Cardiac output is the product of heart rate and stroke volume measured in liters per minute. Measurement of cardiac output is important for managing hemodynamically unstable patients by assessing cardiac preload and response to interventions. Methods for measuring cardiac output include thermodilution, Doppler ultrasound, echocardiography, Fick principle, impedance cardiography, and arterial pressure waveform analysis. Each method uses different physiological indicators like temperature change, blood flow, ultrasound imaging, oxygen consumption, electrical impedance, or arterial pressure to calculate cardiac output.

1. Cardiac Output Measurement
Ms.P.Nishanthi KIT-CBE

2. Introduction to Cardiac Output
● 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.
● SV is the volume of blood ejected during ventricular contraction or
for each stroke of the heart.

3. Importance of Cardiac Output Measurement
● The management of hemodynamically unstable patients requires
an assessment of the cardiac output (CO) and the patients'
intravascular volume status (cardiac preload).
● In most instances the absolute value of the CO is less important
than the response of the CO to a therapeutic intervention.

4. Methods for Cardiac Output Measurement
● Thermodilution
● Doppler Ultrasound
● Echocardiography
● Fick Principle
● Impedance Cardiography
● Arterial Pressure Waveform Analysis

5. Thermodilution Method
● The thermodilution method involves injection of a definite amount
of heat into the bloodstream, and the corresponding downstream
temperature change is recorded.
● A cold fluid is often used as an indicator in the thermodilution
method, because cold fluid is less harmful to the blood and tissue
than a hot fluid.

6. Doppler Ultrasound
● A Doppler ultrasound is a noninvasive test that can be used to
estimate the blood flow through your blood vessels by bouncing
high-frequency sound waves (ultrasound) off circulating red blood
cells.
● A regular ultrasound uses sound waves to produce images, but
can't show blood flow.

7. Echocardiography
● An echocardiogram uses sound waves to create pictures of the
heart. This common test can show blood flow through the heart and
heart valves.
● Your health care provider can use the pictures from the test to find
heart disease and other heart conditions.

8. Fick Principle
● The Fick principle states that uptake of oxygen in blood by the lung
(mL/min) is equal to the product of the AVO2 diff of the oxygen and
the blood flow to the lung.
● Therefore, if the arterial O2 content, venous O2 content and oxygen
consumption are measured, the CO can then be calculated.

9. Impedance Cardiography
● Impedance cardiography and bioreactance are two methods of
quantifying cardiac function without invasive monitoring.
● Both methods use electrophysiology to measure how changes in
aortic blood volume and flow influence transmission of a known
electrical current across the thorax.

10. Arterial Pressure Waveform Analysis
● The arterial waveform reflects the change in pressure over time, or
dP/dt, and thus the slope of the upstroke reflects this.
● Generally speaking, the steeper the slope, the quicker the rise, the
greater the dP/ dt, and the stronger the contractile forces appear.

11. Clinical Applications
● Management of heart failure
● Assessment of shock
● Intraoperative monitoring
● Intensive care settings

12. Factors Affecting Cardiac Output
● Management of heart failure
● Assessment of shock
● Intraoperative monitoring
● Intensive care settings