Non-invasive monitoring of cardiac output

Technically, cardiac output is the amount of blood pumped by the heart per minute. It is calculated as the product of heart rate by stroke volume.

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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 heart rate times stroke volume.

Increasing the heart rate is a compensatory mechanism to increase the oxygen supply to the tissues.

Variables that affect stroke volume — that 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 series of techniques that allow us to obtain measures 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 The Fick technique, which used to be used previously, has been replaced by more modern methods.

Pulse wave analysis has resulted in continuous, minimally invasive measurement of cardiac output. In addition, other methods, such as biorectance, Doppler, or echocardiography, currently allow us to obtain measures of cardiac output in a non-invasive, fast, and reliable way.

Cardiac output concept

Cardiac output is the amount of blood that is pumped by the heart per minute (to the aorta). Assumes the sum of blood flows. Therefore, its value is equal to the beat volume (ml / beat) times the heart rate (beats / min).

Professionals place the values ​​of normal cardiac output in a healthy adult at 4-6.5 l / min in a resting state. During intense exercise, you can pump four to seven times that amount.

It is important to note that cardiac output, being the main determinant of oxygen transport to the body, must be adapted to the needs of the body itself. 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 cardiac function is optimal.

The critically ill patient generally presents abnormal oxygen demands due to the disease’s own triggering process. This is why the value of cardiac output alone, in this case, is not sufficient to assess the state of cardiac function and the patient’s hemodynamic situation.

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Non-invasive monitoring of cardiac output

Hemodynamic monitoring is a widely used tool today. Especially, it is very useful in critically ill patients, since it allows obtaining information about cardiocirculatory pathophysiology .

This method can be supportive in making the diagnosis and guiding the therapy in situations of hemodynamic instability. It is worth mentioning that, in its beginnings, it was limited to critical care units.

The use of this type of monitoring has been increasingly extended to the emergency services. This is so thanks to technological development and especially its increasingly less complexity.

Currently, there are monitors capable of continuously measuring   the patient’s cardiac output in a non-invasive way. That is, it can be measured, for example, by skin electrodes, digital inflatable sleeves, or photospectrometry sensors.

Or, through a minimally invasive way, an option that is also possible. This can be accomplished by channeling a peripheral artery.

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Different techniques for monitoring cardiac output

The factors that must be taken into account when choosing the type of hemodynamic monitoring in the emergency department are the following:

  • The complexity of the painting.
  • The evolution time of hypoperfusion.
  • The availability of equipment in our workplace.

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 quick assessment of the patient’s condition is required.

The monitoring little or no invasive is more effective the sooner you apply and the better the monitor is recognized. So it is a tool that is increasingly used in the emergency and emergency services. To guarantee the adequate supply of oxygen to the tissues in the critically ill patient.

It helps establish the differential diagnosis of possible causes of shock . Also to optimize the treatment, quantify its effects and avoid possible complications derived from it.


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