Comparison of esCCO and transthoracic echocardiography for non-invasive measurement of cardiac output intensive care

The Validation of Cardiac Index and Stroke-Volume Variation Measured by the Pulse-Wave Transit Time-Analysis Versus Conventional Pulse-Contour Analysis After Off-Pump Coronary Artery Bypass Grafting: Observational Study

OBJECTIVE

To compare the reliability of cardiac index (CI) and stroke-volume variation (SVV) measured by the pulse-wave transit-time (PWTT) method using estimated continuous cardiac output (esCCO) technique with conventional pulse-contour analysis after off-pump coronary artery bypass grafting (OPCAB).

DESIGN

A single-center, prospective, observational study.

SETTING

At a 1,000-bed university hospital.

PARTICIPANTS

A total of 21 patients were enrolled after elective OPCAB.

INTERVENTIONS

The study authors performed a method comparison study with simultaneous measurement of CI and SVV based on the esCCO technique (CI_esCCO and esSVV, correspondingly) and pulse-contour analysis (CI_PCA and SVV_PCA, correspondingly). As a secondary analysis, they also assessed the trending ability of CI_esCCO versus CI_PCA. MEASUREMENTS AND MAIN RESULTS: The authors analyzed 178 measurement pairs for CI, and 174 pairs for SVV during the 10 study stages. The mean bias between CI_esCCO and CI_PCA was 0.06 L min/m², with limits of agreement of ± 0.92 L min/m² and a percentage error (PE) of 35.3%. The analysis of the trending ability of CI measured by PWTT revealed a concordance rate of 70%. The mean bias between esSVV and SVV_PCA was -6.1%, with limits of agreement of ± 15.5% and a PE of 137%.

CONCLUSIONS

The overall performance of CI_esCCO and esSVV versus CI_PCA and SVV_PCA is not clinically acceptable. A further improvement of the PWTT algorithm may be required for an accurate and precise assessment of CI and SVV.

Comparison of parameter types for the calibration of noninvasive continuous cardiac output monitoring of patients undergoing lumbar spinal surgery in the prone position

BACKGROUND

Cardiac output (CO) decreases on reversing the patient's position to the prone position. Estimated continuous cardiac output (esCCO) systems can noninvasively and continuously monitor CO calibrated by patient information or transesophageal echocardiogram (TEE).

OBJECTIVE

To compare the accuracy, precision, and trending ability of two calibration methods of CO estimation in patients in prone position.

METHODS

The CO estimates calibrated by TEE (esT) and patient information (esP) of 26 participants were included. CO was collected at four time points. The accuracy and precision of agreement were evaluated using the Bland-Altman method. A four-quadrant plot was used for trending ability analysis.

RESULTS

The bias between esP and TEE and between esT and TEE was 0.2594 L/min (95% limits of agreement (LoA): -1.8374 L/min to 2.3562 L/min) and 0.0337 L/min (95% LoA: -0.7381 L/min to 0.8055 L/min), respectively. A strong correlation was found between ΔesP and ΔTEE (p< 0.001, CCC = 0.700) and between ΔesT and ΔTEE (p< 0.001, CCC = 0.794). The concordance rates between ΔesP and ΔTEE and between ΔesT and ΔTEE were 91.9% and 97.1%, respectively.

CONCLUSION

Despite limited accuracy and precision, esP showed acceptable trending ability. The trending ability of esCCO calibrated by the reference TEE value was comparable with that of TEE.

Optimization of the target strategy of perioperative infusion therapy based on monitoring data of central hemodynamics in order to prevent complications

Enhanced Recovery After Surgery (ERAS) protocols are increasingly used in the perioperative period around the world. The concept of goal-directed fluid therapy (GDT) is a key element of the ERAS protocols. Inadequate perioperative infusion therapy can lead to a number of complications, including the development of an infectious process, namely surgical site infections, pneumonia, urinary tract infections. Optimal infusion therapy is difficult to achieve with standard parameters (e.g., heart rate, blood pressure, central venous pressure), so there are various methods of monitoring central hemodynamics - from invasive, minimally invasive to non-invasive. The latter are increasingly used in clinical practice. The current evidence base shows that perioperative management, specifically the use of GDT guided by real-time, continuous hemodynamic monitoring, helps clinicians maintain a patient's optimal fluid balance. The manuscript presents the analytical data, which describe the benefits and basic principles of perioperative targeted infusion therapy based on central hemodynamic parameters to reduce the risk of complications.

Estimation of cardiac stroke volume from radial pulse waveform by artificial neural network

BACKGROUND AND OBJECTIVES

Stroke volume (SV) and cardiac output (CO) are the key indicators for the evaluation of cardiac function and hemodynamic status during the perioperative period, which are very important in the detection and treatment of cardiovascular diseases. Traditional CO and SV measurement methods have problems such as complex operation, low precision and poor generalization ability.

METHODS

In this paper, a method for estimating stroke volume based on cascade artificial neural network (ANN) and time domain features of radial pulse waveform (SV_ANN) was proposed. The simulation datasets of 4000 radial pulse waveforms and stroke volume (SV_meas) were generated by a 55 segment transmission line model of the human systemic vasculature and a recursive algorithm. The ANN was trained and tested by 10-fold cross-validation, and compared with 12 traditional models.

RESULTS

Experimental results showed that the Pearson correlation coefficients and mean difference between SV_ANN and SV_meas (R=0.95, mean standard deviation (SD) = 0.00 ± 6.45) were better than the best results of the 12 traditional models. Moreover, as increasing the number of training samples, the performance improvement of the ANN (R=0.94(Δ + 0.04), mean ± SD = 0.00 ± 6.38(Δ± 2.02)) was better than the other best model, namely, multiple linear regression model (MLR) (R=0.93(Δ + 0.03), mean ± SD = 0.00 ± 6.99(Δ± 1.50)).

CONCLUSIONS

A method is proposed to estimate cardiac stroke volume by the ANN with time domain features of radial pulse wave. It avoids the complicated modeling process based on hemodynamics within traditional models, improves the estimation accuracy of SV, and has a good generalization ability.

Japanese Acupuncture: A Complementary Approach to the Meridian Balance Method

The association of acupuncture points requires realization of synergistic combinations to be as effective as possible while avoiding possible aggravations. To this end, the meridian balance method is an effective tool. It is based on the 6 systems of Richard T.-F. Tan, MD, which derive from 6 principles of traditional knowledge: (1) Chinese meridian-name sharing; (2) branching meridians (Bie-Jing); (3) interior-exterior pairs (Biao-Li); (4) Chinese clock opposite; (5) Chinese clock neighbor; and (6) the same meridian. However, the results seem to unstable over time, and, therefore, synergies with "root" treatment based on Japanese meridian therapy could help stabilize the therapeutic effects of the meridian balance method. Japanese meridian therapy uses pulse diagnosis to identify 4 basic primary patterns: (1) Liver Deficiency, generally treated with a combination of acupuncture points LR8-KI10; (2) Kidney Deficiency, treated with LU 5-KI 7; (3) Spleen Deficiency, treated with PC 7-SP 3; and (4) Lung Deficiency, treated with SP 3-LU 9. After reviewing the main principles of Japanese acupuncture, a nondogmatic approach coupling Japanese meridian therapy with Dr. Tan's balance method is proposed in order to use the best of each of the 2 methods in an integrative approach.

Continuous Estimation of Cardiac Output in Critical Care: A Noninvasive Method Based on Pulse Wave Transit Time Compared with Transpulmonary Thermodilution

Purpose

Estimation of cardiac output (CO) and evaluation of change in CO as a result of therapeutic interventions are essential in critical care medicine. Whether noninvasive tools estimating CO, such as continuous cardiac output (esCCOTM) methods, are sufficiently accurate and precise to guide therapy needs further evaluation. We compared esCCOTM with an established method, namely, transpulmonary thermodilution (TPTD). Patients and Methods. In a single center mixed ICU, esCCOTM was compared with the TPTD method in 38 patients. The primary endpoint was accuracy and precision. The cardiac output was assessed by two investigators at baseline and after eight hours.

Results

In 38 critically ill patients, the two methods correlated significantly (r = 0.742). The Bland–Altman analysis showed a bias of 1.6 l/min with limits of agreement of −1.76 l/min and +4.98 l/min. The percentage error for CO_esCCO was 47%. The correlation of trends in cardiac output after eight hours was significant (r = 0.442), with a concordance of 74%. The performance of CO_esCCO could not be linked to the patient's condition.

Conclusion

The accuracy and precision of the esCCOTM method were not clinically acceptable for our critical patients. EsCCOTM also failed to reliably detect changes in cardiac output.

Validation of electrical velocimetry in resuscitation of patients undergoing liver transplantation. Observational study

Major hemodynamic changes are frequently noted during liver transplantation (LT). We evaluated the performance of electrical velocimetry (EV) as compared to that of TEE in SV optimization during liver transplantation. This was an observational study in 32 patients undergoing LT. We compared SV values measured simultaneously by EV (SV_EV) and TEE (SV_TEE) at baseline 30 min after induction, at the end of dissection phase, 30 min after anhepatic phase, 30 min after reperfusion. We also evaluated the reliability of EV to track changes In SV before and after 49 fluid challenges. Finally, the SV variation (SVV) and pulse pressure variation (PPV) were tested as predictors for volume responsiveness, defined as an increase in SV ≥ 10% after 250 ml of colloid. For 112 paired SV data, the overall correlation was 0.76 and bias (limits of agreement) 0.3 (- 29 to 29) ml percentage error 62%. The EV was able to track changes in SV with a concordance rate of 97%, and a sensitivity and specificity of 93% to detect a positive fluid challenge. The AUC values (with 95% confidence intervals) for SVV and PPV were 0.68 (0.52-0.83) and 0.72 (0.57-0.86), respectively, indicating low predictive capacity in these setting. The absolute values of SV derived from EV did not agree with SV derived from TEE. However, EV was able to track the direction of changes in SV during hemodynamic management of patients undergoing liver transplantation.Clinical trial registration: Clinicaltrials.gov Identifier: NCT03228329 prospectively Registered on 13-July-2017.

Clinically applicable model-based method, for physiologically accurate flow waveform and stroke volume estimation

BACKGROUND AND OBJECTIVES

Cardiovascular dysfunction can be more effectively monitored and treated, with accurate, continuous, stroke volume (SV) and/or cardiac output (CO) measurements. Since direct measurements of SV/CO are highly invasive, clinical measures are often discrete, or if continuous, can require recalibration with a discrete SV measurement after hemodynamic instability. This study presents a clinically applicable, non-additionally invasive, physiological model-based, SV and CO measurement method, which does not require recalibration during or after hemodynamic instability.

METHODS AND RESULTS

The model's ability to predict flow profiles and SV is assessed in an animal trial, using endotoxin to induce sepsis in 5 pigs. Mean percentage error between beat-to-beat SV measured from an aortic flow probe and estimated by the model was -2%, while 90% of estimations fell within -24.2% and +27.9% error. Error between estimated and measured changes in mean SV following interventions was less than 30% for 4 out of the 5 pigs. Correlations between model estimated and probe measured flow, for each pig and hemodynamic interventions, was r² = 0.58 - 0.96, with 21 of the 25 pig intervention stages having r²  >  0.80.

CONCLUSION

The results demonstrate the model accurately estimates and tracks changes in flow profiles and resulting SV, without requiring model recalibration.

Evaluation of pulse wave transit time analysis for non-invasive cardiac output quantification in pregnant patients

Pregnant patients undergoing minimally-invasive foetoscopic surgery for foetal spina bifida have a need to be subjected to advanced haemodynamic monitoring. This observational study compares cardiac output as measured by transpulmonary thermodilution monitoring with the results of non-invasive estimated continuous cardiac output monitoring. Transpulmonary thermodilution-based pulse contour analysis was performed for usual anaesthetic care, while non-invasive estimated continuous cardiac output monitoring data were additionally recorded. Thirty-five patients were enrolled, resulting in 199 measurement time points. Cardiac output measurements of the non-invasive estimated continuous cardiac output monitoring showed a weak correlation with the corresponding thermodilution measurements (correlation coefficient: 0.44, R2: 0.19; non-invasive estimated continuous cardiac output: 7.4 [6.2-8.1]; thermodilution cardiac output: 8.9 [7.8-9.8]; p ≤ 0.001), while cardiac index experienced no such correlation. Furthermore, neither stroke volume nor stroke volume index correlated with the corresponding thermodilution-based data. Even though non-invasive estimated continuous cardiac output monitoring consistently underestimated the corresponding thermodilution parameters, no trend analysis was achievable. Summarizing, we cannot suggest the use of non-invasive estimated continuous cardiac output monitoring as an alternative to transpulmonary thermodilution for cardiac output monitoring in pregnant patients undergoing minimally-invasive foetoscopic surgery for spina bifida.

[Meta-analyses on measurement precision of non-invasive hemodynamic monitoring technologies in adults]

An ideal non-invasive monitoring system should provide accurate and reproducible measurements of clinically relevant variables that enables clinicians to guide therapy accordingly. The monitor should be rapid, easy to use, readily available at the bedside, operator-independent, cost-effective and should have a minimal risk and side effect profile for patients. An example is the introduction of pulse oximetry, which has become established for non-invasive monitoring of oxygenation worldwide. A corresponding non-invasive monitoring of hemodynamics and perfusion could optimize the anesthesiological treatment to the needs in individual cases. In recent years several non-invasive technologies to monitor hemodynamics in the perioperative setting have been introduced: suprasternal Doppler ultrasound, modified windkessel function, pulse wave transit time, radial artery tonometry, thoracic bioimpedance, endotracheal bioimpedance, bioreactance, and partial CO₂ rebreathing have been tested for monitoring cardiac output or stroke volume. The photoelectric finger blood volume clamp technique and respiratory variation of the plethysmography curve have been assessed for monitoring fluid responsiveness. In this manuscript meta-analyses of non-invasive monitoring technologies were performed when non-invasive monitoring technology and reference technology were comparable. The primary evaluation criterion for all studies screened was a Bland-Altman analysis. Experimental and pediatric studies were excluded, as were all studies without a non-invasive monitoring technique or studies without evaluation of cardiac output/stroke volume or fluid responsiveness. Most studies found an acceptable bias with wide limits of agreement. Thus, most non-invasive hemodynamic monitoring technologies cannot be considered to be equivalent to the respective reference method. Studies testing the impact of non-invasive hemodynamic monitoring technologies as a trend evaluation on outcome, as well as studies evaluating alternatives to the finger for capturing the raw signals for hemodynamic assessment, and, finally, studies evaluating technologies based on a flow time measurement are current topics of clinical research.

Best practice & research clinical anaesthesiology: Advances in haemodynamic monitoring for the perioperative patient: Perioperative cardiac output monitoring

Less invasive or even completely non-invasive haemodynamic monitoring technologies have evolved during the last decades. Even established, invasive devices such as the pulmonary artery catheter and transpulmonary thermodilution have still an evidence-based place in the perioperative setting, albeit only in special patient populations. Accumulating evidence suggests to use continuous haemodynamic monitoring, especially flow-based variables such as stroke volume or cardiac output to prevent occult hypoperfusion and, consequently, decrease morbidity and mortality perioperatively. However, there is still a substantial gap between evidence provided by randomised trials and the implementation of haemodynamic monitoring in daily clinical routine. Given the fact that perioperative morbidity and mortality are higher than anticipated and anaesthesiologists are in charge to deal with this problem, the recent advances in minimally invasive and non-invasive monitoring technologies may facilitate more widespread use in the operating theatre, as in addition to costs, the degree of invasiveness of any monitoring tool determines the frequency of its application, at least perioperatively. This review covers the currently available invasive, non-invasive and minimally invasive techniques and devices and addresses their indications and limitations.

Cardiac output and stroke volume variation measured by the pulse wave transit time method: a comparison with an arterial pressure-based cardiac output system

Hemodynamic monitoring is mandatory for perioperative management of cardiac surgery. Recently, the estimated continuous cardiac output (esCCO) system, which can monitor cardiac output (CO) non-invasively based on pulse wave transit time, has been developed. Patients who underwent cardiovascular surgeries with hemodynamics monitoring using arterial pressure-based CO (APCO) were eligible for this study. Hemodynamic monitoring using esCCO and APCO was initiated immediately after intensive care unit admission. CO values measured using esCCO and APCO were collected every 6 h, and stroke volume variation (SVV) data were obtained every hour while patients were mechanically ventilated. Correlation and Bland-Altman analyses were used to compare APCO and esCCO. Welch's analysis of variance, and four-quadrant plot and polar plot analyses were performed to evaluate the effect of time course, and the trending ability. A p-value < 0.05 was considered statistically significant. Twenty-one patients were included in this study, and 143 and 146 datasets for CO and SVV measurement were analyzed. Regarding CO, the correlation analysis showed that APCO and esCCO were significantly correlated (r = 0.62), and the bias ± precision and percentage error were 0.14 ± 1.94 (L/min) and 69%, respectively. The correlation coefficient, bias ± precision, and percentage error for SVV evaluation were 0.4, - 3.79 ± 5.08, and 99%, respectively. The time course had no effects on the biases between CO and SVV. Concordance rates were 80.3 and 75.7% respectively. While CO measurement with esCCO can be a reliable monitor after cardiovascular surgeries, SVV measurement with esCCO may require further improvement.

Cardiac Output Measurements Based on the Pulse Wave Transit Time and Thoracic Impedance Exhibit Limited Agreement With Thermodilution Method During Orthotopic Liver Transplantation

BACKGROUND

Orthotopic liver transplantation (OLT) is characterized by significant intraoperative hemodynamic variability. Accurate and real-time cardiac output (CO) monitoring aids clinical decision making during OLT. The purpose of this study is to compare accuracy, precision, and trending ability of CO estimation obtained noninvasively using pulse wave transit time (estimated continuous cardiac output [esCCO; Nihon Kohden, Tokyo, Japan]) or thoracic bioimpedance (ICON; Osypka Medical GmbH, Berlin, Germany) to thermodilution cardiac output (TDCO) measured with a pulmonary artery catheter.

METHODS

Nineteen patients undergoing OLT were enrolled. CO measurements were collected with esCCO, ICON, and thermodilution at 5 time points: (T1) pulmonary artery catheter insertion; (T2) surgical incision; (T3) portal reperfusion; (T4) hepatic arterial reperfusion; and (T5) abdominal closure. The results were analyzed with Bland-Altman plot, percentage error (the percentage of the difference between the CO estimated with the noninvasive monitoring device and CO measured with the thermodilution technique), 4-quadrant plot with concordance rate (the percentage of the total number of points in the I and III quadrant of the 4-quadrant plot), and concordance correlation coefficient (a measure of how well the pairs of observations deviate from the 45-degree line of perfect agreement).

RESULTS

Although TDCO increased at T3-T5, both esCCO and ICON failed to track the changes of CO with sufficient accuracy and precision. The mean bias of esCCO and ICON compared to TDCO were -2.0 L/min (SD, ±2.7 L/min) and -3.3 L/min (SD, ±2.8 L/min), respectively. The percentage error was 69% for esCCO and 77% for ICON. The concordance correlation coefficient was 0.653 (95% confidence interval [CI], 0.283-0.853) for esCCO and 0.310 (95% CI, -0.167 to 0.669) for ICON. Nonetheless, esCCO and ICON exhibited reasonable trending ability of TDCO (concordance rate: 95% [95% CI, 88-100] and 100% [95% CI, 93-100]), respectively. The mean bias was correlated with systemic vascular resistance (SVR) and arterial elastance (Ea) for esCCO (SVR, r = 0.610, 95% CI, 0.216-0.833, P < .0001; Ea, r = 0.692, 95% CI, 0.347-0.872; P < .0001) and ICON (SVR, r = 0.573, 95% CI, 0.161-0.815, P < .0001; Ea, r = 0.612, 95% CI, 0.219-0.834, P < .0001).

CONCLUSIONS

The noninvasive CO estimation with esCCO and ICON exhibited limited accuracy and precision, despite with reasonable trending ability, when compared to TDCO, during OLT. The inaccuracy of esCCO and ICON is especially large when SVR and Ea were decreased during the neohepatic phase. Further refinement of the technology is desirable before noninvasive techniques can replace TDCO during OLT.

A review of hemodynamic monitoring techniques, methods and devices for the emergency physician

The emergency department (ED) is frequently the doorway to the intensive care unit (ICU) for a significant number of critically ill patients presenting to the hospital. Hemodynamic monitoring (HDM) which is a key component in the effective management of the critically ill patient presenting to the ED, is primarily concerned with assessing the performance of the cardiovascular system and determining the correct therapeutic intervention to optimise end-organ oxygen delivery. The spectrum of hemodynamic monitoring ranges from simple clinical assessment and routine bedside monitoring to point of care ultrasonography and various invasive monitoring devices. The clinician must be aware of the range of available techniques, methods, interventions and technological advances as well as possess a sound approach to basic hemodynamic monitoring prior to selecting the optimal modality. This article comprises an in depth discussion of an approach to hemodynamic monitoring techniques and principles as well as methods of predicting fluid responsiveness as it applies to the ED clinician. We review the role, applicability and validity of various methods and techniques that include; clinical assessment, passive leg raising, blood pressure, finger based monitoring devices, the mini-fluid challenge, the end-expiratory occlusion test, central venous pressure monitoring, the pulmonary artery catheter, ultrasonography, bioreactance and other modern invasive hemodynamic monitoring devices.

Pilot Study: Estimation of Stroke Volume and Cardiac Output from Pulse Wave Velocity

Background

Transesophageal echocardiography (TEE) is increasingly replacing thermodilution pulmonary artery catheters to assess hemodynamics in patients at high risk for cardiovascular morbidity. However, one of the drawbacks of TEE compared to pulmonary artery catheters is the inability to measure real time stroke volume (SV) and cardiac output (CO) continuously. The aim of the present proof of concept study was to validate a novel method of SV estimation, based on pulse wave velocity (PWV) in patients undergoing cardiac surgery.

Methods

This is a retrospective observational study. We measured pulse transit time by superimposing the radial arterial waveform onto the continuous wave Doppler waveform of the left ventricular outflow tract, and calculated SV (SV_PWV) using the transformed Bramwell-Hill equation. The SV measured by TEE (SV_TEE) was used as a reference.

Results

A total of 190 paired SV were measured from 28 patients. A strong correlation was observed between SV_PWV and SV_TEE with the coefficient of determination (R²) of 0.71. A mean difference between the two (bias) was 3.70 ml with the limits of agreement ranging from -20.33 to 27.73 ml and a percentage error of 27.4% based on a Bland-Altman analysis. The concordance rate of two methods was 85.0% based on a four-quadrant plot. The angular concordance rate was 85.9% with radial limits of agreement (the radial sector that contained 95% of the data points) of ± 41.5 degrees based on a polar plot.

Conclusions

PWV based SV estimation yields reasonable agreement with SV measured by TEE. Further studies are required to assess its utility in different clinical situations.

Monitoring high-risk patients: minimally invasive and non-invasive possibilities

Over the past decades, there has been considerable progress in the field of less invasive haemodynamic monitoring technologies. Substantial evidence has accumulated, which supports the continuous measurement and optimization of flow-based variables such as stroke volume, that is, cardiac output, in order to prevent occult hypoperfusion and consequently to improve patients' outcome in the perioperative setting. However, there is a striking gap between the developments in haemodynamic monitoring and the increasing evidence to implement defined treatment protocols based on the measured variables, and daily clinical routine. Recent trials have shown that perioperative morbidity and mortality is higher than anticipated. This emphasizes the need for the anaesthesia community to address this issue and promotes the implementation of proven concepts into clinical practice in order to improve patients' outcome, especially in high-risk patients. The advances in minimally invasive and non-invasive monitoring techniques can be seen as a driving force in this respect, as the degree of invasiveness of any monitoring tool determines the frequency of its application, especially in the operating room (OR). From this point of view, we are very confident that some of these minimally invasive and non-invasive haemodynamic monitoring technologies will become an inherent part of our monitoring armamentarium in the OR and in the intensive care unit (ICU).

Estimated continuous cardiac output based on pulse wave transit time in off-pump coronary artery bypass grafting: a comparison with transpulmonary thermodilution

To evaluate the accuracy of estimated continuous cardiac output (esCCO) based on pulse wave transit time in comparison with cardiac output (CO) assessed by transpulmonary thermodilution (TPTD) in off-pump coronary artery bypass grafting (OPCAB). We calibrated the esCCO system with non-invasive (Part 1) and invasive (Part 2) blood pressure and compared with TPTD measurements. We performed parallel measurements of CO with both techniques and assessed the accuracy and precision of individual CO values and agreement of trends of changes perioperatively (Part 1) and postoperatively (Part 2). A Bland-Altman analysis revealed a bias between non-invasive esCCO and TPTD of 0.9 L/min and limits of agreement of ±2.8 L/min. Intraoperative bias was 1.2 L/min with limits of agreement of ±2.9 L/min and percentage error (PE) of 64 %. Postoperatively, bias was 0.4 L/min, limits of agreement of ±2.3 L/min and PE of 41 %. A Bland-Altman analysis of invasive esCCO and TPTD after OPCAB found bias of 0.3 L/min with limits of agreement of ±2.1 L/min and PE of 40 %. A 4-quadrant plot analysis of non-invasive esCCO versus TPTD revealed overall, intraoperative and postoperative concordance rate of 76, 65, and 89 %, respectively. The analysis of trending ability of invasive esCCO after OPCAB revealed concordance rate of 73 %. During OPCAB, esCCO demonstrated poor accuracy, precision and trending ability compared to TPTD. Postoperatively, non-invasive esCCO showed better agreement with TPTD. However, invasive calibration of esCCO did not improve the accuracy and precision and the trending ability of method.

[Validation during exercise of a new device for cardiac output measurement using pulse wave transit time (comparison EsCCO(®) vs. Physioflow(®))]

OBJECTIVES

EsCCO is a novel non-invasive continuous cardiac output monitoring system based on pulse wave transit time already validated at rest. The aim of our study was to compare cardiac output measurements obtained simultaneously by EsCCO(®) (Q˙cOP) and impedance cardiography (Physioflow(®) ; Q˙cIMP), in healthy subjects.

PATIENTS AND METHODS

Eight healthy subjects (age: 31±9 years, weight: 76±10kg, height: 179±5cm) realized two exercise tests: an incremental ergocycle test performed until exertion (Pmax=269±48W) and a constant load exercise (P=163±27W). Comparison between measurements (Q˙cOP versus Q˙cIMP) obtained during the first test allowed to evaluate the accuracy of the device. Reliability was determined on three repeated measures during the second test, realized at ventilatory threshold.

RESULTS

Correlation coefficient between both methods is 0.88 (P<0.01). Mean difference is 0.04±1.49L/min (95 % limits of agreement: +2.94 to -3.00L/min) and only 3/74 measures are not included between the limits of agreement. At high intensity and for cardiac output over than 15 L/min, Q˙cOP signal is lost in almost half the time. Concerning reliability, reproducibility coefficient is 0.87 (P<0.05), only 1.8 % of this variability is due to the method.

CONCLUSION

EsCCO(®) measurements are accurate, reliable and allow a good estimation of cardiac output on healthy subjects. The signal lost observed for high cardiac output levels (>15L/min) can limit its utilization during very high intensity exercise.

Comparison of the ability of two continuous cardiac output monitors to measure trends in cardiac output: estimated continuous cardiac output measured by modified pulse wave transit time and an arterial pulse contour-based cardiac output device

Estimated continuous cardiac output (esCCO), a noninvasive technique for continuously measuring cardiac output (CO), is based on modified pulse wave transit time, which in turn is determined by pulse oximetry and electrocardiography. However, its trending ability has never been evaluated in patients undergoing non-cardiac surgery. Therefore, this study examined esCCO's ability to detect the exact changes in CO, compared with currently available arterial waveform analysis methods, in patients undergoing kidney transplantation. CO was measured using an esCCO system and arterial pressure-based CO (APCO), and compared with a corresponding intermittent bolus thermodilution CO (ICO) method. Percentage error and statistical methods, including concordance analysis and polar plot analysis, were used to analyze results from 15 adult patients. The difference in the CO values between esCCO and ICO was -0.39 ± 1.15 L min(-1) (percentage error, 35.6 %). And corrected precision for repeated measures was 1.16 L min(-1) (percentage error for repeated measures, 36.0 %). A concordance analysis showed that the concordance rate was 93.1 %. The mean angular bias was -1.8° and the radial limits of agreement were ±37.6°. The difference between the APCO and ICO CO values was 0.04 ± 1.37 L min(-1) (percentage error, 42.4 %). And corrected precision for repeated measures was 1.37 L min(-1) (percentage error for repeated measures, 42.5 %). The concordance rate was 89.7 %, with a mean angular bias of -3.3° and radial limits of agreement of ±42.2°. This study demonstrated that the trending ability of the esCCO system is not clinically acceptable, as judged by polar plots analysis; however, its trending ability is clinically acceptable based on a concordance analysis, and is comparable with currently available arterial waveform analysis methods.

Advances in photoplethysmography: beyond arterial oxygen saturation

PURPOSE

Photoplethysmography permits continuous measurement of heart rate and peripheral oxygen saturation and has been widely used to inform clinical decisions. Recently, a myriad of noninvasive hemodynamic monitoring devices using this same technology have been increasingly available. This narrative review aims to summarize the principles that form the basis for the function of these devices as well as to comment on trials evaluating their accuracy and clinical application.

PRINCIPAL FINDINGS

Advanced monitoring devices extend photoplethysmography technology beyond measuring oxygen concentration and heart rate. Quantification of respiratory variation of the photoplethysmographic waveform reflects respiratory variation of the arterial pressure waveform and can be used to gauge volume responsiveness. Both the volume-clamp and physiocal techniques are extensions of conventional photoplethysmography and permit continuous measurement of finger arterial blood pressure. Finger arterial pressure waveforms can subsequently inform estimations of cardiac output.

CONCLUSIONS

Although respiratory variations of the plethysmographic waveform correlate only modestly with the arterial blood pressure waveform, fluid responsiveness can be relatively consistently assessed using both approaches. Continuous blood pressure measurements obtained using the volume-clamp technique may be as accurate as conventional brachial noninvasive blood pressure measurements. Most importantly, clinical comparative effectiveness studies are still needed in order to determine if these technologies can be translated into improvement of relevant patient outcomes.

Ability of esCCO to track changes in cardiac output

BACKGROUND

We investigated whether cardiac output measured with pulse wave transit time (esCCO, Nihon Kohden, Tokyo, Japan) is able to track changes in cardiac output induced by an increase in preload (volume expansion/passive leg-raising) or by changes in vasomotor tone (variation in norepinephrine dosage) in critically ill patients.

METHODS

Eighty patients for whom the decision to give fluid (500 mL of saline over 15 min) (n=20), to perform passive leg-raising (n=20), and to increase (n=20) or to decrease (n=20) norepinephrine were included by the physician. Cardiac output was measured with pulse wave transit time (CO-esCCO) and transthoracic echocardiography (CO-TTE) before and after therapeutic intervention.

RESULTS

Comparison between CO-TTE and CO-esCCO showed a bias of -0.7 l min(-1) and limits of agreement of -4.4 to 2.9 l min(-1), before therapeutic intervention and a bias of -0.5 l min(-1) and limits of agreement of -4.2 to 3.2 l min(-1) after therapeutic intervention. Bias was correlated with systemic vascular resistance (r(2)=0.60, P<0.0001). Percentage error was 61% before and 59% after therapeutic intervention. Considering the overall data (n=80), the concordance rate was 84%, polar plot analysis revealed an angular bias (sd) of -11°(35°) and radial limits of agreement of (sd 50°). With regard to passive leg-raising and volume expansion groups (n=40), the concordance rate was 83%, the angular bias (sd) was -20°(36°) and radial limits of agreement ( 50°). Considering variations in norepinephrine dosage groups (n=40), the concordance rate was 86%, the angular bias (sd) was -1.8°(33°) and radial limits of agreement (40°).

CONCLUSIONS

esCCO was not able to track changes in cardiac output, induced by an increase in preload or by variations in vasomotor tone. Therefore, esCCO cannot guide haemodynamic interventions in critically ill patients.

Pulse Wave Transit Time Measurements of Cardiac Output in Septic Shock Patients: A Comparison of the Estimated Continuous Cardiac Output System with Transthoracic Echocardiography

Background

We determined reliability of cardiac output (CO) measured by pulse wave transit time cardiac output system (esCCO system; CO_esCCO) vs transthoracic echocardiography (CO_TTE) in mechanically ventilated patients in the early phase of septic shock. A secondary objective was to assess ability of esCCO to detect change in CO after fluid infusion.

Methods

Mechanically ventilated patients admitted to the ICU, aged >18 years, in sinus rhythm, in the early phase of septic shock were prospectively included. We performed fluid infusion of 500ml of crystalloid solution over 20 minutes and recorded CO by EsCCO and TTE immediately before (T0) and 5 minutes after (T1) fluid administration. Patients were divided into 2 groups (responders and non-responders) according to a threshold of 15% increase in CO_TTE in response to volume expansion.

Results

In total, 25 patients were included, average 64±15 years, 15 (60%) were men. Average SAPSII and SOFA scores were 55±21.3 and 13±2, respectively. ICU mortality was 36%. Mean cardiac output at T0 was 5.8±1.35 L/min by esCCO and 5.27±1.17 L/min by CO_TTE. At T1, respective values were 6.63 ± 1.57 L/min for esCCO and 6.10±1.29 L/min for CO_TTE. Overall, 12 patients were classified as responders, 13 as non-responders by the reference method. A threshold of 11% increase in CO_esCCO was found to discriminate responders from non-responders with a sensitivity of 83% (95% CI, 0.52-0.98) and a specificity of 77% (95% CI, 0.46-0.95).

Conclusion

We show strong correlation esCCO and echocardiography for measuring CO, and change in CO after fluid infusion in ICU patients.

Intraoperative management of heart-lung interactions: "from hypothetical prediction to improved titration"

Extensive literature describes the suitability of dynamic parameters to predict responsiveness in fluid. However, based on heart-lung interactions, these parameters can have serious limitations, including the use of protective lung ventilation. Although the latter seems to be beneficial for healthy patients undergoing high-risk surgery, the intraoperative interpretation of dynamic parameters to predict fluid responsiveness can be hazardous. In this context, the attending physician could, alternatively, titrate the need of fluids with a small fluid challenge, which remains unaffected by low tidal volume, the presence of arrhythmia, or the presence of spontaneous ventilation. When intraoperative prediction of fluid responsiveness is required in mechanically ventilated patients, "improved" titration should be preferred to a hypothetical prediction.

Relationship between stroke volume and pulse pressure during blood volume perturbation: a mathematical analysis

Arterial pulse pressure has been widely used as surrogate of stroke volume, for example, in the guidance of fluid therapy. However, recent experimental investigations suggest that arterial pulse pressure is not linearly proportional to stroke volume. However, mechanisms underlying the relation between the two have not been clearly understood. The goal of this study was to elucidate how arterial pulse pressure and stroke volume respond to a perturbation in the left ventricular blood volume based on a systematic mathematical analysis. Both our mathematical analysis and experimental data showed that the relative change in arterial pulse pressure due to a left ventricular blood volume perturbation was consistently smaller than the corresponding relative change in stroke volume, due to the nonlinear left ventricular pressure-volume relation during diastole that reduces the sensitivity of arterial pulse pressure to perturbations in the left ventricular blood volume. Therefore, arterial pulse pressure must be used with care when used as surrogate of stroke volume in guiding fluid therapy.

Can we obtain a noninvasive and continuous estimation of cardiac output? Comparison between three noninvasive methods

Cardiac output (CO) is often desirable for assessing the hemodynamic condition of a patient, especially in critically ill cardiac patients. Various noninvasive methods are available for this purpose. Inert gas rebreathing (IGR) and 2D-Doppler echocardiography methods have been validated. Based on the relationship between pulse wave transit time and stroke volume, the VISMO® provides an estimated continuous cardiac output (esCCO) measurement using only an electrocardiogram, pulse oximeter wave, and cuff arterial blood pressure. Doppler echocardiography is being currently used in every day practice in this setting and IGR is a validated method, thus we wanted to assess the agreement between these 3 methods for noninvasive CO calculation and reproducibility of esCCO. Patients followed in our cardiology department received on the same day a CO analysis by esCCO, Doppler echocardiography and IGR. Thirty-four patients were included (16 women, mean age 65 ± 15 years). Bland and Altman plots showed a good agreement between IGR and 2D-Doppler echocardiography (bias = 0.31 L/minute). Though there was also an agreement between esCCO and the other 2, the bias was rather large: 1.18 L/minute with IGR and 1.51 L/min with 2D-Doppler echo. The intraclass correlation coefficient was poor whatever the methods. However, esCCO had a satisfactory reproducibility and accuracy compared rather well with the other 2. This method could be suitable for patient screening and monitoring.

Can simulation help to answer the demand for echocardiography education?

There has been a recent explosion of education and training in echocardiography in the specialties of anesthesiology and critical care. These devices, by their impact on clinical management, are changing the way surgery is performed and critical care is delivered. A number of international bodies have made recommendations for training and developed examinations and accreditations.The challenge to medical educators in this area is to deliver the training needed to achieve competence into already over-stretched curricula.The authors found an apparent increase in the use of simulators, with proven efficacy in improving technical skills and knowledge. There is still an absence of evidence on how it should be included in training programs and in the accreditation of certain levels.There is a conviction that this form of simulation can enhance and accelerate the understanding and practice of echocardiography by the anesthesiologist and intensivists, particularly at the beginning of the learning curve.

Less invasive methods of advanced hemodynamic monitoring: principles, devices, and their role in the perioperative hemodynamic optimization

The monitoring of the cardiac output (CO) and other hemodynamic parameters, traditionally performed with the thermodilution method via a pulmonary artery catheter (PAC), is now increasingly done with the aid of less invasive and much easier to use devices. When used within the context of a hemodynamic optimization protocol, they can positively influence the outcome in both surgical and non-surgical patient populations. While these monitoring tools have simplified the hemodynamic calculations, they are subject to limitations and can lead to erroneous results if not used properly. In this article we will review the commercially available minimally invasive CO monitoring devices, explore their technical characteristics and describe the limitations that should be taken into consideration when clinical decisions are made.