Page 297 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 28: Interpretation of Hemodynamic Waveforms 201

Pra
40 40 Pra
NSP INSP
mm Hg 20 20

0 0
3 2

Cardiac output L/min (delta) 1 0

−1
+ve Resp −ve Resp
FIGURE 28-30. Response of right atrial pressure (Pra) to a spontaneous breath. When the Pra remains unchanged (or increases) during inspiration, a positive response to fluid is unlikely.
(Reproduced with permission from Magder S. Fluid status and fluid responsiveness. Curr Opin Crit Care. August 2010;16(4):289-296.).

If the clinical problem is severely impaired oxygenation, then a trial output in response to fluid is very unlikely when Pra exceeds 13 mm Hg
of diuresis is reasonable as long as cardiac output and blood pressure (referenced to midaxillary line). However, one retrospective study inclu-
60
remain within acceptable limits. As with all therapeutic manipulations, ded several individuals who responded to fluid despite a Pra of 14 to
, blood pressure, cardiac output) 16 mm Hg. In brief, there are insufficient data to determine how reliably
4
clinically relevant end points (eg, Pa O 2
should be assessed before and after Ppw reduction. a high Pra will exclude a positive response to fluid.
■ ASSESSMENT OF PRELOAD AND FLUID RESPONSIVENESS that rely on the hemodynamic response to changes in intrathoracic
In contrast to static parameters such as Pra and Ppw, techniques
When afterload and intrinsic contractility are constant, the forcefulness pressure have performed somewhat better at predicting fluid response
of ventricular contraction is determined by end-diastolic fiber length (see Chap. 34). One of these dynamic methods assesses the response
(preload). Both the Ppw and Pra have been widely used as bedside of Pra to the decrease in intrathoracic pressure during a spontaneous
55
indicators of the adequacy of preload. However, factors that alter myo- breath. Normally, the decrease in intrathoracic pressure produces a fall
56
cardial compliance (eg, hypertrophy, ischemia) or juxtacardiac pressure in Pra, increasing the gradient for venous return from extrathoracic
(eg, PEEP, active exhalation) may profoundly influence their reliability veins. However, when the right atrium is at its limits of distensibility, Pra
for assessing preload. Furthermore, due to variation in the cardiac func- may not fall with inspiration. In one study, a positive response to fluid
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tion curve among patients, the same preload may be associated with was seen in most (but not all) patients whose Pra fell with inspiration.
different responses to fluid administration. 57,58 When faced with a In contrast, when there was no decrease in Pra during the inspiratory
patient who has hypotension, oliguria, or tachycardia, the important effort, a fluid challenge seldom produced an increase in cardiac output
63
clinical question is whether or not the patient is likely to have a positive (Fig. 28-30). A subsequent study confirmed that patients with an inspi-
response to a fluid challenge. 59,60 ratory decrease in Pra had a much greater probability of responding to
A review of studies that examined the utility of the Ppw in predicting fluid than did those whose Pra was unaffected by inspiration. 23
fluid responsiveness found that in seven of nine investigations the Ppw
was no different in fluid responders and nonresponders. In agreement,
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a subsequent retrospective analysis of a hemodynamic database reported
extensive overlap between the Ppw of responders and nonresponders. KEY REFERENCES
4
One study did find a significant inverse relationship between Ppw and
fluid-induced change in stroke volume, but the degree of correlation was • Fuchs RM, Heuser RR, Yin FC, Brinker JA. Limitations of pul-
monary wedge v waves in diagnosing mitral regurgitation. Am J
only moderate. These data indicate that the Ppw does not reliably pre-
62
dict fluid responsiveness, at least over the range of values encountered Cardiol. 1982;49:849.
most often in the ICU. • Leatherman JW, Shapiro RS. Overestimation of pulmonary artery
Overall, the data for Pra as a predictor of fluid responsiveness are occlusion pressure in pulmonary hypertension due to partial
similar to that described for the Ppw. 3,4,61 One study found a modest occlusion. Crit Care Med. 2003;31:93.
inverse correlation between Pra and the fluid-induced change in stroke • Magder S. Central venous pressure monitoring. Curr Opinion Crit
volume. However, a review of the literature reported that three of five Care. 2006;12:219.
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studies found no difference between the Pra values of responders and • Magder S. Fluid status and fluid responsiveness. Curr Opin Crit
nonresponders. A more recent analysis of additional studies concluded Care. 2010;16(4):289.
61
that the evidence against Pra as a valid predictor of fluid responsiveness
was so compelling that it should no longer be used for this purpose. 3 • Magder S. How to use central venous pressure measurements.
Despite the apparent limitation of the Pra for predicting response to Curr Opin Crit Care. 2005;11:264.
fluid, it would seem that there might be a threshold value above which • Magder S, Georgiadis G, Cheone T. Respiratory variations in right
the likelihood of fluid response would be negligible. Unfortunately, atrial pressure predict the response to fluid challenge. J Crit Care.
while a number of studies have examined Pra as a predictor of fluid 1992;7:76.
responsiveness, relatively few reported data for individual patients • Michard F, Teboul JL. Predicting fluid responsiveness in ICU
3,61
and those that did included very few individuals with high Pra values patients: a critical analysis of the evidence. Chest. 2002;121:2000.
(eg, ≥14 mm Hg). 4,23,62-65 It has been suggested that an increase in cardiac

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