Cardiac output formula

Based on the Rivers trial of early goal-directed therapy, central venous oxygen saturation (cvO2%) emerged as a resuscitation target. This was recommended for over a decade until the PROCESS, PROMISE, and ARISE trials demonstrated that cvO2% monitoring was unnecessary. Consequently, this has largely fallen by the wayside. However, one niche role of cvO2% in the ICU has persisted. cvO2% continues to be checked occasionally with a goal of trying to sort out which type of shock a patient has. The rationale is that high-output shock states (e.g. sepsis, anaphylaxis) should increase the cvO2%, whereas low-output shock states (e.g. cardiogenic, hemorrhagic) should reduce the cvO2%. This concept has a certain physiologic appeal and has been advocated by some authors ( Recently a few cases at Genius General Hospital have arisen where cvO2% was misleading. Specifically, the cvO2% was elevated despite cardiogenic or hemorrhagic shock. This post will attempt to explore why this might occur. Physiologic rationale for using cvO2% to monitor cardiac output This starts with the Fick equation, which may be derived as follows (where mvO2% is the mixed venous saturation as measured in the pulmonary artery)(5). This equation can be rearranged to allow calculation of the cardiac output (CO) based on the mixed venous oxygen saturation: This is how the cardiac output may be calculated using the mixed venous oxygen saturation (e.g. using a pulmonary artery catheter). If we make the approximation...

Learning Objectives By the end of this section, you will be able to: • Define cardiac output and explain how heart rate and stroke volume effect it • Describe the effect of exercise on cardiac output • Identify cardiovascular centers and cardiac reflexes that regulate heart function • Describe factors affecting heart rate and force of contraction • Explain the connection between preload, contractility, afterload and stroke volume • Distinguish between positive and negative inotropic factors • Summarize factors affecting stroke volume, heart rate and cardiac output The autorhythmicity inherent in cardiac cells keeps the heart beating at a regular pace; however, the heart is regulated by and responds to outside influences as well. Neural and endocrine controls are vital to the regulation of cardiac function. In addition, the heart is sensitive to several environmental factors, including electrolytes. Resting Cardiac Output Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle in one minute. To calculate this value, multiply stroke volume (SV), the amount of blood pumped by each ventricle, by heart rate (HR), in contractions per minute (or beats per minute, bpm). It can be represented mathematically by the following equation: CO = HR × SV SV is normally measured using an echocardiogram to record EDV and ESV, and calculating the difference: SV = EDV – ESV. SV can also be measured using a specialized catheter, but this is an invasive procedure and...

Among all topics taught in cardiac physiology, the concept of cardiac output seems to be the most important. This is because understanding the cardiac output gives an idea of how the cardiac muscle is doing its job pumping blood to the body. In addition, cardiac output has many clinical implications since understanding heart failure, one of the most common heart diseases, is all about understanding the concept of cardiac output. The cardiac output formula is straightforward, and it won’t require lots of effort to interpret or memorize. Nevertheless, we will be spending lots of time here digging deeper into the concept of cardiac output, the factors affecting it, and how doctors use it in real life. How to calculate cardiac output? Cardiac output is defined as the volume of blood the heart pumps through the circulatory system per minute. Normally, it is around 5 L/min at rest. Here is the cardiac output equation: Cardiac output (CO) = Heart rate (HR) x Stroke volume (SV) Where: Heart rate (HR) is the number of beats per minute Stroke volume (SV) is the volume of blood pumped by the left ventricle in a single heartbeat. Stroke volume can also be defined as the end-diastolic volume (EDV) minus end-systolic volume (ESV). What is the relation between stroke volume and cardiac output? Most students confuse Stroke volume is used to calculate the amount of blood pumped in a single heartbeat. In contrast, cardiac output is used to calculate the amount of blood pumped for 1 minute. ...