32. Fritsch-Yelle JM, Convertino VA, Schlegel TT (1999) Acute manipulations of plasma volume
alter arterial pressure responses during Valsalva maneuvers. J Appl Physiol 86:1852–1857
Central Venous Pressure: Uses and Limitations
T. Smith, R. M. Grounds, and A. Rhodes
Introduction
A key component of the management of the critically ill patient is the optimization
of cardiovascular function, including the provision of an adequate circulating
volume and the titration of cardiac preload to improve cardiac output. In spite of
the appearance of several newer monitoring technologies, central venous pressure
(CVP) monitoring remains in common use [1] as an index of circulatory filling
and of cardiac preload. In this chapter we will discuss the uses and limitations of
this monitor in the critically ill patient.
Defining Central Venous Pressure
What is the Central Venous Pressure?
Central venous pressure is the intravascular pressure in the great thoracic veins,
measured relative to atmospheric pressure. It is conventionally measured at the
junction of the superior vena cava and the right atrium and provides an estimate
of the right atrial pressure.
The Central Venous Pressure Waveform
The normal CVP exhibits a complex waveform as illustrated in Figure 1. The
waveform is described in terms of its components, three ascending ‘waves’ and
two descents. The a-wave corresponds to atrial contraction and the x descent to
atrial relaxation. The c wave, which punctuates the x descent, is caused by the
closure of the tricuspid valve at the start of ventricular systole and the bulging of
its leaflets back into the atrium. The v wave is due to continued venous return in
the presence of a closed tricuspid valve. The y descent occurs at the end of
ventricular systole when the tricuspid valve opens and blood once again flows
from the atrium into the ventricle. This normal CVP waveform may be modified
by a number of pathologies.
100 T. Smith, R. M. Grounds, and A. Rhodes
Fig. 1. Central venous pressure waveform from a ventilated patient (bottom) with time synchro-
nized electrocardiograph trace (top). The a-wave represents atrial contraction and occurs imme-
diately after atrial depolarization as represented by the p wave on the EKG. The c-wave represents
bulging of the tricuspid valve in early ventricular systole and is followed by the v-wave, caused by
atrial filling during ventricular systole.
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