Authors: Kylee Greider and Vi Dinh (POCUS 101 Editor)
Cardiac output (CO) is the total volume of blood moved by the heart per minute. It is a product of the left ventricular stroke volume (SV) and the heart rate (HR).
Cardiac output (mL/min) = Stroke Volume (mL/cycle) x Heart Rate (bpm)
By being able to calculate a patient’s cardiac output you can quantitively assess the patient’s cardiac function, optimize vasopressors and fluid resuscitation in critically ill patients, and even distinguish between undifferentiated shock types in critically ill patients.
But how can one estimate cardiac output? Early clinicians relied on using the Fick’s principle to measure cardiac output through thermodilution via a pulmonary artery catheterization. This required an invasive and potentially dangerous procedure, which wasn’t feasible for rapid assessment.
Sonographers in the 1980s began experimenting with alternative methods of estimating cardiac output such as Doppler-assisted calculations that would be more rapidly accessible to clinicians outside of the ICU.
The main barriers for learners attempting to obtain these measurements with ultrasound are:
- Pulse wave Doppler seems too advanced
- There seem to be too many measurements and math following
- Interpreting the waveforms seems difficult and intimidating
Well, the good news is that you only really need to learn how to do TWO measurements:LVOT DiameterandVelocity Time Integral (VTI) to calculate cardiac output with ultrasound. Yes, that’s it!
In this post you will learn:
- How to actually understand the concept of cardiac output and the basic physiology surrounding it
- How to obtain the left ventricular outflow tract (LVOT) diameter to determine the LVOT area
- How to obtain the LVOT velocity time integral (VTI)
- How to use these values to calculate stroke volume and cardiac output
In addition, we made a free downloadable Cardiac Output PDF pocket card for you and even a Cardiac Output Calculator!
Table of Contents
To make this easier, we have put all of the details in a Cardiac Output PDF pocket card, so you can download and keep all of the most important information right at your fingertips. Click HERE to download.
Cardiac Output Calculator
Check out our stroke volume/cardiac output calculator below! You can also always access it HERE is well.
How to Think about Cardiac Output
The first thing we need to focus on when trying to calculate cardiac output is figuring out what the stroke volume is.
This just involves estimating the amount of blood (stroke volume) that comes out of the left ventricle at the left ventricular outflow tract (LVOT). If you think of the volume coming out of the LVOT as the shape of a cylinder you will just need two measurements to make the stroke volume calculation.
First is the LVOT Diameter and the second is the distance that one blood cell travels during one heartbeat (this is calculated by using the velocity-time integral or VTI). The stroke volume is then simply calculated using the formula for the volume of a cylinder.
Once you have the stroke volume just multiply by the heart rate to get the Cardiac Output!
Now that you understand these simple principles let’s show you exactly how to obtain these measurements to calculate SV and Cardiac Output.
Machine and Patient Preparation for Exam
You will need to be able to obtain the parasternal long axis and apical 5 chamber views to measure cardiac output. For a full post on how to obtain each cardiac view in detail, check out our post HERE.
- The patient should be supine or in the left lateral decubitus position
- Ideally, place the machine on the patient’s right side so you can scan with your right hand and manipulate ultrasound buttons with your left hand.
- Transducer: Phased Array Probe
- Exam Preset: Cardiac
- The Indicator should be on the RIGHT side of the screen (cardiac mode)
- You will need a cardiac package on your ultrasound machine in order to do these measurements. If you don’t, unfortunately, you will not be able to measure the velocity time integral (VTI) described below.
- You must also havePulse Wave Doppler capability on your ultrasound system. Most cart-based systems have this, but unfortunately, most hand-held ultrasounds don’t have Pulse Wave Doppler. For a review on how pulse wave doppler works click HERE.
Step by Step Guide to Cardiac Output Measurement
Below we describe the exact steps for you to measure cardiac output in your patients using ultrasound.
Editor’s Note: Our team published one of the first studies using POCUS to measure cardiac output (Dinh 2012). We found it takes about 20 cardiac output measurements until you start getting reliable results. So if you are first starting out don’t be discouraged and keep practicing!
STEP 1: Get the Parasternal Long Axis View
Obtain a Parasternal Long Axis (PSLA) View. You want to clearly visualize your left ventricular outflow tract (LVOT) and the aortic valve. Look to ensure you can see your aortic valve opening and closing.
STEP 2: Measure LVOT Diameter
Once you have obtained the PSLA view, freeze your screen when you have the best view of your aortic valve at mid-systole (when the valves are wide open).
You can also use the zoom feature on your ultrasound machine to get a better view.
Click the calculation package on your ultrasound machine and choose LVOT Diameter. Using your measure tool, measure near the aortic annulus at the base of the leaflets. This is the diameter of your left ventricular outflow tract (LVOT), typically this measurement is around 2 cm.
STEP 3: Get the Apical 5-Chamber View
Using the same phased array transducer, obtain an Apical 5-Chamber View. Again, you will need to visualize the LVOT and aortic valve.
STEP 4: Place PW Doppler Gate at LVOT
Next, position the pulse wave Doppler gate at the LVOT in the Apical 5 Chamber view. This is at the aortic annulus, or base of the aortic valve leaflets. Make sure to align the pulse wave Doppler gate and LVOT as parallel as possible in order to get the best VTI tracing. The more your angle is off the more you will underestimate the cardiac output.
For more information on how to use the pulse wave Doppler, click HERE.
STEP 5: Trace LVOT VTI
Once your Doppler gate is in a good position, activate your pulse wave Doppler.
Then press the Freeze button and then select the cardiac calculation package. Look for LVOT VTI (every machine will have a different way of accessing this calculation).
You will then trace the outline of one of the systolic waveforms (yellow outline). The machine will then calculate the LVOT VTI for you. The LVOT VTI will output as a distance in centimeters (cm) and represents the distance that blood travels in one heartbeat.
POCUS 101 Tip: A rule of thumb we like to use is that a normal LVOT VTI is around 20cm. This is calculated that by assuming a normal stroke volume is 60ml and an average LVOT diameter is 2cm. If you use the cylinder formula to back-calculate this, a “normal” LVOT comes to just about 20cm!
Editor’s Note: Some ultrasound machines will have an “auto tracing VTI” package that does not make you trace the wave and you just need to place the cursor at the beginning and end of the waveform. The ultrasound then auto traces the VTI for you. I find these are hit or miss. Just make sure the tracing is accurate when the computer does it for you.
Here is a quick video we made summarizing exactly how to get the apical 5 chamber view and use the pulse wave Doppler to calculate the LVOT VTI:
STEP 6: Measure Heart Rate
The last step in calculating the cardiac output will be to just get the heart rate.
Measuring the patient’s heart rate can be done using the cardiac package on your ultrasound machine or you can use the heart rate from the patient monitor.
If calculating the heart rate using the ultrasound machine, press the heart rate function and then just place the cursor from one peak of a wave to another peak and the machine should automatically calculate the heart rate for you (the example below shows a heart rate of 75 bpm).
STEP 7: Calculate Cardiac Output
Now after you have completed the 3 measurements (LVOT diameter, LVOT VTI, and heart rate) the machine should automatically calculate the cardiac output for you and it should appear on the screen.
For example below, the cardiac output is 2.46 L/min
However, you can also calculate the Cardiac output yourself if you are having any issues:
|Step 1||Calculate the LVOT area||LVOT Area = π x (LVOT Diameter/2)2 LVOT Area = _______________ cm2|
|Step 2||Calculate Stroke Volume||SV (mL) = LVOT area (cm2) x VTI (cm) SV= _______________ mL|
|Step 3||Calculate Cardiac Output||CO (mL/min) = SV (mL/cycle) x HR (bpm) CO = __________________ mL/min|
Don’t forget to download the Cardiac Output Pocket Card summarizing these values and formulas.
Or you can use this calculator below for even more ease!
Cardiac Output Calculator
- Tintinalli JE, Ma OJ, Hamade B, Huang DT. Hemodynamic Monitoring. In: Tintinalli’s Emergency Medicine: a Comprehensive Study Guide. New York: McGraw-Hill; 2020:212-216.
- Schuster AH, Nanda NC. Doppler echocardiographic measurement of cardiac output: Comparison with a non-golden standard. The American Journal of Cardiology. 1984;53(1):257-259. doi:10.1016/0002-9149(84)90723-9
- Zhang Y, Wang Y, Shi J, Hua Z, Xu J. Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis. Plos One. 2019;14(10). doi:10.1371/journal.pone.0222105
- Costanzo LS. Cardiac Physiology. In: Physiology. Philadelphia, PA: Saunders/Elsevier; 2014:145-158.
- Dinh, V. A. et al. Measuring cardiac index with a focused cardiac ultrasound examination in the ED. Am J Emerg Medicine. 30, 1845–1851 (2012).
Work out the volume of the cylinder – Multiply the area of the LVOT (a circle) by the length the blood travels and you get the stroke volume (ie volume ejected per beat) The stroke volume multiplied by the heart rate gives us the cardiac output (expressed as L/Min).Does an echocardiogram show cardiac output? ›
Cardiac output (CO) is the total volume of blood moved by the heart per minute. It is a product of the left ventricular stroke volume (SV) and the heart rate (HR).How do you calculate cardiac output? ›
Measuring Cardiac Output
We can use this simple calculation to figure out cardiac output: Cardiac Output = Stroke Volume * Heart Rate, which is written CO = SV * HR. Remember, there are two variables that are used to determine the cardiac output. Those are the stroke volume and heart rate.
To summarize, once the diameter of the LVOT is determined (and thus its CSA), and then the LVOT VTI is traced, SV (cm3) is calculated by multiplying the CSA (in cm2) by the VTI (stroke distance in cm): SV = CSA x VTI. This is done automatically by the echocardiographic computer.How do you calculate ejection fraction? ›
The ejection fraction or EF is an indicator of how efficient the ventricle is at emptying itself. It's the percentage of the EDV that is ejected from the ventricle. The formula is: EF=SV/EDV. (If we want to turn this into a percentage, we simply multiply by 100).What is the normal value of cardiac output? ›
Usually, an adult heart pumps about 5 liters of blood per minute at rest.
- Atrial Fibrillation. Atrial fibrillation is a condition that causes an irregular and rapid heartbeat. ...
- Cardiovascular Disease. ...
- Heart Valve Disease. ...
- Thickening of Heart Walls. ...
- Pericardial Effusion.
- The reason(s) your provider ordered the test.
- The size of the heart chambers and thickness of the heart muscle.
- The function of the left and right ventricles (pumping chambers)
- A description of the shape, movement, and function of the heart valves.
An echocardiogram could lead to other tests.
It takes pictures of your heart from inside your esophagus. Your throat may be sore for a few hours afterward. In rare cases the tube can cause injury to the throat. You could also have a bad reaction to the medicine given to help you relax.
Cardiac output is the product of heart rate (HR) and stroke volume (SV) and is measured in liters per minute. HR is most commonly defined as the number of times the heart beats in one minute.
Heart Rate X Stroke Volume= Cardiac Output | Exercise PhysiologyWhat is normal stroke volume on echo? ›
A normal stroke volume index in a healthy adult can be anywhere between 35 ml/m2 and 65 ml/m2 .Can you calculate your own stroke volume? ›
Stroke volume equation
If you remember the definition of the cardiac output, you already know that it is the volume of blood pumped by the heart during one minute. It is easy to convert this number into stroke volume. All you have to do is to divide this number by the number of beats per minute, called the heart rate.
An ejection fraction of 50 percent to 65 percent is considered normal.What does an ejection fraction of 25% mean? ›
As the percentage falls, it tells the doctor that the heart failure is getting worse. In general, if the EF falls below 30%, it's relatively severe. A reading of 20% or below is very severe heart failure.What is the difference between ejection fraction and cardiac output? ›
Cardiac Output, Stroke volume, EDV, ESV, Ejection Fraction - YouTubeWhat 4 factors affect cardiac output? ›
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.What is the maximum cardiac output? ›
Resting cardiac output in both trained and sedentary individuals is approximately 4 to 5 L/min, but during exercise the maximal cardiac output can reach 20 L/min.Why do they check your neck during an echocardiogram? ›
Your two carotid arteries are located on each side of your neck. They deliver blood from your heart to your brain. Carotid ultrasound tests for blocked or narrowed carotid arteries, which can increase the risk of stroke. The results can help your doctor determine a treatment to lower your stroke risk.Why do you hold your breath during an echocardiogram? ›
During a recording, you may be asked to change your position and to hold your breath. This allows the Sonographer to get the best pictures. Sometimes, the Sonographer may push the transducer more firmly against your skin.
How LVEF should be interpreted depends on a patient's clinical status and cardiac condition. While LVEF in the range of 40% to 55% is abnormal, it often has little clinical significance. 6. In moderate or severe mitral regurgitation, however, even a nominally “normal” LVEF of 60% can indicate inadequate LV performance.What is good ejection fraction? ›
A normal ejection fraction is about 50% to 75%, according to the American Heart Association. A borderline ejection fraction can range between 41% and 50%.What is an abnormal echocardiogram? ›
Echo Results and The Functions of The Heart
Walls thicker than 1.5cm are considered abnormal. They may indicate high blood pressure and weak or damaged valves. An echocardiogram can also measure if your heart is pumping enough blood through your body.
Echocardiography accurately detected LVEF <40% in 27 of these 36 (75%) studies. When compared to angiographic LVEF <40%, echocardiography was falsely low in 19 studies. Echocardiographic studies overestimated angiographic LVEF <40% in 9 studies.Can anxiety affect echocardiogram results? ›
In patients without a known clinical history of anxiety or other mental health concerns, short-term nervousness can also disrupt ECG readings. In one case study from the Egyptian Journal of Critical Care Medicine, such apprehension led to reported quadrigeminy in all ECG leads.What should you not do before an echocardiogram? ›
Don't eat or drink anything but water for 4 hours before the test. Don't drink or eat anything with caffeine (such as cola, chocolate, coffee, tea, or medications) for 24 hours before. Don't smoke the day of the test. Caffeine and nicotine might affect the results.How often should you repeat echocardiogram? ›
Depending on the severity of the disease, an echocardiogram might need to be repeated more frequently. For example, Aortic Valve Stenosis (AS) should usually be followed every 6-12 months if the stenosis is severe; otherwise, 3-5 years is the rule for mild disease.What unit is cardiac output measured in? ›
Cardiac output is defined as the volume of blood ejected by the left ventricle per unit time. The volume of blood is called the stroke volume, and the unit used to measure cardiac output is one minute.What is the difference between the maximum and resting cardiac output? ›
The difference between maximum and resting CO is known as the cardiac reserve. It measures the residual capacity of the heart to pump blood.What factors increase cardiac output? ›
- Heart rate. A higher heart rate increases cardiac output as it multiplies by stroke volume. ...
- Stroke volume, which is in turn determined by preload, afterload and contractility.
- Preload. Increased preload leads to an increase in the stroke volume. ...
- Afterload. ...
- Cardiac contractility:
The volume of blood pumped out of the left ventricle in one beat is called the stroke volume. It is 70 ml.What is the theoretical cardiac output of a patient with a heart rate of 70 beats per minute and a stroke volume of 70 ml beat? ›
Cardiac output is stroke volume times heart rate. if you have a SV of 70 and a heart rate of 70, then your cardiac output is 4900.How do you find cardiac output from heart rate and blood pressure? ›
Simple mathematical transforms have been proposed to estimate CO from pulse pressure (PP = mean systolic blood pressure (SBP) minus mean diastolic blood pressure (DBP)), and mean heart rate (HR). Recently we evaluated one such simple technique [CO=(PPxHR)x.What is the difference between stroke volume and cardiac output? ›
Abstract. Stroke volume is defined as end-diastolic volume minus end-systolic volume; cardiac output is the stroke volume times the heart rate.How do you remember preload and afterload? ›
Preload and Afterload Nursing | Stroke Volume, Cardiac Output ExplainedWhat is preload and afterload? ›
Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood.What is the map formula? ›
A common method used to estimate the MAP is the following formula: MAP = DP + 1/3(SP – DP) or MAP = DP + 1/3(PP)What is a normal stroke volume index? ›
Stroke Volume Index (SVI) relates SV to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is millilitres per square metre (ml/m2). SVI = SV/BSA. Normal values for a resting healthy individual would be approximately 35-65mL/m2.How do you calculate cardiac output with a Doppler? ›
Maximum spatial blood velocity and cross sectional aortic area were estimated by the Doppler technique and echocardiography. Cardiac output was calculated by multiplying blood velocity by aortic area at various levels in the ascending aorta.How do you calculate QP QS on Echo? ›
Qp = HR x SVp; Qs = HR x SVs. SVp can be calculated by measuring the cross-sectional area of the right ventricular outflow tract (RVOT) and the quantity of blood flowing through this area. The latter is expressed as the VTI (velocity time integral) of flow across the RVOT*.
Stroke volume is the amount of blood ejected from the ventricle with each cardiac cycle. It can be readily calculated by subtracting the end-systolic volume from the end-diastolic volume. Multiplying the stroke volume by the heart rate yields the cardiac output, typically reported in liters per minute.How is left ventricular output calculated? ›
LVOT VTI is calculated by placing the pulsed Doppler sample volume in the outflow tract below the aortic valve and recording the velocity (cm/s). When the velocity signal is integrated with respect to time, the distance blood moves with each systole is calculated in cm/systole (Fig.How do you calculate cardiac output from blood pressure? ›
Simple mathematical transforms have been proposed to estimate CO from pulse pressure (PP = mean systolic blood pressure (SBP) minus mean diastolic blood pressure (DBP)), and mean heart rate (HR). Recently we evaluated one such simple technique [CO=(PPxHR)x.What is normal stroke volume on echo? ›
A normal stroke volume index in a healthy adult can be anywhere between 35 ml/m2 and 65 ml/m2 .What is the formula for calculating mean arterial pressure? ›
A common method used to estimate the MAP is the following formula: MAP = DP + 1/3(SP – DP) or MAP = DP + 1/3(PP)How do you calculate QP to Qs ratio? ›
This flow ratio is the Qp/Qs ratio, otherwise known as the pulmonary-systemic shunt ratio. To calculate Qp and Qs, we can use the following shunt fraction equations: Qp = RVOT VTI * π * (RVOT / 2) Qs = LVOT VTI * π * (LVOT / 2)What is QP QS stand for? ›
Qp = Pulmonary flow. Qs = Systemic flow. Qp:Qs describes the magnitude of a cardiovascular shunt.How do you calculate pulmonary systemic flow ratio? ›
Pulmonary and aortic flow was calculated as: Q = A x V x ET x CF where, A is the valvular orifice area (cm2), V the mean flow velocity (cm/sec), ET the ejection time (sec) and CF the cardiac frequency (cycles/min).Is ejection fraction the same as cardiac output? ›
Cardiac output equals the volume of blood pumped by the heart per minute, whereas stroke volume (SV) is the amount pumped on a single beat.What is the approximate cardiac output of a person with a heart rate of 70 beats min and a stroke volume of 75 ml? ›
When a person is normally at rest, the average heart rate is 70 beats/min and the average stroke volume is 70mL/beat. Therefore, the average amount of blood being pumped is 4900-5000mL/min at rest.