Clinical evaluation of global ventricular pump function

In the perioperative period, the blood pressure resulting from the interaction between the left ventricle and the systemic vasculature often represents the only monitored index of ventricular performance. Never theless, when normal values of blood pressure are accompanied by normal heart rate and clinical signs of an adequate peripheral circulation (pulse quality, capillary refill time, skin temperature, urine output, pH), it can be assumed that ventricular performance is satisfactory. If more information on the cardiovascular function is required, intracardiac pressures and flows18 as well as blood gases must be measured (Table 2.1).

Cardiac output can be measured invasively (contrast ventriculography, Fick's method, thermodilution) or non-invasively by rebreathing, ultra sonography, or impedance techniques. The output or work data obtained must be evaluated against the actual pulmonary capillary pressure (Frank-Starling relationship) and the adequacy of O2 supply to the tissues as reflected by mixed venous O2 tension or saturation. The most commonly used index of global left ventricular function is the ejection fraction (EF):19

It can be measured non-invasively by radionuclide ventriculography or echocardiography. During anaesthesia, transoesophageal echocardiography allows continuous monitoring of the left ventricular cross sectional area and calculation of left ventricular fractional area change (FAC):

Table 2.1 Clinical assessment of left ventricular performance

18 113

Assessment

Normal values

Symptoms Signs

Haemodynamics

Heart rate

Systolic/diastolic arterial pressure

Mean arterial pressure

Left ventricular end diastolic pressure

Pulmonary capillary wedge pressure

Left ventricular end diastolic volume index

Left ventricular end systolic volume index Cardiac index

Left ventricular stroke volume index Left ventricular ejection fraction Left ventricular mean systolic ejection rate Left ventricular stroke work index Left ventricular stroke power index Oxygen transport parameters O2 consumption

Arteriovenous O2 difference

50-90 beats/min

70-105 mm Hg

4-15 mm Hg

25 ml/m2

110-150 ml/min per m 40-55 ml/1

02 delivery 400-800 ml/min per m2

Mixed venous O2 saturation 65-75%

Mixed venous O2 partial pressure 40-50 mm Hg

End diastolic area - End systolic area End diastolic area x 100.

This has been shown to correlate closely with simultaneously measured radionuclide ejection fraction.— The monitoring of FAC became easier after the introduction of automated border detection (Fig 2.5). The ejection fraction (or FAC) is the most useful and widely used index of global pump function. As an index of left ventricular contractility, however, it has the flaw of being load dependent. On the other hand, this dependency can guide the anaesthetist towards optimising the left ventricular function by primarily adjusting the left ventricular preload and afterload.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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