Performance of a second generation pulmonary capnotracking system for continuous monitoring of cardiac output

Monitoring CO2 kinetics as a marker of cardiopulmonary efficiency

PURPOSE OF REVIEW

To describe current and near future developments and applications of CO2 kinetics in clinical respiratory and cardiovascular monitoring.

RECENT FINDINGS

In the last years, we have witnessed a renewed interest in CO2 kinetics in relation with a better understanding of volumetric capnography and its derived parameters. This together with technological advances and improved measurement systems have expanded the monitoring potential of CO2 kinetics including breath by breath continuous end-expiratory lung volume and continuous noninvasive cardiac output. Dead space has slowly been gaining relevance in clinical monitoring and prognostic evaluation. Easy to measure dead space surrogates such as the ventilatory ratio have demonstrated a strong prognostic value in patients with acute respiratory failure.

SUMMARY

The kinetics of carbon dioxide describe many relevant physiological processes. The clinical introduction of new ways of assessing respiratory and circulatory efficiency based on advanced analysis of CO2 kinetics are paving the road to a long-desired goal in clinical monitoring of critically ill patients: the integration of respiratory and circulatory monitoring during mechanical ventilation.

Comparison between capnodynamic and thermodilution method for cardiac output monitoring during major abdominal surgery: An observational study

BACKGROUND

Cardiac output (CO) monitoring is the basis of goal-directed treatment for major abdominal surgery. A capnodynamic method estimating cardiac output (COEPBF) by continuously calculating nonshunted pulmonary blood flow has previously shown good agreement and trending ability when evaluated in mechanically ventilated pigs.

OBJECTIVES

To compare the performance of the capnodynamic method of CO monitoring with transpulmonary thermodilution (COTPTD) in patients undergoing major abdominal surgery.

DESIGN

Prospective, observational, method comparison study. Simultaneous measurements of COEPBF and COTPTD were performed before incision at baseline and before and after increased (+10 cmH2O) positive end-expiratory pressure (PEEP), activation of epidural anaesthesia and intra-operative events of hypovolemia and low CO. The first 25 patients were ventilated with PEEP 5 cmH2O (PEEP5), while in the last 10 patients, lung recruitment followed by individual PEEP adjustment (PEEPadj) was performed before protocol start.

SETTING

Karolinska University Hospital, Stockholm, Sweden.

PATIENTS

In total, 35 patients (>18 years) scheduled for major abdominal surgery with advanced hemodynamic monitoring were included in the study.

MAIN OUTCOME MEASURES AND ANALYSIS

Agreement and trending ability between COEPBF and COTPTD at different clinical moments were analysed with Bland--Altman and four quadrant plots.

RESULTS

In total, 322 paired values, 227 in PEEP5 and 95 in PEEPadj were analysed. Respectively, the mean COEPBF and COTPTD were 4.5 ± 1.0 and 4.8 ± 1.1 in the PEEP5 group and 4.9 ± 1.2 and 5.0 ± 1.0 l min-1 in the PEEPadj group. Mean bias (levels of agreement) and percentage error (PE) were -0.2 (-2.2 to 1.7) l min-1 and 41% for the PEEP5 group and -0.1 (-1.7 to 1.5) l min-1 and 31% in the PEEPadj group. Concordance rates during changes in COEPBF and COTPTD were 92% in the PEEP5 group and 90% in the PEEPadj group.

CONCLUSION

COEPBF provides continuous noninvasive CO estimation with acceptable performance, which improved after lung recruitment and PEEP adjustment, although not interchangeable with COTPTD. This method may become a tool for continuous intra-operative CO monitoring during general anaesthesia in the future.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03444545.

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.

Journal of Clinical Monitoring and Computing 2018-2019 end of year summary: respiration

This paper reviews 28 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2018 and 2019, within the field of respiration. Papers were published covering endotracheal tube cuff pressure monitoring, ventilation and respiratory rate monitoring, lung mechanics monitoring, gas exchange monitoring, CO2 monitoring, lung imaging, and technologies and strategies for ventilation management.

Performance of a capnodynamic method estimating cardiac output during respiratory failure - before and after lung recruitment

Respiratory failure may cause hemodynamic instability with strain on the right ventricle. The capnodynamic method continuously calculates cardiac output (CO) based on effective pulmonary blood flow (CO_EPBF) and could provide CO monitoring complementary to mechanical ventilation during surgery and intensive care. The aim of the current study was to evaluate the ability of a revised capnodynamic method, based on short expiratory holds (CO_EPBFexp), to estimate CO during acute respiratory failure (LI) with high shunt fractions before and after compliance-based lung recruitment. Ten pigs were submitted to lung lavage and subsequent ventilator-induced lung injury. CO_EPBFexp, without any shunt correction, was compared to a reference method for CO, an ultrasonic flow probe placed around the pulmonary artery trunk (CO_TS) at (1) baseline in healthy lungs with PEEP 5 cmH₂O (HL_P5), (2) LI with PEEP 5 cmH₂O (LI_P5) and (3) LI after lung recruitment and PEEP adjustment (LI_Padj). CO changes were enforced during LI_P5 and LI_Padj to estimate trending. LI resulted in changes in shunt fraction from 0.1 (0.03) to 0.36 (0.1) and restored to 0.09 (0.04) after recruitment manoeuvre. Bias (levels of agreement) and percentage error between CO_EPBFexp and CO_TS changed from 0.5 (− 0.5 to 1.5) L/min and 30% at HL_P5 to − 0.6 (− 2.3 to 1.1) L/min and 39% during LI_P5 and finally 1.1 (− 0.3 to 2.5) L/min and 38% at LI_Padj. Concordance during CO changes improved from 87 to 100% after lung recruitment and PEEP adjustment. CO_EPBFexp could possibly be used for continuous CO monitoring and trending in hemodynamically unstable patients with increased shunt and after recruitment manoeuvre.

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.

Journal of clinical monitoring and computing end of year summary 2018: hemodynamic monitoring and management

Hemodynamic management is a mainstay of patient care in the operating room and intensive care unit (ICU). In order to optimize patient treatment, researchers investigate monitoring technologies, cardiovascular (patho-) physiology, and hemodynamic treatment strategies. The Journal of Clinical Monitoring and Computing (JCMC) is a well-established and recognized platform for publishing research in this field. In this review, we highlight recent advancements and summarize selected papers published in the JCMC in 2018 related to hemodynamic monitoring and management.

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.