- Reusing Open Source Code: Value Creation and Value Appropriation Perspectives on Knowledge Reuse;
- The Maze Runner (Maze Runner Trilogy, Book 1).
- Cardiovascular Hemodynamics for the Clinician.
- Hour of Darkness (Bob Skinner, Book 24).
- What Research Has to Say About Reading Instruction;
- Navigation Bar?
- Drug Discovery and Evaluation.
The remainder of the book is divided into sections on various clinical entities, including valvular heart disease, cardiomyopathies, pericardial disease, coronary hemodynamics and fractional flow reserve, mechanical support devices e. These chapters aid the clinician in interpreting hemodynamic data in various disease states and include numerous pressure tracings.
New chapters cover TAVR, ventricular assist devices, and pulmonic valve disease, and the author expands the treatment of pulmonary hypertension, fractional flow reserve, heart failure with preserved ejection fraction and valvular heart disease. By presenting clinically useful information in a disease-based framework, this concise reference is an essential resource for clinicians who need to extract maximum information from pressure and blood flow in patients with cardiovascular disease.
Cardiovascular Hemodynamics for the Clinician
He served as Director of the Cardiac Catheterization Laboratories and Director of Interventional Cardiology for 14 years before assuming his current role. He has published three textbooks and more than articles including several dealing with the hemodynamics of heart disease. Cardiovascular Hemodynamics for the Clinician, 2nd Edition, provides a useful, succinct and understandable guide to the practical application of hemodynamics in clinical medicine for all trainees and clinicians in the field.
Metrics details. Hemodynamic monitoring plays a fundamental role in the management of acutely ill patients.
Cardiovascular Hemodynamics For The Clinician
In this consensus paper, we try to provide some clarification, offering an objective review of the available monitoring systems, including their specific advantages and limitations, and highlighting some key principles underlying hemodynamic monitoring in critically ill patients. Hemodynamic monitoring plays an important role in the management of today's acutely ill patient. Essentially, hemodynamic monitoring can be helpful in two key settings.
The first is when a problem has been recognized; here, monitoring can help to identify underlying patho-physiological processes so that appropriate forms of therapy can be selected. A typical scenario is the patient in shock for whom options are to give more fluids or to give a vasopressor or an inotropic agent, depending on the hemodynamic evaluation. The second setting is more preventative, with monitoring allowing preemptive actions to be performed before a significant problem arises. A typical scenario here is the perioperative patient in whom monitoring can be used to detect hypovolemia or low oxygen delivery DO 2 early, enabling timely corrective therapy to be initiated.
Although microcirculatory changes are believed to play a major role in the development of organ dysfunction and multiple organ failure and there is increasing interest in new techniques to monitor the microcirculation, these are not yet available for clinical practice, and hemodynamic monitoring, therefore, still focuses on the macro-circulation.
Current hemodynamic monitoring therefore includes measurement of heart rate, arterial pressure, cardiac filling pressures or volumes, cardiac output, and mixed venous oxygen saturation SvO 2. Although not perfect, the pulmonary artery catheter PAC has long been considered the optimal form of hemodynamic monitoring, allowing for the almost continuous, simultaneous recording of pulmonary artery and cardiac filling pressures, cardiac output and SvO 2.
However, although the incidence of complications with the PAC is relatively low, the technique is still quite invasive and there is no clear evidence for improved outcomes associated with its insertion and use to guide therapy [ 1 ]. As a result, interest in alternative monitoring systems has surged in recent years. There are now many different monitoring systems available, and physicians may feel somewhat confused by the multiple possibilities. Classifying them according to how accurate closeness of measured values to the 'true' value, expressed as the bias or precise variability of values due to random errors of measurement [ 2 ] they are is more difficult, in part because of the lack of a perfect 'gold' standard for comparison.
Most devices have been evaluated by comparing their results with those obtained by intermittent thermo-dilution from the PAC as the reference, although this technique has its own limitations and may not represent the best choice of comparator [ 2 ]. Our purpose in this consensus article is not to review the technology or modus operandi of the various systems in any detail, not to provide readers with a shopping list, nor to identify one system that would be suitable in all patients; rather, we will briefly review the advantages and limitations of each system, and propose ten key principles to guide choice of monitoring system s in today's acutely ill patients.
Examples of the main systems that are available for estimating cardiac output are listed in Table 1. The intermittent thermodilution technique, in which boluses of ice-cold fluid are injected into the right atrium via a PAC and the change in temperature detected in the blood of the pulmonary artery used to calculate cardiac output, is still widely considered as the standard method of reference. The averaged values have the advantage of eliminating variability in the presence of arrhythmias, but the disadvantage of not being real-time values, thus limiting the usefulness of this approach for assessing rapid hemodynamic changes in unstable patients.
The PAC has a key advantage over many other systems in that it provides simultaneous measurements of other hemodynamic parameters in addition to cardiac output, including pulmonary artery pressures, right-sided and left-sided filling pressures, and SvO 2. These devices use the same basic principles of dilution to estimate the cardiac output as with PAC thermodilution. Cardiac output values measured using transpulmonary or ultrasound indicator dilution techniques correlate well with those measured using PAC thermodilution [ 3 — 6 ] and may show less respiratory phase-dependent variation [ 4 ].
Each of these systems contains a proprietary algorithm for converting a pressure-based signal into a flow measurement. The level of accuracy and precision of each device needs to be understood as the data cannot be superimposed from one system to another. The advantages of these arterial pressure-based cardiac output monitoring systems over PAC-derived measurements is primarily their less invasive nature. The major weakness of all these devices is the drift in values whenever there is a major change in vascular compliance, as, for example, in vascular leak syndrome with increased vessel wall edema leading to decreased arterial compliance.
Aortic valve regurgitation may further decrease the accuracy of these techniques. Over-or under-damped arterial pressure waveforms will also decrease the precision of these monitors. Echocardiography allows measurement of cardiac output using standard two-dimensional imaging or, more commonly, Doppler-based methods. The main interest in echocardiography in general is that it can be used not only for measurement of cardiac output but also for the additional assessment of cardiac function.
Echocardiography is particularly useful as a diagnostic tool because it allows the visualization of cardiac chambers, valves and pericardium. Small ventricles 'kissing ventricles' may incite fluid administration whereas a poorly contractile myocardium may suggest that a dobutamine infusion is a better choice. Right ventricular dilatation may orient towards the diagnosis of massive pulmonary embolism or myocardial infarction whereas the presence of pericardial fluid may suggest a diagnosis of pericardial tamponade.
Severe valvulopathy can also be recognized promptly. However, echocardiography instruments and expertise may not be readily available everywhere; in some institutions, this is still the domain of the cardiologists and they need to be called to do the procedure.
If an ultrasound beam is directed along the aorta using a probe, part of the ultrasound signal will be reflected back by the moving red blood cells at a different frequency.
Cardiovascular Hemodynamics for the Clinician / Edition 2
The resultant Doppler shift in the frequency can be used to calculate the flow velocity and volume and hence cardiac output. Echo-Doppler evaluation can provide reasonable estimates of cardiac output, but again is operator-dependent and continuous measurement of cardiac output using this technique is not possible. Echo-Doppler evaluation may be applied either transthoracically or transesophageally. However, transthoracic techniques do not always yield good images and transesophageal techniques are more invasive such that some sedation, and often endotracheal intubation, is required in order to obtain reliable measurements.
Moreover, the esophageal probe is uncomfortable in non-intubated patients, although may be better tolerated if inserted nasally, and should be used cautiously in patients with esophageal lesions. The signal produces different waveforms that can be used to distinguish to some extent changes in preload, afterload and left ventricular contractility.
Doppler flow studies focusing on the descending thoracic aorta may not provide a reliable measurement of the total cardiac output for example, with epidural use , and are invalid in the presence of intra-aortic balloon pumping. Echo-Doppler cardiac output estimates vary considerably for several reasons, including difficulty in assessment of the velocity time integral, calculation error due to the angle of insonation, and problems with correct measurement of the cross-sectional area.
Some training is required when using these techniques. Esophageal-Doppler techniques have been shown to be useful for optimizing fluid administration in high risk surgical patients [ 7 , 8 ]. Simplified transesophageal Doppler techniques can be convenient as the probe is smaller than for standard esophageal echocardiography techniques. Simplified trans-thoracic Doppler systems allow estimation of aortic blood flow and may be even less invasive; however, although these techniques can be simple to perform in healthy volunteers, access to good images may be more difficult in critically ill patients.
Moreover, there is a fairly prolonged learning curve for correct use of this system [ 9 ]. These methods need further validation in critically ill patients. CO 2 rebreathing systems, based on the Fick principle, use a CO 2 sensor, a disposable airflow sensor and a disposable rebreathing loop. CO 2 production is calculated from minute ventilation and its CO 2 content, and the arterial CO 2 content is estimated from end-tidal CO 2.
Partial re-breathing reduces CO 2 elimination and increases the end-tidal CO 2. By combining measurements taken during and without rebreathing, venous CO 2 content can be eliminated from the Fick equation. However, intra-pulmonary shunting of blood and rapid hemodynamic changes affect the accuracy of the measurement, so that this technique is not considered to be reliable in acutely ill patients.
Bioimpedance is based on the fact that the conductivity of a high-frequency, low-magnitude alternating current passed across the thorax changes as blood flow varies with each cardiac cycle. These changes can be measured using electrodes placed on a patient's chest and used to generate a waveform from which cardiac output can be calculated.
Bioreactance has developed out of bio-impedance and measures changes in the frequency of the electrical currents traversing the chest, rather than changes in impedance, potentially making it less sensitive to noise. These techniques are non-invasive and can be applied quickly. They have been used for physiological studies in healthy individuals and may be useful in perioperative applications [ 10 ], but are less reliable in critically ill patients [ 11 ].
Electrical interference may also occur in the ICU environment. Having briefly discussed some of the advantages and limitations of the available systems, we now consider some key principles than can help when considering which hemodynamic monitoring system to use. Hemodynamic monitoring can only improve outcomes if three conditions are met: the data obtained from the monitoring device must be sufficiently accurate to be able to influence therapeutic decision making; the data obtained from the monitoring system must be relevant to the patient being monitored; and changes in management made as a result of the data obtained need to be able to improve outcomes.
If the data are interpreted or applied incorrectly, or the therapies themselves are ineffective or harmful, the resultant change in management will not improve patient status and may be deleterious. If these three conditions are not met, monitoring is unlikely to be associated with improved outcomes, and this may account for the lack of evidence of improved outcomes in acutely ill patients with use of any monitoring device, not only the PAC [ 12 ]. The optimal monitoring system will depend on the individual patient, the problem already present or potentially arising for which the monitoring is required, and the devices and expertise available at the institution in question.
For initial evaluation of the critically ill patient, an invasive approach is still often needed, which includes insertion of an arterial catheter and a central venous catheter; this is because of the need for secure intravenous and arterial access in such patients and the presumed increased accuracy of measurements based on direct pressure monitoring. The data provided can already guide initial treatment.
Analysis of the arterial pressure trace can identify fluid responsiveness in mechanically ventilated patients, although there are some limitations to this technique, including adaptation to the respirator often with high doses of sedative agents and even paralysis , need for absence of arrhythmias, and use of relatively large tidal volumes.
Response to passive leg raising can be used if beat-by-beat measurements of stroke volume are monitored. Once stabilized, less invasive monitoring techniques should be employed.
Importantly, monitoring systems are not necessarily mutually exclusive and can sometimes be used to complement each other. For example, echocardiography can provide additional information in the early assessment of critically ill patients Figure 1. Diagnostic algorithm based on use of echocardiography. CVP, central venous pressure; RV, right ventricular.
There is still a place for the PAC Swan-Ganz , which has the advantage of allowing measurement of cardiac filling pressures and pulmonary artery pressures, cardiac output and SvO 2 and now also extravascular lung water. However, although in the past a PAC was inserted early in all critically ill patients, today its insertion is no longer necessary during initial resuscitation, but should rather be reserved for complex cases, for example, patients with right ventricular dysfunction, difficult assessment of optimal fluid management, or specific cases of cardiac failure.
For example, the acceptable minimal arterial pressure may be very different in a young individual without co-morbidity compared to an elderly atherosclerotic, previously hypertensive patient. Likewise, the CVP may remain low in adequately resuscitated patients or may be high at baseline in patients with pulmonary hypertension due to underlying chronic lung disease. Similarly, it is difficult to define an optimal level of cardiac output as cardiac output is an adaptative parameter for which there is no single 'normal' value, but only normal ranges.
Since the purpose of the cardiovascular system is to match blood flow to metabolic demand, and this demand may vary widely even over short time intervals, targeting a specific cardiac output or even sustaining a threshold value may be inappropriate. In the critically ill, cardiac output increases in sepsis, as in anemia, but may be reduced with sedation or anesthesia. Multiple factors therefore need to be considered when determining whether cardiac output is optimal for a particular patient, including the degree of tissue perfusion as estimated from a careful clinical examination and blood lactate levels Figure 2.
Alarms should thus be individualized for each patient and reevaluated regularly. Factors influencing the interpretation of cardiac output CO. Any variable on its own provides relatively little information - it is just one piece of a large puzzle.