Redistribution of cardiac output during hemorrhagic shock in sheep

Refilling and preload dependence failed to predict cardiac index decrease during fluid removal with continuous renal replacement therapy

BACKGROUND

Fluid removal can reduce the burden of fluid overload after initial resuscitation. According to the Frank-Starling model, iatrogenic hypovolemia should induce a decrease in cardiac index. We hypothesized that inadequate refilling detected by haemoconcentration during fluid removal or an increase in cardiac index (CI) during passive leg raising (PLR) could predict CI decrease during mechanical fluid removal with continuous renal replacement therapy (CRRT).

METHODS

We conducted a single-centre prospective diagnostic accuracy study. The primary objective was to investigate the diagnostic performance of plasma protein concentration variations in detecting a CI decrease ≥ 12% during mechanical fluid removal. Secondary objective was to assess other predictive factors of CI change. The attending physician prescribed a fluid removal challenge consisting of a mechanical fluid removal challenge of 500 mL for one hour. Plasma protein concentration, haemoglobin level, PLR and transpulmonary thermodilution were done before and after the fluid removal challenge.

RESULTS

We included 69 adult patients between December 2016 and April 2020. Sixteen patients had a significant CI decrease (23% [95% CI 14-35]). Haemoconcentration and PLR before fluid removal challenge or CI trending failed to predict CI decrease.

CONCLUSION

Haemoconcentration variables, preload dependence status and CI trending failed to predict CI decrease during fluid removal challenge.

Using velocity-pressure loops in the operating room: a new approach of arterial mechanics for cardiac afterload monitoring under general anesthesia

Cardiac afterload is usually assessed in the ascending aorta and can be defined by the association of peripheral vascular resistance (PVR), total arterial compliance (Ctot), and aortic wave reflection (WR). We recently proposed the global afterload angle (GALA) and β-angle derived from the aortic velocity-pressure (VP) loop as continuous cardiac afterload monitoring in the descending thoracic aorta. The aim of this study was to 1) describe the arterial mechanic properties by studying the velocity-pressure relations according to cardiovascular risk (low-risk and high-risk patients) in the ascending and descending thoracic aorta and 2) analyze the association between the VP loop (GALA and β-angle) and cardiac afterload parameters (PVR, Ctot, and WR). PVR, Ctot, WR, and VP loop parameters were measured in the ascending and descending thoracic aorta in 50 anesthetized patients. At each aortic level, the mean arterial pressure (MAP), cardiac output (CO), and PVR were similar between low-risk and high-risk patients. In contrast, Ctot, WR, GALA, and β-angle were strongly influenced by cardiovascular risk factors regardless of the site of measurement along the aorta. The GALA angle was inversely related to aortic compliance, and the β-angle reflected the magnitude of wave reflection in both the ascending and descending aortas (P < 0.001). Under general anesthesia, the VP loop can provide new visual insights into arterial mechanical properties compared with the traditional MAP and CO for the assessment of cardiac afterload. Further studies are necessary to demonstrate the clinical utility of the VP loop in the operating room.NEW & NOTEWORTHY Our team recently proposed the global afterload angle (GALA) and β-angle derived from the aortic velocity-pressure (VP) loop as continuous cardiac afterload monitoring in the descending thoracic aorta under general anesthesia. However, the evaluation of cardiac afterload at this location is unusual. The present study shows that VP loop parameters can describe the components of cardiac afterload both in the ascending and descending thoracic aorta in the operating room. Aging and cardiovascular risk factors strongly influence VP loop parameters. The VP loop could provide continuous visual additional information on the arterial system than the traditional mean arterial pressure and cardiac output during the general anesthesia.

[Pathophysiology of hemorragic shock]

This review addresses the pathophysiology of hemorrhagic shock, a condition produced by rapid and significant loss of intravascular volume, which may lead to hemodynamic instability, decreases in oxygen delivery, decreased tissue perfusion, cellular hypoxia, organ damage, and death. The initial neuroendocrine response is mainly a sympathetic activation. Haemorrhagic shock is associated altered microcirculatory permeability and visceral injury. It is also responsible for a complex inflammatory response associated with hemostasis alteration.

Porcine model of hemorrhagic shock with microdialysis monitoring

BACKGROUND

A number of experimental protocols have been used to try to reproduce the clinical scenarios of hemorrhagic shock. The present study reports on an experimental swine model of controlled hemorrhagic shock that incorporates microdialysis monitoring for the evaluation of tissue perfusion and oxygenation. The aim of our study was to provide a reproducible, accurate, and reliable model for the testing and evaluation of therapeutic interventions in the area of hemorrhagic shock.

METHODS

Landrace swine (n = 8) were subjected to controlled hemorrhagic shock, with a mean arterial pressure of 35 ± 5 as the endpoint. Six more pigs were used as the control group. Microdialysis monitoring of the tissue lactate/pyruvate ratio was used. The mean arterial pressure, heart rate, hematocrit, hemoglobin, and lactate/pyruvate ratio measurements were obtained just before (phase A) and 30 min after (phase B) hemorrhage in the study group; the control group underwent the same measurements at the corresponding points.

RESULTS

The mean arterial pressure, hematocrit, and hemoglobin were lower (P < 0.05) in the study group than in the control group at phase B and compared with the values for the study group at phase A. Also, the lactate/pyruvate ratio and heart rate were greater (P < 0.05) in the study group than in control group at phase B and compared with the values for the study group at phase A.

CONCLUSIONS

This model of hemorrhagic shock is effective and correlates with the clinical parameters of tissue oxygenation, as documented by microdialysis.

Thoracic aortic pulsatility decreases during hypovolemic shock: implications for stent-graft sizing

PURPOSE

To investigate the thoracic aortic pulsatility during hypovolemic shock in an experimental porcine model.

METHODS

The circulating blood volume of 7 healthy Yorkshire pigs was gradually lowered until the subjects had lost 40% of their normal blood volume. Intravascular ultrasound was used to assess the aortic pulsatility in normovolemic and hypovolemic state at the level of the ascending and descending thoracic aorta.

RESULTS

The mean aortic pulsatility at the level of the ascending aorta decreased from 15.9% ± 7.2% (range 6.3%-25.7%) in normovolemia to 6.2% ± 2.8% (range 2.9%-10.7%, p = 0.018) in hypovolemia. At the level of the descending thoracic aorta, the mean aortic pulsatility decreased from 8.7% ± 2.8% (range 4.4%-12.2%) at baseline to 5.6% ± 2.5% (range 1.5%-9.5%, p = 0.028) in hypovolemia. The maximum mean aortic diameter, obtained in cardiac systole, was significantly smaller as well at both evaluated levels during hypovolemic shock compared with the mean diameter in normovolemia.

CONCLUSION

The thoracic aortic diameter and pulsatility decreased significantly during hypovolemic shock in this porcine model, most impressively at the level of the ascending aorta. Electrocardiographically-gated imaging may not be necessary for hypovolemic patients with acute aortic disease requiring endovascular repair because of the minimal aortic pulsatility.

[What non invasive haemodynamic assessment in paediatric intensive care unit in 2009?]

The haemodynamic assessment of the patients is a daily activity in paediatric intensive care unit. It completes and is guided by the clinical examination. The will to develop the least invasive possible coverage of the patients is a constant concern. The haemodynamic monitoring, all the more if it is invasive, ceaselessly has to put in balance the profit and the risk of beginning this technique at a fragile patient. In the last three decades, numerous non-invasive haemodynamic tools were developed. The ideal one must be reliable, reproducible, with a time of fast, easily useful answer, with a total harmlessness, cheap and allowing a monitoring continues. Among all the existing tools (oesophageal Doppler ultrasound method, transthoracic echocardiography, NICO, thoracic impedancemetry, plethysmography, sublingual capnography), no one allies all these qualities. We can consider that the transthoracic echocardiography gets closer to most of these objectives. We shall blame it for its cost and for the fact that it is an intermittent monitoring but both in the diagnosis and in the survey, it has no equal among the non-invasive tools of haemodynamic assessment from part the quality and the quantity of the obtained information. The learning of the basic functions (contractility evaluation, cardiac output, cardiac and the vascular filling) useful for the start of a treatment is relatively well-to-do. We shall miss the absence of training in this tool in France in its paediatric and neonatal specificity within the university or interuniversity framework.

Perioperative hemodynamic monitoring with transesophageal Doppler technology

Invasive cardiac output (CO) monitoring, traditionally performed with transpulmonary thermodilution techniques, is usually reserved for high-risk patients because of the inherent risks of these methods. In contrast, transesophageal Doppler (TED) technology offers a safe, quick, and less invasive method for routine measurements of CO. After esophageal insertion and focusing of the probe, the Doppler beam interrogates the descending aortic blood flow. On the basis of the measured frequency shift between the emitted and received ultrasound frequency, blood flow velocity is determined. From this velocity, combined with the simultaneously measured systolic ejection time, CO and other advanced hemodynamic variables can be calculated, including estimations of preload, afterload, and contractility. Numerous studies have validated TED-derived CO against reference methods. Although the agreement of CO values between TED and the reference methods is limited (95% limits of agreement: median 4.2 L/min, interquartile range 3.3-5.0 L/min), TED has been shown to accurately follow changes of CO over time, making it a useful device for trend monitoring. TED can be used to guide perioperative intravascular volume substitution and therapy, with vasoactive or inotropic drugs. Various studies have demonstrated a reduced postoperative morbidity and shorter length of hospital stay in patients managed with TED compared with conventional clinical management, suggesting that it may be a valuable supplement to standard perioperative monitoring. We review not only the technical basis of this method and its clinical application but also its limitations, risks, and contraindications.

[Minimally invasive hemodynamic monitoring with esophageal echoDoppler]

Hemodynamic monitoring is a key element in the care of the critical patients, providing an unquestionable aid in the attendance to diagnosis and the choice of the adequate treatment. Minimally invasive devices have been emerging over the past few years as an effective alternative to classic monitoring tools. The esophageal echoDoppler is among these. It makes it possible to obtain continuous and minimally invasive monitoring of the cardiac output in addition to other useful parameters by measuring the blood flow rate and the diameter of the thoracic descending aorta, which provides a sufficiently extensive view of the hemodynamic state of the patient and facilitates early detection of the changes produced by a sudden clinical derangement. Although several studies have demonstrated the usefulness of the esophageal Doppler in the surgical scene, there is scarce and dispersed evidence in the literature on its benefits in critical patients. Nevertheless, its advantages make it an attractive element to take into account within the diagnostic arsenal in the intensive care. The purpose of the following article is to describe how it works, its degree of validation with other monitoring methods and the role of esophageal echoDoppler as a minimally invasive monitoring tool for measuring cardiac output in the daily clinical practice, contributing with our own experience in the critical patient.