl starch group (2.7 [2.4; 2.8]; both P < 0.001 for saline vs. hydroxyethyl starch).

Conclusions

Resuscitation with hydroxyethyl starch maintained coherence in hemorrhagic shock. In contrast, saline only improved macro- but not microcirculation. Hemodynamic coherence might be influenced by the choice of resuscitation fluid.