Critical Care Literature Review

Arterial Pressure Cardiac Output Monitoring

 

28: J Cardiovasc Nurs. 2008 Mar-Apr;23(2):105-12.
Arterial pressure-based stroke volume and functional hemodynamic monitoring.
Bridges EJ. Biobehavioral Nursing and Health Systems, University of Washington School of Nursing, and Clinical Nurse Researcher, University of Washington Medical Center, Seattle, USA. ebridges@u.washington.edu

Arterial pressure-based methods are less-invasive methods used to measure stroke volume and to predict fluid responsiveness. An understanding of the assumptions of the measurements and clinical factors that affect their accuracy and ability to predict fluid responsiveness is imperative when deciding when and how to use these new technologies. Frequently asked questions about these technologies and the data provided are addressed.

29: Anesth Analg. 2008 Apr;106(4):1201-6, table of contents.
Comment in: Anesth Analg. 2008 Apr;106(4):1031-3.
Online monitoring of pulse pressure variation to guide fluid therapy after cardiac surgery.
Auler JO Jr, Galas F, Hajjar L, Santos L, Carvalho T, Michard F. Department of Anesthesia and Critical Care, Heart Institute, INCOR, Hospital das Clinicas, University of Sao Paulo, SP, Brazil.

BACKGROUND: The arterial pulse pressure variation induced by mechanical ventilation (deltaPP) has been shown to be a predictor of fluid responsiveness. Until now, deltaPP has had to be calculated offline (from a computer recording or a paper printing of the arterial pressure curve), or to be derived from specific cardiac output monitors, limiting the widespread use of this parameter. Recently, a method has been developed for the automatic calculation and real-time monitoring of deltaPP using standard bedside monitors. Whether this method is to predict reliable predictor of fluid responsiveness remains to be determined. METHODS: We conducted a prospective clinical study in 59 mechanically ventilated patients in the postoperative period of cardiac surgery. Patients studied were considered at low risk for complications related to fluid administration (pulmonary artery occlusion pressure < 20 mm Hg, left ventricular ejection fraction > or = 40%). All patients were instrumented with an arterial line and a pulmonary artery catheter. Cardiac filling pressures and cardiac output were measured before and after intravascular fluid administration (20 mL/kg of lactated Ringer's solution over 20 min), whereas deltaPP was automatically calculated and continuously monitored. RESULTS: Fluid administration increased cardiac output by at least 15% in 39 patients (66% = responders). Before fluid administration, responders and nonresponders were comparable with regard to right atrial and pulmonary artery occlusion pressures. In contrast, deltaPP was significantly greater in responders than in nonresponders (17% +/- 3% vs 9% +/- 2%, P < 0.001). The deltaPP cut-off value of 12% allowed identification of responders with a sensitivity of 97% and a specificity of 95%. CONCLUSION: Automatic real-time monitoring of deltaPP is possible using a standard bedside monitor and was found to be a reliable method to predict fluid responsiveness after cardiac surgery. Additional studies are needed to determine if this technique can be used to avoid the complications of fluid administration in high-risk patients.

30: Anesth Analg. 2008 Mar;106(3):867-72, table of contents.
Cardiac output derived from arterial pressure waveform analysis in patients undergoing cardiac surgery: validity of a second generation device.
Mayer J, Boldt J, Wolf MW, Lang J, Suttner S. Department of Anesthesiology and Intensive Care Medicine, Klinikum Ludwigshafen, Bremserstr. 79, 67063 Ludwigshafen, Germany. j-mayer@gmx.de

BACKGROUND: The performance of a recently introduced, arterial waveform-based device for measuring cardiac output (CO) without the need of invasive calibration (FloTrac/Vigileo) has been controversial. We designed the present study to assess the validity of an improved version of this monitoring technique compared with intermittent thermodilution CO measurement using a pulmonary artery catheter in patients undergoing cardiac surgery. METHODS: Forty ASA III patients scheduled for elective coronary artery bypass grafting with cardiopulmonary bypass (CPB) were studied. Simultaneous CO measurements by bolus thermodilution and the FloTrac/Vigileo device were obtained after induction of anesthesia (T1), before CPB (T2), after CPB (T3), after sternal closure (T4), on arrival in the intensive care unit (T5), 4 h (T6), 8 h (T7), and 24 h after surgery (T8). CO was indexed to the body surface area (cardiac index, CI). A percentage error of 30% or less was established as the criterion for method interchangeability. RESULTS: Two hundred and eighty-two data pairs were analyzed. Thermodilution CI ranged from 1.2 to 4.1 L x min(-1) x m(-2) (mean 2.5 +/- 0.54 L x min(-1) x m(-2)). Bias and precision (1.96 sd of the bias) were 0.19 L x min(-1) x m(-2) and +/- 0.60 L x min(-1) x m(-2), resulting in an overall percentage error of 24.6%. Subgroup analysis revealed a percentage error of 28.3% for data pairs obtained intraoperatively (T1-4) and 20.7% in intensive care unit (T5-8). CONCLUSION: CI values obtained by the improved, second generation semiinvasive arterial waveform device showed good intraoperative and postoperative agreement with intermittent pulmonary artery thermodilution CI measurements in patients undergoing coronary artery bypass graft surgery.

31: Br J Anaesth. 2008 Apr;100(4):451-6. Epub 2008 Feb 6.
Performance of a minimally invasive uncalibrated cardiac output monitoring system (Flotrac/Vigileo) in haemodynamically unstable patients.
Compton FD, Zukunft B, Hoffmann C, Zidek W, Schaefer JH. Department of Nephrology, Charité University Medicine Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, D-12200 Berlin, Germany. friederike.compton@charite.de

BACKGROUND: Early haemodynamic assessment is of particular importance in the evaluation of haemodynamically compromised patients, but is often precluded by the invasiveness and complexity of the established cardiac output (CO) monitoring techniques. The FloTrac/Vigileo system allows minimally invasive CO determination based on the arterial pressure waveform derived from any standard arterial catheter, and the algorithm underlying CO calculation was recently modified to allow a more precise estimate of aortic compliance. METHODS: Using the new software, we studied 25 haemodynamically unstable patients who had a radial artery catheter and underwent invasive haemodynamic monitoring with the PiCCO system. PiCCO-derived transpulmonary thermodilution and pulse contour CO (reference-CO) were compared with the CO values obtained with the FloTrac/Vigileo system (AP-CO). Reported CO values are indexed to body surface area. Agreement between reference-CO and AP-CO recorded during routine clinical care was assessed using Bland-Altman statistics. RESULTS: Overall bias between the reference-CO and the AP-CO (n=324) was 0.68 litre min(-1) m(-2) with a high percentage error of +/- 58.8% (95% limits of agreement +/- 1.94 l min(-1) m(-2)). There was a significant difference (P<0.001) between the radial and the femoral mean arterial pressures, and bias was significantly larger for a mean pressure difference of >5 mm Hg (0.93 vs 0.57 litre min(-1) m(-2), P=0.032). No connection was found between the norepinephrine dose and the CO agreement. CONCLUSIONS: Despite the updated algorithm, AP-CO still showed a limited agreement with the reference-CO and systematically underestimated the CO so that the method is not suitable to replace invasive CO monitoring at present.

32: J Cardiothorac Vasc Anesth. 2008 Feb;22(1):77-83. Epub 2007 May 7.
Comparison of central venous to mixed venous oxygen saturation in patients with low cardiac index and filling pressures after coronary artery surgery.
Yazigi A, El Khoury C, Jebara S, Haddad F, Hayeck G, Sleilaty G. Department of Anesthesia and Surgical Intensive Care, Hotel-Dieu de France Hospital, Saint Joseph University, Beirut, Lebanon. ritalama@idm.net.lb

OBJECTIVE: To evaluate the correlation and agreement between mixed venous oxygen saturation (SvO(2)) and central venous oxygen saturation (ScvO(2)) in patients with low cardiac index and filling pressures after coronary artery surgery. DESIGN: Prospective observational study. SETTING: Tertiary care academic hospital. PARTICIPANTS: Sixty consecutive patients with a cardiac index <2 L/min/m(2) and a pulmonary artery occlusion pressure <12 mmHg after coronary artery surgery were included. INTERVENTIONS: Patients were monitored by a pulmonary artery catheter and a central venous catheter positioned in the superior vena cava. MEASUREMENTS AND RESULTS: SvO(2) and ScvO(2) were simultaneously measured before (T0) and after (T1) normalization of the cardiac index (>2.5 L/min/m(2)) by fluid therapy. Sixty pairs of measures were obtained at T0 and at T1. Bias between SvO(2) and ScvO(2) was -0.6% (T0) and -0.8% (T1). Limits of agreement were from -19.2% to 18% (T0) and from -15.6% to 14% (T1), and the correlation coefficient was 0.463 (T0) and 0.72 (T1). SvO(2) and ScvO(2) changes from T0 to T1 (DeltaSvO(2) and DeltaScvO(2)) were calculated. The bias between DeltaSvO(2) and DeltaScvO(2) was -0.25. Limits of agreement were from -20% to 19.5%, and the correlation coefficient was 0.6. CONCLUSIONS: In patients with low cardiac index and filling pressures after coronary artery surgery, ScvO(2) could not be used as a direct alternative for SvO(2). After fluid therapy and normalization of the cardiac index, differences between individual values remained large, and the disagreement between ScvO(2) and SvO(2) changes was significant.

33: Can J Anaesth. 2008 Jan;55(1):22-8.
Cardiac output determination by thermodilution and arterial pulse waveform analysis in patients undergoing aortic valve replacement
Staier K, Wiesenack C, Günkel L, Keyl C. Department of Anesthesiology, Heart Centre Bad Krozingen, Suedring 15, 79189 Bad Krozingen, Germany.

PURPOSE: To compare the accuracy of cardiac output (CO) measurement by arterial pulse waveform analysis (CO(PW)) to thermodilution assessments in patients with aortic stenosis, a high-risk patient group who may benefit from extended hemodynamic monitoring. METHODS: In 30 patients with aortic stenosis, CO was assessed in triplicate by thermodilution via pulmonary artery catheterization (CO(PAC)), and by arterial pulse waveform analysis (CO(PW)), before and after valve replacement. The techniques were compared by assessing the repeatability coefficient of each method and by calculating the percentage error, bias, and the limits of agreement between methods. RESULTS: The repeatability coefficients of CO(PAC) and CO(PW) were 0.89 L.min(-1) and 1.04 L.min(-1) respectively after induction of anesthesia, which corresponded to 24% of CO(PAC) and 26% of CO(PW), and increased to 33% of CO(PAC) and 32% of CO(PW) immediately after extracorporeal circulation. A systematic error between methods was not observed. The limits of agreement were bias +/- 1.42 L.min(-1) after anesthesia induction, corresponding to a 36% percentage error. The scattering of differences between methods increased markedly after termination of extracorporeal circulation (percentage error 56%). CONCLUSION: The repeatability of CO(PAC), as well as of CO(PW), is reduced in patients with aortic stenosis. The repeatability of both methods, as well as the agreement between methods, decreased markedly immediately after termination of cardiopulmonary bypass.

34: Chest. 2007 Dec;132(6):2020-9.
Hemodynamic evaluation and monitoring in the ICU.
Pinsky MR. Department of Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA. pinskymr@upmc.edu

Hemodynamic monitoring, a cornerstone in the management of the critically ill patient, is used to identify cardiovascular insufficiency, its probable cause, and response to therapy. Still it is difficult to document the efficacy of monitoring because no device improves outcome unless coupled to a treatment that improves outcome. Several clinical trials have consistently documented that preoptimization for high-risk surgery patients treated in the operating room and early (< 12 h) goal-directed resuscitation in septic patients treated in the emergency department reduce morbidity, mortality, and resource use (costs) when the end points of resuscitation were focused on surrogate measures of adequacy of global oxygen delivery (Do2). The closer the resuscitation is to the insult, the greater the benefit. When resuscitation was started after ICU admission in high-risk surgical patients, reduced length of stay was also seen. The focus of these monitoring protocols is to establish a mean arterial pressure > 65 mm Hg and then to increase Do2 to 600 mL/min/m2 within the first few minutes to hours of presentation. To accomplish these goals, hemodynamic monitoring focuses more on measures of cardiac output and mixed venous oxygen saturation to access adequacy of resuscitation efforts than on filling pressures. Although these protocols reduce mortality and morbidity is selected high-risk patient groups, the widespread use of monitoring-driven treatment protocols has not yet happened, presumably because all studies have been single-center trials using a single, proprietary blood flow-monitoring device. Multicenter trials are needed of early goal-directed therapies for all patients presenting in shock of various etiologies and when the protocol and not the monitoring device is the primary variable.

35: Biomed Instrum Technol. 2007 Sep-Oct;41(5):403-11.
Calculating arterial pressure-based cardiac output using a novel measurement and analysis method.
Pratt B, Roteliuk L, Hatib F, Frazier J, Wallen RD. Edwards Lifesciences LLP, Irvine, CA 92614, USA. benjamin_pratt@edwards.com

Work on applying physical and physiological principles for determining cardiac output by analysis of pressure measurements has been pursued for decades. Reference measurements for this kind of cardiac output analysis rely on the pulmonary artery catheter (PAC), considered the clinical gold standard for cardiac output monitoring. Recent advances in signal processing, as well as applied information on the relationships that enable arterial pulse pressure to be used to determine stroke volume, have led to the development of a novel system that can continuously measure cardiac output from an arterial pressure waveform that does not require an external calibration reference method. There are significant challenges in applying statistical- and signal-processing practices to the analysis of complex physiological waveforms. This paper reviews the historical basis for measuring flow from the analysis of pressure in a vessel, establishes the physiological and mathematical basis for this new system and describes its performance under various physiological conditions.

36: J Cardiothorac Vasc Anesth. 2007 Oct;21(5):632-5. Epub 2007 Apr 5.
Comment in: J Cardiothorac Vasc Anesth. 2007 Oct;21(5):629-31.
Cardiac output measured by a new arterial pressure waveform analysis method without calibration compared with thermodilution after cardiac surgery.
Breukers RM, Sepehrkhouy S, Spiegelenberg SR, Groeneveld AB. Intensive Care Unit, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, the Netherlands.

OBJECTIVES: To investigate whether measuring cardiac output and its course after cardiac surgery by a new analysis technique of radial artery pressure waves, without need for calibration (FloTrac/Vigileo [FV]; Edwards Lifesciences, Irvine, CA), conforms to the standard bolus thermodilution method via a pulmonary artery catheter (PAC). DESIGN: Prospective study. SETTING: Intensive care unit of university hospital. PARTICIPANTS: Twenty patients for up to 24 hours after cardiac surgery. INTERVENTIONS: Simultaneous and triplicate PAC thermodilution and FV cardiac output measurements at 1 and 3 hours after surgery and the following morning. MEASUREMENTS AND MAIN RESULTS: Fifty-six simultaneous measurement sets were obtained. Mean cardiac output (PAC) ranged between 2.8 and 10.3 L/min and for the FV method between 3.3 and 8.8 L/min. The coefficient of variation for pooled measurements was 7.3% for the PAC and 3.0% for the FV method. For pooled data, the r2 was 0.55 (p < 0.001), with a bias of -0.14, precision of 1.00 L/min, and 95% limits of agreement between -2.14 and 1.87 L/min in a Bland-Altman plot. Also, the FV method tended to overestimate cardiac output when <7 L/min and increased with time, whereas mean arterial pressure increased and PAC cardiac output did not change. Changes in cardiac output correlated (r2 = 0.52, p < 0.001). CONCLUSIONS: The FV arterial pressure waveform analysis method is a clinically applicable method for cardiac output assessment without calibration, after cardiac surgery. It performs well at low cardiac outputs but remains sensitive to changes in vascular tone.

37: Acta Anaesthesiol Scand. 2007 Oct;51(9):1258-67. Epub 2007 Aug 20.
Limitations of arterial pulse pressure variation and left ventricular stroke volume variation in estimating cardiac pre-load during open heart surgery.
Rex S, Schälte G, Schroth S, de Waal EE, Metzelder S, Overbeck Y, Rossaint R, Buhre W. Department of Anaesthesiology, University Hospital, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen, Germany. srex@ukaachen.de

BACKGROUND: In addition to their well-known ability to predict fluid responsiveness, functional pre-load parameters, such as the left ventricular stroke volume variation (SVV) and pulse pressure variation (PPV), have been proposed to allow real-time monitoring of cardiac pre-load. SVV and PPV result from complex heart-lung interactions during mechanical ventilation. It was hypothesized that, under open-chest conditions, when cyclic changes in pleural pressures during positive-pressure ventilation are less pronounced, functional pre-load indicators may be deceptive in the estimation of ventricular pre-load. METHODS: Forty-five patients undergoing coronary artery bypass grafting participated in this prospective, observational study. PPV and SVV were assessed by pulse contour analysis. The thermodilution technique was used to measure the stroke volume index and global and right ventricular end-diastolic volume index. Trans-oesophageal echocardiography was used to determine the left ventricular end-diastolic area index. All parameters were assessed before and after sternotomy, and, in addition, after weaning from cardiopulmonary bypass before and after chest closure (pericardium left open). Patients were ventilated with constant tidal volumes (8 +/- 2 ml/kg) throughout the study period using pressure control. RESULTS: SVV and PPV decreased after sternotomy and increased after chest closure. However, these changes could not be related to concomitant changes in the ventricular pre-load. The stroke volume index was correlated with SVV and PPV in closed-chest conditions only, whereas volumetric indices reflected cardiac pre-load in both closed- and open-chest conditions. SVV and PPV were correlated with left and right ventricular pre-load in closed-chest-closed-pericardium conditions only (with the best correlation found for the right ventricular end-diastolic volume index). CONCLUSIONS: SVV and PPV may be misleading when estimating cardiac pre-load during open heart surgery.

38: Eur J Anaesthesiol. 2007 Oct;24(10):832-9. Epub 2007 Aug 1.
Comparison of FloTrac cardiac output monitoring system in patients undergoing coronary artery bypass grafting with pulmonary artery cardiac output measurements.
Cannesson M, Attof Y, Rosamel P, Joseph P, Bastien O, Lehot JJ. Hospives Civils de Lyon, Hôpital Louis Pradel, Department of Anesthesiology, Bron, France. maxime_cannesson@hotmail.com

BACKGROUND: Arterial pulse waveform analysis has been proposed for cardiac output (CO) determination and monitoring without calibration or thermodilution (FloTrac/ Vigileo; Edwards Lifesciences, Irvine, CA, USA). The accuracy and clinical applicability of this technology has not been fully evaluated. We designed this prospective study to compare the accuracy of the FloTrac system (CO(FT)) vs. pulmonary artery catheter standard bolus thermodilution (CO(PAC) ) in patients undergoing coronary artery bypass grafting. METHODS: We studied 11 patients referred for coronary artery bypass grafting. CO(FT) and CO(PAC) were determined at six time points in the operating room including before and 5 min after volume expansion (500 mL 6% hetastarch). Measurements were performed on arrival in the intensive care unit and every 4 h afterwards. Bland-Altman analysis was used to assess the agreement between CO(FT) and CO(PAC). RESULTS: CO(PAC) ranged from 2.0 to 7.6 L min-1 and CO(FT) ranged from 1.9 to 8.2 L min-1. There was a significant relationship between CO(PAC) and CO(FT) (r = 0.662; P < 0.001). Agreement between CO(PAC) and CO(FT) was -0.26 +/- 0.87 L min-1. Volume expansion induced a significant increase in both CO(PAC) and CO(FT) (from 3.4 +/- 0.8 to 4.4 +/- 1.0 L min-1; P < 0.001 and from 3.9 +/- 1.2 to 5.0 +/- 1.1 L min-1; P < 0.001, respectively) and there was a significant relationship between percent change in CO(PAC) and CO(FT) following volume expansion (r = 0.722; P = 0.01). CONCLUSION: We found clinically acceptable agreement between CO(FT) and CO(PAC) in this setting. This new device has potential clinical applications.

39: J Clin Monit Comput. 2007 Aug;21(4):227-35. Epub 2007 Jun 1.
Cardiac output derived from left ventricular pressure during conductance catheter evaluations: an extended Modelflow method.
Valsecchi S, Perego GB, Schreuder JJ, Censi F, Jansen JR. Medtronic Italia, Via Lucrezio Caro, Rome, Italy. sergio.valsecchi@medtronic.com

OBJECTIVE: The Modelflow method computes cardiac output (CO) from arterial pressure (CO-MFao) by simulating a non-linear three-element Windkessel model of aortic input impedance. We present a novel technique to apply the Modelflow method to the left ventricular pressure (Plv) signal, to obtain an estimation of CO (CO-MFlv). METHODS: We extended the model by simulating the aortic valve as a resistance placed in series to the characteristic impedance. In our model the valve resistance is infinite in diastole, while it has a patient related value during systole. Twenty one patients with heart failure were studied with a combined pressure-conductance catheter positioned in the left ventricle and a micromanometer in the aorta. CO changes were induced during temporary sequential atrio-biventricular pacing with different atrio-ventricular and inter-ventricular intervals. After a single calibration we compared CO-MFlv with CO-MFao (516 measurement series) and with CO estimated by the conductance catheter volume technique (CO-cond) (267 series). RESULTS: CO ranged from 2.42 to 7.59 l/min with an overall mean of 4.36 (1.38) l/min. Comparing the two Modelflow methods, the bias was -0.04 (0.36) l/min, with limits of agreement of -0.77 and 0.70 l/min, and a coefficient of variation of 8.4%. Of the 516 changes in CO from baseline values, 112 were greater than 0.5 l/min and 110 of these (98%) were scored in the same direction by both methods. For comparisons between CO-MFlv and CO-cond the bias was -0.10 (0.49), with limits of agreement of -1.12 and 0.90 l/min, and a coefficient of variation of 12.5%. CONCLUSIONS: Cardiac output estimates by the modelflow method from aortic pressure and left ventricular pressure are interchangeable in patients without mitral and aortic abnormalities. After an initial calibration, CO-MFlv presents near zero bias and an adequate precision.

40: Minerva Anestesiol. 2008 Jul-Aug;74(7-8):349-51.
Preload index and fluid responsiveness: different aspects of the new concept of functional hemodynamic monitoring.
Della Rocca G, Costa MG.
Editorial – No abstract

41: Anesth Analg. 2008 May;106(5):1480-6, table of contents.
Cardiac output measurement in patients undergoing liver transplantation: pulmonary artery catheter versus uncalibrated arterial pressure waveform analysis.
Biais M, Nouette-Gaulain K, Cottenceau V, Vallet A, Cochard JF, Revel P, Sztark F. Service d'Anesthésie Réanimation I, Hôpital Pellegrin, Place Amélie Raba-Léon, 33076 Bordeaux Cedex, France.

BACKGROUND: Cardiac output (CO) and invasive hemodynamic measurements are useful during liver transplantation. The pulmonary artery catheter (PAC) is commonly used for these patients, despite the potential complications. Recently, a less invasive device (Vigileo/FloTrac) became available, which estimates CO using arterial pressure waveform analysis without external calibration. In this study, we compared CO obtained with a PAC using automatic thermodilution, instantaneous CO stat-mode (ICO(SM)), and CO obtained with the new device, arterial pressure waveform analysis (APCO) in patients undergoing liver transplantation. METHODS: Twenty sets of simultaneous measurements of APCO and ICO(SM) were determined in sedated and mechanically ventilated patients undergoing liver transplantation. Time points were as follows: after PAC insertion (T1-3), after portal clamping (T4-6), during anhepathy (T7-9), after graft reperfusion (T10-15), and in the postoperative period in the intensive care unit (T15-20). RESULTS: We enrolled 20 patients and 400 measurements were obtained. No data were rejected. Bias between ICO(SM) and APCO was 0.8 L/min, 95% limits of agreement were -1.8 to 3.5 L/min. The percentage error was 43%. Bias between ICO(SM) and APCO was correlated with systemic vascular resistance [r(2) = 0.55, P < 0.0001, y = 15.8-2.2 ln(x)] and subgroup analysis revealed an increase in the bias and in the percentage error in patients with low systemic vascular resistance (Child-Pugh grade B and C patients). There was no difference between the different surgical periods. CONCLUSIONS: Our results suggest that Vigileo/FloTrac CO monitoring data do not agree well with those of automatic thermodilution in patients undergoing liver transplantation, especially in Child-Pugh grade B and C patients with low systemic vascular resistance.


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