Point-of-care assessment of microvascular blood flow in critically ill patients

Objective  

Sublingual microvascular videomicroscopy can assess tissue perfusion in critically ill patients; however, data analysis is currently limited to delayed off-line evaluation. We hypothesized that a real-time point-of-care (POC) determination of the microcirculatory flow index (MFI), an established metric for assessing microcirculatory perfusion, agrees well with the conventional off-line analysis.     

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.     

Impairment of renal function using hyperoncotic colloids in a two hit model of shock: a prospective randomized study

Introduction  

One of the therapeutic essentials in severe sepsis and septic shock is an adequate fluid replacement to restore and maintain circulating plasma volume, improve organ perfusion and nutritive microcirculatory flow. The type of solution to be used as a fluid replacement remains under discussion. The aim of the study was to evaluate the effects of clinically used fluid replacement solutions on renal function and inflammatory response.     

Crystalloids versus colloids for goal-directed fluid therapy in major surgery

Introduction  

Perioperative hypovolemia arises frequently and contributes to intestinal hypoperfusion and subsequent postoperative complications. Goal-directed fluid therapy might reduce these complications. The aim of this study was to compare the effects of goal-directed administration of crystalloids and colloids on the distribution of systemic, hepatosplanchnic, and microcirculatory (small intestine) blood flow after major abdominal surgery in a clinically relevant pig model.     

Effects of inducible nitric oxide synthase inhibition or norepinephrine on the neurovascular coupling in an endotoxic rat shock model

Introduction  

The inducible nitric oxide synthase (iNOS) plays a crucial role in early sepsis-related microcirculatory dysfunction. Compared to a catecholamine therapy we tested effects of a specific iNOS-inhibitor (1400W) on the microcirculatory function in the brain.     

Changing sedative infusion from propofol to midazolam improves sublingual microcirculatory perfusion in patients with septic shock

Purpose

The goal of this study was to explore possible microcirculatory alterations by changing sedative infusion from propofol to midazolam in patients with septic shock.

Materials and Methods

Patients (n = 16) were sedated with propofol during the first 24 hours after intubation, then with midazolam, following a predefined algorithm. Systemic hemodynamics, perfusion parameters, and microcirculation were assessed at 2 time points: just before stopping propofol and 30 minutes after the start of midazolam infusion. Sublingual microcirculation was evaluated by sidestream dark-field imaging.

Results

The microvascular flow index and the proportion of perfused small vessels were greater when patients were on midazolam than when on propofol infusion (2.8 [2.4-2.9] vs 2.3 [1.9-2.6] and 96.4% [93.7%-97.6%] vs 92.7% [88.3%-94.7%], respectively; P < .005), and the flow heterogeneity index was greater with propofol than with midazolam use (0.49 [0.2-0.8] vs 0.19 [0.1-0.4], P < .05). There were no significant changes in systemic hemodynamics and perfusion parameters either during propofol use or during midazolam infusions. Data are presented as median (25th-75th percentiles).

Conclusions

In this study, sublingual microcirculatory perfusion improved when the infusion was changed from propofol to midazolam in patients with septic shock. This observation could not be explained by changes in systemic hemodynamics.     

High-dose selenium reduces ventilator-associated pneumonia and illness severity in critically ill patients with systemic inflammation

Purpose  

To confirm the pharmacodynamics and evaluate the efficacy of high-dose selenium (Se) administered by continuous infusion, following an initial loading bolus of selenite, on clinical outcome in critically ill patients with systemic inflammatory response syndrome (SIRS).     

Single bolus versus split dose gadolinium administration in extra-cellular volume calculation at 3 Tesla

Background

Diffuse myocardial fibrosis may be quantified with cardiovascular magnetic resonance (CMR) by calculating extra-cellular volume (ECV) from native and post-contrast T1 values. Accurate ECV calculation is dependent upon the contrast agent having reached equilibrium within tissue compartments. Previous studies have used infusion or single bolus injections of contrast to calculate ECV. In clinical practice however, split dose contrast injection is commonly used as part of stress/rest perfusion studies. In this study we sought to assess the effects of split dose versus single bolus contrast administration on ECV calculation.

Methods

Ten healthy volunteers and five patients ( 4 ischaemic heart disease, 1 hypertrophic cardiomyopathy) were studied on a 3.0 Tesla (Philips Achieva TX) MR system and underwent two (patients) or three (volunteers) separate CMR studies over a mean of 12 and 30 days respectively. Volunteers underwent one single bolus contrast study (Gadovist 0.15mmol/kg). In two further studies, contrast was given in two boluses (0.075mmol/kg per bolus) as part of a clinical adenosine stress/rest perfusion protocol, boluses were separated by 12 minutes. Patients underwent one bolus and one stress perfusion study only. T1 maps were acquired pre contrast and 15 minutes following the single bolus or second contrast injection.

Results

ECV agreed between bolus and split dose contrast administration (coefficient of variability 5.04%, bias 0.009, 95% CI −3.754 to 3.772, r² = 0.973, p = 0.001)). Inter-study agreement with split dose administration was good (coefficient of variability, 5.67%, bias −0.018, 95% CI −4.045 to 4.009, r² = 0.766, p > 0.001).

Conclusion

ECV quantification using split dose contrast administration is reproducible and agrees well with previously validated methods in healthy volunteers, as well as abnormal and remote myocardium in patients. This suggests that clinical perfusion CMR studies may incorporate assessment of tissue composition by ECV based on T1 mapping.     

<Emphasis Type="Italic">In vitro</Emphasis> norepinephrine significantly activates isolated platelets from healthy volunteers and critically ill patients following severe traumatic brain injury

Introduction  

Norepinephrine, regularly used to increase systemic arterial blood pressure and thus improve cerebral perfusion following severe traumatic brain injury (TBI), may activate platelets. This, in turn, could promote microthrombosis formation and induce additional brain damage.     

The role of vasoactive agents in the resuscitation of microvascular perfusion and tissue oxygenation in critically ill patients

Purpose  

The clinical use of vasoactive drugs is not only intended to improve systemic hemodynamic variables, but ultimately to attenuate derangements in organ perfusion and oxygenation during shock. This review aims (1) to discuss basic physiology with respect to manipulating vascular tone and its effect on the microcirculation, and (2) to provide an overview of available clinical data on the relation between vasoactive drugs and organ perfusion, with specific attention paid to recent developments that have enabled direct in vivo observation of the microcirculation and concepts that have originated from it.     

The role of renal hypoperfusion in development of renal microcirculatory dysfunction in endotoxemic rats

Purpose  

To study the role of renal hypoperfusion in development of renal microcirculatory dysfunction in endotoxemic rats.     

Measurement of myocardial blood flow by cardiovascular magnetic resonance perfusion: comparison of distributed parameter and Fermi models with single and dual bolus

Background

Mathematical modeling of cardiovascular magnetic resonance perfusion data allows absolute quantification of myocardial blood flow. Saturation of left ventricle signal during standard contrast administration can compromise the input function used when applying these models. This saturation effect is evident during application of standard Fermi models in single bolus perfusion data. Dual bolus injection protocols have been suggested to eliminate saturation but are much less practical in the clinical setting. The distributed parameter model can also be used for absolute quantification but has not been applied in patients with coronary artery disease. We assessed whether distributed parameter modeling might be less dependent on arterial input function saturation than Fermi modeling in healthy volunteers. We validated the accuracy of each model in detecting reduced myocardial blood flow in stenotic vessels versus gold-standard invasive methods.

Methods

Eight healthy subjects were scanned using a dual bolus cardiac perfusion protocol at 3T. We performed both single and dual bolus analysis of these data using the distributed parameter and Fermi models. For the dual bolus analysis, a scaled pre-bolus arterial input function was used. In single bolus analysis, the arterial input function was extracted from the main bolus. We also performed analysis using both models of single bolus data obtained from five patients with coronary artery disease and findings were compared against independent invasive coronary angiography and fractional flow reserve. Statistical significance was defined as two-sided P value < 0.05.

Results

Fermi models overestimated myocardial blood flow in healthy volunteers due to arterial input function saturation in single bolus analysis compared to dual bolus analysis (P < 0.05). No difference was observed in these volunteers when applying distributed parameter-myocardial blood flow between single and dual bolus analysis. In patients, distributed parameter modeling was able to detect reduced myocardial blood flow at stress (<2.5 mL/min/mL of tissue) in all 12 stenotic vessels compared to only 9 for Fermi modeling.

Conclusions

Comparison of single bolus versus dual bolus values suggests that distributed parameter modeling is less dependent on arterial input function saturation than Fermi modeling. Distributed parameter modeling showed excellent accuracy in detecting reduced myocardial blood flow in all stenotic vessels.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-015-0125-1) contains supplementary material, which is available to authorized users.     

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.     

Monitoring the microcirculation in the critically ill patient: current methods and future approaches

Purpose  

To discuss the techniques currently available to evaluate the microcirculation in critically ill patients. In addition, the most clinically relevant microcirculatory alterations will be discussed.     

Short-Term Effects of Brimonidine/Timolol and Dorzolamide/Timolol on Ocular Perfusion Pressure and Blood Flow in Glaucoma

Introduction  

To examine the comparative short-term effects of brimonidine/timolol and dorzolamide/timolol on ocular perfusion pressure and retrobulbar blood flow in patients with primary open angle glaucoma (OAG).     

High-dose fenoldopam reduces postoperative neutrophil gelatinase-associated lipocaline and cystatin C levels in pediatric cardiac surgery

Introduction  

The aim of the study was to evaluate the effects of high-dose fenoldopam, a selective dopamine-1 receptor, on renal function and organ perfusion during cardiopulmonary bypass (CPB) in infants with congenital heart disease (CHD).     

Effects of changes in arterial pressure on organ perfusion during septic shock

Introduction  

Septic shock is characterized by altered tissue perfusion associated with persistent arterial hypotension. Vasopressor therapy is generally required to restore organ perfusion but the optimal mean arterial pressure (MAP) that should be targeted is uncertain. The aim of this study was to assess the effects of increasing MAP using norepinephrine (NE) on hemodynamic and metabolic variables and on microvascular reactivity in patients with septic shock.     

Hydroxyethylstarch impairs renal function and induces interstitial proliferation, macrophage infiltration and tubular damage in an isolated renal perfusion model

Introduction  

The aim of the study was to evaluate some of the underlying pathomechanisms of hydroxyethylstarch (HES) induced adverse effects on renal function using 24 porcine kidneys in an isolated perfusion model over six hours.     

Effects of dobutamine on systemic, regional and microcirculatory perfusion parameters in septic shock: a randomized, placebo-controlled, double-blind, crossover study

Purpose

The role of dobutamine during septic shock resuscitation is still controversial since most clinical studies have been uncontrolled and no physiological study has unequivocally demonstrated a beneficial effect on tissue perfusion. Our objective was to determine the potential benefits of dobutamine on hemodynamic, metabolic, peripheral, hepatosplanchnic and microcirculatory perfusion parameters during early septic shock resuscitation.

Methods

We designed a randomized, controlled, double-blind, crossover study comparing the effects of 2.5-h infusion of dobutamine (5 mcg/kg/min fixed-dose) or placebo in 20 septic shock patients with cardiac index ≥2.5 l/min/m² and hyperlactatemia. Primary outcome was sublingual perfused microvascular density.

Results

Despite an increasing cardiac index, heart rate and left ventricular ejection fraction, dobutamine had no effect on sublingual perfused vessel density [9.0 (7.9–10.1) vs. 9.1 n/mm (7.9–9.9); p = 0.24] or microvascular flow index [2.1 (1.8–2.5) vs. 2.1 (1.9–2.5); p = 0.73] compared to placebo. No differences between dobutamine and placebo were found for the lactate levels, mixed venous-arterial pCO₂ gradient, thenar muscle oxygen saturation, capillary refill time or gastric-to-arterial pCO₂ gradient. The indocyanine green plasma disappearance rate [14.4 (9.5–25.6) vs. 18.8 %/min (11.7–24.6); p = 0.03] and the recovery slope of thenar muscle oxygen saturation after a vascular occlusion test [2.1 (1.1–3.1) vs. 2.5 %/s (1.2–3.4); p = 0.01] were worse with dobutamine compared to placebo.

Conclusions

Dobutamine failed to improve sublingual microcirculatory, metabolic, hepatosplanchnic or peripheral perfusion parameters despite inducing a significant increase in systemic hemodynamic variables in septic shock patients without low cardiac output but with persistent hypoperfusion.     

Hepatic platelet and leukocyte adherence during endotoxemia

Introduction  

Liver microcirculation disturbances are a cause of hepatic failure in sepsis. Increased leukocyte-endothelial interaction, platelet adherence and impaired microperfusion cause hepatocellular damage. The time course and reciprocal influences of ongoing microcirculatory events during endotoxemia have not been clarified.