Journal of clinical monitoring and computing
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One of the main goals of hemodynamic support is to preserve tissue perfusion. However issue perfusion is related more to microvascular perfusion than aortic blood flow. Monitoring the microcirculation has long been difficult. ⋯ Transcutaneous PCO2 measurement at ear lobe is particularly promising. Finally, near infrared spectroscopy can also provide interesting information, especially using vascular occlusion tests which reactivity of the microcirculation to a transient hypoxic insult. These different devices have provided important data helping us to better understand the pathophysiology of sepsis and multiple organ failure.
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Assessment of the hemodynamics and volume status is an important daily task for physicians caring for critically ill patients. There is growing consensus in the critical care community that the "traditional" methods-e.g., central venous pressure or pulmonary artery occlusion pressure-used to assess volume status and fluid responsiveness are not well supported by evidence and can be misleading. Our purpose is to provide here an overview of the knowledge needed by ICU physicians to take advantage of mechanical cardiopulmonary interactions to assess volume responsiveness. ⋯ We discuss the impact of phasic changes in lung volume and intrathoracic pressure on the pulmonary and systemic circulation and on the heart function. We review how respirophasic changes on the venous side (great veins geometry) and arterial side (e.g., stroke volume/systolic blood pressure and surrogate signals) can be used to detect fluid responsiveness or hemodynamic alterations commonly encountered in the ICU. We review the physiological limitations of this approach.
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The transpulmonary thermodilution technique (TPTD) is a safe, multi-parametric advanced cardiopulmonary monitoring technique that provides important parameters required for making decisions in critically ill patients. The TPTD provides more reliable indicators of preload than filling pressures, the unique measurement of extravascular lung water (EVLW) and comparable accuracy in measuring cardiac output (CO). Intermittent measurement of the CO by TPTD when coupled with pulse contour analysis, offer automatic calibration of continuous CO, as well as accurate assessment of volumetric preload, fluid responsiveness and EVLW. TPTD-guided algorithms have been shown to improve the management of high-risk surgical and critically ill patients.
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Recent advance in imaging modalities used frequently in clinical routine can provide description of the geometrical and hemodynamical properties of the arterial tree in great detail. The combination of such information with models of blood flow of the arterial tree can provide further information, such as details in pressure and flow waves or details in the local flow field. Such knowledge maybe be critical in understanding the development or state of arterial disease and can help clinicians perform better diagnosis or plan better treatments. ⋯ Our development of a generic and patient-specific model of the human arterial tree permitting to study pressure and flow waves propagation in patients is presented. The predicted pressure and flow waveforms are in good agreement with the in vivo measurements. We discuss the utility of these models in different clinical application and future development of interest.