Comparison of esophageal Doppler, pulse contour analysis, and real-time pulmonary artery thermodilution for the continuous measurement of cardiac output

Predicting Fluid Responsiveness Using Carotid Ultrasound in Mechanically Ventilated Patients: A Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies

BACKGROUND

A noninvasive and accurate method of determining fluid responsiveness in ventilated patients would help to mitigate unnecessary fluid administration. Although carotid ultrasound has been previously studied for this purpose, several studies have recently been published. We performed an updated systematic review and meta-analysis to evaluate the accuracy of carotid ultrasound as a tool to predict fluid responsiveness in ventilated patients.

METHODS

Studies eligible for review investigated the accuracy of carotid ultrasound parameters in predicting fluid responsiveness in ventilated patients, using sensitivity and specificity as markers of diagnostic accuracy (International Prospective Register of Systematic Reviews [PROSPERO] CRD42022380284). All included studies had to use an independent method of determining cardiac output and exclude spontaneously ventilated patients. Six bibliographic databases and 2 trial registries were searched. Medline, Embase, Emcare, APA PsycInfo, CINAHL, and the Cochrane Library were searched on November 4, 2022. Clinicaltrials.gov and Australian New Zealand Clinical Trials Registry were searched on February 24, 2023. Results were pooled, meta-analysis was conducted where possible, and hierarchical summary receiver operating characteristic models were used to compare carotid ultrasound parameters. Bias and evidence quality were assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool and the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) guidelines.

RESULTS

Thirteen prospective clinical studies were included (n = 648 patients), representing 677 deliveries of volume expansion, with 378 episodes of fluid responsiveness (58.3%). A meta-analysis of change in carotid Doppler peak velocity (∆CDPV) yielded a sensitivity of 0.79 (95% confidence interval [CI], 0.74-0.84) and a specificity of 0.85 (95% CI, 0.76-0.90). Risk of bias relating to recruitment methodology, the independence of index testing to reference standards and exclusionary clinical criteria were evaluated. Overall quality of evidence was low. Study design heterogeneity, including a lack of clear parameter cutoffs, limited the generalizability of our results.

CONCLUSIONS

In this meta-analysis, we found that existing literature supports the ability of carotid ultrasound to predict fluid responsiveness in mechanically ventilated adults. ∆CDPV may be an accurate carotid parameter in certain contexts. Further high-quality studies with more homogenous designs are needed to further validate this technology.

Indirect measurement of absolute cardiac output during exercise in simulated altered gravity is highly dependent on the method

PURPOSE

Altered gravity environments introduce cardiovascular changes that may require continuous hemodynamic monitoring in both spaceflight and terrestrial analogs. Conditions in such environments are often prohibitive to direct/invasive methods and therefore, indirect measurement techniques must be used. This study compares two common cardiac measurement techniques used in the human spaceflight domain, pulse contour analysis (PCA-Nexfin) and inert gas rebreathing (IGR-Innocor), in subjects completing ergometer exercise under altered gravity conditions simulated using a tilt paradigm.

METHODS

Seven subjects were tilted to three different angles representing Martian, Lunar, and microgravity conditions in the rostrocaudal direction. They completed a 36-min submaximal cardiovascular exercise protocol in each condition. Hemodynamics were continuously monitored using Nexfin and Innocor.

RESULTS

Linear mixed-effects models revealed a significant bias of [Formula: see text] ml ([Formula: see text]) in stroke volume and [Formula: see text] l/min ([Formula: see text]) in cardiac output, with Nexfin measuring greater than Innocor in both variables. These values are in agreement with a Bland-Altman analysis. The correlation of stroke volume and cardiac output measurements between Nexfin and Innocor were [Formula: see text] ([Formula: see text]) and [Formula: see text] ([Formula: see text]) respectively.

CONCLUSION

There is a poor agreement in absolute stroke volume and cardiac output values between measurement via PCA (Nexfin) and IGR (Innocor) in subjects who are exercising in simulated altered gravity environments. These results suggest that the chosen measurement method and device greatly impacts absolute measurements of cardiac output. However, there is a good level of agreement between the two devices when measuring relative changes. Either of these devices seem adequate to capture cardiac changes, but should not be solely relied upon for accurate measurement of absolute cardiac output.

[S3 guidelines on intensive medical care of cardiac surgery patients : Hemodynamic monitoring and cardiovascular system-an update]

An update of the S3- guidelines for treatment of cardiac surgery patients in the intensive care unit, hemodynamic monitoring and cardiovascular system was published by the Association of Scientific Medical Societies in Germany (AWMF) in January 2018. This publication updates the guidelines from 2006 and 2011. The guidelines include nine sections that in addition to different methods of hemodynamic monitoring also reviews the topic of volume therapy as well as vasoactive and inotropic drugs. Furthermore, the guidelines also define the goals for cardiovascular treatment. This article describes the most important innovations of these comprehensive guidelines.

Radiographic Review of Current Therapeutic and Monitoring Devices in the Chest

Chest radiographs are obtained as a standard part of clinical care. Rapid advancements in medical technology have resulted in a myriad of new medical devices, and familiarity with their imaging appearance is a critical yet increasingly difficult endeavor. Many modern thoracic medical devices are new renditions of old designs and are often smaller than older versions. In addition, multiple device designs serving the same purpose may have varying morphologies and positions within the chest. The radiologist must be able to recognize and correctly identify the proper positioning of state-of-the-art medical devices and identify any potential complications that could impact patient care and management. To familiarize radiologists with the arsenal of newer thoracic medical devices, this review describes the indications, radiologic appearance, complications, and magnetic resonance imaging safety of each device. ^©RSNA, 2018.

A System for Continuous Estimating and Monitoring Cardiac Output via Arterial Waveform Analysis

BACKGROUND

Cardiac output (CO) is the total volume of blood pumped by the heart per minute and is a function of heart rate and stroke volume. CO is one of the most important parameters for monitoring cardiac function, estimating global oxygen delivery and understanding the causes of high blood pressure. Hence, measuring CO has always been a matter of interest to researchers and clinicians. Several methods have been developed for this purpose, but a majority of them are either invasive, too expensive or need special expertise and experience. Besides, they are not usually risk free and have consequences.

OBJECTIVE

Here, a semi-invasive system was designed and developed for continuous CO measurement via analyzing and processing arterial pulse waves.

RESULTS

Quantitative evaluation of developed CO estimation system was performed using 7 signals. It showed that it has an acceptable average error of (6.5%) in estimating CO. In addition, this system has the ability to consistently estimate this parameter and to provide a CO versus time curve that assists in tracking changes of CO. Moreover, the system provides such curve for systolic blood pressure, diastolic blood pressure, average blood pressure, heart rate and stroke volume.

CONCLUSION

Evaluation of the results showed that the developed system is capable of accurately estimating CO. The curves which the system provides for important parameters may be valuable in monitoring hemodynamic status of high-risk surgical patients and critically ill patients in Intensive Care Units (ICU). Therefore, it could be a suitable system for monitoring hemodynamic status of critically ill patients.

Pulse waveform hemodynamic monitoring devices: recent advances and the place in goal-directed therapy in cardiac surgical patients

Hemodynamic monitoring has evolved and improved greatly during the past decades as the medical approach has shifted from a static to a functional approach. The technological advances have led to innovating calibrated or not, but minimally invasive and noninvasive devices based on arterial pressure waveform (APW) analysis. This systematic clinical review outlines the physiologic rationale behind these recent technologies. We describe the strengths and the limitations of each method in terms of accuracy and precision of measuring the flow parameters (stroke volume, cardiac output) and dynamic parameters which predict the fluid responsiveness. We also analyzed the place of the APW monitoring devices in goal-directed therapy (GDT) protocols in cardiac surgical patients. According to the data from the three GDT-randomized control trials performed in cardiac surgery (using two types of APW techniques PiCCO and FloTrac/Vigileo), these devices did not demonstrate that they played a role in decreasing mortality, but only decreasing the ventilation time and the ICU and hospital length of stay.

Postoperative Critical Care of the Adult Cardiac Surgical Patient. Part I: Routine Postoperative Care

OBJECTIVES

Cardiac surgery, including coronary artery bypass, cardiac valve, and aortic procedures, is among the most common surgical procedures performed in the United States. Successful outcomes after cardiac surgery depend on optimum postoperative critical care. The cardiac intensivist must have a comprehensive understanding of cardiopulmonary physiology and the sequelae of cardiopulmonary bypass. In this concise review, targeted at intensivists and surgeons, we discuss the routine management of the postoperative cardiac surgical patient.

DATA SOURCE AND SYNTHESIS

Narrative review of relevant English-language peer-reviewed medical literature.

CONCLUSIONS

Critical care of the cardiac surgical patient is a complex and dynamic endeavor. Adequate fluid resuscitation, appropriate inotropic support, attention to rewarming, and ventilator management are key components. Patient safety is enhanced by experienced personnel, a structured handover between the operating room and ICU teams, and appropriate transfusion strategies.

Minimally invasive monitoring

Although use of the classic pulmonary artery catheter has declined, several techniques have emerged to estimate cardiac output. Arterial pressure waveform analysis computes cardiac output from the arterial pressure curve. The method of estimating cardiac output for these devices depends on whether they need to be calibrated by an independent measure of cardiac output. Some newer devices have been developed to estimate cardiac output from an arterial curve obtained noninvasively with photoplethysmography, allowing a noninvasive beat-by-beat estimation of cardiac output. This article describes the different devices that perform pressure waveform analysis.

Arterial waveform analysis

The bedside measurement of continuous arterial pressure values from waveform analysis has been routinely available via indwelling arterial catheterization for >50 years. Invasive blood pressure monitoring has been utilized in critically ill patients, in both the operating room and critical care units, to facilitate rapid diagnoses of cardiovascular insufficiency and monitor response to treatments aimed at correcting abnormalities before the consequences of either hypo- or hypertension are seen. Minimally invasive techniques to estimate cardiac output (CO) have gained increased appeal. This has led to the increased interest in arterial waveform analysis to provide this important information, as it is measured continuously in many operating rooms and intensive care units. Arterial waveform analysis also allows for the calculation of many so-called derived parameters intrinsically created by this pulse pressure profile. These include estimates of left ventricular stroke volume (SV), CO, vascular resistance, and during positive-pressure breathing, SV variation, and pulse pressure variation. This article focuses on the principles of arterial waveform analysis and their determinants, components of the arterial system, and arterial pulse contour. It will also address the advantage of measuring real-time CO by the arterial waveform and the benefits to measuring SV variation. Arterial waveform analysis has gained a large interest in the overall assessment and management of the critically ill and those at a risk of hemodynamic deterioration.

A systematic review of goal directed fluid therapy: rating of evidence for goals and monitoring methods

PURPOSE

To review the literature on goal directed fluid therapy and evaluate the quality of evidence for each combination of goal and monitoring method.

MATERIALS AND METHODS

A search of major digital databases and hand search of references was conducted. All studies assessing the clinical utility of a specific fluid therapy goal or set of goals using any monitoring method were included. Data was extracted using a pre-determined pro forma and papers were evaluated using GRADE principles to assess evidence quality.

RESULTS

Eighty-one papers met the inclusion criteria, investigating 31 goals and 22 methods for monitoring fluid therapy in 13052 patients. In total there were 118 different goal/method combinations. Goals with high evidence quality were central venous lactate and stroke volume index. Goals with moderate quality evidence were sublingual microcirculation flow, the oxygen extraction ratio, cardiac index, cardiac output, and SVC collapsibility index.

CONCLUSIONS

This review has highlighted the plethora of goals and methods for monitoring fluid therapy. Strikingly, there is scant high quality evidence, in particular for non-invasive G/M combinations in non-operative and non-intensive care settings. There is an urgent need to address this research gap, which will be helped by methodologies to compare utility of G/M combinations.

Perioperative fluid management for pulmonary resection surgery and esophagectomy

Perioperative fluid management is of significant importance during pulmonary resection surgery and esophagectomy. Excessive fluid administration has been consistently shown as a risk factor for lung injury after thoracic procedures. Probable causes of this serious complication include fluid overload, lung lymphatics and pulmonary endothelial damage. Along with new insights regarding the Starling equation and the absence of a third space, current evidence supports a restrictive fluid regimen for patients undergoing pulmonary resection surgery and esophagectomy. Multiple minimally invasive hemodyamic monitoring devices, including pulse pressure/stroke volume variation, esophageal Doppler, and extravascular lung water measurement, were evaluated for optimizing perioperative fluid therapy. Further research regarding the prevention, diagnosis, and treatment of acute lung injury after pulmonary resection and esophagectomy is required.

Agreement between cardiac outputs by four-dimensional echocardiography and thermodilution method is poor

OBJECTIVE

The objective of the study was to determine the agreement of cardiac output (CO) measured by four-dimensional echocardiography (4D echo) to simultaneously obtain CO from pulmonary artery catheter (PAC) using thermodilution technique.

MATERIALS AND METHODS

Sixty-three comparable readings from 27 patients scheduled for elective coronary artery bypass were included. All echocardiographic measurements were obtained by one experienced echocardiographer. All echo images were analyzed independently and blinded from PAC-obtained measurements. Analysis was primarily done by Bland and Altman plot. The collected data were further controlled for interobserver bias and image quality.

RESULTS

Differences in CO measurements increased with higher CO, hence values were logarithmically transformed. On the logaritmic scale, the 4D echo underestimated CO by 0.37 l/min compared with PAC, indicating that PAC measurements were 1.45 times higher than the 4D echo (95% confidence interval 1.32-1.52) and limits of agreement 0.97-2.14). The interobserver bias of 4D echo measurement analysis was 0.29 l/min (95% confidence interval 0.16-0.42) and limits of agreement -0.8-1.38). No difference was seen in image quality between comparisons with good agreement compared with comparisons with poor agreement.

CONCLUSION

The agreement between COs by 4D echo and standard PAC thermodilution technique was poor. 4D echo underestimates CO as compared with PAC. This is most likely caused by the analysis software or low frame rate inherent to the technique.

Accuracy of cardiac output measurements during off-pump coronary artery bypass grafting: according to the vessel anastomosis sites

Background

During beating heart surgery, the accuracy of cardiac output (CO) measurement techniques may be influenced by several factors. This study was conducted to analyze the clinical agreement among stat CO mode (SCO), continuous CO mode (CCO), arterial pressure waveform-based CO estimation (APCO), and transesophageal Doppler ultrasound technique (UCCO) according to the vessel anastomosis sites.

Methods

This study was prospectively performed in 25 patients who would be undergoing elective OPCAB. Hemodynamic variables were recorded at the following time points: during left anterior descending (LAD) anastomosis at 1 min and 5 min; during obtuse marginal (OM) anastomosis at 1 min and 5 min: and during right coronary artery (RCA) anastomosis at 1 min and 5 min. The variables measured including the SCO, CCO, APCO, and UCCO.

Results

CO measurement techniques showed different correlations according to vessel anastomosis site. However, the percent error observed was higher than the value of 30% postulated by the criteria of Critchley and Critchley during all study periods for all CO measurement techniques.

Conclusions

In the beating heart procedure, SCO, CCO and APCO showed different correlations according to the vessel anastomosis sites and did not agree with UCCO. CO values from the various measurement techniques should be interpreted with caution during OPCAB.

Third-generation FloTrac/Vigileo does not reliably track changes in cardiac output induced by norepinephrine in critically ill patients

BACKGROUND

The ability of the third-generation FloTrac/Vigileo software to track changes in cardiac index (CI) induced by volume expansion and norepinephrine in critically ill patients is unknown.

METHODS

In subjects with circulatory failure, we administered volume expansion (20 subjects) and increased (20 subjects) or decreased (20 subjects) the dose of norepinephrine. We measured arterial pressure waveform-derived CI provided by the third-generation FloTrac/Vigileo device (CI(pw)) and transpulmonary thermodilution CI (CI(td)) before and after therapeutic interventions.

RESULTS

Considering the pairs of measurements performed before and after all therapeutic interventions (n=60), a bias between the absolute values of CI(pw) and CI(td) was 0.26 (0.94) litre min(-1) m(-2) and the percentage error was 54%. Changes in CI(pw) tracked changes in CI(td) induced by volume expansion with moderate accuracy [n=20, bias=-0.11 (0.54) litre min(-1) m(-2), r(2)=0.26, P=0.02]. When changes in CI(td) were induced by norepinephrine (n=40), a bias between CI(pw) and CI(td) was 0.01 (0.41) litre min(-1) m(-2) (r(2)=0.11, P=0.04). The concordance rates between changes in CI(pw) and CI(td) induced by volume expansion and norepinephrine were 73% and 60%, respectively. The bias between changes in CI(pw) and CI(td) significantly correlated with changes in total systemic vascular resistance (r(2)=0.41, P<0.0001).

CONCLUSIONS

The third-generation FloTrac/Vigileo device was moderately reliable for tracking changes in CI induced by volume expansion and poorly reliable for tracking changes in CI induced by norepinephrine.

[Reliability of the pulse contour analysis for cardiac output measurement for assessing the fluid responsiveness]

BACKGROUND

The cardiac output (CO) is classically measured in intensive care unit patients. pulse contour (PC) method allows monitoring of CO.

OBJECTIVE

The aim of the present study was to assess the ability of PC to assess the fluid responsiveness defined as an increase in CO more than or equal to 15% after 500 mL hydroxyethyl starch over 20 minutes.

PATIENTS AND METHODS

In this observational prospective study, patients in shock in whom a PC method was inserted were included. CO was measure using the PC and thermodilution methods before and after a fluid challenge indicated by the physician. The correlation coefficient was measured, the diagram of Bland and Altman was built and the percentage of error (Critchley and Critchley method) was calculated. The ability of PC to diagnose fluid responsiveness was assessed using a receiver operating characteristics (ROC) curve.

RESULTS

Sixty-two fluid challenges were performed in 37 included patients. After fluid challenge, r(2) was 0.05 (P<0.01), the bias between PC and thermodilution was 0.3 ± 1.2L/min and the percentage of error was 36%. The area of the ROC curve was 0.601 [0.468-0.723].

CONCLUSION

In ICU patients with shock, PC cannot replace thermodilution to diagnose fluid responsiveness.

Vascular procedures in the critically ill obese patient

The increasing societal prevalence of obesity is consequential to the increasing number of critically ill obese patients. Vascular procedures are an essential aspect of care in these patients. This article reviews the general, anatomic, and physiologic considerations pertaining to vascular procedures in critically ill obese patients. In addition, the use of ultrasonography for these procedures is discussed.

Effect of norepinephrine dosage and calibration frequency on accuracy of pulse contour-derived cardiac output

Introduction

Continuous cardiac output monitoring is used for early detection of hemodynamic instability and guidance of therapy in critically ill patients. Recently, the accuracy of pulse contour-derived cardiac output (PCCO) has been questioned in different clinical situations. In this study, we examined agreement between PCCO and transcardiopulmonary thermodilution cardiac output (CO_TCP) in critically ill patients, with special emphasis on norepinephrine (NE) administration and the time interval between calibrations.

Methods

This prospective, observational study was performed with a sample of 73 patients (mean age, 63 ± 13 years) requiring invasive hemodynamic monitoring on a non-cardiac surgery intensive care unit. PCCO was recorded immediately before calibration by CO_TCP. Bland-Altman analysis was performed on data subsets comparing agreement between PCCO and CO_TCP according to NE dosage and the time interval between calibrations up to 24 hours. Further, central artery stiffness was calculated on the basis of the pulse pressure to stroke volume relationship.

Results

A total of 330 data pairs were analyzed. For all data pairs, the mean CO_TCP (±SD) was 8.2 ± 2.0 L/min. PCCO had a mean bias of 0.16 L/min with limits of agreement of -2.81 to 3.15 L/min (percentage error, 38%) when compared to CO_TCP. Whereas the bias between PCCO and CO_TCP was not significantly different between NE dosage categories or categories of time elapsed between calibrations, interchangeability (percentage error <30%) between methods was present only in the high NE dosage subgroup (≥0.1 μg/kg/min), as the percentage errors were 40%, 47% and 28% in the no NE, NE < 0.1 and NE ≥ 0.1 μg/kg/min subgroups, respectively. PCCO was not interchangeable with CO_TCP in subgroups of different calibration intervals. The high NE dosage group showed significantly increased central artery stiffness.

Conclusions

This study shows that NE dosage, but not the time interval between calibrations, has an impact on the agreement between PCCO and CO_TCP. Only in the measurements with high NE dosage (representing the minority of measurements) was PCCO interchangeable with CO_TCP.

Changing paradigms in surgical resuscitation

Patients undergoing emergency surgery typically require resuscitation, either because they are hemorrhaging or because they are experiencing significant internal fluid shifts. Intravascular hypovolemia is common at the time of anesthesia induction and can lead to hemodynamic collapse if not promptly treated. Central pressure monitoring is associated with technical complications and does not improve outcomes in this population. Newer modalities are in use, but they lack validation. Fluid resuscitation is different in bleeding and septic patients. In the former group, it is advisable to maintain a deliberately low blood pressure to facilitate clot formation and stabilization. If massive transfusion is anticipated, blood products should be administered from the outset to prevent the coagulopathy of trauma. Early use of plasma in a ratio approaching 1:1 with red blood cells (RBCs) has been associated with improved outcomes. In septic patients, early fluid loading is recommended. The concept of "goal-directed resuscitation" is based on continuing resuscitation until venous oxygen saturation is normalized. In either bleeding or septic patients, however, the most important goal remains surgical control of the source of pathology, and nothing should be allowed to delay transfer to the operating room. We review the current literature and recommendations for the resuscitation of patients coming for emergency surgery procedures.

Arterial pressure-based cardiac output in septic patients: different accuracy of pulse contour and uncalibrated pressure waveform devices

INTRODUCTION

We compared the ability of two devices estimating cardiac output from arterial pressure-curve analysis to track the changes in cardiac output measured with transpulmonary thermodilution induced by volume expansion and norepinephrine in sepsis patients.

METHODS

In 80 patients with septic circulatory failure, we administered volume expansion (40 patients) or introduced/increased norepinephrine (40 patients). We measured the pulse contour-derived cardiac index (CI) provided by the PiCCO device (CIpc), the arterial pressure waveform-derived CI provided by the Vigileo device (CIpw), and the transpulmonary thermodilution CI (CItd) before and after therapeutic interventions.

RESULTS

The changes in CIpc accurately tracked the changes in CItd induced by volume expansion (bias, -0.20 +/- 0.63 L/min/m2) as well as by norepinephrine (bias, -0.05 +/- 0.74 L/min/m2). The changes in CIpc accurately detected an increase in CItd >or= 15% induced by volume expansion and norepinephrine introduction/increase (area under ROC curves, 0.878 (0.736 to 0.960) and 0.924 (0.795 to 0.983), respectively; P < 0.05 versus 0.500 for both). The changes in CIpw were less reliable for tracking the volume-induced changes in CItd (bias, -0.23 +/- 0.95 L/min/m2) and norepinephrine-induced changes in CItd (bias, -0.01 +/- 1.75 L/min/m2). The changes in CIpw were unable to detect an increase in CItd >or= 15% induced by volume expansion and norepinephrine introduction/increase (area under ROC curves, 0.564 (0.398 to 0.720) and 0.541 (0.377 to 0.700, respectively, both not significantly different from versus 0.500).

CONCLUSIONS

The CIpc was reliable and accurate for assessing the CI changes induced by volume expansion and norepinephrine. By contrast, the CIpw poorly tracked the trends in CI induced by those therapeutic interventions.

Emerging trends in minimally invasive haemodynamic monitoring and optimization of fluid therapy

BACKGROUND

For decades the pulmonary artery catheter has been the mainstay of cardiac output monitoring in critically ill patients, and pressure-based indices of ventricular filling have been used to gauge fluid requirements with acknowledged limitations. In recent years, alternative technologies have become available which are minimally invasive, allow beat-to-beat cardiac output monitoring and permit assessment of fluid requirements by volumetric means and by allowing assessment of heart-lung interaction in mechanically ventilated patients.

METHODS

A qualitative review of the basic science behind the transpulmonary dilution technique used in the measurement of cardiac output, global end-diastolic volume and extravascular lung water; the basic science and validation of pulse contour analysis methods of real-time cardiac output monitoring; the application and limitations of these technologies to guide rational fluid therapy in surgical and critically ill patients.

RESULTS

Transpulmonary dilution techniques correlate well with pulmonary artery catheter-derived measurement of cardiac output. Volumetric measures of preload appear to be superior to central venous and pulmonary artery occlusion pressures. Dynamic indices of preload responsiveness such as stroke volume variation are more useful than static measures in mechanically ventilated patients.

CONCLUSION

In fully mechanically ventilated patients, dynamic measurements of heart-lung interaction such as stroke volume variation are superior to static measures of preload in assessing whether a patient is volume-responsive (i.e. will increase stroke volume in response to a fluid challenge). For patients who are not fully mechanically ventilated, pulse contour analysis allows real-time assessment of increases in cardiac output in response to passive leg-raising.

Perioperative hemodynamic monitoring with transesophageal Doppler technology

Invasive cardiac output (CO) monitoring, traditionally performed with transpulmonary thermodilution techniques, is usually reserved for high-risk patients because of the inherent risks of these methods. In contrast, transesophageal Doppler (TED) technology offers a safe, quick, and less invasive method for routine measurements of CO. After esophageal insertion and focusing of the probe, the Doppler beam interrogates the descending aortic blood flow. On the basis of the measured frequency shift between the emitted and received ultrasound frequency, blood flow velocity is determined. From this velocity, combined with the simultaneously measured systolic ejection time, CO and other advanced hemodynamic variables can be calculated, including estimations of preload, afterload, and contractility. Numerous studies have validated TED-derived CO against reference methods. Although the agreement of CO values between TED and the reference methods is limited (95% limits of agreement: median 4.2 L/min, interquartile range 3.3-5.0 L/min), TED has been shown to accurately follow changes of CO over time, making it a useful device for trend monitoring. TED can be used to guide perioperative intravascular volume substitution and therapy, with vasoactive or inotropic drugs. Various studies have demonstrated a reduced postoperative morbidity and shorter length of hospital stay in patients managed with TED compared with conventional clinical management, suggesting that it may be a valuable supplement to standard perioperative monitoring. We review not only the technical basis of this method and its clinical application but also its limitations, risks, and contraindications.

Noninvasive cardiac output determination: broadening the applicability of hemodynamic monitoring

Although cardiac output (CO) monitoring is usually only used in intensive care units (ICUs) and operating rooms, there is increasing evidence that CO should be determined and optimized as early as possible, even before admission to the ICU, in the care of hemodynamically compromised patients. A variety of different minimally or noninvasive CO determination techniques have been developed, but not all of them are suitable for early hemodynamic monitoring outside the ICU. In this review, the different available methods for CO monitoring are presented and their potential for early hemodynamic assessment is discussed.

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

Bland-Altman analysis is used for assessing agreement between two measurements of the same clinical variable. In the field of cardiac output monitoring, its results, in terms of bias and limits of agreement, are often difficult to interpret, leading clinicians to use a cutoff of 30% in the percentage error in order to decide whether a new technique may be considered a good alternative. This percentage error of ± 30% arises from the assumption that the commonly used reference technique, intermittent thermodilution, has a precision of ± 20% or less. The combination of two precisions of ± 20% equates to a total error of ± 28.3%, which is commonly rounded up to ± 30%. Thus, finding a percentage error of less than ± 30% should equate to the new tested technique having an error similar to the reference, which therefore should be acceptable. In a worked example in this paper, we discuss the limitations of this approach, in particular in regard to the situation in which the reference technique may be either more or less precise than would normally be expected. This can lead to inappropriate conclusions being drawn from data acquired in validation studies of new monitoring technologies. We conclude that it is not acceptable to present comparison studies quoting percentage error as an acceptability criteria without reporting the precision of the reference technique.

Computationally managed bradycardia improved cardiac energetics while restoring normal hemodynamics in heart failure

In acute heart failure, systemic arterial pressure (AP), cardiac output (CO), and left atrial pressure (P (LA)) have to be controlled within acceptable ranges. Under this condition, cardiac energetic efficiency should also be improved. Theoretically, if heart rate (HR) is reduced while AP, CO, and P (LA) are maintained by preserving the functional slope of left ventricular (LV) Starling's curve (S (L)) with precisely increased LV end-systolic elastance (E (es)), it is possible to improve cardiac energetic efficiency and reduce LV oxygen consumption per minute (MVO (2)). We investigated whether this hemodynamics can be accomplished in acute heart failure using an automated hemodynamic regulator that we developed previously. In seven anesthetized dogs with acute heart failure (CO < 70 mL min(-1) kg(-1), P (LA) > 15 mmHg), the regulator simultaneously controlled S (L) with dobutamine, systemic vascular resistance with nitroprusside and stressed blood volume with dextran or furosemide, thereby controlling AP, CO, and P (LA). Normal hemodynamics were restored and maintained (CO; 88 +/- 3 mL min(-1) kg(-1), P (LA); 10.9 +/- 0.4 mmHg), even when zatebradine significantly reduced HR (-27 +/- 3%). Following HR reduction, E (es) increased (+34 +/- 14%), LV mechanical efficiency (stroke work/oxygen consumption) increased (+22 +/- 6%), and MVO (2) decreased (-17 +/- 4%) significantly. In conclusion, in a canine acute heart failure model, computationally managed bradycardia improved cardiac energetic efficiency while restoring normal hemodynamic conditions.

Reliability of continuous cardiac output measurement during intra-abdominal hypertension relies on repeated calibrations: an experimental animal study

INTRODUCTION

Monitoring cardiac output (CO) may allow early detection of haemodynamic instability, aiming to reduce morbidity and mortality in critically ill patients. Continuous cardiac output (CCO) monitoring is recommended in septic or postoperative patients with high incidences of intra-abdominal hypertension (IAH). The aim of the present study was to compare the agreement between three CCO methods and a bolus thermodilution CO technique during acute IAH and volume loading.

METHODS

Ten pigs were anaesthetised and instrumented for haemodynamic measurements. Cardiac output was obtained using CCO by pulse power analysis (PulseCO; LiDCO monitor), using CCO by pulse contour analysis (PCCO; PiCCO monitor) and using CCO by pulmonary artery catheter thermodilution (CCOPAC), and was compared with bolus transcardiopulmonary thermodilution CO (COTCP) at baseline, after fluid loading, at IAH and after an additional fluid loading at IAH. Whereas PulseCO was only calibrated at baseline, PCCO was calibrated at each experimental step.

RESULTS

PulseCO and PCCO underestimated CO, as the overall bias +/- standard deviation was 1.0 +/- 1.5 l/min and 1.0 +/- 1.1 l/min compared with COTCP. A clinically accepted agreement between all of the CCO methods and COTCP was observed only at baseline. Whereas IAH did not influence the CO, increased CO following fluid loading at IAH was only reflected by CCOPAC and COTCP, not by uncalibrated PulseCO and PCCO. After recalibration, PCCO was comparable with COTCP.

CONCLUSIONS

The CO obtained by uncalibrated PulseCO and PCCO failed to agree with COTCP during IAH and fluid loading. In the critically ill patient, recalibration of continuous arterial waveform CO methods should be performed after fluid loading or before a major change in therapy is initiated.

[Minimally invasive hemodynamic monitoring with esophageal echoDoppler]

Hemodynamic monitoring is a key element in the care of the critical patients, providing an unquestionable aid in the attendance to diagnosis and the choice of the adequate treatment. Minimally invasive devices have been emerging over the past few years as an effective alternative to classic monitoring tools. The esophageal echoDoppler is among these. It makes it possible to obtain continuous and minimally invasive monitoring of the cardiac output in addition to other useful parameters by measuring the blood flow rate and the diameter of the thoracic descending aorta, which provides a sufficiently extensive view of the hemodynamic state of the patient and facilitates early detection of the changes produced by a sudden clinical derangement. Although several studies have demonstrated the usefulness of the esophageal Doppler in the surgical scene, there is scarce and dispersed evidence in the literature on its benefits in critical patients. Nevertheless, its advantages make it an attractive element to take into account within the diagnostic arsenal in the intensive care. The purpose of the following article is to describe how it works, its degree of validation with other monitoring methods and the role of esophageal echoDoppler as a minimally invasive monitoring tool for measuring cardiac output in the daily clinical practice, contributing with our own experience in the critical patient.

Closed-loop control of fluid therapy for treatment of hypovolemia

Closed-loop algorithms and resuscitation systems are being developed to control IV infusion rate during early resuscitation of hypovolemia. Although several different physiologic variables have been suggested as an endpoint to guide fluid therapy, blood pressure remains the most used variable for the initial assessment of hemorrhagic shock and the treatment response to volume loading. Closed-loop algorithms use a controller function to alter infusion rate inversely to blood pressure. Studies in hemorrhaged conscious sheep suggest that: (1) a small reduction in target blood pressure can result in a significant reduction in volume requirement; (2) nonlinear algorithms may reduce the risk of increased internal bleeding during resuscitation; (3) algorithm control functions based on proportional-integral, fuzzy logic, or nonlinear decision tables were found to restore and maintain blood pressure equally well. Proportional-integral and fuzzy logic algorithms reduced mean fluid volume requirements compared with the nonlinear decision table; and (4) several algorithms have been constructed to the specific mechanism of injury and the volume expansion properties of different fluids. Closed-loop systems are undergoing translation from animal to patient studies. Future smart resuscitation systems will benefit from new noninvasive technologies for monitoring blood pressure and the development of computer controlled high flow intravenous pumps.

Evaluation of a new arterial pressure-based cardiac output device requiring no external calibration

BACKGROUND

Several techniques have been discussed as alternatives to the intermittent bolus thermodilution cardiac output (COPAC) measurement by the pulmonary artery catheter (PAC). However, these techniques usually require a central venous line, an additional catheter, or a special calibration procedure. A new arterial pressure-based cardiac output (COAP) device (FloTractrade mark, Vigileotrade mark; Edwards Lifesciences, Irvine, CA, USA) only requires access to the radial or femoral artery using a standard arterial catheter and does not need an external calibration. We validated this technique in critically ill patients in the intensive care unit (ICU) using COPAC as the method of reference.

METHODS

We studied 20 critically ill patients, aged 16 to 74 years (mean, 55.5 +/- 18.8 years), who required both arterial and pulmonary artery pressure monitoring. COPAC measurements were performed at least every 4 hours and calculated as the average of 3 measurements, while COAP values were taken immediately at the end of bolus determinations. Accuracy of measurements was assessed by calculating the bias and limits of agreement using the method described by Bland and Altman.

RESULTS

A total of 164 coupled measurements were obtained. Absolute values of COPAC ranged from 2.80 to 10.80 l/min (mean 5.93 +/- 1.55 l/min). The bias and limits of agreement between COPAC and COAP for unequal numbers of replicates was 0.02 +/- 2.92 l/min. The percentage error between COPAC and COAP was 49.3%. The bias between percentage changes in COPAC (DeltaCOPAC) and percentage changes in COAP (DeltaCOAP) for consecutive measurements was -0.70% +/- 32.28%. COPAC and COAP showed a Pearson correlation coefficient of 0.58 (p < 0.01), while the correlation coefficient between DeltaCOPAC and DeltaCOAP was 0.46 (p < 0.01).

CONCLUSION

Although the COAP algorithm shows a minimal bias with COPAC over a wide range of values in an inhomogeneous group of critically ill patients, the scattering of the data remains relative wide. Therefore, the used algorithm (V 1.03) failed to demonstrate an acceptable accuracy in comparison to the clinical standard of cardiac output determination.

Cardiac Output Measured by a New Arterial Pressure Waveform Analysis Method Without Calibration Compared With Thermodilution After Cardiac Surgery

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.