Continuous minimally invasive peri-operative monitoring of cardiac output by pulmonary capnotracking: comparison with thermodilution and transesophageal echocardiography

A multimodal stacked ensemble model for cardiac output prediction utilizing cardiorespiratory interactions during general anesthesia

This study examined the possibility of estimating cardiac output (CO) using a multimodal stacking model that utilizes cardiopulmonary interactions during general anesthesia and outlined a retrospective application of machine learning regression model to a pre-collected dataset. The data of 469 adult patients (obtained from VitalDB) with normal pulmonary function tests who underwent general anesthesia were analyzed. The hemodynamic data in this study included non-invasive blood pressure, plethysmographic heart rate, and SpO2. CO was recorded using Vigileo and EV1000 (pulse contour technique devices). Respiratory data included mechanical ventilation parameters and end-tidal CO2 levels. A generalized linear regression model was used as the metalearner for the multimodal stacking ensemble method. Random forest, generalized linear regression, gradient boosting machine, and XGBoost were used as base learners. A Bland-Altman plot revealed that the multimodal stacked ensemble model for CO prediction from 327 patients had a bias of - 0.001 L/min and - 0.271% when calculating the percentage of difference using the EV1000 device. Agreement of model CO prediction and measured Vigileo CO in 142 patients reported a bias of - 0.01 and - 0.333%. Overall, this model predicts CO compared to data obtained by the pulse contour technique CO monitors with good agreement.

Rapid Ventricular Pacing Facilitates Transarterial Embolization in Vein of Galen Malformations

Background: Mural type vein of Galen malformation (mVOGM) is a congenital high flow arteriovenous shunt between choroidal arteries and the prosencephalic vein of Markowski leading to heart failure and hydrovenous disorder in children. Embolizing fistulous connections can be challenging and typically requires adjunctive techniques such as induced hypotension, balloon-assisted flow control, and creation of a coil basket. These maneuvers add time, complexity, and unpredictability. Rapid ventricular pacing (RVP) has been proposed as an alternative strategy with fewer drawbacks, but has not been well studied. The approach involves catheterizing the right ventricle with a pacing catheter connected to a temporary external pacemaker. Prior to embolization, RVP is initiated to lower cardiac output. Following embolization, pacing is discontinued, and the heart returns to sinus rhythm. Methods: We performed RVP in five mVOGM patients from 4/2020 through 7/2021. Accounting for multiple procedures, RVP was utilized in ten cases and twenty-six pedicles. Results: Ventricular capture was achieved in all instances and was well tolerated, without arrhythmia. Casting the arterial pedicle with liquid embolic immediately adjacent to, or traversing, the fistulous point was achieved in 9/10 cases. There were no procedural complications. In 1 case, creation of a coil basket in the venous pouch was required to achieve a stable arterial cast Conclusions: This report describes the largest case series utilizing RVP in mVOGM. The technique appears safe and well tolerated.

Accuracy and Trending Ability of Electrical Biosensing Technology for Non-invasive Cardiac Output Monitoring in Neonates: A Systematic Qualitative Review

BACKGROUND

Electrical biosensing technology (EBT) is an umbrella term for non-invasive technology utilizing the body's fluctuating resistance to electrical current flow to estimate cardiac output. Monitoring cardiac output in neonates may allow for timely recognition of hemodynamic compromise and allow for prompt therapy, thereby mitigating adverse outcomes. For a new technology to be safely used in the clinical environment for therapeutic decisions, it must be proven to be accurate, precise and be able to track temporal changes. The aim of this systematic review was to identify and analyze studies that describe the accuracy, precision, and trending ability of EBT to non-invasively monitor Left ventricular cardiac output and/or stroke volume in neonates.

METHODS

A qualitative systematic review was performed. Studies were identified from PubMed NCBI, SCOPUS, and EBSCOHost up to November 2021, where EBT technologies were analyzed in neonates, in comparison to a reference technology. Outcome measures were bias, limits of agreement, percentage error for agreement studies and data from 4-quadrant and polar plots for trending studies. Effect direction plots were used to present results.

RESULTS

Fifteen neonatal studies were identified, 14 for agreement and 1 for trending analysis. Only thoracic electrical biosensing technology (TEBT), with transthoracic echocardiography (TTE) as the comparator, studies were available for analyzes. High heterogeneity existed between studies. An equal number of studies showed over- and underestimation of left ventricular output parameters. All studies showed small bias, wide limits of agreement, with most studies having a percentage error >30%. Sub-analyses for respiratory support mode, cardiac anomalies and type of technology showed similar results. The single trending study showed poor concordance, high angular bias, and poor angular concordance.

DISCUSSION

Overall, TEBT shows reasonable accuracy, poor precision, and non-interchangeability with TTE. However, high heterogeneity hampered proper analysis. TEBT should be used with caution in the neonatal population for monitoring and determining therapeutic interventions. The use of TEBT trend monitoring has not been sufficiently studied and requires further evaluation in future trials.

Ventilatory parameters measured during a physiological study of simulated powered air-purifying respirator failure in healthy volunteers

Powered air-purifying respirators (PAPR) are a high level of respiratory personal protective equipment. Like all mechanical devices, they are vulnerable to failure. The precise physiological consequences of failure in live subjects have not previously been reported. We conducted an observational safety study simulating PAPR failure in a group of nine healthy volunteers, wearing loose-fitting hoods, who were observed for a period of ten minutes, or until they requested the experiment be aborted, with continuous monitoring of gas exchange. Relative to baseline, participants demonstrated median reductions in peripheral oxygen saturation of 3.5% (95% confidence interval (CI) -4% to -2%; P = 0.0039) and fraction of inspired oxygen of 0.045 (95% CI -0.05 to -0.04; P = 0.0039), and median increases in inspired partial pressure of carbon dioxide of 27 mmHg (95% CI 23.5-32 mmHg; P = 0.0039), end-tidal partial pressure of carbon dioxide of 11 mmHg (95% CI 7-16 mmHg; P = 0.0039) and minute ventilation of 30 l/min (95% CI 19.4-35.9 l/min; P = 0.0039). Median collateral entrainment of room air into the hood was 17.6 l/min (interquartile range 12.3-27.0 l/min). All subjects reported thermal discomfort, with two (22.2%) requesting early termination of the experiment. Whilst the degree of rebreathing in this experiment was not sufficient to cause dangerous physiological derangement, the degree of reported thermal discomfort combined with the consequences of entrainment of possibly contaminated air into the hood, pose a risk to wearers in the event of failure.

Volumetric and End-Tidal Capnography for the Detection of Cardiac Output Changes in Mechanically Ventilated Patients Early after Open Heart Surgery

Background

Exhaled carbon dioxide (CO₂) reflects cardiac output (CO) provided stable ventilation and metabolism. Detecting CO changes may help distinguish hypovolemia or cardiac dysfunction from other causes of haemodynamic instability. We investigated whether CO₂ measured as end-tidal concentration (EtCO₂) and eliminated volume per breath (VtCO₂) reflect sudden changes in cardiac output (CO).

Methods

We measured changes in CO, VtCO₂, and EtCO₂ during right ventricular pacing and passive leg raise in 33 ventilated patients after open heart surgery. CO was measured with oesophageal Doppler.

Results

During right ventricular pacing, CO was reduced by 21% (CI 18–24; p < 0.001), VtCO₂ by 11% (CI 7.9–13; p < 0.001), and EtCO₂ by 4.9% (CI 3.6–6.1; p < 0.001). During passive leg raise, CO increased by 21% (CI 17–24; p < 0.001), VtCO₂ by 10% (CI 7.8–12; p < 0.001), and EtCO₂ by 4.2% (CI 3.2–5.1; p < 0.001). Changes in VtCO₂ were significantly larger than changes in EtCO₂ (ventricular pacing: 11% vs. 4.9% (p < 0.001); passive leg raise: 10% vs. 4.2% (p < 0.001)). Relative changes in CO correlated with changes in VtCO₂ (ρ=0.53; p=0.002) and EtCO₂ (ρ=0.47; p=0.006) only during reductions in CO. When dichotomising CO changes at 15%, only EtCO₂ detected a CO change as judged by area under the receiver operating characteristic curve.

Conclusion

VtCO₂ and EtCO₂ reflected reductions in cardiac output, although correlations were modest. The changes in VtCO₂ were larger than the changes in EtCO₂, but only EtCO₂ detected CO reduction as judged by receiver operating characteristic curves. The predictive ability of EtCO₂ in this setting was fair. This trial is registered with NCT02070861.

Clinical use of volumetric capnography in mechanically ventilated patients

Capnography is a first line monitoring system in mechanically ventilated patients. Volumetric capnography supports noninvasive and breath-by-breath information at the bedside using mainstream CO₂ and flow sensors placed at the airways opening. This volume-based capnography provides information of important body functions related to the kinetics of carbon dioxide. Volumetric capnography goes one step forward standard respiratory mechanics and provides a new dimension for monitoring of mechanical ventilation. The article discusses the role of volumetric capnography for the clinical monitoring of mechanical ventilation.

New generation continuous cardiac output monitoring from carbon dioxide elimination

Background

There is continuing interest among clinicians in the potential for advanced hemodynamic monitoring and “goal directed” intravenous fluid administration guided by minimally-invasive cardiac output measurement to reduce complication rates in high risk patients undergoing major surgery. However, the adoption of the available technologies has been limited, due to cost, complexity and reliability of measurements provided. We review progress in the development of new generation methods for continuous non-invasive monitoring of cardiac output from measurement of carbon dioxide elimination in ventilated patients using the Differential Fick method.

Main text

The history and underlying theoretical basis are described, and its recent further development and implementation using modern generation anesthesia monitoring and delivery systems by two separate but parallel methods, termed “Capnotracking” and “Capnodynamics”. Both methods generate breath-by-breath hands-free cardiac output monitoring from changes in carbon dioxide elimination produced by automatic computerized modulation of respiratory rate delivered by an electronic ventilator. Extensive preclinical validation in animal models of hemodynamic instability, with implanted ultrasonic flow probes for gold standard reference measurements, shows this approach delivers reliable, continuous cardiac output measurement in real time. The accuracy and precision of measurement by the Capnodynamic method were maintained under a wide range of both hemodynamic and respiratory conditions, including inotropic stimulation, vasodilatation, hemorrhage, caval compression, alveolar lavage, changes in tidal volume and positive end-expiratory pressure, and hypercapnia, with only brief derangement observed in a model of lower body ischemia involving release of prolonged aortic occlusion by an intra-aortic balloon. Phase 2 testing of a Capnotracking system in patients undergoing cardiac surgery and liver transplantation has achieved a percentage error of agreement with thermodilution of +/− 38.7% across a wide range of hemodynamic states.

Conclusions

Progress in development of these technologies suggest that a robust, automated and reliable method of non-invasive cardiac output monitoring from capnography is close at hand for use in major surgery and critical care. The great advantage of this approach is that it can be fully integrated into the anesthesia machine and ventilator, using components that are already standard in modern anesthesia and intensive care workstations, and should be virtually hands-free and automatic.

Validation of capnodynamic determination of cardiac output by measuring effective pulmonary blood flow: a study in anaesthetised children and piglets

BACKGROUND

Effective pulmonary blood flow (CO_EPBF) has recently been validated as a technique for determining cardiac output (CO) in animals of varying sizes. The primary aim of our study was to investigate this new technique in paediatric surgical patients, compared with suprasternal two-dimensional Doppler (CO_SSD).

METHODS

A total of 15 children undergoing cleft lip/palate surgery were investigated. Before the start of surgery, manoeuvres that were anticipated to reduce (increase in PEEP from 3 to 10 cm H₂O) and increase (atropine) CO were undertaken. A study in mechanically ventilated piglets was also undertaken under general anaesthesia, measuring CO_EPBF and pulmonary artery (CO_TS) flow by ultrasonic probe as the comparator. Bias (Bland-Altman plots) and limits of agreement were assessed for effective pulmonary blood flow and CO_SSD or CO_TS.

RESULTS

In paediatric patients (median age 8.5 months), overall bias was -8.1 (limits of agreement -82 to +66) ml kg^-1 min^-1, with a mean percentage error of 48% and a concordance rate of 64%. In the piglet model, overall bias was -1 (-36 to +38) ml kg^-1 min^-1, with a mean percentage error of 31% and a concordance rate of 95%.

CONCLUSIONS

Under controlled experimental conditions, CO_EPBF is associated with excellent agreement and good trending ability when compared with the gold standard CO_TS. In the paediatric clinical setting, CO_EPBF performs well; by contrast, CO_SSD, an operator- and anatomy-dependent technology, appears less reliable than CO_EPBF.

Transesophageal Echocardiographic Measurement of Cardiac Index by the Prosthetic Mitral Valve Method Is Not Similar to the Continuous Thermodilution Method Via a Pulmonary Artery Catheter

OBJECTIVE

To compare the agreement of cardiac index measurements between transesophageal echocardiography across the prosthetic mitral valve and the continuous thermodilution method through a pulmonary artery catheter (PAC-TD) in patients undergoing double-valve replacement.

DESIGN

Observational prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty-five patients undergoing double-valve replacement (12 men and 13 women, age 25-78 years, ASA III-IV, NYHA II-III, LVEF≥45%). Patients were grouped according to their prosthesis (mechanical prosthesis v bioprosthesis).

INTERVENTIONS

All patients underwent cardiac index assessment during double-valve replacement.

MEASUREMENTS AND MAIN RESULTS

Cardiac index across the prosthetic mitral valve was measured simultaneously using transesophageal echocardiography (CI(MV)) and PAC-TD (CI(PAC)) at 15, 30, 45, and 60 minutes after weaning from cardiopulmonary bypass, and at 0, 15, and 30 minutes after incision closure. A correlation was present between CI(MV) and CI(PAC) in both groups (mechanical prosthesis: r = 0.47, p<0.01; bioprosthesis: r = 0.60, p<0.01). In the mechanical prosthesis group, the bias between techniques (CI(PAC) v CI(MV)) was-0.5 L/min/m(2) (95% CI:-1.97 to 0.97), and error was 55%. In the bioprosthesis group, the bias between both techniques was-1.3 L/min/m(2) (95% CI:-3.1 to 0.5), and error was 56%.

CONCLUSIONS

A relatively weak correlation and lack of agreement between values of CI(PAC) and CI(MV) were observed in patients undergoing double-valve replacement. Therefore, transesophageal echocardiography might not be interchangeable with PAC-TD for measuring cardiac output or cardiac index. A regression equation is needed to correct the probable value of CI(PAC). CI(MV) might be useful as a quantitative or semi-quantitative cardiac output measurement.

Hybrid measurement to achieve satisfactory precision in perioperative cardiac output monitoring

Advanced haemodynamic monitoring employing minimally invasive cardiac output measurement may lead to significant improvements in patient outcomes in major surgery. However, the precision (scatter) of measurement of available generic technologies has been shown to be unsatisfactory with percentage error of agreement with bolus thermodilution (% error) of 40% to 50%. Simultaneous measurement and averaging by two or more technologies may reduce random measurement scatter and improve precision. This concept, called the hybrid method, was tested by comparing accuracy and precision of measurement relative to bolus thermodilution using combinations of three component methods. Thirty patients scheduled for either elective cardiac surgery or liver transplantation were studied. Agreement with simultaneous bolus thermodilution of hybrid combinations of continuous thermodilution (QtCCO) or Vigeleo™/FloTrac™ pulse contour measurement (QtFT) with pulmonary Capnotracking (QtCO2) was assessed pre- and post-cardiopulmonary bypass or pre- and post-reperfusion of the donor liver and compared with that of the component methods alone. Hybridisation of QtCO2 (% error 42.2) and QtCCO (% error 51.3) achieved significantly better precision (% error 31.3) than the component methods (P=0.0004) and (P=0.0195). Due to poor inherent precision of QtFT (% error 82.8), hybrid combination of QtFT with QtCO2 did not result in better precision than QtCO2 alone. Hybrid measurement can approach a 30% error, which is recommended as the upper limit for acceptability. This is a practical option where at least one component method, such as Capnotracking, is automated and does not increase the cost or complexity of the measurement process.

Ventilation parameters used to guide cardiopulmonary function during mechanical ventilation

PURPOSE OF REVIEW

To describe the newly introduced ventilation parameters that are used at the bedside to estimate cardiopulmonary function during positive pressure ventilation (PPV).

RECENT FINDINGS

PPV induces right atrial pressure changes over the ventilator cycle. Positive end-expiratory pressure-induced central venous pressure changes and pulse pressure variation have been introduced as parameters that predict fluid responsiveness. Pulse pressure variation seems to be valid even at low tidal volume ventilation. A capnometer can be used to measure low perfusion lung area and to monitor the continuous breath-by-breath cardiac output of ventilated patients. Ultrasound evaluation of the lung parenchyma and diaphragm status is likely to become more popular. To evaluate ventilator settings, functional residual capacity (FRC) measurement and visual lung recruitment estimation via electric impedance tomography (EIT) have been introduced.

SUMMARY

The utility of lung ultrasound is expanding. Although the clinical implications of FRC measurement and lung monitoring with imaging tools such as EIT are starting to be realized, their efficacy in severe hypoxic respiratory failure should be evaluated further in well designed clinical trials. To improve the preemptive management of impending respiratory failure, an alarm index that integrates noninvasive cardiopulmonary function parameters should be developed.

An algorithm to improve the estimation accuracy of a non-invasive method for cardiac output measurement based on prolonged expiration

Cardiac output (CO) monitoring is important in the hemodynamic management of critically ill patients. In a previous study, a novel non-invasive technique for CO monitoring based on prolonged expiration was proposed. The novel method showed good agreement with thermodilution on stable mechanically ventilated patients; unstable patients were excluded. The aim of this study is to improve the outcome of the above mentioned method on hemodynamic unstable patients, requiring vasoactive medications, and showing marked cardiogenic oscillations on waveforms related to expired gases. This prospective study has been carried out on three cardiac surgery patients; eighteen CO measurements were performed on each patient, and these values were compared with data obtained by thermodilution. The designed and tested algorithm allowed to reach a good agreement between CO measured by our method and by thermodilution (e.g., the mean percentage differences were 4%, 11% and 3%). Even though further validation is necessary, the results are quite promising and the adopted solution appears to allow the suitability of the prolonged expiration method also on unstable patients.

Pulmonary carbon dioxide elimination for cardiac output monitoring in peri-operative and critical care patients: history and current status

Minimally invasive measurement of cardiac output as a central component of advanced haemodynamic monitoring has been increasingly recognised as a potential means of improving perioperative outcomes in patients undergoing major surgery. Methods based upon pulmonary carbon dioxide elimination are among the oldest techniques in this field, with comparable accuracy and precision to other techniques. Modern adaptations of these techniques suitable for use in the perioperative and critical are environment are based on the differential Fick approach, and include the partial carbon dioxide rebreathing method. The accuracy and precision of this approach to cardiac output measurement has been shown to be similar to other minimally invasive techniques. This paper reviews the underlying principles and evolution of the method, and future directions including recent adaptations designed to deliver continuous breath-by-breath monitoring of cardiac output.