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ITBV has been found to correlate well with cardiac
volumes and its changes are better correlated with changes
in cardiac volumes than are the filling pressures [13, 15,
16]. Hinder et al. [9] described that changes in ITBV are
well correlated with changes in LVEDA. These echocardiographic
findings may be interpreted as supporting
thermodilution-derived measurements. Furthermore, in
patients with preserved left–right ventricular function [10]
GEDV was found to give a reliable reflection of echocardiographic
changes in left-ventricular preload following
fluid loading.
With respect to assessment of myocardial contractility,
GEF has been found to provide reliable estimation of leftventricular
systolic function but may underestimate it in
the case of isolated right ventricular failure [17]. In our
study, the increase in cardiac volumes was associated with
a significant increase in cardiac output, as expected from
the Frank–Starling law. Thus, GEF was unchanged and this
was confirmed by LV-FAC.
Finally, although the difference was not statistically
significant, also PCCO showed a reversible increase in CO
in our study. So far, pulse contour-derived cardiac output
has been shown to remain reliable during increasing SVR
(using phenylephrine and reversibly increasing MAP
from 68 ± 6to95± 9 mmHg) [18]. In contrast, we used
norepinephrine which is not a pure α-agonist but has
α- andβ-adrenergic properties, because it is the first-line
vasopressor agent in our department.
References
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Meier-Hellmann A (2000) of cardiac
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Pfeiffer UJ (1992) Intrathoracic blood
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Meier-Hellmann A (1999) Comparison
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Our study has several limitations. First, we did not
use the transpulmonary double-indicator technique, which
may be regarded as the clinical reference standard.
Furthermore, one could speculate that an acute increase
in SVR might produce differential effects on cardiac
dimensions depending on basal cardiac function. Unfortunately,
our data are too limited to allow such an analysis.
Although merely two-dimensional echocardiography was
used to assess left-ventricular volume and not volumes
of all cardiac (i.e., right heart) chambers, we found
a similar change in LVEDA and central blood volumes
during increase in SVR. Probably, determination of whole
cardiac blood volume by magnetic resonance imaging
or radionuclide techniques would give more insight.
However, we decided to use a clinical monitoring system
since the above-mentioned techniques are not practicable
in the routine ICU setting.
Conclusion
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An acute increase in systemic vascular resistance by
increasing norepinephrine dosage results in a reversible
increase in central blood volumes (ITBV, GEDV) as measured
by the transpulmonary thermodilution technique.
These findings are supported insofar as two-dimensional
transesophageal echocardiography revealed an increase in
LVEDA.
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Hoeft A, Mollhoff T, Loick HM,
Van Aken H (1998) Assessment of
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echocardiography. Br J Anaesth
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Weyland A (2001) Changes in cardiac
output and intrathoracic blood volume:
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the relationship between
intrathoracic blood volume index and
cardiac index. Intensive Care Med
26:1376–1378