Page 333 - Clinical Application of Mechanical Ventilation

Hemodynamic Monitoring 299

Z
B

dZ/dt max

X
dZ/dt
A C
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TIve

ECG

Figure 10-13 Impedance cardiography waveforms. Z—pulse contour curve; dZ/dt—imped-
ance curve; ECG—electrocardiogram curve; dZ/dt max —maximum value of the first derivative of
the impedance curve; A—opening of the aortic valve; B—maximum systolic value; X—closing of
the aortic valve; C—opening of the pulmonic valve; Tlve—left ventricle ejection time.

Some parameters pro- index, systemic vascular resistance, systemic vascular resistance index, contractility, and
vided by ICG include: cardiac
output, cardiac index, stroke fluid status. Table 10-11 lists some hemodynamic parameters provided by ICG.
volume, stroke volume index, Unlike the thermodilution method in which a pulmonary artery catheter is re-
systemic vascular resistance,
systemic vascular resistance quired, ICG cannot provide the values for pulmonary artery pressure, pulmonary ar-
index, contractility, and fluid tery wedge pressure, pulmonary vascular resistance, and pulmonary vascular resistance
status.
index.

TABLE 10-11 Hemodynamic Parameters Provided by Impedance Cardiography

Measured Calculated

Heart rate Stroke volume/index
Thoracic fluid content Cardiac output/index

Mean arterial pressure a Systemic vascular resistance/index

Acceleration index b Left cardiac work/index
Velocity index c Left stroke work/index

Pre-ejection period d

Left ventricular ejection time e
a If automatic blood pressure (oscillometric method) is used.
b Acceleration of blood flow in the aorta within the first 10 to 20 m/sec after the opening of the aortic valve.
c Peak blood flow velocity in the aorta.
d Time interval from the beginning of electrical stimulation of the ventricles to the opening of the aortic valve
(electrical systole).
e Time interval from the opening to the closing of the aortic valve (mechanical systole).
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