Page 548 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

536 FLUID THERAPY

obtained using a percutaneously placed pulmonary circulation may not be accurately gauged by measuring
arterial catheter, as described in the following section. the filling pressures of the right ventricle. 44,45,163 It is
The effect of fluid therapy on CVP and pulmonary common to observe animals with high pulmonary venous
venous pressure is a prime concern in patients with heart pressure but relatively low CVP. This is especially true
failure and can be a major determinant of the rate of fluid after diuretic therapy. Even in animals with right-sided
administration. Insufficient venous pressure reduces CHF, ascites may continue to develop despite a relatively
cardiac output, whereas very high pressure promotes low CVP, possibly as a result of avid sodium retention,
formation of edema. In heart failure, an optimal venous hypoproteinemia, or the development of cardiac cirrhosis
pressure is necessary to maintain cardiac output, but pul- and portal hypertension secondary to chronic hepatic
monary venous pressure greater than 20 mm Hg and congestion. Noninvasive estimation of cardiac filling
CVP greater than 10 to 12 cm H 2 O may be associated pressures can be accomplished using advanced Doppler
with formation of edema. echocardiographic techniques that record transmitral
The CVP is simple to measure using an indwelling jug- filling, pulmonary venous flow, and tissue ventricular
ular venous catheter, and its determination quantifies and movements during diastole, but these are not widely
indicates the directional changes of right heart filling available and require advanced training to apply with
pressures. More practically, the inspection and estimation any consistency. Experienced clinicians also recognize
of jugular venous pressure provides similar qualitative that a ventricular (S3) gallop sound typically corresponds
information. A CVP line is useful in guiding fluid man- to elevated filling pressures and as such will be diminished
agement of seriously ill patients without heart disease, or eliminated with effective diuresis or management of
but CVP is not an accurate reflection of pulmonary heart failure.
venous pressure in those with left-sided CHF. The ability To obtain direct measurements of pulmonary venous
of the left and right ventricles to accept and pump blood and left-sided cardiac filling pressures, a catheter must
may be different in CHF. Accordingly, the effects of a be advanced into a lobar pulmonary artery under fluoro-
volume infusion on the left ventricle and pulmonary scopic or pressure-monitored guidance (Figure 21-6).

(PCWP)
Thermodilution

Aorta Balloon
Indicator
PA
Caud VC
Cran VC CVP RA

Change, in
RV temperature

A B Time
Figure 21-6 Swan-Ganz pulmonary catheterization. A, Determination of central venous pressure (CVP)
and pulmonary capillary wedge pressure. Determination of right and left ventricular filling pressures (left
lateral view). A balloon-tipped, flow-directed catheter (Swan-Ganz) is inserted into the jugular vein and
passed through the cranial vena cava (Cran VC), right atrium (RA), right ventricle (RV), and pulmonary artery
(PA). Two independent catheter lumina permit pressure determinations in both the right atrium and the
pulmonary artery. The proximal lumen in the RA measures the CVP, and the distal tip measures the PA
pressure. When the balloon is inflated, blood flow is temporarily occluded, and the pulmonary capillary
wedge pressure (PCWP) is measured (inset). Caud VC, Caudal vena cava. B, Cardiac output curve of a 21-kg
dog in heart failure. The curve was obtained using a Swan-Ganz catheter equipped with a distal thermistor tip
for measuring blood temperature. The recording demonstrates the change in blood temperature that
developed after 3 mL of iced 5% dextrose was injected into the right atrial port of the catheter. Cardiac
output is inversely related to the area under the curve. The calculated cardiac output in this case was
2.3 L/min. (A, from Bonagura JD. Fluid management of the cardiac patient. Vet Clin North Am Small Anim
Pract 1982;12:509.)