Respired Gases in Patients Post Cardiac Surgery (REGAPS)

April 29, 2023 updated by: DrDonTishanWellalagodage, University of Oxford

An Observational Study of the Relationship Between Respired Gases, Mixed Venous Oxygen Content and Cardiac Output in Mechanically Ventilated Patients Post Cardiac Surgery

Certain diseases relating to the heart can only be definitively treated with surgery. When untreated, these can lead to heart failure with a lack of supply of oxygen-rich blood to the tissues, leading to damage to other organs.

Adults who undergo heart surgery vary greatly in terms of age and relative health. This has significant implications when predicting outcomes in the aftermath of surgery. For example, a 90-year-old man with a variety of comorbidities such as diabetes and high cholesterol who requires a heart valve replacement may have an unfavourable chance of surviving the postoperative period when compared to an 18-year-old woman with no significant medical history undergoing the same procedure.

Almost invariably, patients are admitted to an Intensive Care Unit (ICU) following heart surgery. This is done to facilitate close monitoring of the patients' vital organ functions and to also provide organ support if needed. For the heart, this can include the administration of drugs to help a heart pump forcibly, cause blood vessels to contract and increase blood pressure. Patients who have undergone heart surgery have been placed on a mechanical ventilator, following a tube placed in their windpipe. This form of ventilation often continues in ICU for a period of time, depending on the patient's condition.

One specific type of ICU level monitoring that occurs in patients who have undergone heart surgery is cardiac output monitoring. This involves a thin tube, called a pulmonary artery catheter, that extends from the skin to the heart, via large blood vessels. Cardiac output monitoring is essential in this patient group to guide organ support and to provide information of how well the heart is functioning.

In this observational study, the investigators wish to study patients who have undergone cardiac surgery, are receiving mechanical ventilation and have pulmonary artery catheters inserted. The investigators will collect cardiopulmonary data in these patients and compare these data with values of exhaled and inhaled gases (oxygen and carbon dioxide) over the same time period. This will enable the investigators to investigate the link between cardiopulmonary data and respired gas values.

A better understanding of this link between cardiopulmonary function and oxygen/carbon dioxide values will then inform future studies aiming to determine the effect of various interventions in similar patient groups.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

The cardiovascular system of patients undergoing major cardiac surgery may be unstable during the immediate post-operative period. The core interventions employed as part of routine cardiothoracic ICU management of such patients include the administration of fluids and blood, cardiac pacing, and inotropic support. All of these therapies can be guided by a knowledge of the patient's cardiac output and mixed venous oxygen saturation (SvO2). Pulmonary artery catheters provide an invasive approach that allows the measurement of SvO2 (by blood sampling) and cardiac output (by thermodilution).

For any particular patient, there is always a trade-off between the risks of placing a pulmonary artery catheter and the advantages that it brings when managing patients whose cardiovascular status may be unstable. The primary objective of this study is to explore whether continuous measurement of respired gas exchange, when coupled with small (clinically insignificant), transient variations in inspired oxygen and alveolar carbon dioxide, can be used to calculate mixed venous oxygenation and cardiac output without pulmonary artery catheterisation. If so, then this might provide the basis for a non-invasive approach by which estimates of these parameters can be obtained in patients for whom the benefits of a placing a pulmonary artery catheter do not outweigh the risks.

In order to know the mixed venous oxygenation and cardiac output, this study needs to be conducted in patients who are undergoing pulmonary artery catheterisation as part of their standard clinical care. Patients receiving non-invasive cardiac output monitoring will also be considered. In relation to this, in the UK there are approximately 34,000 major cardiac surgeries which take place each year. Major surgeries in this context include, but are not limited to, coronary artery bypass grafting (CABG), valve replacement or repair and proximal aortic repairs or reconstruction. Following surgery, these patients will invariably be admitted to a Cardiothoracic Intensive Care Unit (CTICU) for the purposes of close cardiorespiratory monitoring and intervention. Many of the patients admitted to CTICU in the postoperative period will require cardiac output monitoring as well as SvO2 measurement. To facilitate this pulmonary artery (PA) catheters are inserted in the perioperative period or non-invasive cardiac output monitoring is utilised postoperatively. Standard operating procedures in our CTICU involve mixed venous sampling for continuous mixed venous oximetry and modern thermodilution via heated catheter for cardiac output measurements. Arterial blood gas samples are taken approximately every hour while the patient is mechanically ventilated.

If it is possible to use measurements of respired gas exchange to estimate cardiac output and SvO2, then they have to be very accurate. The opportunity to obtain measurements with the required precision has arisen from the development of technology that uses laser absorption spectroscopy to measure gas exchange: the Optical Gas Analyser (OGA).

The predicted cardiac output and mixed venous oxygenation are obtained from the measurements of gas exchange by non-linear regression. This process involves a computational model of the lung and circulation that, given particular physiological parameter values and an overall respired gas flow, can calculate the respired gas flows for oxygen, carbon dioxide and nitrogen. The process of non-linear regression is used progressively to adjust the physiological parameter values of the model until the calculated respired gas flows from the model closely match those measured with the OGA. The parameters of the model then provide the cardiac output and SvO2.

In terms of comparators, thermodilution via pulmonary artery catheterisation is generally considered the 'practical' gold standard for measurement of cardiac output in clinical practice. These measurements are available from the pulmonary artery catheter as part of standard clinical care. However, the direct Fick approach is really the true gold standard for the measurement of cardiac output. This requires the mixed venous oxygen content (from the pulmonary artery catheter), the arterial oxygen content (from arterial blood gas measurements) and the oxygen consumption of the patient. The last of these measurements is not available clinically, and this makes the direct Fick method impractical for uses in standard clinical care. Of note, the OGA will supply this measurement, and so a calculation of cardiac output by the direct Fick approach should also be possible in this study.

In summary, A better understanding of the cardiorespiratory changes that occur in post cardiac surgery patients undergoing mechanical ventilation will aid future studies seeking to determine how best to guide various forms of therapy. This will, hopefully, lead to better medical care and improved outcomes in this patient group.

Study Type

Observational

Enrollment (Anticipated)

30

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • United Kingdom
    • Oxfordshire
      • Oxford, Oxfordshire, United Kingdom, OX3 9DU
        • Recruiting
        • John Radcliffe Hospital
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

Adult patients receiving mechanical ventilation following cardiac surgery

Description

Inclusion Criteria:

  • Participant is willing and able to give informed consent for participation in the study.
  • Male and female, aged 18 years or above
  • Receiving mechanical ventilation via an endotracheal tube in ICU, directly after cardiac surgery
  • Have a pulmonary artery catheter in-situ or receive non-invasive cardiac output monitoring

Exclusion Criteria:

• Patient is receiving palliative care

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Observational Models: Cohort
  • Time Perspectives: Prospective

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Main cohort
Patients undergoing cardiac surgery who will have a pulmonary artery catheter in-situ at the time of admission to cardiac intensive care postoperatively.
Other: Data collection using the Optical Gas Analyser
To allow the OGA to acquire certain physiological data during the study it will be necessary to slightly vary the tension of oxygen and carbon dioxide for short periods. The changes involved will be of a lesser magnitude than those often seen due to natural variation over time in critically ill patients. The FiO2 will be increased by around 20% from baseline for several minutes; this is a far more modest increase than is seen with the practice of pre-oxygenation - a transitory increase in fraction of inspired oxygen ( FiO2) to 100% - performed regularly in ICU patients to make certain routine interventions safer. The end-tidal CO2 level will also briefly (1-2 min) be altered by around 1 kPa by transient adjustment of the ventilator settings.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Oxygen (O2)
Time Frame: Up to 12 hours
Measured from the OGA
Up to 12 hours
Carbon dioxide (CO2)
Time Frame: Up to 12 hours
Measured from the OGA
Up to 12 hours

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Mixed venous oxygen saturation
Time Frame: Up to 12 hours
Measured from pulmonary artery catheter
Up to 12 hours
Cardiac output
Time Frame: Up to 12 hours
Measured from pulmonary artery catheter or non-invasive cardiac output monitor
Up to 12 hours

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Oxford

Investigators

  • Study Director: Peter A Robbins, MBBS DPhil, University of Oxford

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

October 30, 2022

Primary Completion (Anticipated)

March 1, 2024

Study Completion (Anticipated)

March 1, 2024

Study Registration Dates

First Submitted

August 13, 2022

First Submitted That Met QC Criteria

September 5, 2022

First Posted (Actual)

September 7, 2022

Study Record Updates

Last Update Posted (Actual)

May 3, 2023

Last Update Submitted That Met QC Criteria

April 29, 2023

Last Verified

April 1, 2023

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 16070
  • IRAS 306400 (Other Identifier: Health Research Authority NHS UK)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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