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PRINCIPLES OF INVASIVEHEMODYNAMIC
MONITORINGMarelno Zakanito
030.07.153
Pembimbing:dr. Dean Wahjudy ,Sp.OG
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There are four basic parameters necessary to describe
comprehensively the hemodynamic status of any
pregnant patient:
preload,
afterload,
contractility,
and heart rate.
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Preload
Preload refers to the volume of blood contained within a
ventricle at cardiac end-diastole.
Preload is determined by blood return to the ventricle and
thus is directly related to intravascular volume.
If increased amounts of blood enter the heart during
diastole. The normal heart will respond with increased
velocity of contraction and thus increased stroke volume.
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Afterload
Afterload represents the downstream resistance offered to
each ventricle during cardiac systole. Cardiac output is
inversely related to afterload (figure 4-1).
Clinically, afterload is assessed as systemic vascular
resistance, a derived parameter based upon blood
pressure, central venous pressure, and cardiac output.
Right ventricular afterload is represented by pulmonary
vascular resistance, and left ventricular afterload by
systemic vascular resistance.
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Figure 4-1
Cardiac output (CO)
versus mean arterial
pressure (MAP).
Increasing systemicvascular resistance
(SVR) is demonstrated
by isometric lines.
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Figure 4-2 ventricular
end-diastolic volume
versus ventricular
performance. Increased.
Normal and impairedcontractility are
demonstrated.
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Contractility
Contractility refers to the intrinsic contractile property of
the myocardium. While alterations in preload affect the
movement of stroke volume along a given Starling curve,
alterations in contractility affect the Starling curve upon
which the cardiac output operates (figure 4-2)
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Contractility may be altered by various disease states or
by pharmacologic agents that have positive or negative
inotropic effects. One of the most useful measures of
contractility is stroke work index, a derived parameter
(figure 4-3)
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Heart Rate
Cardiac output is also directly affected by heart rate,
independent of either Starlings forces or alterations in
contractility. In the normal heart, cardiac output generally
increases with normal heart rate to the limits of
physiologic tachycardia.
However, at extremely rapid rates, ventricular filling and
end-diastolic volume will be diminished because of
inadequate diastolic filling time; under these
circumstances, cardiac output will decrease.
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Figure4-3
Pulmonary capillary
wedge pressure
(PCWP) versus left
ventricular stroke workindex (LVSWI): Normal
relationship represented
by shaded area.
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Clinical Assessment
In practice, blood pressure, pulse, and body surface area
are measured in standard clinical fashion. Central venous
and pulmonary capillary wedge pressure are measured
from the proximal and distal ports of pulmonary artery
catheter. Cardiac output is measured using thermodilution technique associated with the pulmonary artery
catheter and a cardiac output computer. Once these
parameters have been obtained clinically, derived
parameters such as systemic and pulmonary vascularresistance and left ventricular stroke work index may be
calculated in putting together the complete hemodynamic
picture of the patient.
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Blood Pressure
True interarterial pressures obtained by direct arterial line
measurements are more accurate than cuff pressures. As
a rule, interarterial catheters result in pressure from 4-8
mm higher than corresponding cuff pressures. This
principle, however, is generally valid only in normalpatients; in certain subsets of critically ill patients,
interarterial pressure may be up to 30 mmHg higher than
those obtained from a peripheral cuff.
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Mixed Venous Oxygen Saturation
(SV02) Monitoring SV02 may be assessed either periodically by direct
sampling from the distal port of pulmonary artery catheter
or continuous use of a pulmonary artery catheter
equipped with fiberoptic oximetry sensor. SVo2is
determined by four parameters: cardiac output.
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Pulse Oximetry
Pulse oximetry is based upon the principle of differential lighttransmittance by oxygenated and nonoxygenated hemoglobinand depends upon the use of two light-emitting diode(LED)sources; one red (660 nanometers) and one infrared (940nanometers). Using a spectrophotometric device and an
associated microprocessor, pulse oximeters will evaluate 02saturation with each pulse. In critically ill pregnant patients withtenuous physiologic oxygenation, pulse oximetry is aninvaluable technique. The use of this technique often allows theclinician to avoid multiple arterial blood gases and, at the same
time, provides a continuous rather than intermittent method ofpatient evaluation. This technique should be a routine part ofthe management of any critically ill patient whose oxygenstatus is or may be compromised. Recent investigations intothe use of fetal pulse oximetry may also prove clinically fruitful.