New Developments in Hemodynamic Monitoring
2019; Elsevier BV; Volume: 33; Linguagem: Inglês
10.1053/j.jvca.2019.03.043
ISSN1532-8422
AutoresThomas Scheeren, Michael A. E. Ramsay,
Tópico(s)Ultrasound in Clinical Applications
ResumoHemodynamic monitoring is an essential part of the perioperative management of the cardiovascular patient. It helps to detect hemodynamic alterations, diagnose their underlying causes, and optimize oxygen delivery to the tissues. Furthermore, hemodynamic monitoring is necessary to evaluate the adequacy of therapeutic interventions such as volume expansion or vasoactive medications. Recent developments include the move from static to dynamic variables to assess conditions such as cardiac preload and fluid responsiveness and the transition to less-invasive or even noninvasive monitoring techniques, at least in the perioperative setting. This review describes the available techniques that currently are being used in the care of the cardiovascular patient and discusses their strengths and limitations. Even though the thermodilution method remains the gold standard for measuring cardiac output (CO), the use of the pulmonary artery catheter has declined over the last decades, even in the setting of cardiovascular anesthesia. The transpulmonary thermodilution method, in addition to accurately measuring CO, provides the user with some additional helpful variables, of which extravascular lung water is probably the most interesting. Less-invasive monitoring techniques use, for example, pulse contour analysis to originate flow-derived variables such as stroke volume and CO from the arterial pressure signal, or they may measure the velocity-time integral in the descending aorta to estimate the stroke volume, using, for example, the esophageal Doppler. Completely noninvasive methods such as the volume clamp method use finger cuffs to reconstruct the arterial pressure waveform, from which stroke volume and CO are calculated. All of these less-invasive CO monitoring devices have percentage errors around 40% compared with reference methods (thermodilution), meaning that the values are not interchangeable. Hemodynamic monitoring is an essential part of the perioperative management of the cardiovascular patient. It helps to detect hemodynamic alterations, diagnose their underlying causes, and optimize oxygen delivery to the tissues. Furthermore, hemodynamic monitoring is necessary to evaluate the adequacy of therapeutic interventions such as volume expansion or vasoactive medications. Recent developments include the move from static to dynamic variables to assess conditions such as cardiac preload and fluid responsiveness and the transition to less-invasive or even noninvasive monitoring techniques, at least in the perioperative setting. This review describes the available techniques that currently are being used in the care of the cardiovascular patient and discusses their strengths and limitations. Even though the thermodilution method remains the gold standard for measuring cardiac output (CO), the use of the pulmonary artery catheter has declined over the last decades, even in the setting of cardiovascular anesthesia. The transpulmonary thermodilution method, in addition to accurately measuring CO, provides the user with some additional helpful variables, of which extravascular lung water is probably the most interesting. Less-invasive monitoring techniques use, for example, pulse contour analysis to originate flow-derived variables such as stroke volume and CO from the arterial pressure signal, or they may measure the velocity-time integral in the descending aorta to estimate the stroke volume, using, for example, the esophageal Doppler. Completely noninvasive methods such as the volume clamp method use finger cuffs to reconstruct the arterial pressure waveform, from which stroke volume and CO are calculated. All of these less-invasive CO monitoring devices have percentage errors around 40% compared with reference methods (thermodilution), meaning that the values are not interchangeable. THE GOALS OF precise, personalized hemodynamic monitoring—improving outcomes and patient safety—are the reasons new and better technologies are instituted after they are developed. Clinicians believe that these technologies will improve management of the patient under anesthesia and in the intensive care unit by providing accurate information that can be used to optimize care, provide early diagnosis, and provide feedback that the therapies instituted are improving the perfusion of vital organs and the microcirculation such that the physiological environment is maintained optimally. However, accurate and predictive hemodynamic assessment may be difficult. Anticipating when deterioration is imminent is challenging because the etiology may be multifactorial and involve volume status; myocardial function; vascular tone; and patient resilience, which is still very hard to assess. These monitors are tested in clinical trials with the anticipation that they will provide accuracy (truth) and precision (repeatability), but sometimes they are "black boxes" as far as the user is concerned.1Cannesson M. Shafer S.L. All boxes are black.Anesth Analg. 2016; 122: 309-317Crossref PubMed Scopus (9) Google Scholar However, this is the cost of innovation, and industry and scientists must be encouraged to continue to pursue novel developments but test the outcomes clinically. In the last century, monitoring has developed from initially pressure focused and noninvasive (eg, finger on the pulse and listening to heart and Korotkoff sounds) to invasive (eg, central venous pressure, arterial pressure, and pulmonary artery pressure). However, invasive technology is associated with complications such as infection and perforation. In recent years, the focus has been on trying to develop noninvasive technology without losing significant accuracy and precision, avoiding the complications of invasive monitors, and analyzing flow and response to fluid therapy. In 1968 Prys-Roberts commented on an observation made by Jarisch in 1928 that flow is so much more difficult to measure than pressure but adequate flow is vital for cellular well-being.2Prys-Roberts C. The measurement of cardiac output.Br J Anaesth. 1969; 41: 751-760Abstract Full Text PDF PubMed Scopus (11) Google Scholar Waveform analysis of the pulse contour is used to calculate stroke volume and cardiac output (CO), and the effect of respiratory variation on this waveform has been used to estimate fluid responsiveness or where the patient's volume status is placed on the Frank-Starling curve. The goal of patient-centered hemodynamic monitoring is to make correct therapeutic decisions and optimize the cardiovascular system in the patient undergoing surgery or intensive care treatment. Perioperative acute kidney injury (AKI) is associated with increased morbidity and mortality and until recently has been underdiagnosed. It is estimated that between 22% and 57% of patients admitted to the intensive care unit will develop AKI during their admission3Hoste E.A. Bagshaw S.M. Bellomo R. et al.Epidemiology of acute kidney injury in critically ill patients: The multinational AKI-EPI study.Intensive Care Med. 2015; 41: 1411-1423Crossref PubMed Scopus (1343) Google Scholar and that current AKI classification underestimates long-term mortality.4Bouma H.R. Mungroop H.E. de Geus A.F. et al.Acute kidney injury classification underestimates long-term mortality after cardiac valve operations.Ann Thorac Surg. 2018; 106: 92-98Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar Early diagnosis has been helped by the development of new biomarkers5Su L.J. Li Y.M. Kellum J.A. et al.Predictive value of cell cycle arrest biomarkers for cardiac surgery-associated acute kidney injury: A meta-analysis.Br J Anaesth. 2018; 121: 350-357Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar so that effective preventive and therapeutic measures can be developed. The avoidance of hypotension and renal hypoperfusion and the optimization of volume status are the goals for preventing renal ischemia. Goal-directed fluid therapy guided by dynamic variables such as the pleth variability index (PVI), pulse pressure variation (PPV) and stroke volume variation (SVV) has been developed to measure fluid responsiveness.6Bennett V.A. Aya H.D. Cecconi M. Evaluation of cardiac function using heart-lung interactions.Ann Transl Med. 2018; 6: 356Crossref PubMed Google Scholar The PVI is a measure of the dynamic changes in the perfusion index that occur during 1 or more complete respiratory cycles and is measured using pulse oximetry. This respiratory variation in the pulse oximeter waveform is strongly related to changes in arterial pulse pressure, which is sensitive to changes in ventricular preload in mechanically ventilated patients and more recently has been shown to accurately predict fluid responsiveness.7Hood J.A. Wilson R.J. Pleth variability index to predict fluid responsiveness in colorectal surgery.Anesth Analg. 2011; 113: 1058-1063Crossref PubMed Scopus (56) Google Scholar, 8Cannesson M. Desebbe O. Rosamel P. et al.Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre.Br J Anaesth. 2008; 101: 200-206Abstract Full Text Full Text PDF PubMed Scopus (252) Google Scholar, 9Zimmermann M. Feibicke T. Keyl C. et al.Accuracy of stroke volume variation compared with pleth variability index to predict fluid responsiveness in mechanically ventilated patients undergoing major surgery.Eur J Anaesthesiol. 2010; 27: 555-561Crossref PubMed Scopus (110) Google Scholar The traditional methods of measuring cardiac preload still are used to predict volume responsiveness, but multiple studies have shown inaccuracy in these static variables, such as central venous pressure, pulmonary artery occlusion pressure, left ventricular end-diastolic dimensions, early– or late–diastolic wave ratio, and B-type natriuretic peptide concentration, in demonstrating volume responders from nonresponders.10Monnet X. Teboul J.L. Invasive measures of left ventricular preload.Curr Opin Crit Care. 2006; 12: 235-240Crossref PubMed Scopus (41) Google Scholar, 11Marik P.E. Baram M. Vahid B. Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares.Chest. 2008; 134: 172-178Abstract Full Text Full Text PDF PubMed Scopus (1105) Google Scholar, 12Marik P.E. Cavallazzi R. Does the central venous pressure predict fluid responsiveness? An updated meta-analysis and a plea for some common sense.Crit Care Med. 2013; 41: 1774-1781Crossref PubMed Scopus (529) Google Scholar, 13Osman D. Ridel C. Ray P. et al.Cardiac filling pressures are not appropriate to predict hemodynamic response to volume challenge.Crit Care Med. 2007; 35: 64-68Crossref PubMed Scopus (506) Google Scholar, 14Guerin L. Monnet X. Teboul J.L. Monitoring volume and fluid responsiveness: From static to dynamic indicators.Best Pract Res Clin Anaesthesiol. 2013; 27: 177-185Crossref PubMed Scopus (68) Google Scholar Dynamic tests that challenge the Frank-Starling curve may predict fluid responsiveness but are limited if spontaneous ventilation is present or cardiac arrhythmias are occurring. However, a pulse pressure variation (PPV) or PVI >13% is highly predictive of fluid responsiveness in mechanically ventilated patients in sinus rhythm. Goal-directed fluid management using PVI has been demonstrated to reduce perioperative lactate levels compared with standard measures, including central venous pressure, blood pressure, and fluid challenge. The authors used a PVI threshold of 14% to infuse volume.15Forget P. Lois F. de Kock M. Goal-directed fluid management based on the pulse oximeter-derived pleth variability index reduces lactate levels and improves fluid management.Anesth Analg. 2010; 111: 910-914Crossref PubMed Scopus (178) Google Scholar Central venous pressure is a helpful indicator of cardiac preload, but not preload responsiveness, and depends on the shape of the Frank-Starling curve, as do all static markers of preload. SVV and PPV are other minimally invasive or noninvasive dynamic variables that can be used to guide fluid management. These again are more accurate in mechanically ventilated patients in sinus rhythm. Arterial pulse pressure (systolic minus diastolic) is directly proportional to stroke volume. This PPV reflects the magnitude of respiratory changes in stroke volume and reflects the degree of preload responsiveness. This has been well-demonstrated in patients on mechanical ventilation with normal tidal volumes and sinus rhythm.16Michard F. Boussat S. Chemla D. et al.Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure.Am J Respir Crit Care Med. 2000; 162: 134-138Crossref PubMed Scopus (987) Google Scholar, 17Teboul J.L. Monnet X. Chemla D. et al.Arterial pulse pressure variation with mechanical ventilation.Am J Respir Crit Care Med. 2019; 199: 22-31Crossref PubMed Scopus (50) Google Scholar There undoubtedly has been a trend in recent years from more invasive hemodynamic monitoring tools and techniques (eg, pulmonary artery catheter [PAC] for measuring CO, mixed venous oxygen saturation, and pulmonary arterial pressures), to less-invasive techniques (eg, CO monitoring using arterial pressure waveform analysis or the esophageal Doppler), and even completely noninvasive techniques (eg, volume clamp using finger cuffs, bioimpedance and bioreactance, carbon dioxide (CO2)-rebreathing, and pulse wave transit time). This trend became possible through the technical development of innovative devices that have penetrated the market with variable success. The core question to be asked is whether less invasiveness also is accompanied by less accuracy,18Saugel B. Wagner J.Y. Scheeren T.W. Cardiac output monitoring: Less invasiveness, less accuracy?.J Clin Monit Comput. 2016; 30: 753-755Crossref PubMed Scopus (11) Google Scholar which would limit the use of these devices markedly. Although the pulmonary thermodilution method using the PAC remains the gold standard for measuring CO, the use of these techniques has declined over the last decades.19Wiener R.S. Welch H.G. Trends in the use of the pulmonary artery catheter in the United States, 1993-2004.JAMA. 2007; 298: 423-429Crossref PubMed Scopus (257) Google Scholar, 20Seifi A. Elliott R.J. Elsehety M.A. Usage of Swan-Ganz catheterization during the past 2 decades in United States.J Crit Care. 2016; 35: 213-214Crossref PubMed Scopus (9) Google Scholar Reasons for this include the lack of benefit to treatment algorithms based on PAC measurements.21Sandham J.D. Hull R.D. Brant R.F. et al.A randomized, controlled trial of the use of pulmonary-artery catheters in high-risk surgical patients.N Engl J Med. 2003; 348: 5-14Crossref PubMed Scopus (1178) Google Scholar, 22Shah M.R. Hasselblad V. Stevenson L.W. et al.Impact of the pulmonary artery catheter in critically ill patients: Meta-analysis of randomized clinical trials.JAMA. 2005; 294: 1664-1670Crossref PubMed Scopus (544) Google Scholar, 23Harvey S. Harrison D.A. Singer M. et al.Assessment of the clinical effectiveness of pulmonary artery catheters in management of patients in intensive care (PAC-Man): A randomised controlled trial.Lancet. 2005; 366: 472-477Abstract Full Text Full Text PDF PubMed Scopus (797) Google Scholar This also holds true for the population of high-risk patients undergoing cardiac surgery, for which the PAC still is widely used.24Chiang Y. Hosseinian L. Rhee A. et al.Questionable benefit of the pulmonary artery catheter after cardiac surgery in high-risk patients.J Cardiothorac Vasc Anesth. 2015; 29: 76-81Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar That is slightly different from the transpulmonary thermodilution (TPTD) method, which, although invasive, only necessitates the insertion of a central venous line and an arterial thermistor catheter.25Monnet X. Teboul J.L. Transpulmonary thermodilution: Advantages and limits.Crit Care. 2017; 21: 147Crossref PubMed Scopus (118) Google Scholar CO measured using this method might be considered interchangeable with that obtained by the gold standard (intermittent thermodilution with the PAC).26Reuter D.A. Huang C. Edrich T. et al.Cardiac output monitoring using indicator-dilution techniques: Basics, limits, and perspectives.Anesth Analg. 2010; 110: 799-811Crossref PubMed Scopus (198) Google Scholar In addition to measuring CO with intermittent thermodilution, TPTD systems also provide continuous CO measurements by pulse contour analysis (PCA), which can be calibrated by measurements of bolus thermodilution, increasing their accuracy. In addition to CO, TPTD systems provide the user with additional hemodynamic measurements, including SVV and PPV, for assessing fluid responsiveness, global end-diastolic volume for estimating cardiac preload, extravascular lung water for quantifying pulmonary edema, pulmonary vascular permeability index for evaluating capillary leakage, and cardiac function index and ejection fraction as indicators of systolic pump function of the heart. These measurements allow for a complete hemodynamic evaluation of the patient experiencing shock, therefore TPTD is recommended for evaluating acute circulatory failure that does not respond to initial therapy or that is associated with acute respiratory distress syndrome.27Teboul J.L. Saugel B. Cecconi M. et al.Less invasive hemodynamic monitoring in critically ill patients.Intensive Care Med. 2016; 42: 1350-1359Crossref PubMed Scopus (168) Google Scholar Of these multiple variables, extravascular lung water is probably the most interesting because it clearly correlates with severity categories of acute respiratory distress syndrome28Kushimoto S. Endo T. Yamanouchi S. et al.Relationship between extravascular lung water and severity categories of acute respiratory distress syndrome by the Berlin definition.Crit Care. 2013; 17: R132Crossref PubMed Scopus (61) Google Scholar and with mortality in critically ill patients.29Sakka S.G. Klein M. Reinhart K. et al.Prognostic value of extravascular lung water in critically ill patients.Chest. 2002; 122: 2080-2086Abstract Full Text Full Text PDF PubMed Scopus (323) Google Scholar Amongst the less-invasive hemodynamic monitoring technologies, those based on PCA are the most broadly used. PCA basically transfers a pressure signal (the arterial pressure waveform) into a flow signal. There are several monitors on the market, each of which uses its own proprietary algorithm for analyzing the pulse contour. The most common one uses the FloTrac sensor (Edwards Lifesciences, Irvine, CA), which can be connected to any arterial catheter on the patient side and to either the Vigileo, EV1000, or Hemosphere as the monitor (all Edwards Lifesciences). The system derives stroke volume from the pulse pressure of the arterial pulse wave after correcting for the compliance and the resistance of the vasculature. The accuracy of the CO measurements has been questioned, particularly in patients with low vascular resistance, which has led to multiple software updates of the algorithm to account for these problems. The results of the accuracy of CO data were summarized for the first 3 software generations, showing percentage error deviations from reference CO measurements (mostly PAC or TPTD) ranging from 13% to as high as 75%, depending on the setting.30Marik P.E. Noninvasive cardiac output monitors: A state-of the-art review.J Cardiothorac Vasc Anesth. 2013; 27: 121-134Abstract Full Text Full Text PDF PubMed Scopus (214) Google Scholar After publication of that review, a fourth-generation software was released and tested, concluding that the accuracy of CO values measured with this version has improved greatly compared with previous versions but still did not reach a clinically sufficient level (ie, a percentage error <30%).31Suehiro K. Funao T. Fujimoto Y. et al.Transcutaneous near-infrared spectroscopy for monitoring spinal cord ischemia: An experimental study in swine.J Clin Monit Comput. 2017; 31: 975-979Crossref PubMed Scopus (11) Google Scholar, 32Maeda T. Hamaguchi E. Kubo N. et al.The accuracy and trending ability of cardiac index measured by the fourth-generation FloTrac/Vigileo system and the Fick method in cardiac surgery patients.J Clin Monit Comput. 2018 November 7; ([E-pub ahead of print])PubMed Google Scholar, 33Maeda T. Hattori K. Sumiyoshi M. et al.Accuracy and trending ability of the fourth-generation FloTrac/Vigileo System in patients undergoing abdominal aortic aneurysm surgery.J Anesth. 2018; 32: 387-393Crossref PubMed Scopus (11) Google Scholar Another uncalibrated PCA system for monitoring CO is the ProAQT/PulsioFlex system (Pulsion-Getinge, Feldkirchen, Germany). It essentially uses the PCA-based algorithm of the PiCCO system (Pulsion-Getinge), however, without the possibility of external validation by TPTD. Data regarding the accuracy of this device are scarce but indicate that the ProAQT/PulsioFlex did not reliably estimate the absolute values of CO.34Monnet X. Vaquer S. Anguel N. et al.Comparison of pulse contour analysis by Pulsioflex and Vigileo to measure and track changes of cardiac output in critically ill patients.Br J Anaesth. 2015; 114: 235-243Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar In addition to the accuracy of an absolute CO value, one might be also interested as to whether a monitoring device can track changes in CO, such as after volume expansion or pharmacological interventions. In this respect, both methods (ie, FloTrac and ProAQT) perform better and reliably track these changes. Additional PCA-based CO monitoring systems include the LiDCOrapid (LiDCO, London, UK) and the pressure recording analytical method. Taken in summary, these minimally invasive PCA-based technologies have a moderate accuracy with a percentage error of 41.3% ± 2.7%.35Peyton P.J. Chong S.W. Minimally invasive measurement of cardiac output during surgery and critical care: A meta-analysis of accuracy and precision.Anesthesiology. 2010; 113: 1220-1235Crossref PubMed Scopus (300) Google Scholar The esophageal Doppler (Cardio Q; Deltex Medical, Chichester, UK) measures blood flow in the descending aorta via a flexible Doppler probe introduced into the esophagus of anesthetized patients. Unlike transesophageal echocardiography, the transducer is directed toward the descending aorta to measure the stroke distance (ie, the velocity-time integral), which then is used to estimate the stroke volume.36Cholley B.P. Singer M. Esophageal Doppler: Noninvasive cardiac output monitor.Echocardiography. 2003; 20: 763-769Crossref PubMed Scopus (50) Google Scholar The mean percentage error for this device was 42.1% ± 9.9%.35Peyton P.J. Chong S.W. Minimally invasive measurement of cardiac output during surgery and critical care: A meta-analysis of accuracy and precision.Anesthesiology. 2010; 113: 1220-1235Crossref PubMed Scopus (300) Google Scholar Completely noninvasive hemodynamic monitoring methods come into play when not even the placement of an arterial line is considered necessary for patient care. These methods can be used to measure not only blood pressure continuously, but also CO and dynamic preload variables.37Michard F. Liu N. Kurz A. The future of intraoperative blood pressure management.J Clin Monit Comput. 2018; 32: 1-4Crossref PubMed Scopus (16) Google Scholar The first group of noninvasive CO technologies is based on principles similar to the PCA methods previously described, with the only difference being the arterial pulse wave is obtained noninvasively.27Teboul J.L. Saugel B. Cecconi M. et al.Less invasive hemodynamic monitoring in critically ill patients.Intensive Care Med. 2016; 42: 1350-1359Crossref PubMed Scopus (168) Google Scholar The so-called volume clamp method uses finger cuffs and relies on photoplethysmography to keep the finger blood volume constant,38Saugel B. Cecconi M. Hajjar L.A. Noninvasive cardiac output monitoring in cardiothoracic surgery patients: Available methods and future directions.J Cardiothorac Vasc Anesth. 2018 June 27; ([E-pub ahead of print])PubMed Google Scholar as first described in 1967 by the Czech physiologist Penaz. This way, the arterial pressure waveform can be reconstructed and CO can be calculated using the CO-Trek algorithm.39Truijen J. van Lieshout J.J. Wesselink W.A. et al.Noninvasive continuous hemodynamic monitoring.J Clin Monit Comput. 2012; 26: 267-278Crossref PubMed Scopus (108) Google Scholar This method was incorporated in the Nexfin monitor (BMEYE, Amsterdam, Netherlands), which was adopted by Edwards Lifesciences in 2014 and merchandised under the name Clearsight. Because the technology has not changed, results obtained with the Nexfin also are applicable to the Clearsight system. Studies examining CO estimates by this method show a percentage error ranging from 24% to 58% (average 44%) compared with TPTD.40Ameloot K. Palmers P.J. Malbrain M.L. The accuracy of noninvasive cardiac output and pressure measurements with finger cuff: A concise review.Curr Opin Crit Care. 2015; 21: 232-239Crossref PubMed Scopus (84) Google Scholar A similar technology is used in the CNAP monitor (CNSystems Medizintechnik AG, Graz, Austria), which also has shown acceptable agreement with reference CO obtained using TPTD.41Wagner J.Y. Grond J. Fortin J. et al.Continuous noninvasive cardiac output determination using the CNAP system: Evaluation of a cardiac output algorithm for the analysis of volume clamp method-derived pulse contour.J Clin Monit Comput. 2016; 30: 487-493Crossref PubMed Scopus (43) Google Scholar In a systematic review of noninvasive CO monitoring devices, the noninvasive PCA showed a pooled percentage error of 45%.42Joosten A. Desebbe O. Suehiro K. et al.Accuracy and precision of non-invasive cardiac output monitoring devices in perioperative medicine: A systematic review and meta-analysis.Br J Anaesth. 2017; 118: 298-310Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar Other noninvasive CO monitors that are not based on PCA include bioreactance and bioimpedance,43Fellahi J.L. Fischer M.O. Electrical bioimpedance cardiography: An old technology with new hopes for the future.J Cardiothorac Vasc Anesth. 2014; 28: 755-760Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar partial CO2-rebreathing,44Jaffe M.B. Partial CO2 rebreathing cardiac output—Operating principles of the NICO system.J Clin Monit Comput. 1999; 15: 387-401Crossref PubMed Scopus (103) Google Scholar and pulse wave transit time. These methods recently have been described in detail.38Saugel B. Cecconi M. Hajjar L.A. Noninvasive cardiac output monitoring in cardiothoracic surgery patients: Available methods and future directions.J Cardiothorac Vasc Anesth. 2018 June 27; ([E-pub ahead of print])PubMed Google Scholar, 45Nguyen L.S. Squara P. Non-invasive monitoring of cardiac output in critical care medicine.Front Med. 2017; 4: 200Crossref Scopus (29) Google Scholar, 46Clement R.P. Vos J.J. Scheeren T.W.L. Minimally invasive cardiac output technologies in the ICU: Putting it all together.Curr Opin Crit Care. 2017; 23: 302-309Crossref PubMed Scopus (16) Google Scholar In a recent meta-analysis, percentage errors for these CO monitoring devices were 42% for bioimpedance and bioreactance, 40% for CO2-rebreathing, and 62% for pulse wave transit time.42Joosten A. Desebbe O. Suehiro K. et al.Accuracy and precision of non-invasive cardiac output monitoring devices in perioperative medicine: A systematic review and meta-analysis.Br J Anaesth. 2017; 118: 298-310Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar As stated by a recent expert panel, noninvasive hemodynamic monitors increasingly are being used in the perioperative setting and with further technological improvements have the potential to become the hemodynamic monitoring of the future. This is different for the intensive care unit setting for patients experiencing shock, who necessitate arterial catheterization (eg, for blood sampling), and when abnormal vasomotor states such as sepsis or hepatic failure limit the accuracy of CO measurements.27Teboul J.L. Saugel B. Cecconi M. et al.Less invasive hemodynamic monitoring in critically ill patients.Intensive Care Med. 2016; 42: 1350-1359Crossref PubMed Scopus (168) Google Scholar However, it must be mentioned that the choice of a monitoring technique based on patient factors (eg, comorbidities and risk of surgery) and the setting can be modified if the patient's condition deteriorates (step up approach) or improves (step down) with regard to invasiveness and continuity of measurements.47Wagner J.Y. Saugel B. When should we adopt continuous noninvasive hemodynamic monitoring technologies into clinical routine?.J Clin Monit Comput. 2015; 29: 1-3Crossref PubMed Scopus (24) Google Scholar In the near future, technical developments such as miniaturized and wearable sensors and wireless monitoring will contribute to the widespread use of noninvasive hemodynamic monitoring technologies.48Michard F. 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