J Clin Monit Comput DOI 10.1007/s10877-015-9666-y
ORIGINAL RESEARCH
Agreement between stroke volume measured by oesophageal Doppler and uncalibrated pulse contour analysis during fluid loads in severe aortic stenosis Lars Øivind Høiseth • Ingrid Elise Hoff • Ove Andreas Hagen • Svein Aslak Landsverk Knut Arvid Kirkebøen
•
Received: 12 May 2014 / Accepted: 27 January 2015 Ó Springer Science+Business Media New York 2015
Abstract The purpose of this analysis was to study agreement and trending of stroke volume measured by oesophageal Doppler and 3rd generation Vigileo during fluid loads in patients with severe aortic stenosis. Observational study in 32 patients (30 analyzed) scheduled for aortic valve replacement due to severe aortic stenosis. After induction of anesthesia and before start of surgery, hemodynamic registrations for 1 min were obtained before and after a fluid load. Agreement between stroke volume measured by oesophageal Doppler (SVOD) and Vigileo (SVVig) was evaluated in Bland–Altman plot and trending in four-quadrant and polar plots. Bias ± limits of agreement (LOA) between SVOD and SVVig was 24 ± 37 ml (percentage error 45 %). Concordance of the two methods from before to after a fluid load was 100 %. Angular bias ± LOA was 12° ± 28°. Absolute values of SVOD and SVVig agreed poorly, but changes were highly concordant during fluid loads in aortic stenosis patients. The angular agreement indicated acceptable trending. The two measurement methods are not interchangeable in patients with aortic stenosis. Keywords Stroke volume Aortic valve stenosis Diagnostic techniques Cardiovascular
L. Ø. Høiseth K. A. Kirkebøen Faculty of Medicine, University of Oslo, Oslo, Norway L. Ø. Høiseth (&) I. E. Hoff O. A. Hagen S. A. Landsverk K. A. Kirkebøen Department of Anesthesiology, Oslo University Hospital, Kirkeveien 166, 0450 Oslo, Norway e-mail: [email protected] I. E. Hoff Norwegian Air Ambulance Foundation, Drøbak, Norway
1 Introduction Goal-directed therapy in surgery and critical illness aims to optimize oxygen delivery (DO2). As DO2 is proportional to cardiac output (CO), a prerequisite is to optimize CO. Thermodilution by a pulmonary artery catheter (PAC) is the clinical gold-standard to monitor CO, but is invasive and cumbersome to use. Simpler and less invasive methods to monitor CO have been developed. Among these are oesophageal Doppler (OD) and arterial pulse contour analyses. To evaluate devices to calculate stroke volume (SV), the agreement between methods at some time point is often calculated. However, to optimize CO, it is not imperative that the absolute values are correct, as long as the ability to trend is adequate. In aortic stenosis (AS), the arterial pressure waveform can be affected by the stenotic valve [1]. Lorsomradee et al. [2] and Staier et al. [3] evaluated 2nd generation Vigileo in AS patients. Petzoldt et al. [4] studied 3rd generation software, but trending to a fluid load, important for hemodynamic optimization, was not evaluated. The primary aim of this analysis was to explore the relation between trending of SV with two different minimally invasive devices (OD and 3rd generation Vigileo pulse contour analysis) in AS patients in relation to fluid loads. Several pulse contour analysis-systems exist. Some are calibrated by an indicator dilution with lithium or cold water. The Vigileo-system (Edwards Lifesciences, Irvine, CA, USA) is an uncalibrated pulse contour-analysis system [5]. The algorithm to calculate SV is based on the standard deviation of the arterial pressure and a v-factor. Limitations of 1st and 2nd generation algorithms have mainly been related to changes in peripheral resistance [6]. The ability of 3rd generation Vigileo software to track changes in SV has also been questioned in conditions with changes
123
J Clin Monit Comput
in systemic vascular resistance (SVR), which is one measure of arterial load [7, 8]. Changes in arterial load have been demonstrated to influence the agreement between SV by oesophageal Doppler (SVOD) and non-proprietary pulse contour algorithms [9]. We therefore also related changes in agreement between SVOD and SV measured by Vigileo (SVVig) to changes in arterial load.
2 Methods 2.1 Patients Analyses were performed on data retrieved in an observational study on dynamic variables of fluid responsiveness in AS patients [10]. After regional ethics committee approval (REK Sør-Øst C, 2010/1629) and written informed consent, 32 patients scheduled for aortic valve replacement (AVR) due to AS were included. Inclusion criteria were: AS requiring AVR with no more than mild aortic insufficiency, age[18 years, left ventricular ejection fraction C40 % and sinus rhythm. Exclusion criteria were: right ventricular failure or pulmonary hypertension, other valvular lesions of hemodynamic significance and contraindications to OD monitoring. 2.2 Anesthetic procedure Patients were premedicated with intramuscular morphine/ scopolamine. A 20G arterial cannula was placed in the left radial artery. Anesthesia was induced with diazepam 0.12 (0.02) mg/kg, fentanyl 4.9 (0.9) lg/kg and propofol 0.7 (0.4) mg/kg intravenously (iv) and endotracheal intubation facilitated with cisatracurium 0.16 (0.02) mg/kg iv. Patients were mechanically ventilated and anesthesia maintained with sevoflurane. After placing a central venous catheter in the right internal jugular vein and an OD probe (see below), patients were placed in the horizontal position. A fluid load of 750 ml acetated Ringer’s solution was administered before surgery. The OD probe was removed after the fluid load to enable planned intraoperative transoesophageal echocardiography (TEE) and to avoid possible interferences between the two probes. Thus, no further registrations were performed. 2.3 Monitoring, signal acquisition and analysis An OD probe (DP-12, CardioQ; Deltex Medical, Chichester, UK) was inserted shortly after endotracheal intubation. An optimal signal was achieved by searching for a sharp and well-defined Doppler signal with maximal peak velocity. The probe was then fixed, and care taken not to displace it during the fluid load. Data were extracted beat
123
by beat from the OD-monitor via the serial output to a laptop computer. The arterial line was connected to a FloTrac transducer (Edwards Lifesciences) with one connection leading to a Vigileo monitor (software version 03.02 or 03.06; Edwards Lifesciences). Data were downloaded by the serial output to a custom-made program in LabVIEW (National Instruments, Austin, TX). To synchronize the methods, registrations from the Vigileo monitor were moved 20 s, as values displayed are based on the arterial waveform from the previous 20 s. Other hemodynamic data were downloaded at 1 Hz from a Solar 9500 (General Electric Healthcare, Milwaukee, WI, USA) monitor to the same LabVIEW-program. The following measures of arterial load were examined: mean arterial pressure (MAP), SVR [80 9 (MAP-central venous pressure)/CO], arterial compliance (SV/pulse pressure) and arterial elastance (Ea, 0.9 9 systolic arterial pressure/SV) [9]. Whereas MAP and SVR do not reflect the pulsatile nature of the arterial pressure, arterial compliance and Ea do. SV and CO measured by OD were used in the calculations of SVR, compliance and Ea. 2.4 Protocol Registrations (averaged over 1 min) were made before and after the preoperative fluid load (750 ml Ringer’s acetate). The fluid was infused rapidly, with registrations before and after the fluid load being 3.5 (0.75) min apart. 2.5 Statistics A separate power analysis was not performed for this analysis, as data were sampled when performing a study on fluid responsiveness in AS-patients [10]. Data are mean (SD), unless otherwise stated. Agreements of absolute values are presented in a Bland– Altman plot, correcting for two measurements per subject [11]. Percentage error was calculated relative to the mean of both methods in the Bland–Altman-plot. Relative changes of SVOD versus SVVig are presented in a four-quadrant plot and a polar plot. In a four-quadrant plot, changes in one method are plotted against changes in the other in a four-quadrant scatterplot. After excluding a central zone, the concordance rate, which is the fraction of observations in which SV increases or decreases with both methods (upper right and lower left quadrants) are calculated, as these have the same directional change [12]. The concordance rate does only state if the directional changes of the methods are the same, but not their magnitudes. Furthermore, the distance from origo will be the hypotenuse of a triangle where changes with each method are the catheti, thus always larger than the largest change. The
J Clin Monit Comput
polar plot is rotated 45° so that the line of identity (y = x) is horizontal. Furthermore, the distance from origo is the absolute value of the average of the two changes. Data points \-90° or [90° were rotated 180° so that all data points were in the -90° to 90° range. The angle h to the line of identity was calculated for each observation and mean h with radial limits of agreement (LOA) were calculated as described by Critchley et al. [13]. In the fourquadrant plot, an exclusion zone of 15 % was used. In the polar-plot, the exclusion zone was reduced to 10 % [13]. Precisions within the 1 min registration periods were estimated for each measurement method. The Vigileo device gives one value every 20 s. Thus, SV-measurements from the OD were averaged over the corresponding 20 s, giving three values for each 1 min registration period. As the SD of the three measurements tended to increase with increasing mean values, SV-values were loge-transformed. SD of the loge(SV)-values were calculated in a one-way ANOVA as the root of the residual mean square, with registration period as factor [14]. The coefficient of variation (CV) of SV was approximated as SD[loge(SV)] [14]. This would thus give the within-subject variability (precision) within the 1 min registration periods with a 20 s average as the unit of measurement. The precisions for 1 min registration periods were then estimated as CV for the 20 s periods divided by H3 [15]. Calculations were performed in MedCalc Statistical Software version 12.7.2.0 (MedCalc Software bvba, Ostend, Belgium).
Table 1 Patient characteristics n = 30 Male/female (n)
19/11
Age (years)
69 (10)
Height (cm)
173 (9)
Weight (kg)
81 (15)
Ejection fraction (%)
60 (7)
Aortic valve areaa (cm2)
0.8 (0.2)
Mean gradient (mmHg)
53 (15)
Maximal gradient (mmHg)
83 (23)
Data are mean (SD) unless otherwise stated a
n = 29 (in one patient valve area could not be calculated due to poor echogenicity)
26/26 = 100 %. In the polar plot, mean angle ± LOA was 12° ± 28° (Fig. 2b). For 20 s periods within 1 min registration periods CV were 3.9 % for SVVig and 2.9 % for SVOD, giving estimated CV for the 1 min periods of 3.9 %/H3 = 2.3 % and 2.9 %/H3 = 1.7 %, respectively. Thus, the least significant changes for one min periods were SVVig H2 9 1.96 9 2.3 % = 6.3 % and SVOD H2 9 1.96 9 1.7 % = 4.6 % [16]. Changes in agreement between the methods were associated with changes in arterial load, with the strongest association for Ea (Fig. 3).
3 Results
4 Discussion
32 patients were included. Two patients were excluded, one due to an arrhythmia (bigimeny not present at inclusion 1 day before surgery), and one due to a severely dampened arterial waveform, probably due to a peripheral arterial stenosis. None of the patients received vasoactive or inotropic medications during the fluid loads. One fluid load was performed in each of the 30 patients, with adequate OD registrations in all patients. In two patients, fluid loads were performed in slight head-down position to maintain hemodynamic stability. Patient characteristics are presented in Table 1. All patients were in ASA physical category 3. Seven patients had hypertension, nine had coronary artery disease and three had diabetes. Hemodynamic data before and after fluid loads are presented in Table 2. Bias ± LOA between SVOD and SVVig (absolute values) was 24 ± 37 ml (percentage error 37 ml/ 82 ml = 45 %, Fig. 1). With fluid loads, relative changes in SV as measured by the two methods were correlated (r = 0.62, p \ 0.001, Fig. 2a). Concordance rate was
The main finding in this analysis was that SV measured by OD and 3rd generation Vigileo did not agree well, with wide LOA and a percentage error of 45 %. The concordance of changes to a fluid load was good, but agreement in a polar plot moderate with a high h, and acceptable radial LOA. Precisions of both methods were adequate with least significant changes less than what is usually considered a clinically significant change. As a stenotic aortic valve may affect the arterial pressure waveform [1], uncalibrated pulse contour analysis systems have been evaluated in patients with AS. The 2nd generation Vigileo software had a percentage error of 29 % compared to continuous thermodilution [2], and 36 and 39 % (before and after sternotomy, respectively) compared to intermittent thermodilution [3]. The 3rd generation software had a percentage error of 50 % compared to TEE [4]. When assessing trending, the concordance to intermittent thermodilution was &75 % trending from before to after sternotomy for 2nd generation Vigileo. The 3rd generation had 72 % of the values within 10 % LOA
123
J Clin Monit Comput Table 2 Hemodynamic data n = 30
Before fluid load
After fluid load
MAP (mmHg)
56 (13)
65 (13)
p \ 0.001
SAP (mmHg)
77 (17)
91 (19)
p \ 0.001
DAP (mmHg)
44 (11)
49 (10)
p \ 0.001
HR (beats/min)
61 (15)
58 (14)
p = 0.002
CVP (mmHg)
9.7 (3.6)
13 (3.6)
p \ 0.001
SVVig (ml)
59 (14)
81 (17)
p \ 0.001
3.7 (1.4)
4.5 (1.1)
p \ 0.001
1,072 (211)
918 (165)
p \ 0.001
ComplianceVig (ml/mmHg)
1.8 (0.3)
2.0 (0.4)
p \ 0.001
EaVig (mmHg/ml)
1.2 (0.20)
1.0 (0.22)
p \ 0.001
SVOD (ml) COOD (l/min)
85 (20) 5.0 (1.1)
103 (22) 5.7 (1.4)
p \ 0.001 p = 0.001
SVROD (dyn/s/cm)
753 (184)
742 (201)
p = 0.53
ComplianceOD (ml/mmHg)
2.7 (0.7)
2.6 (0.8)
p = 0.36
COVig (l/min) SVRVig (dyn/s/cm)
EaOD (mmHg/ml)
0.86 (0.27)
0.83 (0.23)
p = 0.14
MA (cm/s2)
4.1 (1.3)
3.9 (1.2)
p = 0.023
FTc (ms)
353 (49)
389 (43)
p \ 0.001
PV (cm/s)
52 (11)
56 (12)
p \ 0.001
SD (cm)
12 (2.8)
15 (3.2)
p \ 0.001
135 (24)
150 (23)
p \ 0.001
FTp (ms)
Hemodynamic data before and after fluid loads. Data are mean (SD). Comparisons by paired samples t tests. MA, FTc, PV, SD and FTp are given by the oesophageal Doppler. SVR, compliance and Ea are calculated based both cardiac output both from the oesophageal Doppler and Vigileo (denoted by OD and Vig, respectively) MAP mean arterial pressure, SAP systolic arterial pressure, DAP diastolic arterial pressure, HR heart rate, CVP central venous pressure, SV stroke volume, CO cardiac output, SVR systemic vascular resistance, Ea arterial elastance, MA mean acceleration, FTc flow time corrected, PV peak velocity, SD stroke distance, FTp flow time to peak
Fig. 1 Bland–Altman plot. Registrations before and after a fluid load, 60 registrations in 30 patients. Bias and 95 % limits of agreement are solid and dashed lines, respectively. PE percentage error, SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
compared with TEE from before to after transcatheter AVR, which indicates acceptable trending ability [4]. The poor agreement found in our study indicates that the two methods are not interchangeable. As none of the methods is a reference technique, this could be caused by measurement error in one or both methods. However,
123
in many protocols for hemodynamic optimization, only changes (relative values, trending) are used. In this case, neither the bias nor the inter-patient error are important, only the intra-patient error (precision). The errors constituting precision are generally considered to be random and normally distributed. From the precision, the least
J Clin Monit Comput
Fig. 2 Trending with the preoperative fluid load. Four-quadrant plot of relative changes SVVig versus relative changes SVOD with 15 % exclusion zone. Solid line is line of identity (y = x) (a). Polar plot of relative changes SVOD versus relative changes SVVig with 10 %
exclusion zone (b). In the polar plot, observations within the exclusion zone are open circles. R is Pearson correlation coefficient. SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
Fig. 3 Scatterplots of associations between arterial load and differences between SV-measurements. Changes in differences between SVOD and SVVig on y-axes. Changes in measures of arterial load on x-axes. All changes are from before to after a fluid load. Pearson correlation coefficients with 95 % CI and p values are given. Lines are least squares regression lines. MAP mean arterial pressure, SVR systemic vascular resistance, Ea arterial elastance, SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
significant change can be calculated [16], denoting how large a measured change should be to represent a likely change of the true value. In our study, the least
significant changes for both methods were smaller than what is in most hemodynamic optimization protocols generally considered clinically significant. Thus, both
123
J Clin Monit Comput
methods seem sufficiently precise to be used for this purpose in patients with AS. It should be noted that this precision only reflects the intra-patient variability. However, in addition to being sufficiently precise, the methods have to change correctly when the true SV is changed. As the methods had a high concordance, they both seem to have this ability in response to a fluid load, but as no reference technique was used, there is still the possibility that both methods had a wrong directional change compared to the true value. The relative changes did however not agree well in magnitude, as the h-value in the polar plot was high. We studied the measurement methods and their response to a fluid load. This may be the intervention during which pulse contour analyses perform the best. The agreement with other methods as well as the trending ability for 3rd generation Vigileo has been questioned during changes in peripheral resistance and arterial compliance [7, 8, 17, 18]. Recently, measures of arterial load have been related to the agreement between non-proprietary pulse pressure algorithms and oesophageal Doppler CO measurements [9]. We therefore plotted the changes in differences between SVmeasurements by the two methods from before to after the fluid loads against the concomitant changes in measures of arterial load (Fig. 3). As in the study by Monge Garcia et al. [9], the discrepancy between SVVig and SVOD seems to be related to arterial load, with the strongest association for Ea. Norepinephrine use and change in MAP with a fluid load has been shown to be associated with reduced agreement for trending a fluid load using OD and a calibrated pulse contour analysis system [19]. Furthermore, the findings are consistent with other studies in patients without AS [7, 8, 17, 18], and do therefore not seem to be specific for AS patients.
5 Methodological considerations All the plots and calculations in this analysis display how the two methods relate. However, as a reference method was not used we cannot say how any of the two methods relate to the true value. The OD measures a velocity–time integral of the blood flow in the descending aorta. The angle of insonation and fraction of CO distributed to the descending aorta are assumed, whereas the aortic diameter is calculated based on demographic data. Given an adequate signal, the sources of error with this method are mainly these assumptions. When using OD as a trend monitor, the magnitudes of these three factors are unimportant, if they are constant. Accordingly, the OD monitor is believed to have high validity to monitor changes in CO [20]. The assumption of unaltered diameter of the descending aorta has been questioned, as the aortic diameter increased with increased
123
MAP during a fluid load in intensive care unit patients [21]. However, aortic diameter also tended to increase with reduced MAP by vasodilation [22]. We are not aware of specific validations studies of OD in patients with AS or specific reasons to question the aforementioned assumptions in AS patients. Although we moved the data from the Vigileo 20 s to increase synchronization, the v-factor is only updated every 60 s. Therefore, at least some of the values are calculated based on conditions that may have changed. All patients had their arterial catheters placed in the radial artery. Results could have been different with femoral catheterization [23]. Polar plots have recently been introduced to assess trending abilities. In polar plots, the distance of each data point from origo is the absolute value of the average of the two changes. Thus, discordant values will tend to fall into the central exclusion zone as their averages tend to be small. In fact, perfectly discordant values (where the changes have the same magnitude, but in opposite directions), no matter how great, will be located in the origo and never be visible in a polar plot. Precision of 1 min periods have been estimated based on calculations from 20 s periods. This estimate assumes that this within-patient measurement error is random and normally distributed [15]. In Fig. 3, as in the study by Monge Garcia et al. [9], SVOD is included in the calculation of the value on the y-axis, but also the calculation of SVR, compliance and arterial elastance on the x-axes. These may thus be subject to mathematical coupling. Furthermore, arterial pressures used in the calculations were measured peripherally, and not in the aorta. Measures of arterial load were based on the OD-measurements, but should ideally have been based on a reference technique. Using Vigileo-measurements to calculate measures of arterial load made all the correlations in Fig. 3 non-significant, consistent with the notion that OD is the most independent technique. Although the Vigileo has been believed to be prone to misinterpret changes in arterial vascular properties [7], we cannot from our data interpret from which of the two methods the errors leading to the divergence stems. In conclusion, SVOD and SVVig agreed poorly in patients with severe AS, with wide LOA and a high percentage error. Changes during a fluid load were highly concordant. The angular agreement indicated acceptable trending. Precisions of both methods seemed adequate to track clinically relevant changes in SV. The agreement between the two methods seemed to depend on arterial load. The two measurement methods are not interchangeable in patients with AS. Conflict of interest
The authors declare no conflicts of interest.
J Clin Monit Comput
References 1. Stergiopulos N, Young DF, Rogge TR. Computer simulation of arterial flow with applications to arterial and aortic stenoses. J Biomech. 1992;25(12):1477–88. 2. Lorsomradee S, Lorsomradee S, Cromheecke S, De Hert SG. Uncalibrated arterial pulse contour analysis versus continuous thermodilution technique: effects of alterations in arterial waveform. J Cardiothorac Vasc Anesth. 2007;21(5):636–43. doi:10. 1053/j.jvca.2007.02.003. 3. Staier K, Wiesenack C, Gunkel L, Keyl C. Cardiac output determination by thermodilution and arterial pulse waveform analysis in patients undergoing aortic valve replacement. Can J Anaesth. 2008;55(1):22–8. doi:10.1007/BF03017593. 4. Petzoldt M, Riedel C, Braeunig J, Haas S, Goepfert MS, Treede H, Baldus S, Goetz AE, Reuter DA. Stroke volume determination using transcardiopulmonary thermodilution and arterial pulse contour analysis in severe aortic valve disease. Intensive Care Med. 2013;39(4):601–11. doi:10.1007/s00134-012-2786-7. 5. Manecke GR. Edwards FloTrac sensor and Vigileo monitor: easy, accurate, reliable cardiac output assessment using the arterial pulse wave. Expert Rev Med Devices. 2005;2(5):523–7. doi:10. 1586/17434440.2.5.523. 6. Critchley LA. Pulse contour analysis: is it able to reliably detect changes in cardiac output in the haemodynamically unstable patient? Crit Care. 2011;15(1):106. doi:10.1186/cc9381. 7. Meng L, Tran NP, Alexander BS, Laning K, Chen G, Kain ZN, Cannesson M. The impact of phenylephrine, ephedrine, and increased preload on third-generation Vigileo–FloTrac and esophageal doppler cardiac output measurements. Anesth Analg. 2011;113(4):751–7. doi:10.1213/ANE.0b013e31822649fb. 8. Monnet X, Anguel N, Jozwiak M, Richard C, Teboul JL. Thirdgeneration FloTrac/Vigileo does not reliably track changes in cardiac output induced by norepinephrine in critically ill patients. Br J Anaesth. 2012;108(4):615–22. doi:10.1093/bja/aer491. 9. Monge Garcia MI, Gracia Romero M, Gil Cano A, Rhodes A, Grounds RM, Cecconi M. Impact of arterial load on the agreement between pulse pressure analysis and esophageal Doppler. Crit Care. 2013;17(3):R113. doi:10.1186/cc12785. 10. Hoiseth LO, Hoff IE, Hagen OA, Landsverk SA, Kirkeboen KA. Dynamic variables and fluid responsiveness in patients for aortic stenosis surgery. Acta Anaesthesiol Scand. 2014;58(7):826–34. doi:10.1111/aas.12328. 11. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat. 2007;17(4):571–82. doi:10.1080/10543400701329422. 12. Critchley LA, Lee A, Ho AM. A critical review of the ability of continuous cardiac output monitors to measure trends in cardiac output. Anesth Analg. 2010;111(5):1180–92. doi:10.1213/ANE. 0b013e3181f08a5b. 13. Critchley LA, Yang XX, Lee A. Assessment of trending ability of cardiac output monitors by polar plot methodology.
14. 15.
16.
17.
18.
19.
20.
21.
22.
23.
J Cardiothorac Vasc Anesth. 2011;25(3):536–46. doi:10.1053/j. jvca.2011.01.003. Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res. 1999;8(2):135–60. Cecconi M, Rhodes A, Poloniecki J, Della Rocca G, Grounds RM. Bench-to-bedside review: the importance of the precision of the reference technique in method comparison studies—with specific reference to the measurement of cardiac output. Crit Care. 2009;13(1):201. doi:10.1186/cc7129. Cecconi M, Dawson D, Grounds RM, Rhodes A. Lithium dilution cardiac output measurement in the critically ill patient: determination of precision of the technique. Intensive Care Med. 2009;35(3):498–504. doi:10.1007/s00134-008-1292-4. Suehiro K, Tanaka K, Funao T, Matsuura T, Mori T, Nishikawa K. Systemic vascular resistance has an impact on the reliability of the Vigileo–FloTrac system in measuring cardiac output and tracking cardiac output changes. Br J Anaesth. 2013;111(2):170–7. doi:10.1093/bja/aet022. Sotomi Y, Iwakura K, Higuchi Y, Abe K, Yoshida J, Masai T, Fujii K. The impact of systemic vascular resistance on the accuracy of the FloTrac/Vigileo system in the perioperative period of cardiac surgery: a prospective observational comparison study. J Clin Monit Comput. 2013;27(6):639–46. doi:10.1007/ s10877-013-9481-2. Feldheiser A, Hunsicker O, Krebbel H, Weimann K, Kaufner L, Wernecke KD, Spies C. Oesophageal Doppler and calibrated pulse contour analysis are not interchangeable within a goaldirected haemodynamic algorithm in major gynaecological surgery. Br J Anaesth. 2014;113(5):822–31. doi:10.1093/bja/aeu241. Dark PM, Singer M. The validity of trans-esophageal Doppler ultrasonography as a measure of cardiac output in critically ill adults. Intensive Care Med. 2004;30(11):2060–6. doi:10.1007/ s00134-004-2430-2. Monnet X, Chemla D, Osman D, Anguel N, Richard C, Pinsky MR, Teboul JL. Measuring aortic diameter improves accuracy of esophageal Doppler in assessing fluid responsiveness. Crit Care Med. 2007;35(2):477–82. doi:10.1097/01.CCM.0000254725. 35802.17. Heerman JR, Segers P, Roosens CD, Gasthuys F, Verdonck PR, Poelaert JI. Echocardiographic assessment of aortic elastic properties with automated border detection in an ICU: in vivo application of the arctangent Langewouters model. Am J Physiol Heart Circ Physiol. 2005;288(5):H2504–11. doi:10.1152/ ajpheart.00368.2004. Schramm S, Albrecht E, Frascarolo P, Chassot PG, Spahn DR. Validity of an arterial pressure waveform analysis device: does the puncture site play a role in the agreement with intermittent pulmonary artery catheter thermodilution measurements? J Cardiothorac Vasc Anesth. 2010;24(2):250–6. doi:10.1053/j.jvca. 2009.05.029.
123
ORIGINAL RESEARCH
Agreement between stroke volume measured by oesophageal Doppler and uncalibrated pulse contour analysis during fluid loads in severe aortic stenosis Lars Øivind Høiseth • Ingrid Elise Hoff • Ove Andreas Hagen • Svein Aslak Landsverk Knut Arvid Kirkebøen
•
Received: 12 May 2014 / Accepted: 27 January 2015 Ó Springer Science+Business Media New York 2015
Abstract The purpose of this analysis was to study agreement and trending of stroke volume measured by oesophageal Doppler and 3rd generation Vigileo during fluid loads in patients with severe aortic stenosis. Observational study in 32 patients (30 analyzed) scheduled for aortic valve replacement due to severe aortic stenosis. After induction of anesthesia and before start of surgery, hemodynamic registrations for 1 min were obtained before and after a fluid load. Agreement between stroke volume measured by oesophageal Doppler (SVOD) and Vigileo (SVVig) was evaluated in Bland–Altman plot and trending in four-quadrant and polar plots. Bias ± limits of agreement (LOA) between SVOD and SVVig was 24 ± 37 ml (percentage error 45 %). Concordance of the two methods from before to after a fluid load was 100 %. Angular bias ± LOA was 12° ± 28°. Absolute values of SVOD and SVVig agreed poorly, but changes were highly concordant during fluid loads in aortic stenosis patients. The angular agreement indicated acceptable trending. The two measurement methods are not interchangeable in patients with aortic stenosis. Keywords Stroke volume Aortic valve stenosis Diagnostic techniques Cardiovascular
L. Ø. Høiseth K. A. Kirkebøen Faculty of Medicine, University of Oslo, Oslo, Norway L. Ø. Høiseth (&) I. E. Hoff O. A. Hagen S. A. Landsverk K. A. Kirkebøen Department of Anesthesiology, Oslo University Hospital, Kirkeveien 166, 0450 Oslo, Norway e-mail: [email protected] I. E. Hoff Norwegian Air Ambulance Foundation, Drøbak, Norway
1 Introduction Goal-directed therapy in surgery and critical illness aims to optimize oxygen delivery (DO2). As DO2 is proportional to cardiac output (CO), a prerequisite is to optimize CO. Thermodilution by a pulmonary artery catheter (PAC) is the clinical gold-standard to monitor CO, but is invasive and cumbersome to use. Simpler and less invasive methods to monitor CO have been developed. Among these are oesophageal Doppler (OD) and arterial pulse contour analyses. To evaluate devices to calculate stroke volume (SV), the agreement between methods at some time point is often calculated. However, to optimize CO, it is not imperative that the absolute values are correct, as long as the ability to trend is adequate. In aortic stenosis (AS), the arterial pressure waveform can be affected by the stenotic valve [1]. Lorsomradee et al. [2] and Staier et al. [3] evaluated 2nd generation Vigileo in AS patients. Petzoldt et al. [4] studied 3rd generation software, but trending to a fluid load, important for hemodynamic optimization, was not evaluated. The primary aim of this analysis was to explore the relation between trending of SV with two different minimally invasive devices (OD and 3rd generation Vigileo pulse contour analysis) in AS patients in relation to fluid loads. Several pulse contour analysis-systems exist. Some are calibrated by an indicator dilution with lithium or cold water. The Vigileo-system (Edwards Lifesciences, Irvine, CA, USA) is an uncalibrated pulse contour-analysis system [5]. The algorithm to calculate SV is based on the standard deviation of the arterial pressure and a v-factor. Limitations of 1st and 2nd generation algorithms have mainly been related to changes in peripheral resistance [6]. The ability of 3rd generation Vigileo software to track changes in SV has also been questioned in conditions with changes
123
J Clin Monit Comput
in systemic vascular resistance (SVR), which is one measure of arterial load [7, 8]. Changes in arterial load have been demonstrated to influence the agreement between SV by oesophageal Doppler (SVOD) and non-proprietary pulse contour algorithms [9]. We therefore also related changes in agreement between SVOD and SV measured by Vigileo (SVVig) to changes in arterial load.
2 Methods 2.1 Patients Analyses were performed on data retrieved in an observational study on dynamic variables of fluid responsiveness in AS patients [10]. After regional ethics committee approval (REK Sør-Øst C, 2010/1629) and written informed consent, 32 patients scheduled for aortic valve replacement (AVR) due to AS were included. Inclusion criteria were: AS requiring AVR with no more than mild aortic insufficiency, age[18 years, left ventricular ejection fraction C40 % and sinus rhythm. Exclusion criteria were: right ventricular failure or pulmonary hypertension, other valvular lesions of hemodynamic significance and contraindications to OD monitoring. 2.2 Anesthetic procedure Patients were premedicated with intramuscular morphine/ scopolamine. A 20G arterial cannula was placed in the left radial artery. Anesthesia was induced with diazepam 0.12 (0.02) mg/kg, fentanyl 4.9 (0.9) lg/kg and propofol 0.7 (0.4) mg/kg intravenously (iv) and endotracheal intubation facilitated with cisatracurium 0.16 (0.02) mg/kg iv. Patients were mechanically ventilated and anesthesia maintained with sevoflurane. After placing a central venous catheter in the right internal jugular vein and an OD probe (see below), patients were placed in the horizontal position. A fluid load of 750 ml acetated Ringer’s solution was administered before surgery. The OD probe was removed after the fluid load to enable planned intraoperative transoesophageal echocardiography (TEE) and to avoid possible interferences between the two probes. Thus, no further registrations were performed. 2.3 Monitoring, signal acquisition and analysis An OD probe (DP-12, CardioQ; Deltex Medical, Chichester, UK) was inserted shortly after endotracheal intubation. An optimal signal was achieved by searching for a sharp and well-defined Doppler signal with maximal peak velocity. The probe was then fixed, and care taken not to displace it during the fluid load. Data were extracted beat
123
by beat from the OD-monitor via the serial output to a laptop computer. The arterial line was connected to a FloTrac transducer (Edwards Lifesciences) with one connection leading to a Vigileo monitor (software version 03.02 or 03.06; Edwards Lifesciences). Data were downloaded by the serial output to a custom-made program in LabVIEW (National Instruments, Austin, TX). To synchronize the methods, registrations from the Vigileo monitor were moved 20 s, as values displayed are based on the arterial waveform from the previous 20 s. Other hemodynamic data were downloaded at 1 Hz from a Solar 9500 (General Electric Healthcare, Milwaukee, WI, USA) monitor to the same LabVIEW-program. The following measures of arterial load were examined: mean arterial pressure (MAP), SVR [80 9 (MAP-central venous pressure)/CO], arterial compliance (SV/pulse pressure) and arterial elastance (Ea, 0.9 9 systolic arterial pressure/SV) [9]. Whereas MAP and SVR do not reflect the pulsatile nature of the arterial pressure, arterial compliance and Ea do. SV and CO measured by OD were used in the calculations of SVR, compliance and Ea. 2.4 Protocol Registrations (averaged over 1 min) were made before and after the preoperative fluid load (750 ml Ringer’s acetate). The fluid was infused rapidly, with registrations before and after the fluid load being 3.5 (0.75) min apart. 2.5 Statistics A separate power analysis was not performed for this analysis, as data were sampled when performing a study on fluid responsiveness in AS-patients [10]. Data are mean (SD), unless otherwise stated. Agreements of absolute values are presented in a Bland– Altman plot, correcting for two measurements per subject [11]. Percentage error was calculated relative to the mean of both methods in the Bland–Altman-plot. Relative changes of SVOD versus SVVig are presented in a four-quadrant plot and a polar plot. In a four-quadrant plot, changes in one method are plotted against changes in the other in a four-quadrant scatterplot. After excluding a central zone, the concordance rate, which is the fraction of observations in which SV increases or decreases with both methods (upper right and lower left quadrants) are calculated, as these have the same directional change [12]. The concordance rate does only state if the directional changes of the methods are the same, but not their magnitudes. Furthermore, the distance from origo will be the hypotenuse of a triangle where changes with each method are the catheti, thus always larger than the largest change. The
J Clin Monit Comput
polar plot is rotated 45° so that the line of identity (y = x) is horizontal. Furthermore, the distance from origo is the absolute value of the average of the two changes. Data points \-90° or [90° were rotated 180° so that all data points were in the -90° to 90° range. The angle h to the line of identity was calculated for each observation and mean h with radial limits of agreement (LOA) were calculated as described by Critchley et al. [13]. In the fourquadrant plot, an exclusion zone of 15 % was used. In the polar-plot, the exclusion zone was reduced to 10 % [13]. Precisions within the 1 min registration periods were estimated for each measurement method. The Vigileo device gives one value every 20 s. Thus, SV-measurements from the OD were averaged over the corresponding 20 s, giving three values for each 1 min registration period. As the SD of the three measurements tended to increase with increasing mean values, SV-values were loge-transformed. SD of the loge(SV)-values were calculated in a one-way ANOVA as the root of the residual mean square, with registration period as factor [14]. The coefficient of variation (CV) of SV was approximated as SD[loge(SV)] [14]. This would thus give the within-subject variability (precision) within the 1 min registration periods with a 20 s average as the unit of measurement. The precisions for 1 min registration periods were then estimated as CV for the 20 s periods divided by H3 [15]. Calculations were performed in MedCalc Statistical Software version 12.7.2.0 (MedCalc Software bvba, Ostend, Belgium).
Table 1 Patient characteristics n = 30 Male/female (n)
19/11
Age (years)
69 (10)
Height (cm)
173 (9)
Weight (kg)
81 (15)
Ejection fraction (%)
60 (7)
Aortic valve areaa (cm2)
0.8 (0.2)
Mean gradient (mmHg)
53 (15)
Maximal gradient (mmHg)
83 (23)
Data are mean (SD) unless otherwise stated a
n = 29 (in one patient valve area could not be calculated due to poor echogenicity)
26/26 = 100 %. In the polar plot, mean angle ± LOA was 12° ± 28° (Fig. 2b). For 20 s periods within 1 min registration periods CV were 3.9 % for SVVig and 2.9 % for SVOD, giving estimated CV for the 1 min periods of 3.9 %/H3 = 2.3 % and 2.9 %/H3 = 1.7 %, respectively. Thus, the least significant changes for one min periods were SVVig H2 9 1.96 9 2.3 % = 6.3 % and SVOD H2 9 1.96 9 1.7 % = 4.6 % [16]. Changes in agreement between the methods were associated with changes in arterial load, with the strongest association for Ea (Fig. 3).
3 Results
4 Discussion
32 patients were included. Two patients were excluded, one due to an arrhythmia (bigimeny not present at inclusion 1 day before surgery), and one due to a severely dampened arterial waveform, probably due to a peripheral arterial stenosis. None of the patients received vasoactive or inotropic medications during the fluid loads. One fluid load was performed in each of the 30 patients, with adequate OD registrations in all patients. In two patients, fluid loads were performed in slight head-down position to maintain hemodynamic stability. Patient characteristics are presented in Table 1. All patients were in ASA physical category 3. Seven patients had hypertension, nine had coronary artery disease and three had diabetes. Hemodynamic data before and after fluid loads are presented in Table 2. Bias ± LOA between SVOD and SVVig (absolute values) was 24 ± 37 ml (percentage error 37 ml/ 82 ml = 45 %, Fig. 1). With fluid loads, relative changes in SV as measured by the two methods were correlated (r = 0.62, p \ 0.001, Fig. 2a). Concordance rate was
The main finding in this analysis was that SV measured by OD and 3rd generation Vigileo did not agree well, with wide LOA and a percentage error of 45 %. The concordance of changes to a fluid load was good, but agreement in a polar plot moderate with a high h, and acceptable radial LOA. Precisions of both methods were adequate with least significant changes less than what is usually considered a clinically significant change. As a stenotic aortic valve may affect the arterial pressure waveform [1], uncalibrated pulse contour analysis systems have been evaluated in patients with AS. The 2nd generation Vigileo software had a percentage error of 29 % compared to continuous thermodilution [2], and 36 and 39 % (before and after sternotomy, respectively) compared to intermittent thermodilution [3]. The 3rd generation software had a percentage error of 50 % compared to TEE [4]. When assessing trending, the concordance to intermittent thermodilution was &75 % trending from before to after sternotomy for 2nd generation Vigileo. The 3rd generation had 72 % of the values within 10 % LOA
123
J Clin Monit Comput Table 2 Hemodynamic data n = 30
Before fluid load
After fluid load
MAP (mmHg)
56 (13)
65 (13)
p \ 0.001
SAP (mmHg)
77 (17)
91 (19)
p \ 0.001
DAP (mmHg)
44 (11)
49 (10)
p \ 0.001
HR (beats/min)
61 (15)
58 (14)
p = 0.002
CVP (mmHg)
9.7 (3.6)
13 (3.6)
p \ 0.001
SVVig (ml)
59 (14)
81 (17)
p \ 0.001
3.7 (1.4)
4.5 (1.1)
p \ 0.001
1,072 (211)
918 (165)
p \ 0.001
ComplianceVig (ml/mmHg)
1.8 (0.3)
2.0 (0.4)
p \ 0.001
EaVig (mmHg/ml)
1.2 (0.20)
1.0 (0.22)
p \ 0.001
SVOD (ml) COOD (l/min)
85 (20) 5.0 (1.1)
103 (22) 5.7 (1.4)
p \ 0.001 p = 0.001
SVROD (dyn/s/cm)
753 (184)
742 (201)
p = 0.53
ComplianceOD (ml/mmHg)
2.7 (0.7)
2.6 (0.8)
p = 0.36
COVig (l/min) SVRVig (dyn/s/cm)
EaOD (mmHg/ml)
0.86 (0.27)
0.83 (0.23)
p = 0.14
MA (cm/s2)
4.1 (1.3)
3.9 (1.2)
p = 0.023
FTc (ms)
353 (49)
389 (43)
p \ 0.001
PV (cm/s)
52 (11)
56 (12)
p \ 0.001
SD (cm)
12 (2.8)
15 (3.2)
p \ 0.001
135 (24)
150 (23)
p \ 0.001
FTp (ms)
Hemodynamic data before and after fluid loads. Data are mean (SD). Comparisons by paired samples t tests. MA, FTc, PV, SD and FTp are given by the oesophageal Doppler. SVR, compliance and Ea are calculated based both cardiac output both from the oesophageal Doppler and Vigileo (denoted by OD and Vig, respectively) MAP mean arterial pressure, SAP systolic arterial pressure, DAP diastolic arterial pressure, HR heart rate, CVP central venous pressure, SV stroke volume, CO cardiac output, SVR systemic vascular resistance, Ea arterial elastance, MA mean acceleration, FTc flow time corrected, PV peak velocity, SD stroke distance, FTp flow time to peak
Fig. 1 Bland–Altman plot. Registrations before and after a fluid load, 60 registrations in 30 patients. Bias and 95 % limits of agreement are solid and dashed lines, respectively. PE percentage error, SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
compared with TEE from before to after transcatheter AVR, which indicates acceptable trending ability [4]. The poor agreement found in our study indicates that the two methods are not interchangeable. As none of the methods is a reference technique, this could be caused by measurement error in one or both methods. However,
123
in many protocols for hemodynamic optimization, only changes (relative values, trending) are used. In this case, neither the bias nor the inter-patient error are important, only the intra-patient error (precision). The errors constituting precision are generally considered to be random and normally distributed. From the precision, the least
J Clin Monit Comput
Fig. 2 Trending with the preoperative fluid load. Four-quadrant plot of relative changes SVVig versus relative changes SVOD with 15 % exclusion zone. Solid line is line of identity (y = x) (a). Polar plot of relative changes SVOD versus relative changes SVVig with 10 %
exclusion zone (b). In the polar plot, observations within the exclusion zone are open circles. R is Pearson correlation coefficient. SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
Fig. 3 Scatterplots of associations between arterial load and differences between SV-measurements. Changes in differences between SVOD and SVVig on y-axes. Changes in measures of arterial load on x-axes. All changes are from before to after a fluid load. Pearson correlation coefficients with 95 % CI and p values are given. Lines are least squares regression lines. MAP mean arterial pressure, SVR systemic vascular resistance, Ea arterial elastance, SVOD stroke volume measured by oesophageal Doppler, SVVig stroke volume measured by Vigileo
significant change can be calculated [16], denoting how large a measured change should be to represent a likely change of the true value. In our study, the least
significant changes for both methods were smaller than what is in most hemodynamic optimization protocols generally considered clinically significant. Thus, both
123
J Clin Monit Comput
methods seem sufficiently precise to be used for this purpose in patients with AS. It should be noted that this precision only reflects the intra-patient variability. However, in addition to being sufficiently precise, the methods have to change correctly when the true SV is changed. As the methods had a high concordance, they both seem to have this ability in response to a fluid load, but as no reference technique was used, there is still the possibility that both methods had a wrong directional change compared to the true value. The relative changes did however not agree well in magnitude, as the h-value in the polar plot was high. We studied the measurement methods and their response to a fluid load. This may be the intervention during which pulse contour analyses perform the best. The agreement with other methods as well as the trending ability for 3rd generation Vigileo has been questioned during changes in peripheral resistance and arterial compliance [7, 8, 17, 18]. Recently, measures of arterial load have been related to the agreement between non-proprietary pulse pressure algorithms and oesophageal Doppler CO measurements [9]. We therefore plotted the changes in differences between SVmeasurements by the two methods from before to after the fluid loads against the concomitant changes in measures of arterial load (Fig. 3). As in the study by Monge Garcia et al. [9], the discrepancy between SVVig and SVOD seems to be related to arterial load, with the strongest association for Ea. Norepinephrine use and change in MAP with a fluid load has been shown to be associated with reduced agreement for trending a fluid load using OD and a calibrated pulse contour analysis system [19]. Furthermore, the findings are consistent with other studies in patients without AS [7, 8, 17, 18], and do therefore not seem to be specific for AS patients.
5 Methodological considerations All the plots and calculations in this analysis display how the two methods relate. However, as a reference method was not used we cannot say how any of the two methods relate to the true value. The OD measures a velocity–time integral of the blood flow in the descending aorta. The angle of insonation and fraction of CO distributed to the descending aorta are assumed, whereas the aortic diameter is calculated based on demographic data. Given an adequate signal, the sources of error with this method are mainly these assumptions. When using OD as a trend monitor, the magnitudes of these three factors are unimportant, if they are constant. Accordingly, the OD monitor is believed to have high validity to monitor changes in CO [20]. The assumption of unaltered diameter of the descending aorta has been questioned, as the aortic diameter increased with increased
123
MAP during a fluid load in intensive care unit patients [21]. However, aortic diameter also tended to increase with reduced MAP by vasodilation [22]. We are not aware of specific validations studies of OD in patients with AS or specific reasons to question the aforementioned assumptions in AS patients. Although we moved the data from the Vigileo 20 s to increase synchronization, the v-factor is only updated every 60 s. Therefore, at least some of the values are calculated based on conditions that may have changed. All patients had their arterial catheters placed in the radial artery. Results could have been different with femoral catheterization [23]. Polar plots have recently been introduced to assess trending abilities. In polar plots, the distance of each data point from origo is the absolute value of the average of the two changes. Thus, discordant values will tend to fall into the central exclusion zone as their averages tend to be small. In fact, perfectly discordant values (where the changes have the same magnitude, but in opposite directions), no matter how great, will be located in the origo and never be visible in a polar plot. Precision of 1 min periods have been estimated based on calculations from 20 s periods. This estimate assumes that this within-patient measurement error is random and normally distributed [15]. In Fig. 3, as in the study by Monge Garcia et al. [9], SVOD is included in the calculation of the value on the y-axis, but also the calculation of SVR, compliance and arterial elastance on the x-axes. These may thus be subject to mathematical coupling. Furthermore, arterial pressures used in the calculations were measured peripherally, and not in the aorta. Measures of arterial load were based on the OD-measurements, but should ideally have been based on a reference technique. Using Vigileo-measurements to calculate measures of arterial load made all the correlations in Fig. 3 non-significant, consistent with the notion that OD is the most independent technique. Although the Vigileo has been believed to be prone to misinterpret changes in arterial vascular properties [7], we cannot from our data interpret from which of the two methods the errors leading to the divergence stems. In conclusion, SVOD and SVVig agreed poorly in patients with severe AS, with wide LOA and a high percentage error. Changes during a fluid load were highly concordant. The angular agreement indicated acceptable trending. Precisions of both methods seemed adequate to track clinically relevant changes in SV. The agreement between the two methods seemed to depend on arterial load. The two measurement methods are not interchangeable in patients with AS. Conflict of interest
The authors declare no conflicts of interest.
J Clin Monit Comput
References 1. Stergiopulos N, Young DF, Rogge TR. Computer simulation of arterial flow with applications to arterial and aortic stenoses. J Biomech. 1992;25(12):1477–88. 2. Lorsomradee S, Lorsomradee S, Cromheecke S, De Hert SG. Uncalibrated arterial pulse contour analysis versus continuous thermodilution technique: effects of alterations in arterial waveform. J Cardiothorac Vasc Anesth. 2007;21(5):636–43. doi:10. 1053/j.jvca.2007.02.003. 3. Staier K, Wiesenack C, Gunkel L, Keyl C. Cardiac output determination by thermodilution and arterial pulse waveform analysis in patients undergoing aortic valve replacement. Can J Anaesth. 2008;55(1):22–8. doi:10.1007/BF03017593. 4. Petzoldt M, Riedel C, Braeunig J, Haas S, Goepfert MS, Treede H, Baldus S, Goetz AE, Reuter DA. Stroke volume determination using transcardiopulmonary thermodilution and arterial pulse contour analysis in severe aortic valve disease. Intensive Care Med. 2013;39(4):601–11. doi:10.1007/s00134-012-2786-7. 5. Manecke GR. Edwards FloTrac sensor and Vigileo monitor: easy, accurate, reliable cardiac output assessment using the arterial pulse wave. Expert Rev Med Devices. 2005;2(5):523–7. doi:10. 1586/17434440.2.5.523. 6. Critchley LA. Pulse contour analysis: is it able to reliably detect changes in cardiac output in the haemodynamically unstable patient? Crit Care. 2011;15(1):106. doi:10.1186/cc9381. 7. Meng L, Tran NP, Alexander BS, Laning K, Chen G, Kain ZN, Cannesson M. The impact of phenylephrine, ephedrine, and increased preload on third-generation Vigileo–FloTrac and esophageal doppler cardiac output measurements. Anesth Analg. 2011;113(4):751–7. doi:10.1213/ANE.0b013e31822649fb. 8. Monnet X, Anguel N, Jozwiak M, Richard C, Teboul JL. Thirdgeneration FloTrac/Vigileo does not reliably track changes in cardiac output induced by norepinephrine in critically ill patients. Br J Anaesth. 2012;108(4):615–22. doi:10.1093/bja/aer491. 9. Monge Garcia MI, Gracia Romero M, Gil Cano A, Rhodes A, Grounds RM, Cecconi M. Impact of arterial load on the agreement between pulse pressure analysis and esophageal Doppler. Crit Care. 2013;17(3):R113. doi:10.1186/cc12785. 10. Hoiseth LO, Hoff IE, Hagen OA, Landsverk SA, Kirkeboen KA. Dynamic variables and fluid responsiveness in patients for aortic stenosis surgery. Acta Anaesthesiol Scand. 2014;58(7):826–34. doi:10.1111/aas.12328. 11. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat. 2007;17(4):571–82. doi:10.1080/10543400701329422. 12. Critchley LA, Lee A, Ho AM. A critical review of the ability of continuous cardiac output monitors to measure trends in cardiac output. Anesth Analg. 2010;111(5):1180–92. doi:10.1213/ANE. 0b013e3181f08a5b. 13. Critchley LA, Yang XX, Lee A. Assessment of trending ability of cardiac output monitors by polar plot methodology.
14. 15.
16.
17.
18.
19.
20.
21.
22.
23.
J Cardiothorac Vasc Anesth. 2011;25(3):536–46. doi:10.1053/j. jvca.2011.01.003. Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res. 1999;8(2):135–60. Cecconi M, Rhodes A, Poloniecki J, Della Rocca G, Grounds RM. Bench-to-bedside review: the importance of the precision of the reference technique in method comparison studies—with specific reference to the measurement of cardiac output. Crit Care. 2009;13(1):201. doi:10.1186/cc7129. Cecconi M, Dawson D, Grounds RM, Rhodes A. Lithium dilution cardiac output measurement in the critically ill patient: determination of precision of the technique. Intensive Care Med. 2009;35(3):498–504. doi:10.1007/s00134-008-1292-4. Suehiro K, Tanaka K, Funao T, Matsuura T, Mori T, Nishikawa K. Systemic vascular resistance has an impact on the reliability of the Vigileo–FloTrac system in measuring cardiac output and tracking cardiac output changes. Br J Anaesth. 2013;111(2):170–7. doi:10.1093/bja/aet022. Sotomi Y, Iwakura K, Higuchi Y, Abe K, Yoshida J, Masai T, Fujii K. The impact of systemic vascular resistance on the accuracy of the FloTrac/Vigileo system in the perioperative period of cardiac surgery: a prospective observational comparison study. J Clin Monit Comput. 2013;27(6):639–46. doi:10.1007/ s10877-013-9481-2. Feldheiser A, Hunsicker O, Krebbel H, Weimann K, Kaufner L, Wernecke KD, Spies C. Oesophageal Doppler and calibrated pulse contour analysis are not interchangeable within a goaldirected haemodynamic algorithm in major gynaecological surgery. Br J Anaesth. 2014;113(5):822–31. doi:10.1093/bja/aeu241. Dark PM, Singer M. The validity of trans-esophageal Doppler ultrasonography as a measure of cardiac output in critically ill adults. Intensive Care Med. 2004;30(11):2060–6. doi:10.1007/ s00134-004-2430-2. Monnet X, Chemla D, Osman D, Anguel N, Richard C, Pinsky MR, Teboul JL. Measuring aortic diameter improves accuracy of esophageal Doppler in assessing fluid responsiveness. Crit Care Med. 2007;35(2):477–82. doi:10.1097/01.CCM.0000254725. 35802.17. Heerman JR, Segers P, Roosens CD, Gasthuys F, Verdonck PR, Poelaert JI. Echocardiographic assessment of aortic elastic properties with automated border detection in an ICU: in vivo application of the arctangent Langewouters model. Am J Physiol Heart Circ Physiol. 2005;288(5):H2504–11. doi:10.1152/ ajpheart.00368.2004. Schramm S, Albrecht E, Frascarolo P, Chassot PG, Spahn DR. Validity of an arterial pressure waveform analysis device: does the puncture site play a role in the agreement with intermittent pulmonary artery catheter thermodilution measurements? J Cardiothorac Vasc Anesth. 2010;24(2):250–6. doi:10.1053/j.jvca. 2009.05.029.
123
