Predicting fluid responsiveness in theatre
Glasgow, UK
* E-mail: colin.runcie{at}northglasgow.scot.nhs.uk
Editor—I read with interest the article by Solus-Biguenet and colleagues1 which demonstrated clearly the ability of dynamic tests of the circulation to predict fluid responsiveness intraoperatively. They are the first group to do so with a non-invasive dynamic test, namely respiratory variations in non-invasive pulse pressure but they have not discussed the value of systolic pressure variation (SPV) with respiration and I think this is an omission.
In 2003, Tavernier and colleagues2 found that the delta down component of SPV could guide fluid therapy during phaechromocytoma surgery, illustrating its ability to clarify the mechanism of hypotension after tumour removal and showing the value of dynamic tests during haemodynamic instability in theatre. When patients have reached the flat part of their Starling curve, they no longer respond to fluids by increasing cardiac output and require other treatments if increased cardiac output is desired. This can be identified rapidly in mechanically ventilated patients by demonstrating minimal SPV and this was clear in Tavernier's report. The ability of dynamic tests to identify the point at which resuscitation with fluids should stop and be followed by resuscitation with inotropes is a clinically invaluable feature not possessed by other measurement techniques.
Other features make SPV the most valuable dynamic test of the circulation. It employs widely available equipment which can be calibrated easily by users using the fast-flush technique to ensure optimal damping.3 Repeated assessments of SPV can be made in theatre or at the bedside by labelling arterial pressure as pulmonary artery pressure and then using the wedge pressure function of the monitor. This has the effect of displaying two mechanical breaths on the screen accompanied by a simultaneous arterial pressure trace. SPV can be easily seen and quantified if desired using a cursor. This technique was described by Tavernier and amplified recently by Gouvea.4 An additional refinement is that pausing mechanical ventilation allows end-expiratory systolic pressure to be measured and delta down calculated. It is not currently possible to measure pulse pressure variation in real time in theatre; perhaps, software updates will change this.
Another benefit of SPV is that it does not depend on manufacturers' algorithms or their choice of measurement periods. The latter has rendered stroke volume variation by pulse contour analysis slightly less precise than pulse pressure or systolic pressure variation as a predictor of fluid responsiveness.5
Insertion of an arterial cannula under local anaesthesia (LA) before induction of general anaesthesia allows the circulatory changes of induction to be observed and treated. SPV subsequently serves as a good predictor of fluid responsiveness, even if there is haemodynamic instability, and can identify when patients with impaired ventricular function have reached the flat part of their Starling curve. The future may lie with observation of non-invasive pulse pressure variation but for the moment arterial cannulation under LA remains the core skill for anaesthetists managing the circulation of mechanically ventilated patients.
Lille, France
* E-mail: btavernier{at}chru-lille.fr
Editor—We thank Dr Runcie for his interest in our article1 and for his additional comments, which put forward the value of the arterial SPV and its expiratory component (delta down) in assessing fluid responsiveness and regrets that these indices were not measured in our patients. In fact, the main aim of our study was to assess the value of various non-invasive variables for predicting fluid responsiveness in the operating theatre. This evaluation necessitated the selection of a ‘gold standard’ measure and, from the currently available literature, the arterial pulse pressure variation (PPV) is the best candidate. The pulse pressure is directly proportional to stroke volume and inversely related to arterial compliance. Therefore, the respiratory variation in left ventricular stroke volume is the main determinant of PPV. In contrast, because the systolic pressure depends on both pulse and diastolic pressures, SPV also depends on changes in extramural aortic pressure, that is, changes in pleural pressure.6 Accordingly, several studies have found that PPV predicted haemodynamic response to fluid expansion slightly but significantly better than SPV and delta down,5 7 and PPV correlated more closely with the increase in stroke volume resulting from fluid infusion than both SPV and delta down.8 A recent study analysed the correlation and agreement between PPV, SPV, and delta down and their corresponding photoplethysmographic indices (expressed in %).9 Cardiac output was not measured, and thus fluid responsiveness was not directly assessed. The study, however, suggested that pulse variation was the only photoplethysmographic indice that may identify patients likely to respond to fluid administration (as assessed from arterial PPV and delta down values).
We agree with Dr Runcie that, when using the ‘wedge pressure’ menu of the monitor for quantification of respiratory changes in arterial pressure, as previously proposed by us2 and others,4 SPV and delta down are obtained more easily and rapidly than PPV. The latter, however, can be measured and calculated in 1–2 min using this procedure, and this is now routinely done by many anaesthetists at our institution. Dr Runcie also claims that a benefit of SPV is that it does not depend on manufacturers' algorithm or their choice of measurement periods. Stroke volume variation by pulse contour analysis was indeed shown less precise than PPV or SPV as a predictor of fluid responsiveness.5 However, this result may depend only on a lack of accuracy for assessment of rapid changes (over a single breath) in stroke volume from the arterial pressure contour, and thus not concern automated calculation of PPV. Moreover, from a strictly evidence-based point of view, the value of PPV, SPV, and delta down as predictors of fluid responsiveness has been established from off-line measurements on computer recordings, not from the ‘frozen’ arterial trace on the monitor screen. We believe that dynamic indices will be widely used by clinicians only when monitors allow automatic calculation and real monitoring. These evolutions should be effective in most monitors in the near future.
References
1 Solus-Biguenet H, Fleyfel M, Tavernier B, et al. (2006) Non-invasive prediction of fluid responsiveness during major hepatic surgery. Br J Anaesth 97:808–16.
2 Mallat J, Pironkov A, Destandau M, Tavernier B. (2003) Systolic pressure variation (
down) can guide fluid therapy during pheochromocytoma surgery. Can J Anesth 50:998–1003.
3 Gardner RM. (1981) Direct blood pressure measurement: dynamic response requirements. Anesthesiology 54:227–36.[ISI][Medline]
4 Gouvea G and Gouvea FG. (2005) Measurement of systolic pressure variation on a Datex AS/3 monitor. Anesth Analg 100:1864.
5 Preisman S, Kogan S, Berkenstadt H, Perel A. (2005) Predicting fluid responsiveness in patients undergoing cardiac surgery: functional haemodynamic parameters including the Respiratory Systolic Variation Test and static preload indicators. Br J Anaesth 95:746–55.
6 Michard F. (2005) Changes in arterial pressure during mechanical ventilation. Anesthesiology 103:419–28.[CrossRef][ISI][Medline]
7 Michard F, Boussat S, Chemla D, et al. (2000) Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure. Am J Respir Crit Care Med 162:134–8.
8 Bendjelid K, Suter PM, Romand JA. (2004) The respiratory change in preejection period: A new method to predict fluid responsiveness. J Appl Physiol 96:337–42.
9 Natalini G, Rosano A, Franceschetti ME, Facchetti P, Bernardini A. (2006) Variations in arterial blood pressure and photoplethysmography during mechanical ventilation. Anesth Analg 103:1182–8.
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