Descending aortic blood flow and cardiac output: a clinical and experimental study of continuous oesophageal echo-Doppler flowmetry

Improving the precision of shock resuscitation by predicting fluid responsiveness with machine learning and arterial blood pressure waveform data

Fluid bolus therapy (FBT) is fundamental to the management of circulatory shock in critical care but balancing the benefits and toxicities of FBT has proven challenging in individual patients. Improved predictors of the hemodynamic response to a fluid bolus, commonly referred to as a fluid challenge, are needed to limit non-beneficial fluid administration and to enable automated clinical decision support and patient-specific precision critical care management. In this study we retrospectively analyzed data from 394 fluid boluses from 58 pigs subjected to either hemorrhagic or distributive shock. All animals had continuous blood pressure and cardiac output monitored throughout the study. Using this data, we developed a machine learning (ML) model to predict the hemodynamic response to a fluid challenge using only arterial blood pressure waveform data as the input. A Random Forest binary classifier referred to as the ML fluid responsiveness algorithm (MLFRA) was trained to detect fluid responsiveness (FR), defined as a ≥ 15% change in cardiac stroke volume after a fluid challenge. We then compared its performance to pulse pressure variation, a commonly used metric of FR. Model performance was assessed using the area under the receiver operating characteristic curve (AUROC), confusion matrix metrics, and calibration curves plotting predicted probabilities against observed outcomes. Across multiple train/test splits and feature selection methods designed to assess performance in the setting of small sample size conditions typical of large animal experiments, the MLFRA achieved an average AUROC, recall (sensitivity), specificity, and precision of 0.82, 0.86, 0.62. and 0.76, respectively. In the same datasets, pulse pressure variation had an AUROC, recall, specificity, and precision of 0.73, 0.91, 0.49, and 0.71, respectively. The MLFRA was generally well-calibrated across its range of predicted probabilities and appeared to perform equally well across physiologic conditions. These results suggest that ML, using only inputs from arterial blood pressure monitoring, may substantially improve the accuracy of predicting FR compared to the use of pulse pressure variation. If generalizable, these methods may enable more effective, automated precision management of critically ill patients with circulatory shock.

The clinical value of passive leg raising plus ultrasound to predict fluid responsiveness in children after cardiac surgery

Background

There are few non-invasive monitoring methods that can reliably predict fluid responsiveness (FR) in children. Here, we interrogate the value of doppler ultrasound evaluation of passive leg raising (PLR)-induced changes in stroke volume (SV) and cardiac output (CO) as a predictor of FR in children with mechanical ventilation after congenital cardiac surgery.

Methods

A total of 40 children with mechanical ventilation following congenital cardiac surgery, who required volume expansion (VE) were included in this study. Hemodynamic parameters such as heart rate (HR), mean arterial pressure (MAP), SV, and central venous pressure (CVP) were monitored before and after PLR and VE. Besides, we assessed changes in SV and CO by bedside ultrasound. Patients showing > 10 % increase in SV in response to VE were considered to be responders (26 patients), while the rest (14 patients) were defined as non-responders.

Results

Our data demonstrated that ΔSV-PLR and ΔCO- PLR were positively correlated with ΔSV-VE (r = 0.683, p < 0.001 and r = 0.374, p = 0.017, respectively), and the area under the ROC curve (AUC) of ΔSV-PLR was 0.879 (95 % CI [0.745 1.000], p < 0.001). The best cut-off value for ΔSV-PLR in predicting FR was 13 %, with its sensitivity and specificity were 81.8 and 86.3 %, respectively. ΔCVP, ΔHR, and ΔMAP were weak predictors of FR in the children.

Conclusions

Our study demonstrated that SV changes, as evaluated by noninvasive ultrasound combined with PLR, could effectively evaluate FR in children under mechanical ventilation after congenital cardiac surgery.

Can the descending aortic stroke volume be estimated by transesophageal descending aortic photoplethysmography?

PURPOSE

The aim of this study was to investigate the ability of transesophageal photoplethysmography detected from the descending aorta (dPPG) for predicting low descending aortic stroke volume (dSV) level in cardiac surgical patients.

METHODS

Fifteen patients scheduled for elective cardiac surgery were enrolled in our study. A transesophageal echocardiography (TEE) probe with an attached oximetry sensor was placed into the esophagus for paired dPPG signal and descending aortic Doppler blood flow signal acquisition. Metrics, including alternating current (AC), direct current (DC), area under the curve (AUC) and width (W), were extracted from the dPPG signals. The TEE-measured dSV, which was defined as the blood flow through the descending aorta during a cardiac cycle, was chosen as the standard reference. A receiver operating characteristic (ROC) curve was built to evaluate the performance of dPPG metrics in predicting low dSV level, and dSV measuring agreement between TEE and dPPG was analyzed by the Bland-Altman method.

RESULTS

A total of 644 paired dPPG and Doppler signals of the descending aorta were acquired. Significant correlations were found between the dPPG metrics and TEE-measured dSV, and the correlation coefficients between TEE-measured dSV and AUC or AC were 0.64 and 0.66, respectively. AUC and AC values obviously decreased with the reduction of dSV level among the three groups (<20 mL, from 20-40 mL, and >40 mL). The areas under the ROC curve for AUC and AC in predicting low dSV level (<20 mL) were 0.85 and 0.88, respectively. Bland-Altman plot showed a small bias (0.02 mL) but a wide limit of agreement (-18.62 to 18.66 mL) in dSV measurement between dPPG and Doppler technology.

CONCLUSIONS

The AC and AUC extracted from the dPPG signal provided a sensitive and qualitative prediction for dSV level. The dSV value could not be accurately measured by dPPG metrics.

TRIAL REGISTRATION

Chinese Clinical Trials Register Identifier: ChiCTR-OCS-12002789.

Transesophageal Doppler reliably tracks changes in cardiac output in comparison with intermittent pulmonary artery thermodilution in cardiac surgery patients

In this study a comparison of cardiac output (CO) measurements obtained with CardioQ transesophageal Doppler (TED) and pulmonary artery catheter (PAC) thermodilution (TD) technique was done in a systematic set-up, with induced changes in preload, afterload and heart rate. Twenty-five patients completed the study. Each patient were placed in the following successive positions: (1) supine, (2) head-down tilt, (3) head-up tilt, (4) supine, (5) supine with phenylephrine administration, (6) pace heart rate 80 beats per minute (bpm), (7) pace heart rate 110 bpm. The agreement of compared data was investigated by Bland-Altman plots, and to assess trending ability a four quadrants plot and a polar plot were constructed. Both methods showed an acceptable precision 6.4 % (PAC TD) and 12.8 % (TED). In comparison with PAC TD, the TED was associated with a mean bias in supine position of -0.30 l min^-1 (95 % CI -0.88; 0.27), wide limits of agreement, a percentage error of 69.5 %, and a trending ability with a concordance rate of 92 %, angular bias of 1.1° and a radial sector size of 40.0° corresponding to an acceptable trending ability. In comparison with PAC TD, the CardioQ TED showed a low mean bias, wide limits of agreement and a larger percentage error than should be expected from the precision of the two methods. However, an acceptable trending ability was found. Thus, the CardioQ TED should not replace CO measurements done by PAC TD, but could be a valuable tool in guiding therapy.

Measurement of renal blood flow by phase-contrast magnetic resonance imaging during septic acute kidney injury: a pilot investigation

OBJECTIVE

In septic patients, decreased renal perfusion is considered to play a major role in the pathogenesis of acute kidney injury. However, the accurate measurement of renal blood flow in such patients is problematic and invasive. We sought to overcome such obstacles by measuring renal blood flow in septic patients with acute kidney injury using cine phase-contrast magnetic resonance imaging.

DESIGN

Pilot observational study.

SETTING

University-affiliated general adult intensive care unit.

PATIENTS

Ten adult patients with established septic acute kidney injury and 11 normal volunteers.

INTERVENTIONS

Cine phase-contrast magnetic resonance imaging measurement of renal blood flow and cardiac output.

MEASUREMENTS AND MAIN RESULTS

The median age of the study patients was 62.5 yrs and eight were male. At the time of magnetic resonance imaging, eight patients were mechanically ventilated, nine were on continuous hemofiltration, and five required vasopressors. Cine phase-contrast magnetic resonance imaging examinations were carried out without complication. Median renal blood flow was 482 mL/min (range 335-1137) in septic acute kidney injury and 1260 mL/min (range 791-1750) in healthy controls (p = .003). Renal blood flow indexed to body surface area was 244 mL/min/m2 (range 165-662) in septic acute kidney injury and 525 mL/min/m2 (range 438-869) in controls (p = .004). In patients with septic acute kidney injury, median cardiac index was 3.5 L/min/m2 (range 1.6-8.7), and median renal fraction of cardiac output was only 7.1% (range 4.4-10.8). There was no rank correlation between renal blood flow index and creatinine clearance in patients with septic acute kidney injury (r = .26, p = .45).

CONCLUSIONS

Cine phase-contrast magnetic resonance imaging can be used to noninvasively and safely assess renal perfusion during critical illness in man. Near-simultaneous accurate measurement of cardiac output enables organ blood flow to be assessed in the context of the global circulation. Renal blood flow seems consistently reduced as a fraction of cardiac output in established septic acute kidney injury. Cine phase-contrast magnetic resonance imaging may be a valuable tool to further investigate renal blood flow and the effects of therapies on renal blood flow in critical illness.

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

Background

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

Methods

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

Results

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

Conclusions

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

Residents and ICU nurses get reliable static and dynamic haemodynamic assessments with aortic oesophageal Doppler

BACKGROUND

Aortic oesophageal Doppler (ODM) allows continuous non-invasive haemodynamic monitoring. We tested to confirm if residents and nurses were able to reposition oesophageal probe (OP), obtain aortic blood flow of good quality and so perform reliable static and dynamic haemodynamic assessments.

METHODS

Prospective observational study assessing ODM measurements were obtained by six residents and three nurses after they have participated in training. Measured (aortic diameter) and calculated haemodynamic data [indexed stroke volume (SVI), cardiac index] were directly obtained from ODM, after residents and nurses repositioned the OP. In a second group of patients, we tested the ability of residents and nurses to detect rapid haemodynamic changes after a passive leg raising. SVI comparison was the primary end point. Statistical analysis was performed using the method of Bland and Altman.

RESULTS

Sixty-six haemodynamic measurements were performed on 42 patients. Mean bias for SVI between the skilled physician and residents, and between the skilled physician and nurses were -0.9 ± 5.2 ml/m(2) (P = 0.15), with a percentage error of 31%, and 0.9 ± 5.1 ml/m(2) (P = 0.14), with a percentage error of 33%, respectively. There was an excellent correlation for SVI between the physician and residents (r = 0.9; P < 0.0001) and between the physician and nurses (r = 0.9; P < 0.0001). Induced changes in SVI measured by residents and nurses strongly followed those of our skilled physician.

CONCLUSION

Residents and nurses get reliable static and dynamic haemodynamic assessments with ODM compared to our skilled physician.

Perioperative hemodynamic monitoring with transesophageal Doppler technology

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

[Minimally invasive hemodynamic monitoring with esophageal echoDoppler]

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

Transoesophageal echo-Doppler vs. thermodilution cardiac output measurement during hepatic vascular exclusion in liver transplantation

BACKGROUND AND OBJECTIVE

Continuous monitoring of cardiac output during liver transplantation is essential to evaluate the patient's haemodynamic tolerance to acute volume variations. The aim of this study was to compare the cardiac output values obtained with a transoesophageal echo-Doppler and those obtained with a continuous thermodilution cardiac output pulmonary artery catheter.

METHODS

Twenty adult patients were prospectively studied during a 5 min hepatic vascular exclusion test performed at the end of the dissection phase. Echo-Doppler and continuous thermodilution cardiac output, mean arterial pressure and end-tidal CO2 were measured before and at the end of the test.

RESULTS

Before the test, echo-Doppler cardiac output was 7.0 +/- 2.7 L min(-1) and thermodilution was 9.4 +/- 3.1 L min(-1), (R = 0.85, P < 0.001). The end test values were, respectively, 3.5 +/- 2.7 and 7.8 +/- 3.5 L min(-1) (R = 0.23, P = 0.34). Bland and Altman analysis showed a bias of -2.2 before the test, which increased to -4.4 at the end of the test. Mean arterial pressure decreased from 85.5 +/- 15 to 66.8 +/- 16 mmHg, end-tidal CO2 from 31.4 +/- 2.3 to 23.8 +/- 2.7 mmHg.

CONCLUSION

Echo-Doppler cardiac output values are different from those measured by thermodilution cardiac output in these patients. Echo-Doppler cardiac output monitoring seems to detect the output changes, which can occur during acute haemodynamic changes more rapidly than thermodilution cardiac output in the course of liver transplantation.

Cardiac output measurement during infrarenal aortic surgery: echo-esophageal Doppler versus thermodilution catheter

OBJECTIVE

Aortic surgery is associated with various hemodynamic and cardiac output modifications. These disorders may be partly caused by blood flow redistribution between supra-aortic and descending aorta regions during clamping and unclamping. A new echo-esophageal Doppler (Hemosonic 100; Arrow, Reading, PA) calculates cardiac output from a simultaneous measurement of blood flow velocity and diameter of the descending aorta. This calculation may be affected by blood redistribution during aortic clamping. The aim of this study was to compare cardiac output measured by echo-esophageal Doppler and by bolus thermodilution catheter during infrarenal aortic surgery.

DESIGN

Prospective, observational study.

SETTING

University hospital, single institution.

PARTICIPANTS

Twenty-two adult patients.

INTERVENTIONS

Infrarenal aortic surgery.

MEASUREMENTS AND MAIN RESULTS

Cardiac outputs monitored by both devices were highly correlated during the whole surgical procedure (r2 ranging from 0.54 to 0.76). Bland and Altman analysis showed absence of significant bias before and after clamping (ranging from 0.1 +/- 0.73 L/min to 0.18 +/- 1 L/min, p > 0.05) and a significant bias of 0.5 +/- 1.05 L/min (p < 0.05) during aortic clamping. Limits of agreement did not differ significantly during the whole surgical procedure (ranging from -1.36/2.19 to -2.23/2.49). During clamping and unclamping, changes in cardiac output obtained by both methods were positively correlated (r2 = 0.7).

CONCLUSIONS

Bias between both methods was clinically acceptable, and limits of agreement were not significantly modified by aortic clamping. However, larger studies including homogenous aortic pathologies are necessary to validate this method during infrarenal aortic surgery.

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

OBJECTIVE

Continuous measurement of cardiac output (CCO) is of great importance in the critically ill. However, pulmonary artery thermodilution has been questioned for possible complications associated with right heart catheterization. Furthermore, measurements are delayed in the continuous mode during rapid hemodynamic changes. A new pulmonary artery catheter CCO device (Aortech, Bellshill, Scotland) enabling real-time update of cardiac output was compared with 2 different, less-invasive methods of CCO determination, esophageal Doppler and pulse contour analysis.

DESIGN

Prospective, observational study.

SETTING

University hospital, single institution.

PARTICIPANTS

Patients scheduled for elective coronary artery bypass grafting (CABG).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

CCO measurements were analyzed using a Bland-Altman plot. Bias between CCO and pulse contour cardiac output (PCCO), and Doppler-derived cardiac output (UCCO) was (mean +/- 1 SD) -0.71 +/- 1 L/min versus -0.15 +/- 1.09 L/min, and between UCCO and PCCO -0.58 +/- 1.06 L/min. Bias was not significantly different among methods, nor were comparative values before and after cardiopulmonary bypass (p > 0.05).

CONCLUSIONS

Agreement between the CCO method and both less-invasive measurements was clinically acceptable. There were no adverse events associated with the use of either device.