Comprehensive Hemodynamic Evaluation
What is it?
Hemodynamic evaluation is a method of studying your blood pressure and blood flow and how well your body transports the oxygen in your blood to the tissues of your body. Your blood brings oxygen to all tissues throughout your body by way of your blood vessels. Your heart moves the blood (and the oxygen) throughout your body. So, the ultimate job of the cardiovascular system (made up of your heart and blood vessels) is to carry and deliver oxygen where it needs to be when it needs to be there so your tissues can work properly. Hemodynamics is complex, but basically, when your heart pumps properly, your blood flows as it should, and the oxygen levels in your blood are adequate, you are in a normal hemodynamic state (normohemodynamic). This is important to good overall cardiovascular health, which is why we perform hemodynamic evaluations on many of our cardiovascular patients.
Medicine has advanced far beyond the stage where hemodynamics consisted of a blood pressure reading from a standard cuff. There are many different pieces that make up a complete picture of hemodynamics, and all of them can have an effect on blood pressure and cardiovascular health. These include:
Intravascular volume is commonly known as blood volume. Normovascular means that the volume of your blood is within the normal range. Being hypervolemic means you have an increased volume of blood, and being hypovolemic means you have a decreased volume of blood. Many things can affect blood volume. Not taking in enough fluids or losing them too quickly, due to problems like diarrhea or excessive sweating, can lead to hypovolemia. And retaining fluids, due to eating too much salt or experiencing kidney malfunction, can lead to hypervolemia.
Inotropes are hormone-like substances that circulate through the blood and act on the heart muscles to increase or decrease the heart rate. Positive inotropes increase heart rate, and negative inotropes decrease heart rate.
Vasoactivity is anything that affects the diameter of the blood vessels. Healthy blood vessels at a normal diameter allow blood to pass through smoothly and without difficulty. Many things can cause the diameter of your blood vessels to change – some of them are normal (like changing positions from lying down to standing up), and some are due to diseases and disorders. Vasoconstriction is the constriction, or narrowing, of blood vessels, and it can lead to decreased blood flow and increased blood pressure. Vasodilation is the dilation, or widening, of blood vessels, which can lead to increased blood flow and decreased blood pressure.
There are many cardiovascular diseases and disorders that can be managed therapeutically by achieving and maintaining a normohemodynamic state, but it takes more than a simple blood pressure reading to know exactly which piece(s) of the hemodynamic puzzle to treat. For example, high blood pressure could be caused by vasoconstriction, which requires your heart pump harder to get enough blood through narrowed vessels, or it could be caused by hypervolemia, which requires your heart to work harder to handle the excess blood volume. That’s where hemodynamic evaluation comes in – to find out exactly what mechanism in your body is malfunctioning and what treatment regimen should be started.
Hemodynamic evaluation allows clinicians to make timely patient assessment, diagnosis, prognosis, and treatment decisions. Many studies have shown that physicians, regardless of their level of expertise and training, are unable to accurately estimate cardiac output through physical exam and assessment alone. So hemodynamic evaluation is a valuable tool that can help physicians provide effective, efficient healthcare.
How is it done?
Invasive hemodynamic evaluation
Hemodynamic evaluation is important in interventional cardiology, such as during and after heart surgery. Traditionally, hemodynamic evaluation was done invasively, through a pulmonary artery catheter (commonly known as the Swan-Ganz catheter). Although the Swan-Gantz catheter offers accurate measurements and helps with hemodynamic evaluation, it is expensive and risky for patients. Because of the risk, it is typically used in a very small percentage of cardiology inpatients. It also takes time, skill, and a sterile environment to place the catheter, so it’s not always possible or practical to perform invasive hemodynamic evaluation in an emergency room setting. It is definitely not meant to measure hemodynamics in the general cardiovascular patient population.
Non-invasive hemodynamic evaluation
Now, we have the technology to measure many pieces of the puzzle with a non-invasive technology called impedance cardiography (ICG). ICG is also referred to as electrical impedance plethysmography (EIP) and thoracic electrical bioimpedance (TEB). ICG was first used by NASA to assess the cardiovascular health of astronauts. As scientists and physicians began to better understand the interactivity of hemodynamics, ICG technology became even better and more useful in a general medicine setting. It is now used in a cardiac output mobile monitoring system (hemodynamic patient monitoring system) that enables physicians to quickly and accurately analyze the hemodynamic state of patients in real time in a non-invasive, more cost-effective way. Clinical studies involving hundreds of patients have validated the reproductability and accuracy of ICG when compared to the invasive Swan-Ganz catheter.
Through four external sensors attached to the outside of your neck and chest, the ICG monitor gathers data through the electrical conductivity in the thorax and translates it into blood flow data that can be used to measure and calculate hemodynamic parameters. It measures 15 parameters, including cardiac index (CI), systemic vascular resistance (vasoactivity), and thoracic fluid content (intravascular volume).
Non-invasive hemodynamic evaluation can provide clinical value because physicians can obtain data similar to that available from invasive hemodynamic evaluation at a much lower cost and with no risk. It can be used in patients who previously would have required invasive catheter evaluation, but it offers even more value to patients in environments where invasive hemodynamic monitoring was not previously possible or worth the risk.
Because of its safety and low cost, hemodynamic evaluation can be performed on significantly more patients, including outpatients who have chronic diseases. For example, hemodynamic evaluation can now play an important role in diagnosis, and treatment of patients who are experiencing congestive heart failure (CHF), hypertension (high blood pressure), and dyspnea (shortness of breath) and in patients who have a pacemaker. Hemodynamic evaluation using ICG can improve blood pressure control in patients with resistant hypertension. It can also help predict worsening status in heart failure.
Some of the benefits of non-invasive hemodynamic evaluation using ICG are:
- Decreased risk and fewer complications – because all tests are non-invasive, there are virtually no risks or complications
- Real time measurements and increased access to data – because the non-invasive evaluation is less risky, quicker, easier, and less expensive than invasive evaluation is, it is more readily available to a wider patient population
- Decreased cost with similar effectiveness – it is far less expensive, and many studies have shown similar effectiveness to invasive techniques