Michard 25/7/08 02:45 Page 100
Haemodynamic Management
Starling curve. In brief, in patients operating on the flat portion of the induce any significant change in SV, even in fluid-responsive patients.
10
Frank-Starling curve, SVV is low (<12%) and volume loading does not result Small variations in pleural pressure may be observed in spontaneously
in a significant increase in SV. Conversely, in patients operating on the breathing patients, in patients receiving mechanical ventilation with small
steep portion of the pre-load–SV relationship (and who are thus sensitive tidal volumes, e.g. 6ml/kg, or in patients with increased chest
to cyclic changes in pre-load induced by mechanical ventilation), SVV is compliance, e.g. open chest. In this context, caution should be exercised
high (>12%) and volume loading leads to a significant increase in SV.
It is important to understand that fluid responsiveness (SVV >12%) does
Venous oxygen saturation is the
not mean that fluid is needed.
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Most healthy subjects are fluid-
responsive. Fortunately, this does not mean that they need volume gold standard for defining global
expansion. Before using SVV, the first question must be: ‘Does my patient
adequacy between oxygen transport
need an increase in SV or in cardiac output?’ SVV will not definitively
answer this question. To answer this, both clinical examination – e.g.
and oxygen demand.
hypotension, mottling and oliguria – and biological tests – e.g. renal
failure and lactate concentration – are of value, but they lack sensitivity
and specificity to identify patients in whom cardiac output is insufficient. before concluding that a patient will not respond to a fluid challenge
Venous oxygen saturation is the gold standard for defining global because SVV is low (false-negative). However, a high SVV is usually
adequacy between oxygen transport and oxygen demand, and can be indicative that the patient will be fluid-responsive.
used as a trigger for deciding to increase cardiac output.
In terms of predicting fluid responsiveness in such
Are there limitations to the use of stroke patients, how would you overcome the limitations
volume variation? in the use of stroke volume variation?
First, in patients with cardiac arrhythmia the beat-to-beat variation in SV In situations where it is not possible to use SVV, it can be useful
may no longer reflect the effects of mechanical ventilation.
10
This is a to mimic the effects of fluid loading by a passive leg raising (PLR) manoeuvre,
limitation only in patients with atrial fibrillation or frequent extrasystoles. and to check the efficacy of such a manoeuvre on SV and cardiac output
online. PLR at 45º can effectively translocate the venous blood in the legs to
the intrathoracic compartment. In patients who are pre-load-responsive, this
We must keep in mind that the creates a transient increase in cardiac output. Clinical studies have confirmed
physiological relationship between
that if a patient is responding to PLR, he or she will be responsive to fluid
administration.
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The PLR test is reversible. Therefore, it is particularly useful
ventricular end-diastolic pressure
in patients at risk of fluid-loading-related complications, e.g. patients with
and volume is not linear but
severe hypoxaemia. In other patients, the continuous monitoring of SV and
cardiac output during a fluid challenge, e.g. 250ml of fluid over a short
curvilinear, and highly dependent
period of time, can be used to check online the efficacy of fluid therapy.
on cardiac compliance.
The continuous monitoring of cardiac output is now possible using
minimally invasive technologies. Most of them are based on the analysis
Indeed, most SVV calculation software is now able to detect and exclude of the arterial pressure tracing and require frequent manual recalibrations
few (and far between) premature heart beats, and hence provide an by an independent technique of cardiac output measurement.
12
A
accurate estimation of SVV even in this context. method that does not require intermittent manual calibration does exist
on the market, and has the great advantage of being easy to set up.
Second, if pleural pressure changes are small over a single respiratory Importantly, it automatically adjusts to changes in vascular tone every
cycle, cardiac pre-load changes will be small and inspiration will not minute, and has been shown to be as accurate as other methods.
13–16
■
1. Michard F, Teboul JL, Predicting fluid responsiveness in ICU 6. Michard F, Changes in arterial pressure during mechanical vascular tone on the agreement between pulse contour and
patients: a critical analysis of the evidence, Chest, 2002;121: ventilation, Anesthesiology, 2005;103:419–28 transpulmonary thermodilution cardiac output measurements
2000–2008. 7. Kumar A, Anel R, Bunnell E, et al., Pulmonary artery occlusion within an up to 6-hour calibration-free period, Crit Care Med,
2. Berkenstadt H, Margalit N, Hadani M, et al., Stroke volume pressure and central venous pressure fail to predict ventricular 2008;36:434–40.
variation as a predictor of fluid responsiveness in patients filling volume, cardiac performance, or the response to volume 13. de Wall EE, Kalkman CJ, Rex S, Buhre WF, Validation of a new
undergoing brain surgery, Anesth Analg, 2001;92:984–9. infusion in normal subjects, Crit Care Med, 2004;32:691–9. arterial pulse contour-based cardiac output device, Crit Care Med,
3. Reuter DA, Felbinger TW, Schmidt C, et al., Stroke volume 8. Osman D, Ridel C, Ray P, et al., Cardiac filling pressures are not 2007;35:1904–9.
variations for assessment of cardiac responsiveness to volume appropriate to predict hemodynamic response to volume 14. Button D, Weibel L, Reuthebuch O, et al., Clinical evaluation of
loading in mechanically ventilated patients after cardiac surgery, challenge, Crit Care Med, 2007;35:64–8. the FloTrac/Vigileo
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system and two established continuous
Intensive Care Med, 2002;28:392–8. 9. Pinsky M, Vincent JL, De Smet JM, Estimating left ventricular cardiac output monitoring devices in patients undergoing cardiac
4. Marx G, Cope T, McCrossan L, et al., Assessing fluid filling pressure during positive end-expiratory pressure in humans, surgery, Br J Anaesth, 2007;99(3):329–36.
responsiveness by stroke volume variation in mechanically Am Rev Respir Dis, 1991;143:993–4. 15. Prasser C, Trabold B, Schwab A, et al., Evaluation of an improved
ventilated patients with severe sepsis, Eur J Anaesth, 2004; 10. Michard F, Volume management using dynamic parameters: the algorithm for arterial pressure-based cardiac output assessment
21:132–8. good, the bad, and the ugly, Chest, 2005;128:1902–3. without external calibration, Intensive Care Med, 2007;33:2223–5.
5. Hofer CK, Muller SM, Furrer L, et al., Stroke volume and pulse 11. Monnet X, Rienzo M, Osman D, et al., Passive leg raising predicts 16. Mayer J, Boldt J, Wolf MW, et al., Cardiac output derived from
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100 EUROPEAN CARDIOLOGY
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