Page 318 - Clinical Application of Mechanical Ventilation

284 Chapter 10

TABLE 10-6 Conditions That Affect the Central Venous Pressure

Change Examples

Decrease in CVP Absolute hypovolemia (blood loss,
dehydration)
Relative hypovolemia (shock,
vasodilation)
Increase in CVP Positive pressure ventilation
Increased pulmonary vascular
resistance
Hypervolemia
Right ventricular failure
Left ventricular failure (late change
in CVP)
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CVP Measurements

CVP is reported as a mean pressure and its normal range in the vena cava is from 0 to
6 mm Hg. When the measurement is taken in the right atrium, the normal value range
is from 2 to 7 mm Hg, slightly higher than the CVP reading (Christensen, 1992a,
1992b).
Since venous return is determined by the pressure gradient between the mean
venous return: Blood flow from
the systemic venous circulation to arterial pressure and CVP, an increased CVP leads to a smaller pressure gradient
the right heart. and a lower blood return to the right heart. This condition is observed during
positive pressure ventilation or as a result of right ventricular failure (e.g., cor
pulmonale due to chronic pulmonary hypertension; right-sided myocardial infarc-
tion). The conditions that may affect the CVP measurements are summarized in
Table 10-6.

PULMONARY ARTERY CATHETER

The first pulmonary artery catheter was developed in 1953 and used in dogs by the
U.S. physiologists Michael Lategola and Hermann Rahn. In the late 1960s, a more
refined pulmonary artery catheter was developed and used in humans by the U.S.
physicians Harold James Swan and William Ganz (Swan et al., 1970). The cur-
rent pulmonary artery catheter (Swan-Ganz catheter) is a flow-directed, balloon-
tipped catheter. The addition of thermistor (for cardiac output measurement),
cardiac output: Blood volume
pumped by the heart in 1 min. and light-reflective fiberoptic element (for mixed venous oxygen saturation mea-
Normal range is 4–8 L/min. surement) to the catheter greatly expanded the scope and capability of hemody-
namic monitoring.

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