1 Institute of Anaesthesiology and Intensive Care Medicine and 3 Division of Cardiac Surgery, Triemli City Hospital, Zurich, Switzerland. 2 Statistics, Department of Psychosocial Medicine University Hospital Zurich, Zurich, Switzerland
* Corresponding author: Institute of Anaesthesiology and Intensive Care Medicine, Triemli City Hospital, Birmensdorferstr. 497, 8063 Zurich, Switzerland. E-mail: christoph.hofer{at}triemli.stzh.ch
Accepted for publication February 2, 2005.
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Methods. Twenty patients undergoing elective cardiac surgery with preserved leftright ventricular function were studied after induction of anaesthesia. Conventional haemodynamic variables, global end-diastolic volume index using the pulse contour cardiac output (PiCCO) system (GEDVIPiCCO), continuous end-diastolic volume index (CEDVIPAC) measured by a modified pulmonary artery catheter (PAC), left ventricular end-diastolic area index (LVEDAI) using TOE and stroke volume indices (SVI) were recorded before and 20 and 40 min after fluid replacement therapy. Analysis of variance (BonferroniDunn), BlandAltman analysis and linear regression were performed.
Results. GEDVIPiCCO, CEDVIPAC, LVEDAI and SVIPiCCO/PAC increased significantly after fluid load (P<0.05). An increase >10% for GEDVIPiCCO and LVEDAI was observed in 85% and 90% of the patients compared with 45% for CEDVIPAC. Mean bias (2 SD) between percentage changes () in GEDVIPiCCO and
LVEDAI was 3.2 (17.6)% and between
CEDVIPAC and
LVEDAI 8.7 (30.0)%. The correlation coefficient (r2) for
GEDVIPiCCO vs
LVEDAI was 0.658 and for
CEDVIPAC vs
LVEDAI 0.161. The relationship between
GEDVIPiCCO and
SVIPiCCO was stronger (r2=0.576) than that between
CEDVIPAC and
SVIPAC (r2=0.267).
Conclusion. GEDVI assessed by the PiCCO system gives a better reflection of echocardiographic changes in left ventricular preload, in response to fluid replacement therapy, than CEDVI measured by a modified PAC.
Keywords: heart, cardiac output ; heart, coronary artery bypass ; heart, myocardial function
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Two different techniques, transpulmonary and pulmonary artery thermodilution, are used in commercially available monitoring devices. The PiCCO system (Pulse Contour Cardiac Output system; Pulsion Medical Systems, Munich, Germany) uses integrated transpulmonary thermodilution to measure the volumetric preload parameter global end-diastolic volume index (GEDVI) and includes the total volumes of cardiac atria and ventricles as well as part of the systemic vascular blood volume. Compared with conventional pressure-derived preload assessment, volumetric preload determination by the PiCCO system has been shown to better reflect left ventricular filling.4 5 Pulmonary artery thermodilution, on the other hand, determines right ventricular end-diastolic volume index (RVEDVI). This volume index also showed a better correlation with cardiac performance than cardiac filling pressures in studies performed in critically ill patients.68 A recent modification of pulmonary artery thermodilution catheters allows the automatic and continuous determination of RVEDVI, the continuous end-diastolic volume index (CEDVI; Swan-Ganz Continuous Cardiac Output/End Diastolic Volume Thermodilution Catheter; CCOmbo CCO/SvO2/CEDV catheter 774HF75; Edwards Lifesciences, Irvine, CA, USA).
The aim of this study was to compare volumetric preload as measured by transpulmonary thermodilution (GEDVIPiCCO) and monitored by pulmonary artery thermodilution (CEDVIPAC) with left ventricular preload estimates assessed by transoesophageal echocardiography (TOE). Our hypothesis was that both volume preload parameters would comparably reflect left ventricular preload monitored by TOE.
![]() |
Patients and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Anaesthetic technique
After application of the routine haemodynamic monitoring (pulse oximetry, five-lead ECG and non-invasive blood pressure monitoring; CMS, Philips Medical Systems, Andover, MA, USA) a peripheral radial arterial and an i.v. line were inserted and lactated Ringer's solution 2 ml kg1 h1 i.v. was given continuously. Anaesthesia was induced using fentanyl 1030 µg kg1 i.v., lidocaine 1.5 mg kg1 i.v. and propofol up to 2 mg kg1 i.v., and was maintained with additional propofol (1.53 mg kg1 h1) and fentanyl (10 µg kg1 i.v.). Muscle paralysis was achieved with pancuronium bromide (0.1 mg kg1 i.v.). The trachea was intubated and the lungs mechanically ventilated without positive end-expiratory pressure using an inspired oxygen of 50% and tidal volume of 8 ml kg1 to maintain end-expiratory at 44.5 kPa during the study period. Thus, effective applied mean tidal volumes were 610 (73) ml and peak airway pressure ranged from 14 to 24 cm H2O (mean=18 [2] cm H2O).
Haemodynamic monitoring and transoesophageal echocardiography
A 4 F thermistor-tipped arterial catheter (Pulsiocath thermodilution catheter; Pulsion Medical Systems, Munich, Germany) was inserted in the left femoral artery; its tip advanced to the abdominal aorta, and it was connected to the PiCCOplus (version 5.2.2; Pulsion Medical Systems). Cardiac output (COPiCCO), stroke volume (SVPiCCO) and global end-diastolic volume (GEDVIPiCCO) were determined using a triplicate injection of 15 ml ice-cold normal saline through an additional 7 F central venous catheter introduced in the right subclavian vein. GEDVIPiCCO is calculated from the difference of mean indicator transit time and exponential indicator down-slope time and from the cardiac index obtained from transpulmonary thermodilution. The basis of this method has been described in detail previously.9 10 The PiCCO system also displays intrathoracic blood volume index (ITBVI) as an additional volume preload variable. This variable is calculated from GEDVIPiCCO based on a fixed algorithm, established from data obtained from earlier double-indicator transpulmonary thermodilution. The bolus thermodilution measurements were made by the same observer to avoid interobserver variation.
A 7.5 F pulmonary artery catheter (Swan-Ganz Continuous Cardiac Output/End Diastolic Volume Thermodilution Catheter CCOmbo CCO/SvO2/CEDV catheter 774HF75 Edwards Lifesciences) was introduced into the right internal jugular vein and attached to the Vigilance monitor for measurement of cardiac output (COPAC), stroke volume (SVPAC) and continuous end-diastolic volume (CEDVIPAC). CEDVIPAC is determined by analysis of the thermal washout curve using plateau and exponential curve analysis by analogy to the determination of right-ventricular ejection fraction and right-ventricular end-diastolic volume assessment by the fast-response thermistor-tipped pulmonary artery catheter. Details of this method have been published elsewhere.11 Central venous and pulmonary capillary wedge pressures were measured using standard transducers (CMS; Philips Medical Systems).
TOE was performed using a Philips Sonos 5500 system with an Omniplane III-TOE probe (Philips Medical Systems). The probe was positioned to obtain the transgastric midpapillary short-axis view of the left ventricle. Left ventricular end-diastolic area (LVEDA) and left ventricular end-systolic area (LVESA) were measured by manual planimetry of the area circumscribed by the leading edge of the endocardial border in this position. LVEDA was determined as the largest left ventricular cross-sectional area after the electrocardiographic T wave and LVESA as the smallest left ventricular cross-sectional area after the R wave. All TOE measurements were performed, recorded and calculated by an experienced operator blinded to the results of the haemodynamic measurements.
Experimental protocol
After induction of anaesthesia and a 15 min period of haemodynamic stabilization, haemodynamic measurements were performed before (T0) and 20 min (T1) and 40 min (T2) after a volume load. Hydroxyethyl starch solution 6% (HES 130/0.4; Voluven®; Fresenius Kabi, Stans, Switzerland) was given i.v. in a dose of 10 ml kg1 (ideal body weight) over a period of 20 min (mean volume, 730 [60] ml). At each time point heart rate, MAP, mean pulmonary arterial pressure (MPAP), central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP) and PiCCO measurements and the COPAC readings were recorded. TOE was performed simultaneously. Surgery started after measurements at T2 were completed.
Data analysis
A sample size of >15 patients was calculated on the hypothesis of an expected 10% change in haemodynamic variables after fluid replacement (level of significance=0.05%; power=90%) according to initial observations using the different methods of preload assessment.
All haemodynamic measurements were recorded as the mean of three consecutive readings at intervals of 3 min. Ejection fraction (%) was calculated post hoc from TOE measurements: 100xLVEDA1x(LVEDALVESA). All haemodynamic values were indexed to body surface area (BSA) by means of the Du Bois formula (BSA=body weight [kg]0.425xbody length[cm]0.725x71.84). Statistical analysis was performed using Statview 5.01® Software (SAS Institute, Cary, NC, USA). Analysis of variance (ANOVA) with post hoc BonferroniDunn correction was done for comparison of haemodynamic data during the study period (T0T2). Two-tailed Student's t-test was used to determine differences in preload changes and stroke volume changes between methods. BlandAltman analysis12 was performed to compare the preload and stroke volume changes assessed by all three techniques and absolute values of cardiac output determined by the two thermodilution methods. The Pearson correlation was established for absolute values and changes between preload and stroke volume indices. Relationships between the corresponding values obtained from one method and relationships between values recorded from the different methods were calculated to exclude the possibility of mathematical coupling;13 Fisher's z transformation and a HotellingWilliams test were used to compare correlation coefficients for statistical difference. A P-value <0.05 was considered statistically significant. Unless otherwise stated, data are presented as mean (SD).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
As with previously published results, conventional pressure preload parameters did not adequately reflect left ventricular filling,1 2 48 indicating superiority of volumetric monitoring of cardiovascular volume status over conventional preload pressure monitoring. In clinical practice, when logistic and financial considerations limit the use of echocardiography and other imaging technologies, thermodilution-based volume assessment must be regarded as the preferred method. However, to our knowledge, a comparison of the different commercially available volumetric preload assessment techniques has not been performed.
Transpulmonary thermodilution integrated in the PiCCO system does not require pulmonary artery catheter placement and thus avoids the related risks.14 Based on the injection site (usually central venous access) and the detection site (thermistor in the distal descending aorta) the measured volume includes the total volumes of the heart and the aortic blood volume (GEDVI). In most studies published during the last decade, GEDVI and the closely related intrathoracic blood volume index (ITBVI), which includes the central blood volumes of GEDVI and the pulmonary blood volume, were both assessed by a double-indicator (iced water and indocyanine green injection) dilution technique using the COLD system (Pulsion Medical Systems). These studies were performed in a variety of clinical settings (critically ill,15 sepsis,16 cardiac surgery,17 neurosurgery18). Results indicate that these volume preload indices are closely correlated to volume status and to changes in cardiac output in response to changes in circulating blood volume. Moreover, this method of volumetric preload assessment has been shown to be a measure of cardiac preload equivalent to preload assessment by TOE.19 However, the results raised concerns of mathematical coupling which can occur if two variables calculated from the same measurement are compared, allowing correlations between the variables to be artificially improved.20 This issue has been addressed in studies by changing cardiac output using dobutamine21 or ß-antagonists.22 In our study, independent changes in cardiac output and volume preload indices mean that correlations between measured volumes and cardiac output were unlikely to be attributed primarily to mathematical coupling.
Recently, the time-consuming and expensive double-indicator technique (COLD system) has been replaced by a single-indicator technique (PiCCO system). Using the PiCCO system, GEDVI is measured and ITBVI is calculated from GEDVI based on a fixed algorithm established with data from the double-indicator technique. Adequate accuracy and precision between end-diastolic volume assessment by the COLD system and the PiCCO system has been demonstrated.23 Furthermore, the superiority of the PiCCO system as a left ventricular preload monitoring compared with conventional pressure preload assessment was confirmed4 5 and the influence of mathematical coupling was again found to be negligible.10
In contrast to the global end-diastolic volume assessed by the PiCCO system, continuous end-diastolic volume index (CEDVIPAC) is measured using a pulmonary artery catheter and the continuous cardiac output measurement technique; thus, end-diastolic volume of the right heart is determined. Earlier versions of a modified pulmonary artery catheter (mounted with fast reacting thermistors) assessed right ventricular end-diastolic volume (RVEDVI) by the iced water bolus method. RVEDVI has been validated against radionuclide angiography, contrast ventriculography and echocardiography of the right heart.11 24 Several studies on RVEDVI, used as left ventricular preload substitute in critically ill patients, showed a superior relationship between this preload variable and cardiac output compared with standard pressure measurement8 25 and mathematical coupling was also not a factor.2527 However, difficulties in correct catheter placement prevented wider clinical use of this technique. The modified pulmonary artery catheter (CCOMBO-EDV) gives access to continuous volumetric preload assessment of the right heart.
To our knowledge, the present data on CEDVIPAC represent the first clinical experience with this technique. CEDVIPAC reflected left ventricular preload better than the conventional cardiac filling pressures and the results are comparable with previous clinical investigations of RVEDVI as volume preload index. However, a poorer relationship between CEDVIPAC and echocardiographic preload assessment and poorer performance in comparison with GEDVIPiCCO or stroke volume indices highlight major limitations in using right-heart catheterization for volumetric left ventricular preload assessment. Right ventricular function differs considerably from left ventricular function. The major determinant of left ventricular function is myocardial wall tension, whereas for the right it is ventricular afterload, which is primarily controlled by pulmonary vascular resistance and indirectly by left ventricular function and various pulmonary factors.28 Based on clinical experience, excluding the right ventricle from the circulation, the right heart may act as a conductance vessel and therefore the influence of right ventricular end-diastolic volume on cardiac performance may be limited.29 Furthermore, CEDVIPAC readings may be influenced by interventricular dependence, right ventricular dysfunction and increased right ventricular afterload. Therefore, the relationship between right ventricular preload assessment and cardiac output readings may be weak. However, our findings do not preclude a valid assessment of right heart end-diastolic volumes. In addition, delayed reactivity to rapid changes of intravascular volume by the pulmonary artery catheter compared with the PiCCO system could explain different findings for CEDVIPAC and GEDVIPiCCO. However, stroke volume changes in this study assessed with both the PiCCO system and the pulmonary artery catheter were comparable.
Certain limitations of the clinical utility of CEDVIPAC monitoring have to be considered. CEDVIPAC was assessed here as a substitute for left ventricular preload only and has not been validated as right ventricular preload parameter against radionuclide angiography or magnetic resonance imaging. However, valid echocardiographic monitoring of right heart volume based on anatomical structures is questionable due to lack of suitable mathematical models. Moreover, CEDVIPAC has not been tested in patients with clinical left- or right-heart failure and its value in this context is unknown. The limitations of transoesophageal echocardiography as the gold standard for monitoring left ventricular preload have to be emphasized. Quantitative assessment of left ventricular end-diastolic area by transoesophageal echocardiography may not necessarily reflect volume status due to myocardial wall motion abnormalities in patients undergoing cardiac surgery, and may be altered by dislocation of the probe from the midpapillary level.30
In conclusion, the present study, comparing two thermodilution-based volumetric preload assessment tools with echocardiographic preload monitoring, indicates that GEDVI assessed by the PiCCO system better reflects left ventricular preload than CEDVI measured by a modified pulmonary artery catheter.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
2 Kumar A, Anel R, Bunnell E, et al. Pulmonary artery occlusion pressure and central venous pressure fail to predict ventricular filling volume, cardiac performance, or the response to volume infusion in normal subjects. Crit Care Med 2004; 32: 6919[CrossRef][ISI][Medline]
3 Malm S, Frigstad S, Sagberg E, et al. Accurate and reproducible measurement of left ventricular volume and ejection fraction by contrast echocardiography: a comparison with magnetic resonance imaging. J Am Coll Cardiol 2004; 44: 10305[CrossRef][ISI][Medline]
4 Della Rocca G, Costa GM, Coccia C, et al. Preload index: pulmonary artery occlusion pressure versus intrathoracic blood volume monitoring during lung transplantation. Anesth Analg 2002; 95: 83543
5 Wiesenack C, Prasser C, Keyl C, et al. Assessment of intrathoracic blood volume as an indicator of cardiac preload: single transpulmonary thermodilution technique versus assessment of pressure preload parameters derived from a pulmonary artery catheter. J Cardiothorac Vasc Anesth 2001; 15: 5848[CrossRef][ISI][Medline]
6 Chang MC, Blinman TA, Rutherford EJ, et al. Preload assessment in trauma patients during large-volume shock resuscitation. Arch Surg 1996; 131: 72831[Abstract]
7 Cheatham ML, Block EF, Nelson LD, et al. Superior predictor of the hemodynamic response to fluid challenge in critically ill patients. Chest 1998; 114: 12267[ISI][Medline]
8 Diebel LN, Wilson RF, Tagett MG et al. End-diastolic volume. A better indicator of preload in the critically ill. Arch Surg 1992; 127: 81721[Abstract]
9 Newman EV, Merrell M, Genecin A, et al. The dye dilution method for describing the central circulation. An analysis of factors shaping the timeconcentration curves. Circulation 1951; 4: 73546[ISI][Medline]
10 Reuter DA, Felbinger TW, Moerstedt K, et al. Intrathoracic blood volume index measured by thermodilution for preload monitoring after cardiac surgery. J Cardiothorac Vasc Anesth 2002; 16: 1915[CrossRef][ISI][Medline]
11 Vincent JL, Thirion M, Brimioulle S, et al. Thermodilution measurement of right ventricular ejection fraction with a modified pulmonary artery catheter. Intensive Care Med 1986; 12: 338[CrossRef][ISI][Medline]
12 Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 30710[CrossRef][ISI][Medline]
13 Nelson LD, Safcsak K, Cheatham ML, et al. Mathematical coupling does not explain the relationship between right ventricular end-diastolic volume and cardiac output. Crit Care Med 2001; 29: 9403[CrossRef][ISI][Medline]
14 Chittock DR, Dhingra VK, Ronco JJ, et al. Severity of illness and risk of death associated with pulmonary artery catheter use. Crit Care Med 2004; 32: 9115[CrossRef][ISI][Medline]
15 Bindels AJ, van der Hoeven JG, Graafland AD, et al. Relationships between volume and pressure measurements and stroke volume in critically ill patients. Crit Care 2000; 4: 1939[CrossRef][ISI][Medline]
16 Sakka SG, Bredle DL, Reinhart K, et al. Comparison between intrathoracic blood volume and cardiac filling pressures in the early phase of hemodynamic instability of patients with sepsis or septic shock. J Crit Care 1999; 14: 7883[CrossRef][ISI][Medline]
17 Goedje O, Seebauer T, Peyerl M, et al. Hemodynamic monitoring by double-indicator dilution technique in patients after orthotopic heart transplantation. Chest 2000; 118: 77581
18 Buhre W, Weyland A, Buhre K, et al. Effects of the sitting position on the distribution of blood volume in patients undergoing neurosurgical procedures. Br J Anaesth 2000; 84: 3547[Abstract]
19 Buhre W, Buhre K, Kazmaier S, et al. Assessment of cardiac preload by indicator dilution and transoesophageal echocardiography. Eur J Anaesthesiol 2001; 18: 6627[CrossRef][ISI][Medline]
20 Moreno LF, Stratton HH, Newell JC, et al. Mathematical coupling of data: correction of a common error for linear calculations. J Appl Physiol 1986; 60: 33543
21 Lichtwarck-Aschoff M, Beale R, Pfeiffer UJ. Central venous pressure, pulmonary artery occlusion pressure, intrathoracic blood volume, and right ventricular end-diastolic volume as indicators of cardiac preload. J Crit Care 1996; 11: 1808[CrossRef][ISI][Medline]
22 Buhre W, Kazmaier S, Sonntag H, et al. Changes in cardiac output and intrathoracic blood volume: a mathematical coupling of data? Acta Anaesthesiol Scand 2001; 45: 8637[CrossRef][ISI][Medline]
23 Sakka SG, Reinhart K, Wegscheider K, et al. Comparison of cardiac output and circulatory blood volumes by transpulmonary thermo-dye dilution and transcutaneous indocyanine green measurement in critically ill patients. Chest 2002; 121: 55965
24 Urban P, Scheidegger D, Gabathuler J, et al. Thermodilution determination of right ventricular volume and ejection fraction: a comparison with biplane angiography. Crit Care Med 1987; 15: 6525[ISI][Medline]
25 Martyn JA, Snider MT, Farago LF, et al. Thermodilution right ventricular volume: a novel and better predictor of volume replacement in acute thermal injury. J Trauma 1981; 21: 61926[ISI][Medline]
26 Durham R, Neunaber K, Vogler G, et al. Right ventricular end-diastolic volume as a measure of preload. J Trauma 1995; 39: 21823[ISI][Medline]
27 Chang MC, Black CS, Meredith JW. Volumetric assessment of preload in trauma patients: addressing the problem of mathematical coupling. Shock 1996; 6: 3269[ISI][Medline]
28 Hurford WE, Zapol WM. The right ventricle and critical illness: a review of anatomy, physiology, and clinical evaluation of its function. Intensive Care Med 1988; 14: 44857[ISI][Medline]
29 Takagaki M, Ishino K, Kawada M, et al. Total right ventricular exclusion improves left ventricular function in patients with end-stage congestive right ventricular failure. Circulation 2003; 108: 2269[CrossRef]
30 Cheung AT, Savino JS, Weiss SJ, et al. Echocardiographic and hemodynamic indexes of left ventricular preload in patients with normal and abnormal ventricular function. Anesthesiology 1994; 81: 37687[ISI][Medline]
|