A comparison of transoesophageal echocardiographic Doppler across the aortic valve and the thermodilution technique for estimating cardiac output

Cardiac output estimation using ballistocardiography: a feasibility study in healthy subjects

There is no reliable automated non-invasive solution for monitoring circulation and guiding treatment in prehospital emergency medicine. Cardiac output (CO) monitoring might provide a solution, but CO monitors are not feasible/practical in the prehospital setting. Non-invasive ballistocardiography (BCG) measures heart contractility and tracks CO changes. This study analyzed the feasibility of estimating CO using morphological features extracted from BCG signals. In 20 healthy subjects ECG, carotid/abdominal BCG, and invasive arterial blood pressure based CO were recorded. BCG signals were adaptively processed to isolate the circulatory component from carotid (CCc) and abdominal (CCa) BCG. Then, 66 features were computed on a beat-to-beat basis to characterize amplitude/duration/area/length of the fluctuation in CCc and CCa. Subjects' data were split into development set (75%) to select the best feature subset with which to build a machine learning model to estimate CO and validation set (25%) to evaluate model's performance. The model showed a mean absolute error, percentage error and 95% limits of agreement of 0.83 L/min, 30.2% and - 2.18-1.89 L/min respectively in the validation set. BCG showed potential to reliably estimate/track CO. This method is a promising first step towards an automated, non-invasive and reliable CO estimator that may be tested in prehospital emergencies.

Correlation of Impedance Cardiography-Derived and Cardiac Magnetic Resonance-Derived Stroke Volumes

Cardiac output (CO) and other hemodynamic parameter measurements play an important role in the management of cardiovascular conditions; however, due to limitations of current day technologies, such measurements are either not routinely performed or incorporated into clinical practice. Moreover, measurement of these hemodynamic parameters in the outpatient setting at different time points to assess interval change is currently not feasible. We attempted to validate total-body impedance cardiography-based Non-Invasive Cardiac System (NICaS) derived stroke volume (SV) with that from cardiac magnetic resonance (CMR), a current day gold standard method of assessment. We compared SV, as it is the primary unit of measurement utilized by both technologies. Forty-one consecutive patients undergoing CMR were also investigated by NICaS following CMR. The consistency of non-invasive technology-derived SV measurement was validated by NICaS measurement in 10 subjects, both before and after CMR. Of the 41 enrolled patients; data from 38 patients was adequate for comparison (motion artifact prevented CMR measures in 3 patients). Fourteen patients (37%) were female; mean age was 55 ± 15 years (28-87 years) and body-mass index was 28.7 ± 5.5 kg/m² (20.5-41.9 kg/m²). Hypertrophic cardiomyopathy (9/41) was the most common study indication for CMR. NICaS-derived SV strongly correlated with CMR [NICaS 77 ± 20 ml (31-123 ml) and CMR 84 ± 23 ml (47-132 ml); P < 0.001; r = 0.77; ICC = 0.73]. The Bland-Altman limits of agreement between NICaS and CMR were -26.7% and 39.9%. NICaS-derived SV collected before and after MRI did not differ [80 ± 18 ml (51-102 ml) pre and 76 ± 17 ml (50-99 ml) post; P = 0.0007, Kappa = 1]. Agreement between NICaS-derived and CMR-derived SV was within the acceptable range of boundaries set by the US Food and the Drug Administration. Consistency in SV measurement at different time-points may allow use of this technology to identify interval hemodynamic changes noninvasively.

Hemodynamic monitoring using trans esophageal echocardiography in patients with shock

Circulatory shock is a life-threatening condition responsible for inadequate tissue perfusion. The objectives of hemodynamic monitoring in this setting are multiple: identifying the mechanisms of shock (hypovolemic, distributive, cardiogenic, obstructive); choosing the adequate therapeutic intervention, and evaluating the patient's response. Echocardiography is proposed as a first line tool for this assessment in the intensive care unit. As compared to trans-thoracic echocardiography (TTE), trans-esophageal echocardiography (TEE) offers a better echogenicity and is the best way to evaluate deep anatomic structures. The therapeutic implication of TEE leads to frequent changes in clinical management. It also allows depicting sources of inaccuracy of thermodilution-based hemodynamic monitoring. It is a semi invasive tool with a low rate of complications. The first step in the hemodynamic evaluation of shock is to characterize the mechanisms of circulatory failure among hypovolemia, vasoplegia, cardiac dysfunction, and obstruction. Echocardiographic evaluation includes evaluation of LV systolic and diastolic function, as well as RV function, pericardium, measure of stroke volume and cardiac output, and evaluation of hypovolemia and fluid responsiveness. TEE can be used as a semi-continuous monitoring tool and can be repeated before and after therapeutic interventions (vasopressors, inotropes, fluid therapy, specific treatment such as pericardial effusion evacuation) to evaluate efficacy and tolerance of therapeutic interventions. In conclusion, TEE plays an important role in the management of circulatory failure when TTE is not enough to answer to the questions, although it is not a continuous tool of monitoring. TEE results must be integrated in a global evaluation, the first step being clinical examination. Whether TEE-directed therapy and close hemodynamic monitoring of shock has an impact on outcome remains debated.

Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis

Echocardiography, as a noninvasive hemodynamic evaluation technique, is frequently used in critically ill patients. Different opinions exist regarding whether it can be interchanged with traditional invasive means, such as the pulmonary artery catheter thermodilution (TD) technique. This systematic review aimed to analyze the consistency and interchangeability of cardiac output measurements by ultrasound (US) and TD. Five electronic databases were searched for studies including clinical trials conducted up to June 2019 in which patients’ cardiac output was measured by ultrasound techniques (echocardiography) and TD. The methodological quality of the included studies was evaluated by two independent reviewers who used the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2), which was tailored according to our systematic review in Review Manager 5.3. A total of 68 studies with 1996 patients were identified as eligible. Meta-analysis and subgroup analysis were used to compare the cardiac output (CO) measured using the different types of echocardiography and different sites of Doppler use with TD. No significant differences were found between US and TD (random effects model: mean difference [MD], -0.14; 95% confidence interval, -0.30 to 0.02; P = 0.08). No significant differences were observed in the subgroup analyses using different types of echocardiography and different sites except for ascending aorta (AA) (random effects model: mean difference [MD], -0.37; 95% confidence interval, -0.74 to -0.01; P = 0.05) of Doppler use. The median of bias and limits of agreement were -0.12 and ±0.94 L/min, respectively; the median of correlation coefficient was 0.827 (range, 0.140–0.998). Although the difference in CO between echocardiography by different types or sites and TD was not entirely consistent, the overall effect of meta-analysis showed that no significant differences were observed between US and TD. The techniques may be interchangeable under certain conditions.

Comparison of Cardiac Output of Both 2-Dimensional and 3-Dimensional Transesophageal Echocardiography With Transpulmonary Thermodilution During Cardiac Surgery

OBJECTIVES

To compare agreement and variability of cardiac output measurement of 2-dimensional (2D) and 3D transesophageal echocardiography (TEE) with thermodilution before and after bypass.

DESIGN

Prospective observational study.

SETTING

Two tertiary hospitals.

INTERVENTIONS

Cardiac output (CO) was measured simultaneously with thermodilution and TEE by multiplying either the left ventricular outflow tract area (LVOTA) or aortic valve area (AVA), the velocity-time integral (VTI) of flow at the same site, and heart rate. The LVOTA was calculated using diameter for 2D TEE. Planimetry was used for 3D TEE. The AVA was measured using planimetry.

PARTICIPANTS

The study comprised 82 adult patients undergoing coronary or valve surgery.

MEASUREMENTS AND MAIN RESULTS

One hundred fifty-four complete sets of measurements were obtained (82 prebypass and 72 postbypass). All TEE methods had acceptable correlation and absence of proportional or fixed bias except for the left ventricular outflow tract (LVOT) VTI modal trace method, which had poor correlation and proportional but not fixed bias (regression coefficient [95% confidence interval], bias [percentage of mean CO]): 2D LVOT VTI modal trace 0.67 (0.54-0.80), -36.4%; 2D LVOT VTI outer edge trace 0.96 (0.80-1.12), -15.3%; 2D AVA planimetry 0.96 (0.75-1.18), +4.9%; 3D LVOT area planimetry 1.18 (0.96-1.41), +0.8%; 3D AVA planimetry 1.20 (0.93-1.46), +0.4%. All TEE methods had wide levels of agreement compared with thermodilution (-3.94 to +0.23 L/min, -2.83 to +1.28 L/min, -2.23 to +2.73 L/min, -2.35 to +2.42 L/min, and -2.57 to +2.61 L/min, respectively). Measurement variability was superior for all TEE methods compared with thermodilution before but not after bypass.

CONCLUSIONS

Although limits of agreement of CO measurement with 3D TEE and thermodilution are wide, 2D planimetry of the AVA and continuous wave Doppler may be substituted for thermodilution before and after bypass.

Critical care echocardiography and outcomes in the critically ill

PURPOSE OF REVIEW

Critical care echocardiography offers a comprehensive assessment of cardiac anatomy and function performed by the intensivist at point of care. This has resulted in widespread use of critical care echocardiography in ICUs leading to the question if this increased usage has resulted in improved patient outcomes.

RECENT FINDINGS

Recent studies have evaluated the role of critical care echocardiography in the ICU with an emphasis on establishing accurate diagnosis and measurement of haemodynamic variables. There are no prospective randomized controlled trials that have examined the effect of critical care echocardiography on patient outcomes SUMMARY: Although the effect of critical care echocardiography on patient outcomes has not yet been established, its value as a diagnostic tool has been well demonstrated. We can only assume that its diagnostic capability leads to an improvement in patient outcomes.

Transthoracic echocardiography: an accurate and precise method for estimating cardiac output in the critically ill patient

Background

Cardiac output (CO) monitoring is a valuable tool for the diagnosis and management of critically ill patients. In the critical care setting, few studies have evaluated the level of agreement between CO estimated by transthoracic echocardiography (CO-TTE) and that measured by the reference method, pulmonary artery catheter (CO-PAC). The objective of the present study was to evaluate the precision and accuracy of CO-TTE relative to CO-PAC and the ability of transthoracic echocardiography to track variations in CO, in critically ill mechanically ventilated patients.

Methods

Thirty-eight mechanically ventilated patients fitted with a PAC were included in a prospective observational study performed in a 16-bed university hospital ICU. CO-PAC was measured via intermittent thermodilution. Simultaneously, a second investigator used standard-view TTE to estimate CO-TTE as the product of stroke volume and the heart rate obtained during the measurement of the subaortic velocity time integral.

Results

Sixty-four pairs of CO-PAC and CO-TTE measurements were compared. The two measurements were significantly correlated (r = 0.95; p < 0.0001). The median bias was 0.2 L/min, the limits of agreement (LOAs) were –1.3 and 1.8 L/min, and the percentage error was 25%. The precision was 8% for CO-PAC and 9% for CO-TTE. Twenty-six pairs of ΔCO measurements were compared. There was a significant correlation between ΔCO-PAC and ΔCO-TTE (r = 0.92; p < 0.0001). The median bias was –0.1 L/min and the LOAs were –1.3 and +1.2 L/min. With a 15% exclusion zone, the four-quadrant plot had a concordance rate of 94%. With a 0.5 L/min exclusion zone, the polar plot had a mean polar angle of 1.0° and a percentage error LOAs of –26.8 to 28.8°. The concordance rate was 100% between 30 and –30°. When using CO-TTE to detect an increase in ΔCO-PAC of more than 10%, the area under the receiving operating characteristic curve (95% CI) was 0.82 (0.62–0.94) (p < 0.001). A ΔCO-TTE of more than 8% yielded a sensitivity of 88% and specificity of 66% for detecting a ΔCO-PAC of more than 10%.

Conclusion

In critically ill mechanically ventilated patients, CO-TTE is an accurate and precise method for estimating CO. Furthermore, CO-TTE can accurately track variations in CO.

The Routine Use of the Pulmonary Artery Catheter Should Be Abandoned

The pulmonary artery catheter (PAC) is the most common method of measuring cardiac output in cardiac surgery. However, its use has always been questioned in terms of survival benefit, specifically with regard to the accuracy of its measurements and its invasive nature, with the potential for serious complications. In this review we aimed to develop a clear understanding of the pitfalls of the use of PAC, and discuss its risks and available alternatives. We conclude that there is no indication for the routine use of PAC such that clinicians should carefully consider the clinical risks and benefits on a patient by patient basis.

Minimally invasive beat-by-beat monitoring of cardiac power in normal hearts and during acute ventricular dysfunction

Cardiac power, the product of aortic flow and blood pressure, appears to be a fundamental cardiovascular parameter. The simplified version named cardiac power output (CPO), calculated as the product of cardiac output (CO) in L/min and mean arterial pressure (MAP) in mmHg divided by 451, has shown great ability to predict outcome in a broad spectrum of cardiac disease. Beat‐by‐beat evaluation of cardiac power (PWR) therefore appears to be a possibly valuable addition when monitoring circulatory unstable patients, providing parameters of overall cardiovascular function. We have developed a minimally invasive system for cardiac power measurement, and aimed in this study to compare this system to an invasive method (ttPWR). Seven male anesthetized farm pigs were included. A laptop with in‐house software gathered audio from Doppler signals of aortic flow and blood pressure from the patient monitor to continuously calculate and display a minimally invasive cardiac power trace (uPWR). The time integral per cardiac cycle (uPWR‐integral) represents cardiac work, and was compared to the invasive counterpart (ttPWR‐integral). Signals were obtained at baseline, during mechanically manipulated preload and afterload, before and after induced global ischemic left ventricular dysfunction. We found that the uPWR‐integral overestimated compared to the ttPWR‐integral by about 10% (P < 0.001) in both normal hearts and during ventricular dysfunction. Bland–Altman limits of agreement were at +0.060 and −0.054 J, without increasing spread over the range. In conclusion we find that the minimally invasive system follows its invasive counterpart, and is ready for clinical research of cardiac power parameters.

Ultrasonic evaluation of the heart

PURPOSE OF REVIEW

To discuss the role of echocardiography for the hemodynamic evaluation of critically ill patients.

RECENT FINDINGS

In addition to its crucial role in evaluating heart abnormalities as in the classical cardiological approach, echocardiography is now frequently used by intensivists for noninvasive hemodynamic evaluation of the critically ill patient. Using echocardiography, it is possible to measure cardiac output, intravascular pressures and volumes, systolic and diastolic function of both ventricles, and preload responsiveness. This not only allows characterization of the precise nature of hemodynamic alterations in patients with circulatory and respiratory failure, but also provides guidance for hemodynamic optimization and optimization of ventilatory settings. There are now many data showing how echocardiography can be useful in detecting otherwise unrecognized myocardial depression in sepsis and right ventricular dysfunction in mechanically ventilated patients. The main limitation of echocardiography for hemodynamic monitoring is its intermittent nature. Hence, echocardiography is often combined with other monitoring devices, allowing continuous measurement of flow and triggering new echocardiographic evaluations.

SUMMARY

Echocardiography has now become an important tool for hemodynamic evaluation of the critically ill patient. Echocardiography should be performed in most patients with circulatory and respiratory failure.

Measurements of cardiac output obtained with transesophageal echocardiography and pulmonary artery thermodilution are not interchangeable

BACKGROUND

Echocardiography is increasingly becoming an integrated tool for circulatory evaluation in the intensive care unit and the operating room. Therefore, it is imperative to know the reproducibility of measurements obtained by echocardiography. In this study, a comparison of cardiac output (CO) measurements obtained with transesophageal echocardiography (TEE) and pulmonary artery catheter (PAC) thermodilution (TD) was carried out to test the precision, accuracy and trending ability of CO measurements obtained with TEE.

METHODS

Twenty-five patients completed the study. Each patient was placed in the following successive positions: supine, head-down tilt, head-up tilt, supine, supine with phenylephrine administration, pace heart rate 80 beats per minute (bpm), pace heart rate 110 bpm. TEE CO and PAC CO were measured simultaneously. The agreement was analysed by Bland-Altman plots, and to assess trending ability, a polar plot was constructed.

RESULTS

Both methods showed an acceptable precision 8% (PAC TD) and 16% (TEE). In comparison with PAC TD, the TEE was associated with a bias of -0.22 l/minute [95% confidence interval: -0.54; 0.10], wide limits of agreement (-1.73 l/minute; 1.29 l/minute), a percentage error of 38.6% and a trending ability with a radial degree of 53.6°, corresponding to a poor trending ability.

CONCLUSION

In comparison, CO measurements obtained with TEE and PAC TD had wide limits of agreement, a larger percentage error than would be expected from the precision of the two methods, and a poor trending ability. Thus, TEE is not interchangeable with PAC TD for measuring CO.

Point of care cardiac ultrasound applications in the emergency department and intensive care unit--a review

The use of point of care echocardiography by non-cardiologist in acute care settings such as the emergency department (ED) or the intensive care unit (ICU) is very common. Unlike diagnostic echocardiography, the scope of such point of care exams is often restricted to address the clinical questions raised by the patient's differential diagnosis or chief complaint in order to inform immediate management decisions. In this article, an overview of the most common applications of this focused echocardiography in the ED and ICU is provided. This includes but is not limited to the evaluation of patients experiencing hypotension, cardiac arrest, cardiac trauma, chest pain and patients after cardiac surgery.

Nuclear factor-kappa B mediates one-lung ventilation-induced acute lung injury in rabbits

INTRODUCTION

Several studies have revealed the adverse effect of one-lung ventilation (OLV) on pulmonary function. Nuclear factor-kappa B (NF-κB) is a principal transcription factor of proinflammatory genes. This study was designed to investigate the role of NF-κB in OLV-mediated lung injury.

METHODS

Male rabbits, weighing 2.2 ± 0.3 kg, were randomly divided into five groups: sham tracheostomized (Sham), OLV (V(T) = 10 ml/kg, FiO(2) = 1.0), two-lung ventilation (TLV, V(T) = 10 ml/kg, FiO(2) = 1.0), OLV preceded by the treatment with NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC, 50 mg/kg, i.v.), and TLV with the PDTC pretreatment. Arterial blood gases, lung pathological changes, and production of proinflammatory cytokines (tumor necrosis factor-α and interleukin-8) were assessed. NF-κB activation was determined by electrophoretic mobility shift assay (EMSA) and western blotting of nuclear NF-κB p65.

RESULTS

The OLV significantly decreased the ratio of partial pressure of oxygen and fraction inspired oxygen (PaO(2)/FiO(2)) compared to the Sham group (p < .01). However, the TLV had no evident effect on the PaO(2)/FiO(2) ratio. The pretreatment with PDTC significantly reversed the OLV-induced reduction in the PaO(2)/FiO(2) ratio. The PDTC pretreatment also markedly attenuated the OLV-mediated lung injury and proinflammatory cytokine production. The OLV potentiated the NF-κB DNA binding activity assessed by EMSA and the NF-κB nuclear translocation. The OLV-mediated NF-κB activation was markedly inhibited by the PDTC pretreatment.

CONCLUSION

Our data collectively demonstrate that OLV can cause lung injury through the activation of NF-κB and the production of proinflammatory cytokines. Blocking NF-κB reduces lung inflammation and may be an effective strategy in the management of OLV-induced lung damage.

Echocardiography in the sepsis syndromes

Purpose of the review

Non-invasiveness and instantaneous diagnostic capability are prominent features of the use of echocardiography in critical care. Sepsis and septic shock represent complex situations where early hemodynamic assessment and support are among the keys to therapeutic success. In this review, we discuss the range of applications of echocardiography in the management of the septic patient, and propose an echocardiography-based goal-oriented hemodynamic approach to septic shock.

Recent findings

Echocardiography can play a key role in the critical septic patient management, by excluding cardiac causes for sepsis, and mostly by guiding hemodynamic management of those patients in whom sepsis reaches such a severity to jeopardize cardiovascular function. In recent years, there have been both increasing evidence and diffusion of the use of echocardiography as monitoring tool in the patients with hemodynamic compromise. Also thanks to echocardiography, the features of the well-known sepsis-related myocardial dysfunction have been better characterized. Furthermore, many of the recent echocardiographic indices of volume responsiveness have been validated in populations of septic shock patients.

Conclusion

Although not proven yet in terms of patient outcome, echocardiography can be regarded as an ideal monitoring tool in the septic patient, as it allows (a) first line differential diagnosis of shock and early recognition of sepsis-related myocardial dysfunction; (b) detection of pre-existing cardiac pathology, that yields precious information in septic shock management; (c) comprehensive hemodynamic monitoring through a systematic approach based on repeated bedside assessment; (d) integration with other monitoring devices; and (e) screening for cardiac source of sepsis.

Hemodynamic monitoring in acute heart failure

Hemodynamic monitoring has moved in the last few years from being the holy grail of evaluating patients with acute heart failure to being all but extinct. Recent studies have not demonstrated any sustained benefits from right heart catheterization, and some studies have even suggested harm due to adverse events related to this invasive procedure. It is possible that this lack of efficacy is related to multiple inherent deficiencies in the design of these studies, including the inclusion of patients with chronic heart failure or mild acute heart failure, use of the reduction in pulmonary artery occlusion pressure as the main hemodynamic target for intervention, choice of treatment algorithms, and selection of ambitious long-term efficacy and safety end points. This review discusses the role of hemodynamic monitoring in patients with acute heart failure. We suggest that right heart catheterization should be reserved for patients with acute heart failure and impending respiratory or circulatory failure especially in the presence of a diagnostic or therapeutic dilemma or when encountering acute heart failure or hemodynamic lability refractory to conventional therapy. Therapeutic algorithms emphasizing modern variables for cardiovascular performance and using safer and more efficacious individualized therapies and possibly noninvasive measurement of certain hemodynamic variables may enhance the likelihood of a beneficial effect for hemodynamic guided therapy.

Transoesophageal echocardiography accurately detects cardiac output variation: a prospective comparison with thermodilution in cardiac surgery

BACKGROUND AND OBJECTIVE

Intraoperative Doppler ultrasound can be used to measure cardiac output by transoesophageal echocardiography. Recently, its reliability, when compared to the thermodilution technique, has been questioned. The purpose of this study was to compare intraoperative changes in cardiac output measured by echo-Doppler and by thermodilution in cardiac surgery. We also assessed the agreement between the techniques.

METHODS

Fifty cardiac surgical patients (38 male, 12 female, mean age of 63.4 +/- 14.3 yr) were prospectively included after approval by the Ethics Committee of the Institution. Cardiac output was assessed by thermodilution, with 10 mL saline at 12 degrees C, and simultaneously and blindly by echo-Doppler in deep transgastric view with pulsed wave Doppler at the level of the left ventricular outflow tract. Matched thermodilution cardiac output and echo-Doppler cardiac output measurements were taken three times at the end of expiration, both pre- and post-cardiopulmonary bypass.

RESULTS

Echo-Doppler measurements were obtained in 44 patients (88%). In three patients, Doppler recordings could not be obtained adequately, and three developed left ventricular outflow tract obstruction after bypass. Bland-Altman analysis revealed a bias of 0.015 L min(-1), with narrow limits of agreement (-1.21 to 1.22 L min(-1)) and 29.1% error. Echo-Doppler was accurate (92% sensitivity and 71% specificity, P = 0.008 by receiver operating characteristic curves) for detecting more than 10% of change in thermodilution cardiac output. There were no complications related to the study.

CONCLUSIONS

The agreement between cardiac output by echo-Doppler and by thermodilution is clinically acceptable and transoesophageal echocardiography is a reliable tool to assess significant cardiac output changes in a population of selected patients.

[Pulmonary artery catheter in anaesthesiology and intensive care medicine]

The indication for the use of the pulmonary artery catheter (PAC) in high-risk patients is still a matter of discussion. Observational studies suggested that the use of the PAC did not result in decreased mortality but may even lead to increased mortality and morbidity. Therefore, a number of randomized controlled trials have been performed throughout recent years in patients suffering from sepsis/ARDS, congestive heart failure, multi-organ failure and those undergoing high-risk non-cardiac surgery. The majority of recent randomized studies failed to demonstrate any benefit of the PAC with respect to mortality and morbidity. However, the use of the PAC was also regularly not associated with an increase in morbidity and/or mortality. This review gives an overview of measurement parameters obtained by the current generation of PACs, alternatives to the PAC and recent studies on the use of the PAC in clinical practice.

Comparison of electrical velocimetry and transoesophageal Doppler echocardiography for measuring stroke volume and cardiac output † †Declaration of interest. This study was supported by Osypka Medical GmbH, Berlin, Germany

BACKGROUND

Impedance cardiography (ICG) has been used extensively to estimate stroke volume (SV) and cardiac output (CO) from changes of thoracic electrical bioimpedance (TEB). However, studies comparing ICG with reference methods have questioned the reliability of this approach. Electrical velocimetry (EV) provides a new algorithm to calculate CO from variations in TEB. As the transoesophageal Doppler echocardiographic quantification of CO (TOE-CO) has emerged as a reliable method, the purpose of this study was to determine the limits of agreement between CO estimations using EV (EV-CO) and TOE-CO.

METHODS

Standard ECG electrodes were used for non-invasive EV-CO measurements. These were placed on 37 patients scheduled for coronary artery surgery necessitating transoesophageal echocardiography monitoring. Simultaneous EV-CO and TOE-CO measurements were recorded after induction of anaesthesia. EV-CO was calculated using the Bernstein-Osypka equation. TOE-CO was measured across the aortic valve using continuous-wave Doppler echocardiography and a triangular orifice model.

RESULTS

A significant high correlation was found between the TOE-CO and the EV-CO measurements (r2=0.86). Data were related linearly. The slope of the line (1.10 (se 0.07)) was not significantly different from unity, and the point at which it intersected the ordinate (-0.46 (0.32) litre min(-1)) was not significantly different from zero. Bland-Altman analysis revealed a bias of 0.18 litre min(-1) with narrow limits of agreement (-0.99 to 1.36 litre min(-1)).

CONCLUSIONS

The agreement between EV-CO and TOE-CO is clinically acceptable, and these two techniques can be used interchangeably.

Effective systolic orifice area of the aortic valve: implications for Doppler echocardiographic cardiac output determinations

BACKGROUND

Substantial research using echocardiography has established that stroke volume (SV) or cardiac output (CO) can be measured non-invasively at the level of the aortic valve (AV) with high accuracy. Stroke volume is the product of the velocity time integral occurring at the sampling site and the effective systolic AV orifice area (AVOAeff). Nevertheless, a generally accepted method for the determination of AVOAeff is still lacking.

METHODS

Aortic valve OAeff was measured in 228 consecutive patients scheduled for coronary artery surgery. Two widely adopted methods were applied to approximate the constantly changing orifice area of the AV: (1) the circular orifice model (AVOA-CM), and (2) the triangular orifice model (AVOA-TM). Aortic valve OA-CM assumes the shape of a circle as an appropriately time averaged geometrical model, and AVOA-TM takes the shape of an equilateral triangle for granted.

RESULTS

The AV was easily imaged by echocardiography in both short- and long-axis views in all patients. Relying on AVOA-CM, AVOAeff was 3.49+/-0.77 cm2. AVOA-TM estimates were 2.80+/-0.55 cm2 (mean+/-SD). The results did not agree (bias analysis).

CONCLUSIONS

The echocardiographic measurement of SV or CO at the level of the AV has to be reconsidered.

Hemodynamic assessment of critically ill patients using echocardiography Doppler

PURPOSE OF REVIEW

The evaluation of hemodynamic status in critically ill patients is a leading recommended indication of transesophageal echocardiography in the intensive care unit. Advantages and diagnostic yield of transesophageal echocardiography in this setting are particularly relevant when considering limitations and questioned prognostic impact of pulmonary artery catheterization.

RECENT FINDINGS

Recent clinical studies have been performed to validate and assess the value of transesophageal echocardiography in determining cardiac output, cardiac preload dependence, right ventricular function, and left ventricular filling pressure. In addition, diagnostic capacity and therapeutic impact of transesophageal echocardiography have been widely reported in various intensive care unit settings.

SUMMARY

Transesophageal echocardiography appears well suited for the determination of cardiac index and to track its variations after therapeutic interventions. Although repeated measurements of left ventricular end-diastolic dimension allows to accurately track preload variations, a single determination is not reliable to predict fluid responsiveness in intensive care unit patients. Identification of preload dependence in hemodynamically unstable patients currently tends to rely mainly on dynamic parameters that use cardiopulmonary interactions under mechanical ventilation. Transesophageal echocardiography also allows to adequately assess right ventricular function and left ventricular filling pressure using combined Doppler modalities. Adequate education and training of intensivists and anesthesiologists is crucial to further develop the use of transesophageal echocardiography in the intensive care unit setting. Despite the absence of randomized controlled studies documenting transesophageal echocardiography benefits on patient outcome, present evidence and experience strongly recommend a larger use of echocardiography Doppler for a comprehensive functional hemodynamic assessment of critically ill patients with circulatory failure.

The Effects of Acute Isovolemic Hemodilution on Oxygenation During One-Lung Ventilation

Data on the effects of isovolemic hemodilution (IH) on oxygenation during one-lung ventilation (OLV) are lacking. We studied 47 patients with hemoglobin >14 g/dL who were scheduled for lung surgery (17 with normal lung function [group NL], 17 with chronic obstructive pulmonary disease [COPD] [group COPD], and 13 with COPD as control for time/anesthesia effects [group CTRL]). Anesthesia was standardized. The tracheas were intubated with a double-lumen tube. Ventilatory settings and fraction of inspired oxygen remained constant. The study was performed with patients in the supine position before surgery. OLV was initiated for 15 min. Two-lung ventilation was reinstituted, and IH was performed (500 mL); an identical volume of hydroxyethyl starch was administered. Subsequently, OLV was again performed for 15 min. In group CTRL, the same sequences of OLV were performed without IH. At the end of each period of OLV, pulmonary mechanics and blood gases were recorded. Data were analyzed by analysis of variance (mean +/- sd). In group NL and group CTRL, the arterial oxygen partial pressure remained constant, whereas it decreased in group COPD from 119 +/- 21 mm Hg before IH to 86 +/- 16 mm Hg after IH (P <0.01). Mild IH impairs gas exchange during OLV in COPD patients, but not in patients with normal lung function.

Non-invasive cardiac output monitoring

Outcomes in the management of critically ill patients may be improved using goal-directed peri-operative haemodynamic monitoring. A conservative approach may no longer be acceptable but in view of the significant morbidity associated with balloon tipped flow directed pulmonary artery catheters a non-invasive approach would be preferable. In this review we consider the different non-invasive techniques available and discuss the advantages and disadvantages of each technique.

Therapeutic impact of intra-operative transoesophageal echocardiography during noncardiac surgery

The impact of transoesophageal echocardiography on haemodynamic management during elective noncardiac surgery was assessed during this observational prospective database analysis. Ninety-nine consecutive patients were studied, who were at risk of intra-operative myocardial ischaemia or haemodynamic instability (Class II indications) and were undergoing vascular, visceral or chest surgery. A total of 165 new echocardiographic findings were recorded. Based on these findings changes in drug therapy were made in 47% and changes in fluid therapy in 24% of patients. Left ventricular wall motion abnormalities were seen in 32% and other relevant diagnoses made in 10%. Echocardiography showed a significant impact on drug therapy in patients with pre-operative systolic wall motion abnormalities (vasodilators: OR = 7.1, CI 95% = 2.1/24.0; vasopressors: OR = 3.3, CI 95% = 1.2/9.1) and patients with a history of left heart failure (vasodilators: OR = 5.2, CI 95% = 1.0/31.4). Fluid therapy was significantly influenced by echocardiographic findings during liver and lung transplantation (50% compared with 24% during other surgical interventions, p < 0.05).

Survey of observer variation in transesophageal echocardiography: comparison of anesthesiology and cardiology literature

OBJECTIVE

Transesophageal echocardiographic examination tends to be somewhat observer and experience dependent, and observer bias can arise easily when data are calculated and interpreted by unskilled, nonblinded, or single observers. The study plan was to see whether authors have adequately described how observer bias is minimized in their studies. Thus, a study was conducted systematically reviewing methods reported in transesophageal echocardio graphy articles in peer-reviewed anesthesiology journals versus those reported in peer-reviewed cardiology journals.

INTERVENTIONS

After MEDLINE searches of the literature published from 1997 through 1999, the authors investigated 56 anesthesiology reports and 56 randomly selected, year-matched cardiology reports. An 8-item questionnaire was developed that examined several factors: the number of observers and their experience levels, whether observers were blind to clinical data, whether low-quality images were excluded, the use of on-line or off-line analysis, and observer variability.

MAIN RESULTS

The analysis revealed inadequacies in reporting of important information that relates to bias and quality in 91.1% of anesthesiology and 98.2% of cardiology articles. Observer variability was not reported in 50.0% of the anesthesiology reports and 67.9% of the cardiology reports; however, difference between the 2 bodies of literature was not significant. The journal impact factor was significantly higher for the cardiology literature than for the anesthesiology literature (2.42 [0.386-10.893] v 1.07 [0.664-3.439]; median [range], p < 0.001).

CONCLUSION

Articles reviewed had at least some inadequacies in reporting the methods to minimize observer bias in both the anesthesiology and cardiology literature. Reporting methodology standards in TEE examinations remain to be established.

Use of multi-plane transoesophageal echocardiography in visualization of the main hepatic veins and acquisition of Doppler sonography curves. Comparison with the transabdominal approach

The role of multi-plane transoesophageal echocardiography (TOE) in the visualization of the three main hepatic veins and acquisition of Doppler sonography curves has not been established. We have studied this diagnostic option of TOE in 34 patients during general anaesthesia. The findings were compared with the results of conventional transabdominal sonography (TAS). Using TOE, each of the three main hepatic veins could be visualized in all patients. In contrast, TAS allowed adequate two-dimensional visualization of the right, middle, and left hepatic vein in only 97%, 85%, and 61% of the patients, respectively. Adequate Doppler tracings of the right and middle hepatic vein could be obtained in 100% and 97% of the patients by TOE and in 91% and 50% of the patients by TAS. Doppler tracings of the left hepatic vein could only be acquired in 18% of the patients by TOE, but in 47% of the patients by TAS. As blood flow may be calculated from the diameter of the vessel, velocity time integral of the Doppler curve and heart rate, TOE may provide an interesting non-invasive tool to monitor blood flow in the right and middle hepatic vein.

Transesophageal echocardiography (TEE) in the critical care patient

Critically ill patients often pose special diagnostic problems to the clinician, intensified by limited physical examination findings and difficulty in transportation to imaging suites. Mechanical ventilation and the limited ability to position the patient make transthoracic echocardiography difficult. Transesophageal echocardiographic (TEE) imaging, however, is well suited to the critical care patient and is frequently used to evaluate hemodynamic status, the presence of vegetations, a cardioembolic source, and an intracardiac cause of hypoxemia. Using proper precautions, TEE can be performed safely in unstable patients and frequently leads to important changes in management.