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Critical Care (London, England) Oct 2018Measurement of arterial pressure is one of the most basic elements of patient management. Arterial pressure is determined by the volume ejected by the heart into the... (Review)
Review
Measurement of arterial pressure is one of the most basic elements of patient management. Arterial pressure is determined by the volume ejected by the heart into the arteries, the elastance of the walls of the arteries, and the rate at which the blood flows out of the arteries. This review will discuss the three forces that determine the pressure in a vessel: elastic, kinetic, and gravitational energy. Emphasis will be placed on the importance of the distribution of arterial resistances, the elastance of the walls of the large vessels, and critical closing pressures in small arteries and arterioles. Regulation of arterial pressure occurs through changes in cardiac output and changes in vascular resistance, but these two controlled variables can sometimes be in conflict.
Topics: Blood Pressure; Blood Pressure Determination; Cardiac Output; Humans; Monitoring, Physiologic
PubMed: 30305136
DOI: 10.1186/s13054-018-2171-1 -
Critical Care (London, England) 2008Cardiac output is the amount of blood the heart pumps in 1 minute, and it is dependent on the heart rate, contractility, preload, and afterload. Understanding of the...
Cardiac output is the amount of blood the heart pumps in 1 minute, and it is dependent on the heart rate, contractility, preload, and afterload. Understanding of the applicability and practical relevance of each of these four components is important when interpreting cardiac output values. In the present article, we use a simple analogy comparing cardiac output with the speed of a bicycle to help appreciate better the effects of various disease processes and interventions on cardiac output and its four components.
Topics: Animals; Cardiac Output; Heart Rate; Humans; Myocardial Contraction; Practice Guidelines as Topic; Stroke Volume
PubMed: 18771592
DOI: 10.1186/cc6975 -
Annals of Cardiac Anaesthesia 2019The accurate quantification of cardiac output (CO) is given vital importance in modern medical practice, especially in high-risk surgical and critically ill patients. CO... (Review)
Review
The accurate quantification of cardiac output (CO) is given vital importance in modern medical practice, especially in high-risk surgical and critically ill patients. CO monitoring together with perioperative protocols to guide intravenous fluid therapy and inotropic support with the aim of improving CO and oxygen delivery has shown to improve perioperative outcomes in high-risk surgical patients. Understanding of the underlying principles of CO measuring devices helps in knowing the limitations of their use and allows more effective and safer utilization. At present, no single CO monitoring device can meet all the clinical requirements considering the limitations of diverse CO monitoring techniques. The evidence for the minimally invasive CO monitoring is conflicting; however, different CO monitoring devices may be used during the clinical course of patients as an integrated approach based on their invasiveness and the need for additional hemodynamic data. These devices add numerical trend information for anesthesiologists and intensivists to use in determining the most appropriate management of their patients and at present, do not completely prohibit but do increasingly limit the use of the pulmonary artery catheter.
Topics: Calibration; Cardiac Output; Electric Impedance; Humans; Monitoring, Physiologic; Thermodilution
PubMed: 30648673
DOI: 10.4103/aca.ACA_41_18 -
Critical Care (London, England) May 2022Venous return is the flow of blood from the systemic venous network towards the right heart. At steady state, venous return equals cardiac output, as the venous and... (Review)
Review
Venous return is the flow of blood from the systemic venous network towards the right heart. At steady state, venous return equals cardiac output, as the venous and arterial systems operate in series. However, unlike the arterial one, the venous network is a capacitive system with a high compliance. It includes a part of unstressed blood, which is a reservoir that can be recruited via sympathetic endogenous or exogenous stimulation. Guyton's model describes the three determinants of venous return: the mean systemic filling pressure, the right atrial pressure and the resistance to venous return. Recently, new methods have been developed to explore such determinants at the bedside. In this narrative review, after a reminder about Guyton's model and current methods used to investigate it, we emphasize how Guyton's physiology helps understand the effects on cardiac output of common treatments used in critically ill patients.
Topics: Blood Pressure; Cardiac Output; Heart; Humans; Models, Cardiovascular; Vascular Resistance; Veins
PubMed: 35610620
DOI: 10.1186/s13054-022-04024-x -
Critical Care (London, England) Sep 2016Volume infusions are one of the commonest clinical interventions in critically ill patients yet the relationship of volume to cardiac output is not well understood.... (Review)
Review
Volume infusions are one of the commonest clinical interventions in critically ill patients yet the relationship of volume to cardiac output is not well understood. Blood volume has a stressed and unstressed component but only the stressed component determines flow. It is usually about 30 % of total volume. Stressed volume is relatively constant under steady state conditions. It creates an elastic recoil pressure that is an important factor in the generation of blood flow. The heart creates circulatory flow by lowering the right atrial pressure and allowing the recoil pressure in veins and venules to drain blood back to the heart. The heart then puts the volume back into the systemic circulation so that stroke return equals stroke volume. The heart cannot pump out more volume than comes back. Changes in cardiac output without changes in stressed volume occur because of changes in arterial and venous resistances which redistribute blood volume and change pressure gradients throughout the vasculature. Stressed volume also can be increased by decreasing vascular capacitance, which means recruiting unstressed volume into stressed volume. This is the equivalent of an auto-transfusion. It is worth noting that during exercise in normal young males, cardiac output can increase five-fold with only small changes in stressed blood volume. The mechanical characteristics of the cardiac chambers and the circulation thus ultimately determine the relationship between volume and cardiac output and are the subject of this review.
Topics: Blood Circulation; Blood Pressure; Blood Volume; Cardiac Output; Humans; Stroke Volume
PubMed: 27613307
DOI: 10.1186/s13054-016-1438-7 -
Journal of Cardiothoracic and Vascular... Aug 2019Hemodynamic monitoring is an essential part of the perioperative management of the cardiovascular patient. It helps to detect hemodynamic alterations, diagnose their... (Review)
Review
Hemodynamic monitoring is an essential part of the perioperative management of the cardiovascular patient. It helps to detect hemodynamic alterations, diagnose their underlying causes, and optimize oxygen delivery to the tissues. Furthermore, hemodynamic monitoring is necessary to evaluate the adequacy of therapeutic interventions such as volume expansion or vasoactive medications. Recent developments include the move from static to dynamic variables to assess conditions such as cardiac preload and fluid responsiveness and the transition to less-invasive or even noninvasive monitoring techniques, at least in the perioperative setting. This review describes the available techniques that currently are being used in the care of the cardiovascular patient and discusses their strengths and limitations. Even though the thermodilution method remains the gold standard for measuring cardiac output (CO), the use of the pulmonary artery catheter has declined over the last decades, even in the setting of cardiovascular anesthesia. The transpulmonary thermodilution method, in addition to accurately measuring CO, provides the user with some additional helpful variables, of which extravascular lung water is probably the most interesting. Less-invasive monitoring techniques use, for example, pulse contour analysis to originate flow-derived variables such as stroke volume and CO from the arterial pressure signal, or they may measure the velocity-time integral in the descending aorta to estimate the stroke volume, using, for example, the esophageal Doppler. Completely noninvasive methods such as the volume clamp method use finger cuffs to reconstruct the arterial pressure waveform, from which stroke volume and CO are calculated. All of these less-invasive CO monitoring devices have percentage errors around 40% compared with reference methods (thermodilution), meaning that the values are not interchangeable.
Topics: Cardiac Output; Hemodynamic Monitoring; Hemodynamics; Humans; Stroke Volume; Thermodilution
PubMed: 31279355
DOI: 10.1053/j.jvca.2019.03.043 -
Journal of Clinical Monitoring and... Feb 2022Nowadays, the classical pulmonary artery catheter (PAC) has an almost 50-year-old history of its clinical use for hemodynamic monitoring. In recent years, the PAC... (Review)
Review
Nowadays, the classical pulmonary artery catheter (PAC) has an almost 50-year-old history of its clinical use for hemodynamic monitoring. In recent years, the PAC evolved from a device that enabled intermittent cardiac output measurements in combination with static pressures to a monitoring tool that provides continuous data on cardiac output, oxygen supply and-demand balance, as well as right ventricular performance. In this review, which consists of two parts, we will introduce the difference between intermittent pulmonary artery thermodilution using bolus injections, and the contemporary PAC enabling continuous measurements by using a thermal filament which heats up the blood. In this second part, we will discuss in detail the measurements of the contemporary PAC, including continuous cardiac output measurement, right ventricular ejection fraction, end-diastolic volume index, and mixed venous oxygen saturation. Limitations of all of these measurements are highlighted as well. We conclude that thorough understanding of measurements obtained from the PAC is the first step in successful application of the PAC in daily clinical practice.
Topics: Cardiac Output; Catheterization, Swan-Ganz; Catheters; Humans; Middle Aged; Pulmonary Artery; Stroke Volume; Thermodilution; Ventricular Function, Right
PubMed: 33646499
DOI: 10.1007/s10877-021-00673-5 -
Critical Care (London, England) Feb 2018The central venous pressure (CVP) is the most frequently used variable to guide fluid resuscitation in critically ill patients, although its use has been challenged. In...
The central venous pressure (CVP) is the most frequently used variable to guide fluid resuscitation in critically ill patients, although its use has been challenged. In this viewpoint, we use a question and answer format to highlight the potential advantages and limitations of using CVP measurements to guide fluid resuscitation.
Topics: Cardiac Output; Central Venous Pressure; Fluid Therapy; Hemodynamics; Humans; Monitoring, Physiologic
PubMed: 29471884
DOI: 10.1186/s13054-018-1959-3 -
JACC. Heart Failure Feb 2018
Topics: Cardiac Output; Exercise Tolerance; Heart Failure; Humans; Stroke Volume
PubMed: 29226813
DOI: 10.1016/j.jchf.2017.10.002 -
Heart Rhythm Mar 2016The simple faint is secondary to hypotension and bradycardia resulting in transient loss of consciousness. According to Ohm's law applied to the circulation, BP = SVR ×... (Review)
Review
The simple faint is secondary to hypotension and bradycardia resulting in transient loss of consciousness. According to Ohm's law applied to the circulation, BP = SVR × CO, hypotension can result from a decrease in systemic vascular resistance (SVR), cardiac output (CO), or both. It is important to understand that when blood pressure (BP) is falling, SVR and CO do not change reciprocally as they do in the steady state. In 1932, Lewis, assuming that decreased SVR alone accounted for hypotension, defined "the vasovagal response" along pathophysiologic lines to denote the association of vasodilation with vagal-induced bradycardia in simple faint. Studies performed by Barcroft and Sharpey-Schafer between 1940 and 1950 used volume-based plethysmography to demonstrate major forearm vasodilation during extreme hypotension and concluded that the main mechanism for hypotension was vasodilation. Plethysmographic measurements were intermittent and not frequent enough to capture rapid changes in blood flow during progressive hypotension. However, later investigations by Weissler, Murray, and Stevens performed between 1950 and 1970 used invasive beat-to-beat BP measurements and more frequent measurements of CO using the Fick principle. They demonstrated that CO significantly fell before syncope, and little vasodilation occurred until very late in the vasovagal reaction Thus, since the 1970s, decreasing cardiac output rather than vasodilation has been regarded as the principal mechanism for the hypotension of vasovagal syncope.
Topics: Cardiac Output; Cardiology; Humans; Periodicals as Topic; Syncope, Vasovagal; Vasodilation
PubMed: 26598322
DOI: 10.1016/j.hrthm.2015.11.023