A new technique for measurement of cardiac output by thermodilution in man

The use of Guyton's approach to the control of cardiac output for clinical fluid management

Infusion of fluids is one of the most common medical acts when resuscitating critically ill patients. However, fluids most often are given without consideration of how fluid infusion can actually improve tissue perfusion. Arthur Guyton's analysis of the circulation was based on how cardiac output is determined by the interaction of the factors determining the return of blood to the heart, i.e. venous return, and the factors that determine the output from the heart, i.e. pump function. His theoretical approach can be used to understand what fluids can and cannot do. In his graphical analysis, right atrial pressure (RAP) is at the center of this interaction and thus indicates the status of these two functions. Accordingly, trends in RAP and cardiac output (or a surrogate of cardiac output) can provide important guides for the cause of a hemodynamic deterioration, the potential role of fluids, the limits of their use, and when the fluid is given, the response to therapeutic interventions. Use of the trends in these values provide a physiologically grounded approach to clinical fluid management.

Measuring Absolute Coronary Flow and Microvascular Resistance by Thermodilution: JACC Review Topic of the Week

Diagnosing coronary microvascular dysfunction remains challenging, primarily due to the lack of direct measurements of absolute coronary blood flow (Q) and microvascular resistance (Rμ). However, there has been recent progress with the development and validation of continuous intracoronary thermodilution, which offers a simplified and validated approach for clinical use. This technique enables direct quantification of Q and Rμ, leading to precise and accurate evaluation of the coronary microcirculation. To ensure consistent and reliable results, it is crucial to follow a standardized protocol when performing continuous intracoronary thermodilution measurements. This document aims to summarize the principles of thermodilution-derived absolute coronary flow measurements and propose a standardized method for conducting these assessments. The proposed standardization serves as a guide to ensure the best practice of the method, enhancing the clinical assessment of the coronary microcirculation.

Hemodynamic monitoring in liver transplantation 'the hemodynamic system'

PURPOSE OF REVIEW

The purpose of this article is to provide a comprehensive review of hemodynamic monitoring in liver transplantation.

RECENT FINDINGS

Radial arterial blood pressure monitoring underestimates the aortic root arterial blood pressure and causes excessive vasopressor and worse outcomes. Brachial and femoral artery monitoring is well tolerated and should be considered in critically ill patients expected to be on high dose pressors. The pulmonary artery catheter is the gold standard of hemodynamic monitoring and is still widely used in liver transplantation; however, it is a highly invasive monitor with potential for serious complications and most of its data can be obtained by other less invasive monitors. Rescue transesophageal echocardiography relies on few simple views and should be available as a standby to manage sudden hemodynamic instability. Risk of esophageal bleeding from transesophageal echocardiography in liver transplantation is the same as in other patient populations. The arterial pulse waveform analysis based cardiac output devices are minimally invasive and have the advantage of real-time beat to beat monitoring of cardiac output. No hemodynamic monitor can improve clinical outcomes unless integrated into a goal-directed hemodynamic therapy. The hemodynamic monitoring technique should be tailored to the patient's medical status, surgical technique, and the anesthesiologist's level of expertise.

SUMMARY

The current article provides a review of the current hemodynamic monitoring systems and their integration in goal-directed hemodynamic therapy.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Comparison between Cardiac Output and Pulmonary Vascular Pressure Measured by Indirect Fick and Thermodilution Methods

INTRODUCTION

Right heart catheterization (RHC) is a diagnostic procedure, the main purpose of which is to diagnose pulmonary hypertension and investigate its etiology and treatability. In addition to measuring blood pressure in heart chambers, it includes estimating cardiac output (CO) and calculation of pulmonary vascular resistance (PVR) derived from the CO. There are two common methods to evaluate the CO-the indirect Fick method and the thermodilution method. Depending on the clinical conditions, either of the two may be considered better. Several studies have showed that, in most cases, there is no difference between measurements rendered by the two methods. Other studies have raised suspicion of a discrepancy between the two methods in a substantial number of patients. A clear opinion on this matter is missing.

AIM

To evaluate the agreement between the values of the CO and PVR found by the thermodilution and indirect Fick methods.

METHODS

We retrospectively included patients that underwent RHC in Kaplan Medical Center during the last two years with a measurement of the CO using both the thermodilution and the indirect Fick methods. The measurements obtained upon RHC and the clinical data of the patients were collected. The values of the CO and PVR measured or calculated using the two methods were compared for each patient.

RESULTS

We included 55 patients that met the inclusion criteria in this study. The mean CO measured by the thermodilution method was 4.94 ± 1.17 L/min and the mean CO measured by the indirect Fick method was 5.82 ± 1.97 L/min. The mean PVR calculated using the thermodilution method was 3.33 ± 3.04 Woods' units (WU) and the mean PVR calculated using the indirect Fick method was 2.71 ± 2.76 WU. Among the patients with normal mPAP, there was a strong and statistically significant correlation between the PVR values calculated by the two methods (Peasron's R² = 0.78, p-value = 0.004), while among the patients with elevated mPAP, the correlation between the PVR values calculated by the two methods was not statistically significant.

CONCLUSION

The findings of this small study demonstrate that, in a proportion of patients, the indirect Fick method and thermodilution method classify the PVR value differently. In our experience, it seems that, in these patients, the indirect Fick method misclassified patients with a pathological finding as normal. We, therefore, recommend that upon performing RHC, at least in patients with mPAP > 25 mmHg, both the thermodilution and indirect Fick methods be performed and, whenever they disagree, the values obtained from the thermodilution method should be preferred.

Accuracy of a noninvasive estimated continuous cardiac output measurement under different respiratory conditions: a prospective observational study

PURPOSE

The estimated continuous cardiac output (esCCO) system was recently developed as a noninvasive hemodynamic monitoring alternative to the thermodilution cardiac output (TDCO). However, the accuracy of continuous cardiac output measurements by the esCCO system compared to TDCO under different respiratory conditions remains unclear. This prospective study aimed to assess the clinical accuracy of the esCCO system by continuously measuring the esCCO and TDCO.

METHODS

Forty patients who had undergone cardiac surgery with a pulmonary artery catheter were enrolled. We compared the esCCO with TDCO from mechanical ventilation to spontaneous respiration through extubation. Patients undergoing cardiac pacing during esCCO measurement, those receiving treatment with an intra-aortic balloon pump, and those with measurement errors or missing data were excluded. In total, 23 patients were included. Agreement between the esCCO and TDCO measurements was evaluated using Bland-Altman analysis with a 20 min moving average of the esCCO.

RESULTS

The paired esCCO and TDCO measurements (939 points before extubation and 1112 points after extubation) were compared. The respective bias and standard deviation (SD) values were 0.13 L/min and 0.60 L/min before extubation, and - 0.48 L/min and 0.78 L/min after extubation. There was a significant difference in bias before and after extubation (P < 0.001); the SD before and after extubation was not significant (P = 0.315). The percentage errors were 25.1% before extubation and 29.6% after extubation, which is the criterion for acceptance of a new technique.

CONCLUSION

The accuracy of the esCCO system is clinically acceptable to that of TDCO under mechanical ventilation and spontaneous respiration.

Validation of cardiac output estimation using the fourth-generation FloTrac/EV1000™ system in patients undergoing robotic-assisted off-pump coronary artery bypass surgery

The pulmonary artery catheter (PAC)-despite its invasiveness-remains the gold standard for cardiac output (CO) monitoring. The FloTrac system, a less invasive hemodynamic monitor has been developed, which estimates CO using arterial pressure waveform analysis without external calibration. Recently, an upgraded version of FloTrac system with improved algorithm to follow changes in vascular resistance was introduced into the market. The aim of this study was to assess the reliability of the CO estimated from the fourth-generation FloTrac/EV1000 system (CO_FT) compared to that measured with PAC using the thermodilution method (CO_PAC) during robotic-assisted off-pump coronary artery bypass (OPCAB) surgery. CO_FT and CO_PAC were obtained simultaneously at 4 predefined time points during robotic-assisted OPCAB: 5 min after the induction of general anesthesia (T1), after starting one-lung ventilation (T2), after capnothorax (T3), and after mini-thoracotomy was performed (T4). The agreement of data was investigated by Bland-Altman analysis. Thirty-four patients were initially enrolled. After exclusion, 32 patients and a total of 128 paired CO measurements were obtained. The overall bias was 1.46 L/min, the 95% limits of agreements were - 3.40 to 6.33 L/min, and the percentage error was 72.98%. Regression analysis of the systemic vascular resistance index (SVRI) and the bias between CO_PAC and CO_FT showed that the bias was moderately correlated with the SVRI (r² = 0.43; p < 0.0001). Despite a software upgrade, the reliability of the fourth-generation FloTrac/EV1000™ system during robotic-assisted OPCAB to estimate CO was not acceptable, especially in patients with low SVRI.

Noninvasive evaluation of the hemodynamic status in patients after heart transplantation or left ventricular assist device implantation

INTRODUCTION

Hemodynamic assessment is crucial after heart transplantation (HTX) or left ventricular assist device (LVAD) implantation. Gold-standard is invasive assessment via thermodilution (TD). Noninvasive pulse contour analysis (NPCA) is a new technology that is supposed to determine hemodynamics completely noninvasive. We aimed to validate this technology in HTX and LVAD patients and conducted a prospective single-center cohort study.

METHODS

Patients after HTX or LVAD implantation underwent right heart catheterization including TD. NPCA using the CNAP Monitor (V.5.2.14; CNSystems Medizintechnik AG, Graz, Austria) was performed simultaneously. Three TD measurements were compared with simultaneous NPCA measurements for hemodynamic assessment. To describe the agreement between TD and NPCA, Bland-Altman analysis was done.

RESULTS

In total, 28 patients were prospectively enrolled (HTX: n = 10, LVAD: n = 18). Bland-Altman analysis revealed a mean bias of +1.05 l/min (limits of agreement ± 4.09 l/min, percentage error 62.1%) for cardiac output (CO). In LVAD patients, no adequate NPCA signal could be obtained. In 5 patients (27.8%), any NPCA signal could be detected, but was considered as low signal quality.

CONCLUSION

In conclusion, according to our limited data in a small cohort of HTX and LVAD patients, NPCA using the CNAP Monitor seems not to be suitable for noninvasive evaluation of the hemodynamic status.

The interplay between pressure, flow, and resistance in neonatal pulmonary hypertension

Pulmonary hypertension, conventionally defined by absolute pulmonary artery pressure, is the result of a range of diagnoses that can result in clinical problems in neonatal practice. Causes include persistent pulmonary hypertension of the newborn, congenital heart disease, and left heart dysfunction, as well as the normally high pulmonary artery resistance in neonates. Elucidating the cause of pulmonary hypertension is vital to guide appropriate management. A first principles approach based on hemodynamic calculations provides a framework for the diagnostic work up and subsequent therapy. Central to this is the equation 'pressure = flow x resistance' and knowledge of factors contributing to flow and resistance and their impact on pulmonary artery pressure. While formal, accurate, calculation of each element is usually not required or deliverable in small infants, clinical and echocardiographic parameters, combined with an understanding of the interplay between pressure, flow, and resistance, significantly improves the assessment and management of neonatal pulmonary hemodynamics.

Comparison of Accuracy of Estimation of Cardiac Output by Thermodilution Versus the Fick Method Using Measured Oxygen Uptake

The thermodilution (TD) method is routinely used for the estimation of cardiac output (Q̇_C). However, its accuracy, compared with the gold-standard Fick method, where systemic oxygen uptake (V̇O₂) is directly measured, and Q̇_C calculated from V̇O₂ and the arterio-venous oxygen difference ("direct" Fick), has not been well validated. The present study determined the agreement between TD and Fick methods in consecutive patients who underwent pulmonary artery catheterization for a broad range of clinical conditions. This is a subanalysis of a previous study comparing the indirect versus Fick method based on a prospective, consecutive patient registry of 253 patients who underwent pulmonary artery catheterization for clinical indications at a single center between 1999 and 2005. We included patients that had an estimation of Q̇_C both by the Fick method using measured V̇O₂ by exhaled gas analyses from timed Douglas bag collections and by TD. Cardiac index was classified as low when ≤2.2 L/min/m² or normal when >2.2 L/min/m². The median (25th, 75th percentile) age of the cohort was 59 (50,67) years, and 50% were female. A total of 43.5% had normal left ventricular function by ventriculography, and 25.7% had ischemic heart disease. Median overall Fick and TD Q̇_C were 4.4 (3.5, 5.5) and 4.3 (3.7, 5.2) L/min, respectively (p = 0.04). The median absolute percent error between Fick and TD Q̇_C was 17.5 (7.7, 28.4)%, with a typical error of 0.88 L/min (95% confidence interval [CI] 0.82 to 0.95). Median absolute percent error was comparable in the low (n = 118) and normal Q̇_CI (n = 135) groups (16.9% vs 18.9%, respectively, p = 0.88). typical error was 0.3 (95% CI 0.27 to 0.33) and 0.49 (95% CI 0.45 to 0.55) L/min/m² in that comparison. Percent error >25% between Fick and TD Q̇_C was observed in over 30% of patients. Overall, Fick and TD Q̇_C modestly correlated (R_s = 0.64, p <0.001), with a nondirectional error introduced by TD Q̇_C [mean bias of 0.21 (-2.2, 2.7) L/min]. There was poor agreement between TD and the gold-standard Fick method, highlighting the limitations of making clinical decisions based on TD.

Left ventricular dysfunction and intra-ventricular dyssynchrony in idiopathic pulmonary arterial hypertension

BACKGROUND

Left ventricular (LV) filling pressures are normal in idiopathic pulmonary arterial hypertension (IPAH). However, direct and indirect interactions between the RV and LV can affect LV performance. We explored LV strain and LV intra-ventricular dyssynchrony in IPAH using feature tracking CMR (CMR-FT).

METHODS

Seventy IPAH patients and 40 healthy volunteers were included. Patients underwent CMR and right heart catheterisation. The 4-chamber cine was used to calculate LV longitudinal strain (Ell_LV). LV circumferential (Ecc_LV) and radial strain (Err_LV) were derived from a short axis cine. LV longitudinal, circumferential and radial intra-ventricular dyssynchrony indices were calculated.

RESULTS

There were no differences between the IPAH and healthy volunteer group in LV ejection fraction (66.1% vs 64.2% p = 0.6672). Ecc_LV (-29.1 vs -32.1 p = 0.0323) and Ell_LV (-16.6 vs -23.7 p < 0.0001) were lower in IPAH. In patients with more severe disease, there was greater impairment of Err_LV compared to mild disease (50.9 vs 87.5 P < 0.0001). LV synchrony was impaired in all directions in IPAH. Err_LV was associated with RV ejection fraction (r = 0.66), RV end-systolic volume index (r = -0.59), pulmonary vascular resistance (PVR)(r = 0.51) and stroke volume index (SVI)(r = 0.44). In a multivariate model with age, SVI and PVR, Err_LV (HR 0.970 p = 002) and radial dyssynchrony (HR 3.759 p < 0.0001) independently predicted survival.

CONCLUSION

In IPAH, LV is dyssynchronous with impaired function. Measures of LV strain and intraventricular synchrony were associated with known markers of disease severity. These LV variables which are likely to be related to ventricular interaction, may add incremental value to known prognostic variables in IPAH.

A comparison of ClearSight noninvasive cardiac output and pulmonary artery bolus thermodilution cardiac output in cardiac surgery patients

BACKGROUND

The ClearSight system measures blood pressure non-invasively and determines cardiac output by analyzing the continuous pressure waveform. We performed a multi-center clinical study in China to test the equivalence of cardiac output measured with the ClearSight system (CSCO) and cardiac output measured with the pulmonary artery catheter bolus thermodilution (TDCO) method.

METHODS

We included adult patients undergoing cardiac surgery in three Chinese hospitals and measured TDCO and CSCO simultaneously after induction of anesthesia. Hemodynamic stability was required during measurement of TDCO and CSCO. At least four TDCO determinations were performed. The corresponding CSCO was determined as the average over a 30-s period following the injection of each bolus. A data pair for the comparison included the average of three or four accepted TDCO values and the average of the matching CSCO values. Main outcomes included Bland-Altman analysis of bias and standard deviation (SD) and the percentage error (PE).

RESULTS

One hundred twenty-five subjects were enrolled, and 122 TDCO and CSCO data pairs were available for analysis. Ninety-five (75.4%) data pairs were collected in hemodynamically stable conditions, mean (SD) CSCO was 4.21 (0.78) l/min, and mean TDCO was 3.90 (0.67) l/min. Bias was 0.32 (0.51) l/min, and PE was 25.2%. Analyzing all 122 data pairs resulted in a mean CSCO of 4.19 (0.82) l/min and a mean TDCO of 3.83 (0.71) l/min. Resulting bias was 0.36 (0.53) l/min, and PE was 26.4%.

CONCLUSIONS

CSCO and TDCO agreed with a low systematic bias. Besides, mean PE was well below the pre-defined 30%. Hemodynamic stability only had a small impact on the analysis. We conclude that CSCO is equivalent to TDCO in cardiac surgery patients. The trial was retrospectively registered in ClinicalTrials.gov, identifier NCT03807622 ; January 17, 2019.

Application of perioperative hemodynamics today and potentials for tomorrow

Hemodynamic (HD) monitoring remains integral to the assessment and management of perioperative and critical care patients. This review article seeks to provide an update on the different types of flow-guided HD monitoring technologies available, highlight their limitations, and review the therapies associated with the application of these technologies. Additionally, we will also comment on the expanding roles of HD monitoring in the future.

Lithium dilution cardiac output measurements in isoflurane-anaesthetised goats: Jugular versus cephalic lithium chloride administration

The administration of lithium chloride (LiCl) for cardiac output (CO) measurement via a peripheral instead of a central vein has been described previously as a valid alternative route in pigs and dogs. The aim of the study was to compare CO measurements after administration of LiCl using two peripheral veins, cephalic or jugular, in goats. Ten adult, female, experimental goats undergoing bilateral stifle arthrotomy were recruited for the study. Paired CO measurements were taken two minutes apart during stable conditions in isoflurane-anaesthetised goats. Forty-two paired CO measurements were taken in total, and the median (range) of paired CO measurement per goat were 4.5 (3-6). The mean (SD) CO using the cephalic and jugular vein for injection of LiCl was 5.28 (1.29) L min^-1 and 5.20 (1.24) L min^-1 respectively. The Bland-Altman analysis showed an acceptable agreement with a mean bias of 1.33% with limits of agreement (LoA) of -18.43 to 21.09%. The percentage of error was 25%. The four-quadrant plot analysis showed a poor agreement (71%) between the two routes. The polar plot showed a poor trending ability. An 86% inclusion rate (18/21 points) was reached with a ± 35° radial sector size. The findings revealed that the agreement between the two routes is not as precise as the authors expected, however the results are comparable with studies published previously.

Effect of thermodilution injectate volume and temperature on the accuracy and precision of cardiac output measurements for healthy anesthetized horses

OBJECTIVE

To compare the accuracy and precision of cardiac output (CO) measurements derived from 4 thermodilution protocols that used different injectate temperatures and volumes in healthy adult horses.

ANIMALS

8 healthy adult horses.

PROCEDURES

Horses were anesthetized and instrumented with Swan-Ganz catheters. The CO was derived from each of 4 thermodilution protocols (IV injection of physiologic saline [0.9% NaCl] solution chilled to < 5 °C at volumes of 1 mL/15 kg of body weight [protocol A; control], 1 mL/25 kg [protocol B], and 1 mL/35 kg [protocol C] or maintained at 17 °C at a volume of 1 mL/15 kg [protocol D]) 3 times during each of 5 measurement cycles, with a 30-minute interval between cycles. During each measurement cycle, protocol A was performed first, and protocols B, C, and D were performed in a randomized order. Mean CO and within-subject variance in CO were compared among the 4 protocols.

RESULTS

Mean CO did not differ significantly among the 4 protocols. The within-subject variance for CO measurements derived from protocols C and D, but not protocol B, was significantly greater than that for protocol A (control).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that, in healthy adult horses, decreasing the thermodilution injectate volume to 1 mL/25 kg from the recommended volume of 1 mL/15 kg did not adversely affect the accuracy or precision of CO measurements. However, use of smaller injectate volumes or use of injectate at approximately room temperature is not recommended owing to a clinically unacceptable increase in CO measurement variability.

Increased FIO2 influences SvO2 interpretation and accuracy of Fick-based cardiac output assessment in cardiac surgery patients: A prospective randomized study

INTRODUCTION

The study aimed to reveal how the fraction of inspired oxygen (FIO2) affected the value of mixed venous oxygen saturation (SvO2) and the accuracy of Fick-equation-based cardiac output (Fick-CO).

METHODS

Forty two adult patients who underwent elective cardiac surgery were enrolled and randomly divided into 2 groups: FIO2 < 0.7 or >0.85. Under stable general anesthesia, thermodilution-derived cardiac output (TD-CO), SvO2, venous partial pressure of oxygen, hemoglobin, arterial oxygen saturation, arterial partial pressure of oxygen, and blood pH levels were recorded before surgical incision.

RESULTS

Significant differences in FIO2 values were observed between the 2 groups (0.56 ± 0.08 in the <70% group and 0.92 ± 0.03 in the >0.85 group; P < .001). The increasing FIO2 values lead to increases in SvO2, venous partial pressure of oxygen, and arterial partial pressure of oxygen, with little effects on cardiac output and hemoglobin levels. When comparing to TD-CO, the calculated Fick-CO in both groups had moderate Pearson correlations and similar linear regression results. Although the FIO2 <0.7 group presented a less mean bias and a smaller limits of agreement, neither group met the percentage error criteria of <30% in Bland-Altman analysis.

CONCLUSION

Increased FIO2 may influence the interpretation of SvO2 and the exacerbation of Fick-CO estimation, which could affect clinical management.

TRIAL REGISTRATION

ClinicalTrials.gov ID number: NCT04265924, retrospectively registered (Date of registration: February 9, 2020).

Comparing Doppler Echocardiography and Thermodilution for Cardiac Output Measurements in a Contemporary Cohort of Comatose Cardiac Arrest Patients Undergoing Targeted Temperature Management

Measuring cardiac output is used to guide treatment during postresuscitation care. The aim of this study was to compare Doppler echocardiography (Doppler-CO) with thermodilution using pulmonary artery catheters (PAC-CO) for cardiac output estimation in a large cohort of comatose out-of-hospital cardiac arrest (OHCA) patients undergoing targeted temperature management (TTM). Single-center substudy of 141 patients included in the TTM trial randomly assigned to 33 or 36°C for 24 hours after OHCA. Per protocol, PAC-CO and Doppler-CO were measured simultaneously shortly after admission and again at 24 and 48 hours. Linear correlation was assessed between methods and positive predictive value (PPV) and negative predictive value (NPV) of Doppler to estimate low cardiac output (<3.5 L/min) was calculated. A total of 301 paired cardiac output measurements were available. Average cardiac output was 5.28 ± 1.94 L/min measured by thermodilution and 4.06 ± 1.49 L/min measured by Doppler with a mean bias of 1.22 L/min (limits of agreements -1.92 to 4.36 L/min). Correlation between methods was moderate (R² = 0.36). Using PAC-CO as the gold standard, PPV of a low cardiac output measurement (<3.5 L/min) by Doppler was 33%. However, the NPV was 92%. Hypothermia at 33°C did not negatively affect the correlations of CO methods. In the lowest quartile of Doppler, 13% had elevated lactate (>2 mmol/L). In the lowest quartile of thermodilution, 36% had elevated lactate (>2 mmol/L). In ventilated OHCA patients, the two methods for estimating cardiac output correlated moderately and there was a consistent underestimation of Doppler-CO. Absolute cardiac output values from Doppler-CO should be interpreted with caution. However, Doppler can be used to exclude low cardiac output with high accuracy. TTM at 33°C did not negatively affect the correlation or bias of cardiac output measurements. ClinicalTrials.gov ID: NCT01020916.

Basics of Coronary Thermodilution

Coronary microvascular dysfunction is a highly prevalent condition in both obstructive and nonobstructive coronary artery disease. Intracoronary thermodilution is a promising technique to investigate coronary microvascular (dys)function in vivo and to assess its most important metric: microvascular resistance. Here, the authors provide a practical review of bolus and continuous thermodilution for the measurement of coronary flow and microvascular resistance. The authors describe the basic principles of indicator-dilution theory and of coronary thermodilution and detail the practicalities of their application in the catheterization laboratory. Finally, the authors discuss contemporary clinical applications of coronary thermodilution-based microvascular assessment in humans and future perspectives.

Pressure-dimension index: A novel "morphologic-functional" index of right ventricle that predicts short-term survival after left ventricular assist device implantation

BACKGROUND

Right ventricular failure (RVF) after left ventricular assist device (LVAD) implantation is a major cause of postoperative morbidity and mortality. Despite the availability of multiple imaging parameters, none of these parameters had adequate predictive accuracy for post-LVAD RVF.

AIM

To study whether right ventricular pressure-dimension index (PDI), which is a novel echocardiographic index that combines both morphologic and functional aspects of the right ventricle, is predictive of post-LVAD RVF and survival.

METHODS

49 cases that underwent elective LVAD implantation were retrospectively analyzed using data from an institutional registry. PDI was calculated by dividing systolic pulmonary artery pressure to the square of the right ventricular minor diameter. Cases were categorized according to tertiles.

RESULTS

Patients within the highest PDI tertile (PDI>3.62 mmHg/cm² ) had significantly higher short-term mortality (42.8%) and combined short-term mortality and severe RVF (50%) compared to other tertiles (P < .05 for both, log-rank p for survival to 15th day 0.014), but mortality was similar across tertiles in the long-term follow-up. PDI was an independent predictor of short-term mortality (HR:1.05-26.49, P = .031) and short-term composite of mortality and severe RVF (HR:1.37-38.87, P = .027).

CONCLUSIONS

Increased PDI is a marker of an overburdened right ventricle. Heart failure patients with a high PDI are at risk for short-term mortality following LVAD implantation.

Image-derived mean velocity measurement for prediction of coronary flow reserve in a canonical stenosis phantom using magnetic particle imaging

INTRODUCTION

Aim of this study is to evaluate whether magnetic particle imaging (MPI) is capable of measuring velocities occurring in the coronary arteries and to compute coronary flow reserve (CFR) in a canonical phantom as a preliminary study.

METHODS

For basic velocity measurements, a circulation phantom was designed containing replaceable glass tubes with three varying inner diameters, matching coronary-vessel diameters. Standardised boluses of superparamagnetic-iron-oxide-nanoparticles were injected and visualised by MPI. Two image-based techniques were competitively applied to calibrate the respective glass tube and to compute the mean velocity: full-duration-at-half-maximum (FDHM) and tracer dilution (TD) method. For CFR-calculation, four necessary settings of the circulation model of a virtual vessel with an inner diameter of 4 mm were generated using differently sized glass tubes and a stenosis model. The respective velocities in stenotic glass tubes were computed without recalibration.

RESULTS

On velocity level, comparison showed a good agreement (rFDHM = 0.869, rTD = 0.796) between techniques, preferably better for 4 mm and 6 mm inner diameter glass tubes. On CFR level MPI-derived CFR-prediction performed considerably inferior with a relative error of 20-44%.

CONCLUSIONS

MPI has the ability to reliably measure coronary blood velocities at rest as well as under hyperaemia and therefore may be suitable for CFR calculation. Calibration-associated accuracy of CFR-measurements has to be improved substantially in further studies.

Invasive Hemodynamic and Metabolic Evaluation of HFpEF

Purpose of review

Heart failure with preserved ejection fraction (HFpEF) is a complex and heterogeneous condition of multiple causes, characterized by a clinical syndrome resulting from elevated left ventricular filling pressures, with an apparently unimpaired left ventricular systolic function. Although HFpEF has been long recognized as a distinct entity with significant morbidity for patients, its diagnosis remains challenging to this day. In recent years, few diagnostic algorithms have been postulated to aid in the identification of this condition. Invasive hemodynamic and metabolic evaluation is often warranted for the conclusive diagnosis and risk stratification of HFpEF, in patients presenting with undifferentiated DOE.

Recent findings

Rest and provoked hemodynamics remain the golden-standard diagnostic tool to unequivocally confirm the diagnosis of both established and incipient HFpEF, respectively. Cycle exercise hemodynamics is the paramount provocative maneuver to unveil this condition. Rapid saline loading does not offer a significant benefit over that of cycle exercise. Vasoactive agents can also uncover and confirm incipient HFpEF disease. The role of metabolic evaluation in patients presenting with idiopathic dyspnea on exertion (DOE) is of unparalleled value for those who have expertise in cardiopulmonary exercise test (CPET) interpretation; however, the average clinician who focuses solely on oxygen consumption will find it underwhelming. Invasive CPET stands alone as the ultimate diagnostic tool to discriminate between pulmonary, cardiovascular, and skeletal muscle disorders, and their respective contribution to DOE and exercise intolerance.

Summary

Several hemodynamic and metabolic parameters have demonstrated not only strong diagnostic value, but also predictive power in HFpEF. Additionally, these diagnostic methods have given rise to several therapeutic interventions that are now part of our clinical armamentarium. Regrettably, due to the heterogeneity and multicausality of HFpEF, none of the targeted interventions have been so far successful in decreasing the mortality burden of this prevalent condition.

Cardiothoracic Anesthesia and Critical Care in the United Kingdom (UK) Part 1: Some Insights Into the History and Development

This review is intended to highlight some of the historic events that contributed to the development of thoracic and cardiac anesthesia and surgery in Great Britain and Northern Ireland (UK). The aim of this first of two parts is to concentrate on the development of techniques, facilities, and pharmacology that allowed progress and advancement in patient management that were developed primarily in the UK. However, progress usually requires input from a wide variety of sources of knowledge, and cardiothoracic practice is no exception. Reference is, thus, made to sources outside of the UK that guided, influenced, or inspired changes in practice, such as the techniques of operating on the heart and great vessels in war casualties, developed by Dr. Dwight Harken, or the demonstration of the Blalock-Thomas-Taussig shunt by Alfred Blalock. In addition to advances in medical equipment, such as computed tomography, the UK contributed greatly to pharmacologic interventions that were unique at the time in such varied areas as nonflammable volatile anesthetic agents, heart failure treatments, and neuromuscular blocking agents for both cardiac and thoracic surgical practice.

Narrative History of the Swan-Ganz Catheter: Development, Education, Controversies, and Clinician Acumen

The year 2020 marks the 50th anniversary of the landmark publication on the bedside clinical use of a flow-directed catheter. The catheter, now known as the Swan-Ganz catheter, truly revolutionized practice and care of the critically ill. Use of the catheter proliferated nearly without rigorous validation or evidence base until a moratorium was called in regard to its use. This article describes the history of the development of the Swan-Ganz catheter, its uses, and its near downfall. The authors, both involved in educating clinicians in the use of the pulmonary artery catheter, hope that telling this story shares tribal knowledge and lessons learned with newer generations of nurses who did not experience the explosion of development and knowledge in the area of hemodynamic monitoring. Partly because of advances in technology, and the catheter's application for heart failure in particular, use of the pulmonary catheter is being resurrected.

Current state of noninvasive, continuous monitoring modalities in pediatric anesthesiology

PURPOSE OF REVIEW

The last decades, anesthesia has become safer, partly due to developments in monitoring. Advanced monitoring of children under anesthesia is challenging, due to lack of evidence, validity and size constraints. Most measured parameters are proxies for end organ function, in which an anesthesiologist is actually interested. Ideally, monitoring should be continuous, noninvasive and accurate. This present review summarizes the current literature on noninvasive monitoring in noncardiac pediatric anesthesia.

RECENT FINDINGS

For cardiac output (CO) monitoring, bolus thermodilution is still considered the gold standard. New noninvasive techniques based on bioimpedance and pulse contour analysis are promising, but require more refining in accuracy of CO values in children. Near-infrared spectroscopy is most commonly used in cardiac surgery despite there being no consensus on safety margins. Its place in noncardiac anesthesia has yet to be determined. Transcutaneous measurements of blood gases are used mainly in the neonatal intensive care unit, and is finding its way to the pediatric operation theatre. Especially CO2 measurements are accurate and useful.

SUMMARY

New techniques are available to assess a child's hemodynamic and respiratory status while under anesthesia. These new monitors can be used as complementary tools together with standard monitoring in children, to further improve perioperative safety.

Haemodynamics of an iatrogenic atrial septal defect after MitraClip implantation

BACKGROUND

The MitraClip procedure requires transseptal access of the left atrium with a 24F guiding sheath. We evaluated invasively whether a MitraClip induced iatrogenic atrial septal defect (IASD) leads to development of a relevant interatrial shunt and right ventricular overload.

METHODS

A total of 69 patients who underwent a MitraClip procedure due to a severe mitral valve regurgitation (MVR) were included in the observational, retrospective cohort study. All pressures were directly measured throughout the procedure. Cardiac index (CI), systemic (Qs) and pulmonary (Qp) flow were calculated using the Fick method.

RESULTS

Successful MitraClip implantation increased CI (2.5 ± 0.62 vs 3.05 ± 0.77 L/min/m² ; P < .0001), whereas SVR (1491 ± 474 vs 997 ± 301 dyn s/cm⁵ ; P < .0001), PVR (226 ± 121 vs 188 ± 96 dyn/s/cm⁵ ; P = .04), PCWP (23 ± 6.1 vs 20 ± 4.7 mm Hg; P = .0031), PA pressure (33.6 ± 7.2 vs 31.9 ± 6.6 mm Hg; P = .1437) and LA pressure (21.5 ± 5.4 vs 18.7 ± 4.9 mm Hg; P < .0001) all decreased. The effect on LA pressure was further enhanced by guiding catheter retrieval (14.4 ± 4.6 mm Hg; P < .0001). At the end of the procedure, Qp (6.033 ± 1.3 L/min) exceeded Qs (5.537 ± 1.3 L/min) by 0.496 L/min leading to a Qp:Qs ratio of 1.09 (P = .007). After 6 months, echocardiography revealed no changes in RV diameter (42.96 ± 6.95 mm vs 43.81 ± 7.67 mm; P = .62) and TAPSE (17.13 ± 3.33 mm vs 17.36 ± 3.24 mm; P = .48).

CONCLUSION

Our data show that the MitraClip procedure does not induce a relevant interatrial shunt or right ventricular overload. In fact, future studies will have to show whether the IASD may even be beneficial in selected patient populations by left atrial volume and pressure relief.

4D flow MRI applications in congenital heart disease

Advances in the diagnosis and management of congenital heart disease (CHD) have resulted in a growing population of patients surviving well into adulthood and requiring lifelong follow-up. Flow quantification is a central component in the assessment of patients with CHD. 4D flow magnetic resonance imaging (MRI) has emerged as a tool that enables comprehensive study of flow. It involves the acquisition of a three-dimensional time-resolved volume with velocity encoding in all three spatial directions along the cardiac cycle. This allows flow quantification and visualization of blood flow patterns as well as the study of advanced hemodynamic parameters as kinetic energy and wall shear stress. 4D flow MRI-based study of flow has given insight into the altered hemodynamics in CHD particularly in bicuspid aortic valve disease and Fontan circulation. The aim of this review is to discuss the expanding clinical and research applications of 4D flow MRI in CHD as well its limitations.Key Points• Three-dimensional velocity encoding allows not only flow quantification but also the visualization of multidirectional flow patterns and the study of advanced hemodynamic parameters.• 4D flow MRI has added insight into the abnormal hemodynamics involved in congenital heart disease in particular in bicuspid aortic valve and Fontan circulation.• The main limitation of 4D flow MRI in congenital heart disease is the relatively long scan duration required for the complete coverage of the heart and great vessels with adequate spatiotemporal resolution.

Ventilation/Perfusion Relationships and Gas Exchange: Measurement Approaches

Ventilation-perfusion ( V ˙ A / Q ˙ ) matching, the regional matching of the flow of fresh gas to flow of deoxygenated capillary blood, is the most important mechanism affecting the efficiency of pulmonary gas exchange. This article discusses the measurement of V ˙ A / Q ˙ matching with three broad classes of techniques: (i) those based in gas exchange, such as the multiple inert gas elimination technique (MIGET); (ii) those derived from imaging techniques such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), computed tomography (CT), and electrical impedance tomography (EIT); and (iii) fluorescent and radiolabeled microspheres. The focus is on the physiological basis of these techniques that provide quantitative information for research purposes rather than qualitative measurements that are used clinically. The fundamental equations of pulmonary gas exchange are first reviewed to lay the foundation for the gas exchange techniques and some of the imaging applications. The physiological considerations for each of the techniques along with advantages and disadvantages are briefly discussed. © 2020 American Physiological Society. Compr Physiol 10:1155-1205, 2020.

Mixed Venous Oxygen Saturation Is a Better Prognosticator Than Cardiac Index in Pulmonary Arterial Hypertension

BACKGROUND

European Society of Cardiology (ESC) and European Respiratory Society (ERS) guidelines include thermodilution cardiac index (TDCI) and mixed venous oxygen saturation (SvO₂) as two of the three hemodynamic determinations used in risk assessment of patients with pulmonary arterial hypertension (PAH). SvO₂ may be a better measurement than TDCI to assess prognosis in patients with either idiopathic or heritable PAH.

RESEARCH QUESTION

What is the concordance between TDCI and SvO₂ ESC/ERS risk group allocation and their prognostic value in patients with PAH?

STUDY DESIGN AND METHODS

In this retrospective study, we assessed the correlation between SvO₂ and TDCI in patients with idiopathic and heritable PAH. We determined concordance in the ESC/ERS risk group allocation and association with survival, both at baseline and follow-up.

RESULTS

A total of 158 patients (mean age, 58 ± 17 years; 72% women) with idiopathic (91%) and heritable (9%) PAH were included. There was moderate association between TDCI and SvO₂ (r = 0.50; 95% CI, 0.37-0.62). Weighted kappa revealed a fair agreement between TDCI and SvO₂ (κ = 0.30; 95% CI, 0.18-0.42), with concordance in risk group allocation in 49% of patients. During a median follow-up of 45 months (interquartile range, 23-105), 62 patients (39%) died. Using Kaplan-Meier analysis, survival was impacted by the SvO₂ (log rank = 0.002) but not by the TDCI risk group allocation (log-rank = 0.51). Using the Cox proportional hazard model, adjusted for age and sex, SvO₂ (but not TDCI) was associated with mortality (hazard ratio per 1% change, 0.94; 95% CI, 0.91-0.97; P < .001).

INTERPRETATION

When using the cutoffs proposed by the ESC/ERS guidelines, we noted poor concordance in risk score allocation between TDCI and SvO₂. In patients with idiopathic or heritable PAH, SvO₂ measurements are superior to TDCI in predicting long-term mortality.

Enabling the assessment of trauma-induced hemorrhage via smart wearable systems

As the leading cause of trauma-related mortality, blood loss due to hemorrhage is notoriously difficult to triage and manage. To enable timely and appropriate care for patients with trauma, this work elucidates the externally measurable physiological features of exsanguination, which were used to develop a globalized model for assessing blood volume status (BVS) or the relative severity of blood loss. These features were captured via both a multimodal wearable system and a catheter-based reference and used to accurately infer BVS in a porcine model of hemorrhage (n = 6). Ultimately, high-level features of cardiomechanical function were shown to strongly predict progression toward cardiovascular collapse and used to estimate BVS with a median error of 15.17 and 18.17% for the catheter-based and wearable systems, respectively. Exploring the nexus of biomedical theory and practice, these findings lay the groundwork for digital biomarkers of hemorrhage severity and warrant further study in human subjects.

Continuous cardiac output assessment or serial echocardiography during septic shock resuscitation?

Septic shock is the leading cause of cardiovascular failure in the intensive care unit (ICU). Cardiac output is a primary component of global oxygen delivery to organs and a sensitive parameter of cardiovascular failure. Any mismatch between oxygen delivery and rapidly varying metabolic demand may result in tissue dysoxia, hence organ dysfunction. Since the intricate alterations of both vascular and cardiac function may rapidly and widely change over time, cardiac output should be measured repeatedly to characterize the type of shock, select the appropriate therapeutic intervention, and evaluate patient's response to therapy. Among the numerous techniques commercially available for measuring cardiac output, transpulmonary thermodilution (TPT) provides a continuous monitoring with external calibration capability, whereas critical care echocardiography (CCE) offers serial hemodynamic assessments. CCE allows early identification of potential sources of inaccuracy of TPT, including right ventricular failure, severe tricuspid or left-sided regurgitations, intracardiac shunt, very low flow states, or dynamic left ventricular outflow tract obstruction. In addition, CCE has the unique advantage of depicting the distinct components generating left ventricular stroke volume (large cavity size vs. preserved contractility), providing information on left ventricular diastolic properties and filling pressures, and assessing pulmonary artery pressure. Since inotropes may have deleterious effects if misused, their initiation should be based on the documentation of a cardiac dysfunction at the origin of the low flow state by CCE. Experts widely advocate using CCE as a first-line modality to initially evaluate the hemodynamic profile associated with shock, as opposed to more invasive techniques. Repeated assessments of both the efficacy (amplitude of the positive response) and tolerance (absence of side-effect) of therapeutic interventions are required to best guide patient management. Overall, TPT allowing continuous tracking of cardiac output variations and CCE appear complementary rather than mutually exclusive in patients with septic shock who require advanced hemodynamic monitoring.

Impact of Anesthetic and Ventilation Strategies on Invasive Hemodynamic Measurements in Pediatric Heart Transplant Recipients

BACKGROUND

Care of pediatric heart transplant recipients relies upon serial invasive hemodynamic evaluation, generally performed under the artificial conditions created by anesthesia and supportive ventilation.

OBJECTIVES

This study aimed to evaluate the hemodynamic impacts of different anesthetic and ventilatory strategies.

METHODS

We compared retrospectively the cardiac index, right- and left-sided filling pressures, and pulmonary and systemic vascular resistances of all clinically well and rejection-free heart transplant recipients catheterized from 2005 through 2017. Effects of spontaneous versus positive pressure ventilation and of sedation versus general anesthesia were tested with generalized linear mixed models for repeated measures using robust sandwich estimators of the covariance matrices. Least squared means showed adjusted mean outcome values, controlled for appropriate confounders.

RESULTS

720 catheterizations from 101 recipients met inclusion criteria. Adjusted cardiac index was 3.14 L/min/m² (95% CI 3.01-3.67) among spontaneously breathing and 2.71 L/min/m² (95% CI 2.56-2.86) among ventilated recipients (p < 0.0001). With spontaneous breathing, left filling pressures were lower (9.9 vs 11.0 mmHg, p = 0.030) and systemic vascular resistances were higher (24.0 vs 20.5 Woods units, p < 0.0001). After isolating sedated from anesthetized spontaneously breathing patients, the observed differences in filling pressures and resistances emerged as a function of sedation versus general anesthesia rather than of spontaneous versus positive pressure ventilation.

CONCLUSION

In pediatric heart transplant recipients, positive pressure ventilation reduces cardiac output but does not alter filling pressures or vascular resistances. Moderate sedation yields lower left filling pressures and higher systemic vascular resistances than does general anesthesia. Differences are quantitatively small.

cBIN1 Score (CS) Identifies Ambulatory HFrEF Patients and Predicts Cardiovascular Events

BACKGROUND

Cardiac Bridging Integrator 1 (cBIN1) is a membrane deformation protein that generates calcium microdomains at cardiomyocyte t-tubules, whose transcription is reduced in heart failure, and is released into blood. cBIN1 score (CS), an inverse index of plasma cBIN1, measures cellular myocardial remodeling. In patients with heart failure with preserved ejection fraction (HFpEF), CS diagnoses ambulatory heart failure and prognosticates hospitalization. The performance of CS has not been tested in patients with heart failure with reduced ejection fraction (HFrEF).

METHODS AND RESULTS

CS was determined from plasma of patients recruited in a prospective study. Two comparative cohorts consisted of 158 ambulatory HFrEF patients (left ventricular ejection fraction (LVEF) ≤ 40%, 57 ± 10 years, 80% men) and 115 age and sex matched volunteers with no known history of HF. N-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations were also analyzed for comparison. CS follows a normal distribution with a median of 0 in the controls, which increases to a median of 1.9 (p < 0.0001) in HFrEF patients. CS correlates with clinically assessed New York Heart Association Class (p = 0.007). During 1-year follow-up, a high CS (≥ 1.9) in patients predicts increased cardiovascular events (43% vs. 26%, p = 0.01, hazard ratio 1.9). Compared to a model with demographics, clinical risk factors, and NT-proBNP, adding CS to the model improved the overall continuous net reclassification improvement (NRI 0.64; 95% CI 0.18-1.10; p = 0.006). Although performance for diagnosis and prognosis was similar to CS, NT-proBNP did not prognosticate between patients whose NT-proBNP values were > 400 pg/ml.

CONCLUSION

CS, which is mechanistically distinct from NT-proBNP, successfully differentiates myocardial health between patients with HFrEF and matched controls. A high CS reflects advanced NYHA stage, pathologic cardiac muscle remodeling, and predicts 1-year risk of cardiovascular events in ambulatory HFrEF patients. CS is a marker of myocardial remodeling in HFrEF patients, independent of volume status.

Comparison of cardiovascular parameter estimation methods using swine data

In this study, new and existing methods of estimating stroke volume, cardiac output and total peripheral resistance from analysis of the arterial blood pressure waveform were tested over a wide range of conditions. These pulse contour analysis methods (PCMs) were applied to data obtained in six swine during infusion of volume, phenylephrine, dobutamine, isoproterenol, esmolol and nitroglycerine as well as during progressive hemorrhage. Performance of PCMs was compared using true end-ejection pressures as well as estimated end-ejection pressures. There was considerable overlap in the accuracies of the PCMs when using true end-ejection measures. However, for perhaps the most clinically relevant condition, where radial artery pressure is the input, only Wesseling's Corrected Impedance method and the Kouchoukos Correction method achieved statistically superior results. We introduced a method of estimating end-ejection by determining when the systolic pressure dropped to a value equal to the sum of the end-diastolic pressure plus a fraction of the pulse pressure. The most accurate estimation of end-ejection was obtained when that fraction was set to 60% for the central arterial pressure and to 50% for the femoral and radial arterial pressures. When the estimated end-ejection measures were used for the PCMs that depend on end-ejection measures and when radial artery pressure was used as the input, only Wesseling's Corrected Impedance method and the modified Herd's method achieved statistically superior results. This study provides a systematic comparison of multiple PCMs' ability to estimate stroke volume, cardiac output, and total peripheral resistance and introduces a new method of estimating end-systole.

Accuracy and precision of cardiac output estimation by an automated, brachial cuff-based oscillometric device in patients with shock

Non-invasive monitoring of cardiac output is a technological and clinical challenge, especially for critically ill, surgically operated, or intensive care unit patients. A brachial cuff-based, automated, oscillometric device used for blood pressure and arterial stiffness ambulatory monitoring (Mobil-O-Graph) provides a non-invasive estimation of cardiac output values simultaneously with regular blood pressure measurement. The aim of the study was to evaluate the feasibility of this apparatus to estimate cardiac output in intensive care unit patients and to compare the non-invasive estimated cardiac output values with the respective gold standard method of thermodilution during pulmonary artery catheterization. Repeated sequential measurements of cardiac output were performed, in random order, by thermodilution (reference) and Mobil-O-Graph (test), in 24 patients hospitalized at intensive care unit. Reproducibility and accuracy of the test device were evaluated by Bland–Altman analysis, intraclass correlation coefficient, and percentage error. Mobil-O-Graph underestimated significantly the cardiac output by −1.12 ± 1.38 L/min ( p < 0.01) compared to thermodilution. However, intraclass correlation coefficient was >0.7 indicating a fair agreement between the test and the reference methods, while percentage error was approximately 39% which is considered to be within the acceptable limits. Cardiac output measurements were reproducible by both Mobil-O-Graph (intraclass correlation coefficient = 0.73 and percentage error = 27.9%) and thermodilution (intraclass correlation coefficient = 0.91 and percentage error = 26.7%). We showed for the first time that cardiac output estimation in intensive care unit patients using a non-invasive, automated, oscillometric, cuff-based apparatus is reproducible (by analyzing two repeated cardiac output measurements), exhibiting similar precision to thermodilution. However, the accuracy of Mobil-O-Graph (error compared to thermodilution) could be considered fairly acceptable. Future studies remain to further examine the reliability of this technology in monitoring cardiac output or stroke volume acute changes which is a more clinically relevant objective.

Automated echocardiography for measuring and tracking cardiac output after cardiac surgery: a validation study

Echocardiographic measurement of cardiac output with automated software analyses of spectral curves in the left ventricular outflow tract has been introduced. This study aimed to assess the precision and accuracy of cardiac output measurements as well as the ability to track cardiac output changes over time comparing the automated echocardiographic method with the continuous pulmonary artery thermodilution cardiac output technique and the manual echocardiographic method in cardiac surgery patients. Cardiac output was measured simultaneously with all three methods in 50 patients on the morning after cardiac surgery. A second comparison was performed 90-180 min later. Precisions for each method were measured. Bias and limits of agreement (LoA) between methods were assessed and concordance- and polar plots were used for evaluating trending of cardiac output. When comparing the automated echocardiographic method with the thermodilution technique, the mean bias was 0.72 L/min with LoA - 1.89; 3.33 L/min corresponding to a percentage error of 46%. The concordance rate was 47%. The mean bias between the automated- and the manual echocardiographic methods was - 0.06 L/min (95% LoA - 2.33; 2.21 L/min, percentage error 42%). The concordance rate was 79%. The automated echocardiographic method did not meet the criteria for interchangeability with the thermodilution technique or the manual echocardiographic method. Trending ability was poor when compared to the continuous thermodilution technique, but moderate when compared to the manual echocardiographic method.Trial registry number: NCT03372863. Retrospectively registered December 14th 2017.

Leveraging Device-Arterial Coupling to Determine Cardiac and Vascular State

OBJECTIVE

Limitations in available diagnostic metrics restrict the efficacy of managing therapies for cardiogenic shock. In current clinical practice, cardiovascular state is inferred through measurement of pulmonary capillary wedge pressure and reliance on linear approximations between pressure and flow to estimate peripheral vascular resistance. Mechanical circulatory support devices residing within the left ventricle and aorta provide an opportunity for both determining cardiac and vascular state and offering therapeutic benefit. We leverage the controllable mode of operation and transvalvular position of an indwelling percutaneous ventricular assist device to assess vascular and, in turn, cardiac state through the effects of device-arterial coupling across different levels of device support.

METHODS

Vascular state is determined by measuring changes in the pressure waveforms induced through intentional variation in the device generated blood flow. We evaluate this impact by applying a lumped parameter model to quantify state-specific vascular resistance and compliance and calculate beat-to-beat stroke volume and cardiac output in both animal models and retrospective patient data without external calibration.

RESULTS

Vascular state was accurately predicted in patients and animals in both baseline and experimental conditions. In the animal, stroke volume was predicted within a total root mean square error of 3.71 mL (n = 482).

CONCLUSION

We demonstrate that device-arterial coupling is a powerful tool for evaluating patient and state specific parameters of cardiovascular function.

SIGNIFICANCE

These insights may yield improved clinical care and support the development of next generation mechanical circulatory support devices that determine and operate in tandem with the supported organ.

Comparison of echocardiographic indices of right ventricular systolic function and ejection fraction obtained with continuous thermodilution in critically ill patients

Background

Though echocardiographic evaluation assesses the right ventricular systolic function, which of the existing parameters best reflects the right ventricular ejection fraction (RVEF) in the critically ill patients is still uncertain. We aimed to determine the relationship between echocardiographic indices of right ventricular systolic function and RVEF.

Methods

Prospective observational study was conducted in a mixed Surgical Intensive Care Unit (Hôpital Lariboisière, Paris, France) from November 2017 to November 2018. All critically ill patients monitored with a pulmonary artery catheter were assessed. We collected echocardiographic indices of right ventricular function (tricuspid annular plane systolic excursion, TAPSE; peak systolic velocity of pulsed tissue Doppler at lateral tricuspid annulus, S′; fractional area change, FAC; right ventricular index of myocardial performance, RIMP; isovolumic acceleration, IVA; end-diastolic diameter ratio, EDDr) and compared them with the RVEF obtained from continuous volumetric pulmonary artery catheter.

Results

Twenty-five patients were analyzed. Admission diagnosis was acute heart failure in 11 patients and septic shock in 14 patients. Median age was 70 years [57–80], norepinephrine median dose was 0.29 μg/kg/min [0.14–0.50], median Sequential Organ Failure Assessment score was 12 [10–14], and mortality at day 28 was 56%. When compared to RVEF, TAPSE had the highest correlation coefficient (rho = 0.78, 95% CI 0.52 to 0.89, p < 0.001). S′ was also correlated to RVEF (rho = 0.64, 95% CI 0.60 to 0.80, p = 0.001) whereas FAC, RIMP, IVA, and EDDr did not. TAPSE lower than 16 mm, S′ lower than 11 cm/s, and EDDr higher than 1 were always associated with a reduced RVEF.

Conclusions

We found that amongst indices of right ventricular systolic function, TAPSE and S′ were well correlated with thermodilution-derived RVEF in critically ill patients.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2582-7) contains supplementary material, which is available to authorized users.

Right Heart Catheterization-Background, Physiological Basics, and Clinical Implications

The idea of right heart catheterization (RHC) grew in the milieu of modern thinking about the cardiovascular system, influenced by the experiments of William Harvey, which were inspired by the treatises of Greek philosophers like Aristotle and Gallen, who made significant contributions to the subject. RHC was first discovered in the eighteenth century by William Hale and was subsequently systematically improved by outstanding experiments in the field of physiology, led by Cournand and Dickinson Richards, which finally resulted in the implementation of pulmonary artery catheters (PAC) into clinical practice by Jeremy Swan and William Ganz in the early 1970s. Despite its premature euphoric reception, some further analysis seemed not to share the early enthusiasm as far as the safety and effectiveness issues were concerned. Nonetheless, RHC kept its significant role in the diagnosis, prognostic evaluation, and decision-making of pulmonary hypertension and heart failure patients. Its role in the treatment of end-stage heart failure seems not to be fully understood, although it is promising. PAC-guided optimization of the treatment of patients with ventricular assist devices and its beneficial introduction into clinical practice remains a challenge for the near future.

Usefulness of right ventricular contraction pressure index to predict short-term mortality and right heart failure in patients who underwent continuous-flow left ventricular assist device implantation

Background:

Right ventricular stroke work index is a useful but invasively measured parameter that can be used to predict right heart failure following continuous-flow left ventricular assist device implantation. Right ventricular contraction pressure index is a novel parameter that was developed to measure right ventricular stroke work index with echocardiography. We aimed to investigate the clinical usefulness of right ventricular contraction pressure index to predict short-term mortality and right heart failure in patients who underwent continuous-flow left ventricular assist device implantation.

Methods:

A total of 49 patients who participated in institutional advanced heart failure registry and underwent continuous-flow left ventricular assist device implantation with a bridge-to-candidacy indication were analyzed retrospectively. Right ventricular contraction pressure index was calculated using offline measurements. Demographic, clinical and outcome data were obtained from the registry data. Patients were grouped according to right ventricular contraction pressure index quartiles.

Results:

Patients within the lowest right ventricular contraction pressure index quartile had a trend toward higher short-term mortality (46.2%, p = 0.056) and combined short-term mortality and definitive right heart failure (53.8%, p = 0.054) at 15th day postoperatively. Similarly, short-term survival or survival free of definite right heart failure were significantly lower in the lowest right ventricular contraction pressure index quartile (log-rank p = 0.045 and log-rank p = 0.03, respectively). In a proportional hazards model that included echocardiographic parameters, right ventricular contraction pressure index was an independent predictor for short-term mortality (odds ratio: 6.777, 95% confidence interval: 1.118–41.098, p = 0.037), but not for combined short-term mortality and definite right heart failure. No such associations were found for long-term mortality. Right ventricular contraction pressure index had a statistically significant correlation with invasively measured pulmonary capillary wedge pressure, pulmonary vascular resistance, mean pulmonary pressure, and right ventricular stroke work index.

Conclusion:

Right ventricular contraction pressure index was found as a useful parameter for determining short-term postoperative mortality in patients undergoing continuous-flow left ventricular assist device implantation.

Thermodilution vs Estimated Fick Cardiac Output Measurement in Clinical Practice: An Analysis of Mortality From the Veterans Affairs Clinical Assessment, Reporting, and Tracking (VA CART) Program and Vanderbilt University

Importance

Thermodilution (Td) and estimated oxygen uptake Fick (eFick) methods are widely used to measure cardiac output (CO). They are often used interchangeably to make critical clinical decisions, yet few studies have compared these approaches as applied in medical practice.

Objectives

To assess agreement between Td and eFick CO and to compare how well these methods predict mortality.

Design, Setting, and Participants

This investigation was a retrospective cohort study with up to 1 year of follow-up. The study used data from the Veterans Affairs Clinical Assessment, Reporting, and Tracking (VA CART) program. The findings were corroborated in a cohort of patients cared for at Vanderbilt University, an academic referral center. Participants were more than 15 000 adults who underwent right heart catheterization, including 12 232 in the Veterans Affairs cohort between October 1, 2007, and September 30, 2013, and 3391 in the Vanderbilt cohort between January 1, 1998, and December 31, 2014.

Exposures

A single cardiac catheterization was performed on each patient with CO estimated by both Td and eFick methods. Cardiac output was indexed to body surface area (cardiac index [CI]) for all analyses.

Main Outcomes and Measures

All-cause mortality over 90 days and 1 year after catheterization.

Results

Among 12 232 VA patients (mean [SD] age, 66.4 [9.9] years; 3.3% female) who underwent right heart catheterization in this cohort study, Td and eFick CI estimates correlated modestly (r = 0.65). There was minimal mean difference (eFick minus Td = -0.02 L/min/m2, or -0.4%) but wide 95% limits of agreement between methods (-1.3 to 1.3 L/min/m2, or -50.1% to 49.4%). Estimates differed by greater than 20% for 38.1% of patients. Low Td CI (<2.2 L/min/m2 compared with normal CI of 2.2-4.0 L/min/m2) more strongly predicted mortality than low eFick CI at 90 days (Td hazard ratio [HR], 1.71; 95% CI, 1.47-1.99; χ2 = 49.5 vs eFick HR, 1.42; 95% CI, 1.22-1.64; χ2 = 20.7) and 1 year (Td HR, 1.53; 95% CI, 1.39-1.69; χ2 = 71.5 vs eFick HR, 1.35; 1.22-1.49; χ2 = 35.2). Patients with a normal CI by both methods had 12.3% 1-year mortality. There was no significant additional risk for patients with a normal Td CI but a low eFick CI (12.9%, P = .51), whereas a low Td CI but normal eFick CI was associated with higher mortality (15.4%, P = .001). The results from the Vanderbilt cohort were similar in the context of a more balanced sex distribution (46.6% female).

Conclusions and Relevance

There is only modest agreement between Td and eFick CI estimates. Thermodilution CI better predicts mortality and should be favored over eFick in clinical practice.

Effects of Acute GLP-1 Infusion on Pulmonary and Systemic Hemodynamics in Patients With Heart Failure: A Pilot Study

PURPOSE

Cardiovascular-safety studies assessing glucagon-like peptide (GLP)-1 receptor agonists and dipeptidyl peptidase 4 inhibitors have provided inconsistent data on the risk for developing heart failure. Animal studies have shown that GLP-1 is a vasodilator; if confirmed in humans, this may ameliorate heart failure symptoms.

METHODS

In a single-center, observational pilot study, we recruited 10 patients with advanced heart failure undergoing right heart catheterization, and we recorded pulmonary hemodynamic measures, including cardiac output calculated by thermodilution and the indirect Fick method before and after a 15-minute continuous infusion of native GLP-1 (7-36) NH₂.

FINDINGS

There was a neutral effect of GLP-1 on all pressure and hemodynamics indices as derived by cardiac output calculated by thermodilution. However, there was a small but consistent reduction in cardiac output as calculated by the indirect Fick method after GLP-1 infusion (baseline, 4.0 [1.1] L/min vs GLP-1, 3.6 [0.9] L/min; P = 0.003), driven by a consistent reduction in mixed venous oxygen saturation after GLP-1 infusion (baseline, 62.2% [7.0%] vs GLP-1, 59.3% [6.8%]; P < 0.001), whereas arterial saturation remained constant (baseline, 96.8% [3.3%] vs GLP-1, 97.0% [3.2%]; P = 0.34). This resulted in an increase in systemic vascular resistance by Fick (baseline, 1285 [228] dyn · s/cm⁵ vs GLP-1, 1562 [247] dyn · s/cm⁵; P = 0.001).

IMPLICATIONS

Acute infusion of GLP-1 has a neutral hemodynamic effect, when assessed by thermodilution, in patients with heart failure. However, GLP-1 reduces mixed venous oxygen saturation. ClinicalTrials.gov identifier: NCT02129179.

Comparison of three non-invasive hemodynamic monitoring methods in critically ill children

Introduction

Hemodynamic parameters measurements were widely conducted using pulmonary artery catheter (PAC) with thermodilution as a reference standard. Due to its technical difficulties in children, transthoracic echocardiography (TTE) has been widely employed instead. Nonetheless, TTE requires expertise and is time-consuming. Noninvasive cardiac output monitoring such as ultrasonic cardiac output monitor (USCOM) and electrical velocimetry (EV) can be performed rapidly with less expertise requirement. Presently, there are inconsistent evidences, variable precision, and reproducibility of EV, USCOM and TTE measurements. Our objective was to compare USCOM, EV and TTE in hemodynamic measurements in critically ill children.

Materials and methods

This was a single center, prospective observational study in critically ill children. Children with congenital heart diseases and unstable hemodynamics were excluded. Simultaneous measurements of hemodynamic parameters were conducted using USCOM, EV, and TTE. Inter-rater reliability was determined. Bland-Altman plots were used to analyse agreement of assessed parameters.

Results

Analysis was performed in 121 patients with mean age of 4.9 years old and 56.2% of male population. Interrater reliability showed acceptable agreement in all measured parameters (stroke volume (SV), cardiac output (CO), velocity time integral (VTI), inotropy (INO), flow time corrected (FTC), aortic valve diameter (AV), systemic vascular resistance (SVR), and stroke volume variation (SVV); (Cronbach’s alpha 0.76–0.98). Percentages of error in all parameters were acceptable by Bland-Altman analysis (9.2–28.8%) except SVR (30.8%) and SVV (257.1%).

Conclusion

Three noninvasive methods might be used interchangeably in pediatric critical care settings with stable hemodynamics. Interpretation of SVV and SVR measurements must be done with prudence.

Clinical examination for diagnosing circulatory shock

PURPOSE OF REVIEW

In the acute setting of circulatory shock, physicians largely depend on clinical examination and basic laboratory values. The daily use of clinical examination for diagnostic purposes contrasts sharp with the limited number of studies. We aim to provide an overview of the diagnostic accuracy of clinical examination in estimating circulatory shock reflected by an inadequate cardiac output (CO).

RECENT FINDINGS

Recent studies showed poor correlations between CO and mottling, capillary refill time or central-to-peripheral temperature gradients in univariable analyses. The accuracy of physicians to perform an educated guess of CO based on clinical examination lies around 50% and the accuracy for recognizing a low CO is similar. Studies that used predefined clinical profiles composed of several clinical examination signs show more reliable estimations of CO with accuracies ranging from 81 up to 100%.

SUMMARY

Single variables obtained by clinical examination should not be used when estimating CO. Physician's educated guesses of CO based on unstructured clinical examination are like the 'flip of a coin'. Structured clinical examination based on combined clinical signs shows the best accuracy. Future studies should focus on using a combination of signs in an unselected population, eventually to educate physicians in estimating CO by using predefined clinical profiles.

Carbonic anhydrase is not a relevant nitrite reductase or nitrous anhydrase in the lung

KEY POINTS

Carbonic anhydrase (CA) inhibitors such as acetazolamide inhibit hypoxic pulmonary vasoconstriction (HPV) in humans and other mammals, but the mechanism of this action remains unknown. It has been postulated that carbonic anhydrase may act as a nitrous anhydrase in vivo to generate nitric oxide (NO) from nitrite and that this formation is increased in the presence of acetazolamide. Acetazolamide reduces HPV in pigs without evidence of any NO generation, whereas nebulized sodium nitrite reduces HPV by NO formation; however; combined infusion of acetazolamide with sodium nitrite inhalation did not further increase exhaled NO concentration over inhaled nitrite alone in pigs exposed to alveolar hypoxia. We conclude that acetazolamide does not function as either a nitrous anhydrase or a nitrite reductase in the lungs of pigs, and probably other mammals, to explain its vasodilating actions in the pulmonary or systemic circulations.

ABSTRACT

The carbonic anhydrase (CA) inhibitors acetazolamide and its structurally similar analogue methazolamide prevent or reduce hypoxic pulmonary vasoconstriction (HPV) in dogs and humans in vivo, by a mechanism unrelated to CA inhibition. In rodent blood and isolated blood vessels, it has been reported that inhibition of CA leads to increased generation of nitric oxide (NO) from nitrite and vascular relaxation in vitro. We tested the physiological relevance of augmented NO generation by CA from nitrite with acetazolamide in anaesthetized pigs during alveolar hypoxia in vivo. We found that acetazolamide prevents HPV in anaesthetized pigs, as in other mammalian species. A single nebulization of sodium nitrite reduces HPV, but this action wanes in the succeeding 3 h of hypoxia as nitrite is metabolized and excreted. Pulmonary artery pressure reduction and NO formation as measured by exhaled gas concentration from inhaled sodium nitrite were not increased by acetazolamide during alveolar hypoxia. Thus, our data argue against a physiological role of carbonic anhydrase as a nitrous anhydrase or nitrite reductase as a mechanism for its inhibition of HPV in the lung and blood in vivo.