Cardiac output is a concept used in medicine that refers to the amount of blood expelled by the heart in one minute. Technically, it is calculated as the product of the heart rate by the stroke volume. The increase in heart rate is a compensatory mechanism to increase the supply of oxygen to tissues.
The variables that affect systolic volume¸is the volume of blood that the heart expels into the aorta during the contraction period, are preload, afterload and contractile function.
Today, there are a number of techniques that allow us to obtain measurements of cardiac output in a very effective and non-invasive way. The Fick technique, which used to be used previously, has been replaced by more modern methods.
The analysis of the pulse wave has resulted in obtaining a continuous and minimally invasive measurement of cardiac output. In addition, other methods, such as bioremediation, Doppler or echocardiography, allow us to obtain measurements of cardiac output in a non-invasive, fast and reliable way.
Concept of cardiac output
The cardiac output consists of the amount of blood that pumps the heart per minute (towards the aorta). It supposes the sum of the blood flows. Therefore, its value is equal to the beat volume (ml / beat) for the heart rate (beats / min).
The professionals place the values of normality of cardiac output in a healthy adult at 4-6.5 l / min at rest. During intense exercise you can pump four to seven times that amount.
It is important to bear in mind that cardiac output, being the main determinant of oxygen transport to the organism, has to adapt to the needs of the same organism. It is a value that depends on the activity and the moment in which the person is. This means that a value within the range of “normality” does not serve, as the only data, to indicate that the cardiac function is optimal.
The critical patient usually presents abnormal oxygen demands due to the very process that triggers the disease. This is why the cardiac output value alone, in this case, is not enough to assess the state of cardiac function and hemodynamic situation of the patient.
Non-invasive monitoring of cardiac output
Hemodynamic monitoring is a tool currently used. Especially, it is very useful in critically ill patients, since it allows obtaining information about the cardiocirculatory physiopathology.
This method can be a support to make the diagnosis and guide the therapy in situations of hemodynamic instability. It should be mentioned that, in its beginnings, it was limited to critical care units.
The use of this type of monitoring has been increasingly extended to emergency services. This is so thanks to technological development and especially to its increasingly less complex.
Currently, monitors are available capable of continuously measuring the cardiac output of the patient non-invasively. That is, it can be measured, for example, by cutaneous electrodes, digital inflatable cuffs or photospectrometry sensors. Or, through a minimally invasive, option that is also possible. This can be done by channeling a peripheral artery.
Different cardiac output monitoring techniques
The factors that must be taken into account when choosing the type of hemodynamic monitoring in emergencies are the following:
- The complexity of the picture.
- The evolution time of hypoperfusion.
- The availability of equipment in our field of work.
A less invasive technique may be preferable if it can be obtained more quickly and easily, even if it is slightly less accurate. Especially in situations where a rapid assessment of the patient’s condition is required.
The little or non-invasive monitoring is more effective the sooner it is applied and the better the monitor is recognized. That is why it is a tool that is increasingly used in emergency and emergency services. To guarantee the adequate supply of oxygen to the tissues in the critical patient.
It helps to establish the differential diagnosis of the possible causes of shock. Also to optimize the treatment, quantify its effects and avoid the possible complications derived from it.