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Cardiac output - definition

Created: 15/8/2005

The volume of blood pumped by the heart per minute is called the cardiac output (CO) and is the product of the stroke volume (SV) and the heart rate (HR).

At rest, in the average adult, the CO is 5 L/min and in exercise it may rise to 35 L/min.

The CO is often corrected for body surface area (cardiac index=2.5-4.2 L/min/m2).

The CO is pivotal in maintaining arterial BP (BP=CO X SVR) and oxygen delivery.

Distribution of normal CO

Heart 5%
Brain 14%
Muscle 20%
Kidneys 22%
Liver 25%
Rest of the body 14%

Effects of intravenous anaesthetic agents on CO

CO reduced by Propofol>Thiopentone>Etomidate, secondary to decreased contractility. Propofol also causes vasodilatation and bradycardia. 

Ketamine causes an increase in the cardiac output secondary to an increase in sympathetic tone.

Effects of inhalational anaesthetic agents on CO

CO reduced by Enflurane>Halothane>Isoflurane/Desflurane>Sevoflurane>N2O
Secondary to direct myocardial depression, inhibition of the sympathetic nervous system outflow and altered baroreceptor activity.

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