The ability to measure stroke volume variations obtained

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The ability to measure stroke volume variations obtained with vigileo/ FloTrac system to monitor fluid responsiveness in mechanically ventilated patients Anesth Analg 2009;108:513-17:

The ability to measure stroke volume variations obtained with vigileo / FloTrac system to monitor fluid responsiveness in mechanically ventilated patients Anesth Analg 2009;108:513-17

Predictors of fluid responsiveness:

Predictors of fluid responsiveness Static indicators : CVP PCWP LVED area Dynamic indicators : better; Inspiratory rt. ventricular stroke volume Respiratory variations in arterial pulse pressure ( ∆ PP)- requires specific devices, monitors and algorithms

Vigileo- FloTrac:

Vigileo - FloTrac Automatic and continuous monitoring of cardiac output (CO) based on pulse contour analysis and of respiratory variations in stroke volume variation (SVV) The accuracy of this device to assess CO has been tested in numerous settings with various results However, the ability of SVV to predict fluid responsiveness in mechanically ventilated patients has not been fully evaluated

Methods:

Methods Informed and written consent 25 patients undergoing CABG (m=20, f=5) Mean age (67 +/- 9) yr Pts. With cardiac arrhythmias and intracardiac shunts have been excluded

Induction of anaesthesia:

Induction of anaesthesia Propofol 3-5 mg/kg. Sufentanyl 0.5 to 1 mcg./kg. Cisatracurium 0.15mg/kg to facilitate endotracheal intubation

Invasive monitoring :

Invasive monitoring 8cm. 5 fr . Catheter- left or right radial artery Tripple lumen 16 cm. 8.5 fr . Central venous catheter and a PAC., Swan Ganz 7.5 fr . : rt. IJV Pressure transducers ( medex medical, rossendale , lancashire , UK. and Flo- Trac and Vigileo systems, version 1.10, edwards lifescinces , irvine , CA) were leveled at the midaxillary line and fixed to the operating table and zeroed to atm. pr. Correct position of PAC in west’s zone 3

Slide 7:

CO was measured by thermodilution technique, using the average of 5 successive measurements randomly obtained by injection of 10 ml.of dextrose at room temperature during the respiratory cycle. Cardiac index (CI) and stroke volume index (SVI), were calculated

Slide 8:

Anaesthesia was maintained with continuous infusion of propofol 5-8 mg./kg/hr. and sufentanil 0.7- 1.0 mcg/kg/hr. in order to keep a BIS (Aspect 1000) between 40-50. All patients were ventilated in a volume controlled mode with a tidal volume 8-10 ml/kg. of body wt. at a freq of 12-15 cycles/min. PEEP was set between 0-2.

Data Recording and analysis:

Data Recording and analysis Arterial pressure waveforms were recorded from a bedside monitor, ( intellivue MP70, philips medical system) and were analyzed by an observer who had no knowledge of ∆ PP or any other hemodynamic data. All hemodynamic data were recorded after 3 min. of hemodynamic stability.

Respiratory variations in pulse pressure analysis:

Respiratory variations in pulse pressure analysis PP was defined as the difference between systolic and diastolic pressure. Maximum( PPmax ) and minimal( PPmin ) values were determined over the same respiratory cycle. ∆ PP then calculated as described by its authors ∆ PP={ Pmax-Pmin / Pax-Pmin }/2

Automated calculation of SVV:

Automated calculation of SVV Arterial waveform is used to determine SV Doesn’t require prior calibration Pressure transducer which can be attached to any arterial catheter Waveform is assessed at 100 Hz The SD of PP is determined over a 20 sec. period

Calculation of CO and SVV:

Calculation of CO and SVV Vigileo software uses an algorithm based on relationship between arterial pulse pressure and stroke volume. It considers vessel compliance estimated from nomograms based on age, gender, height, and weight and peripheral resistance determined from arterial waveform characteristics

Other hemodynamic measurements:

Other hemodynamic measurements Following variables were recorded both before and after intravascular volume expansion: Systolic arterial blood pressure Mean arterial blood pressure Diastolic arterial blood pressure Heart rate End expiratory CVP End expiratory PCWI SVI CI SVRI

Experimental protocol:

Experimental protocol All pts. Were studied after induction of anaesthesia and 3 min. after hemodynamic stability Baseline measurements were obtained and then followed by an intravascular volume expansion consisting of 500 ml. of 6% hetastarch given over a period of 10 min. SVV was determined in real time and ∆PP was determined rost hoc based upon recorded waveforms.

Statistics:

Statistics All data presented as mean±standard deviation Changes in hemodynamic variables were assessed by Mann- Whitney U test or Wilcoxon’s ranked sum test Pts. were divided into two groups according to the percent increase in CI after intravascular volume expansion

Slide 16:

Responders: ≥15% increase in CI Nonresponders:‹15% change in CI Receiver operating characteristic (ROC) curves were generated for CI, CVP, PCWP, ∆PP and SVV Area under the ROC curves were calculated and compared. Blind- Altman analysis was performed to assess agreement between ∆PP and SVV P value ‹0.05 was considered statistically significant

Results:

Results Changes in hemodynamic variables after intravascular volume expansion: significant increase in CI (from 2.1±0.4 to 2.5±0.5 L/min/m²; p‹0.001) MAP (from 67±12 to 76±12 mmhg; p‹0.001) PCWP (from16±4 to 17±4 mmhg; p‹0.02)

Slide 18:

Significant decrease in: ∆PP (from11±6 to 5 ±4 %; p‹0.01) And SVV ( from 13±6 to 7±3%; p‹0.01) No significant changes in HR (from 62±13 to 59±15bpm; p=0.21) SVRI (from 2161±565 to 2033±459 dyn/s/cm⁵; p= 0.07)

SVV to predict fluid responsiveness:

SVV to predict fluid responsiveness 17 pts were responders and 8 pts were non responders to intravascular volume expansion. Their hemodynamic data are shown table 1

Slide 21:

∆PP and SVV were significantly higher in responders than in nonresponders (14±5 vs 6±4% , 15 ±5% vs 7±4% respectively; p‹0.01) There was no difference in PCWP ( 15 ± 4 mmhg in responders vs. 17 ±4 mmhg in nonresponders ; p=0.22) there was no difference in CVP (11 ±5mmhg in responders vs. 11±4 mmhg in nonresponders ; p= 0.74) Statistically, there was no difference in CI (2.0 ±0.4 ml/min/m² in responders vs. 2.3±0.3 ml/min/m² in nonresponders ; p= 0.06), but reached statistical significance between these two groups

Slide 23:

The areas under the ROC curves (± SE) were as follows : 0.857±0.084 for ∆PP, 0.871 ±0.085 for SVV, 0.533±0.118 for CVP, 0.338±0.126 for PCWP, and 0.298±0.112 for CI; fig n o.2) The areas for ∆PP and SVV were significantly higher than the areas for CVP, PCWP and CI (p‹0.05 for both) The difference in area under the curve between ∆PP and SVV did not reach significance (p=0.78)

Slide 24:

Setting a threshold ∆PP value of 10% discriminated between responders and nonresponders with a sensitivity of 88% and a specificity of 87% The threshold SVV value of 10% discriminated between responders and nonresponders with a sensitivity of 82% and a specificity of 88%

SVV to quantify response to intravascular volume expansion:

SVV to quantify response to intravascular volume expansion There was a statistically significant positive linear correlation between ∆PP at baseline and percent changes in CI induced by intravascular volume expansion (∆CI) (r= 0.47; p=0.02) as well as between SVV and ∆CI). There was no statistically significant relationship between CVP at baseline and ∆CI (r= -0.06; p= 0.75) and between PCWP at baseline and ∆CI ( r= -0.20; p= 0.33).

Discussion:

Discussion This study demonstration the ability of SVV obtained using the Vigileo Flo- Trac system to predict fluid responsiveness in mechanically ventilated patients in the operating room. Fluid responsiveness has been widely studied over the last over the last 10 years and it has consistently been demonstrated that dynamic indicators based on cardiopulmonary interactions are the best indicators in mechanically ventilated patients..

Discussion cont..:

Discussion cont.. The major limitation of most of current dynamic indicators is there inability to be automatically and continuously monitored. This is of concern since a recent study suggests that intraoperative goal- directed fluid optimization based on minimizing ∆PP has the ability to reduce perioperative morbidity and cost of surgery.

Discussion…:

Discussion… Consequently, recent studies have explored the ability of algorithms to automatically and continuously monitor dynamic indicators of fluid responsiveness, translating the concept from physiology to technology. In the present study, we explored the ability of the Vigileo- Flot-Trac system to predict fluid responsiveness in mechanically ventilated patients.

Disc..:

Disc.. This system is based on pulse contour analysis and allows for continuous CO monitoring from a single arterial catheter. The accuracy of this system for CO determination has been largely explored with very divergent results and it seems that it does not accurately determine CO absolute value in cases of profound systemic vasodilatation (systemic vascular resistance ‹700 d.sec -1 .cm -5 or SVRI ‹410 d.sec -1 .cm -5 .m -2 )

Disc..:

Disc.. However, the usefulness of SVV has not been fully evaluated and only one study, using the first version of the software (1.01), focused on the ability of SVV to predict fluid responsiveness. In this study the authors found that SVV was a poor predicator of fluid responsiveness in mechanically ventilated patients.

Disc..:

Disc.. For the authors, the lack of sensitivity and specificity of SVV was related to the software version, they used in their study. However, in our opinion, other factors may have influenced these results. First, CO was determined using the PICCO system and we believe that the PAC and thermo dilution method still remain the “gold standard” for CO determination.

Disc..:

Disc.. Second tidal volume was not provided and it strongly impacts the accuracy of dynamic indicators. Third, only 18 patients were studied. Finally, the previous version used in this study differs from our version (1.10) by the fact that one of the variables used for CO determination is updated every minute instead of every 10 minutes.

Slide 34:

However, SVV is not based on CO or SV absolute value but on their relative changes over the respiratory cycle. Thus, it would not be surprising to find an accurate ability of SVV to predict fluid responsiveness even if the absolute CO is different from the gold standard (thermo dilution using a PAC). However, further studies are required to investigate this question.

Slide 35:

In our study, we found acceptable sensitivity and specificity for SVV to predict fluid responsiveness. These results are consistent with those obtained with clinically accepted dynamic variables of fluid responsiveness. Moreover, the ability of SVV to predict fluid responsiveness was significantly better than daily used variables, such as CVP and PCWP in the present study.

Slide 36:

Consequently we feel that SVV may be useful in daily clinical practice for the purpose of fluid responsiveness assessment. From our present data, 15 patients presented with a SVV value ›10% at baseline. Of these 15 patients 14 were responders to intravascular volume expansion (positive predictive value =93%). Of the 10 patients presenting with SVV ‹10% at baseline, 7 were nonresponders to intravascular volume expansion (Negative predictive value = 70%) .

Slide 37:

In the present study, we chose to give a fixed amount of fluid to the patient whatever their body weight or surface area. In previously published studies, some authors chose to give an amount of fluid based on patient’s weight. It is possible that such an approach would have impacted our results. However, this impact would have been the same on any of the studied variable.

Study limitations:

In the present study, we excluded patients with cardiac arrhythmias. Dynamic indicators of fluid responsiveness cannot be used in the setting of cardiac arrhythmias. However, we noticed that SVV was still displayed by the monitor screen even in the presence of arrhythmia. Study limitations

Slide 39:

Potential users should be aware of this limitation. Interpretation of SVV should also be cautious in patients with spontaneous breathing activity, open chest conditions and right and/or left ventricular dysfunction. In the present study, we focused on patients in the operating room before any surgical stress was induced.

Slide 40:

Consequently, whether SVV has the same predictive value for fluid responsiveness assessment intraoperatively or in the setting of resuscitation still has to be demonstrated. Another major point is that the SVV value has to be considered after at least 1-min period of hemodynamic stability in order to avoid misleading values that may have been induced by any acute change in HR or Map.

Slide 41:

Because this algorithm relies on a mean ∆PP, it is important to observe steady hemodynamic state before accepting the SVV value. However this limitation is observed with most dynamic indicators.

Conclusion:

Conclusion We found that SVV displayed by the Vigileo- Flo- Trac system predicted fluid responsiveness in mechanically ventilated patients with an acceptable sensitivity and specificity. Further study is needed to determine the clinical utility of this automatically calculated index for guiding fluid resuscitation in the operating room and/or the intensive care unit.

Slide 43:

Thank you

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