Page 317 - Clinical Application of Mechanical Ventilation

Hemodynamic Monitoring 283

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mm Hg ECG . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . © Cengage Learning 2014
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Figure 10-5 Tracing of a central venous pressure waveform and the corresponding ECG
electrical conduction.
tracing as shown in Figure 10-5. Infection, bleeding, and pneumothorax are
potential complications of central venous catheter insertion.
Components of Central Venous
Pressure Waveform
Figures 10-5 shows the ECG tracing and the corresponding CVP waveform. Note
that the ECG electrical conduction precedes the pressure waveform by a fraction of
a second. The upstroke a wave reflects right atrial contraction (follows the p wave
on the ECG), c wave reflects closure of the tricuspid valve during systole (appears
within the QRS complex on the ECG), x downslope occurs as the right atrium
relaxes, v wave is caused by right ventricular contraction (appears at the T wave on
the ECG), and y downslope reflects ventricular relaxation and rapid filling of blood
from the right atrium to the right ventricle.
Abnormal Right Atrial Pressure Waveform. Since each wave or downslope on the right
atrial waveform coincides with an event during systole or diastole, changes in the
hemodynamic status of the heart will cause changes to certain components of the
waveform, particularly the a and v waves (Schriner, 1989).
The a wave on the right atrial waveform may be elevated in conditions in which
the resistance to right ventricular filling is increased. Examples include tricuspid
valve stenosis, decreased right ventricular compliance due to ischemia or infarction,
right ventricular volume overload or failure, pulmonic valve stenosis, and primary
pulmonary hypertension. The a wave may be absent if atrial activity is absent or
extremely weak.
Reflux of blood into the right atrium during contraction due to an incompetent
triscupid valve will cause an elevated v wave. Elevation of a and v waves may be
seen in conditions such as cardiac tamponade, volume overload, or left ventricular
failure.
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