Condition category
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status
Results overdue

Plain English Summary

Background and study aims
After recovery from acute events that have led to intubation and ventilation, weaning from mechanical ventilation is the essential and usual component in the management of critically ill patients. Weaning failure, which occurs in approximately 25 to 42% of patients meeting the readiness criteria, is associated with prolonged mechanical ventilation, increased morbidity, and mortality. Thus, early identification of patients that are going to fail the liberation from mechanical ventilation is of paramount importance to improve the outcome of these critically ill patients.
Discontinuation of ventilatory support can be very challenging for clinicians mainly because the pathophysiology of weaning failure is complex and not fully understood. This study aims to investigate the central venous-to-arterial difference in carbon dioxide in patients who fail a weaning trial.

Who can participate?
Patients aged 18 years or older under mechanical ventilation for at least 48 hours who fulfil the inclusion criteria

What does the study involve?
Treatment will be continued as normal. Data will be collected on the success or failure of weaning from mechanical ventilation

What are the possible benefits and risks of participating?
The possible benefits are: It is well known that critically ill patients under mechanical ventilation who fail the extubation are at high risk of getting aspiration pneumonia, increased morbidity, and mortality. Weaning failure still occurs in as high as 40% of patients who already met the standard criteria for weaning as established by different societies of respiratory and critical care medicine. Therefore, looking for new indices that help to predict the weaning outcome accurately is of utmost importance to reduce the incidence of weaning failure, which is associated with high morbidity and mortality. We found that the combination of changes in CO2gap (difference between venous-to arterial PCO2 difference) and ScvO2 (central venous oxygen saturation) during a spontaneous breathing reliably predict the weaning outcome and can assist the Physician in his/her decision to extubate the patient in minimalization the risk of failure and its associated elevated morbidity and mortality.
Theoretically, there is no risk in participating in this study as the included patients have already venous central and arterial catheters inserted before being included in the study. Also, the decision of extubation was left at the discretion of the attending Physician who was following the standard international criteria of readiness for extubation.

Where is the study run from?
1. Centre Hospitalier de Lens
2. Centre Hospitalier d'Arras
3. Centre Hospitalier de Cambrai

When is the study starting and how long is it expected to run for?
December 2016 to February 2018

Who is funding the study?
Investigator initiated and funded

Who is the main contact?
Dr Jihad Mallat

Trial website

Contact information



Primary contact

Dr Jihad Mallat


Contact details

99 Route de la bassee

Additional identifiers

EudraCT number

Nil known number

Nil known

Protocol/serial number


Study information

Scientific title

Combination of central venous-to-arterial PCO2 difference and central venous oxygen saturation accurately predict weaning outcome from mechanical ventilation


Study hypothesis

PCO2 gap is able to accurately predict the weaning outcome from mechanical ventilation in critically ill patients

Ethics approval

Approved 01/12/2016, Centre Hospitalier de Lens Comité d’éthique (99 route de la Bassée, 62307, Lens Cedex, France; +33 321691234;, ref: 160402

Study design

Prospective multi-center study

Primary study design


Secondary study design

Cohort study

Trial setting


Trial type


Patient information sheet

Not available in web format. Please use contact details to request a participant information sheet.


Mechanical ventilation


A patient was included when readiness to wean criteria were met (see inclusion criteria)

A spontaneous breathing trial (SBT) was then performed, in semi-recumbent patients, on a T-piece with supplementary humidified oxygen to achieve arterial oxygen saturation >90% as measured by pulse oximetry. The duration of the SBT was 60 minutes. Criteria for poor SBT tolerance were:
1. Diaphoresis
2. Use of accessory respiratory muscles
3. RR > 35/min
4. Oxygen saturation by pulse oximetry <90% with FiO2 ≥50%
5. HR >140/min or greater than a 20% increase from baseline
6. Systolic blood pressure >180 mmHg or <90 mmHg
7. Development of cardiac arrhythmias; and/or low level of consciousness (Glasgow Coma Scale score <13).

The decision to stop SBT was made by physicians. Patients who did not tolerate the SBT were reconnected to a ventilator.

Patients who successfully completed the SBT were extubated and followed up for 72 hours. Weaning failure was diagnosed if SBT was aborted because of clinical intolerance or if the patient was extubated but required mechanical ventilation (invasive or non-invasive), because of respiratory failure, within the following 48 hours. Respiratory failure after extubation was defined as the development of at least one of the following:
1. Respiratory acidosis with pH <7.32 and arterial CO2 pressure (PaCO2) >45 mmHg
2. Arterial oxygen saturation <90% with FiO2 >0.5
3. RR>35/min
4. Clinical signs of respiratory fatigue

The management of post-extubation respiratory failure was not protocolized and left to the physician’s discretion

Intervention type



Drug names

Primary outcome measure

Weaning failure rate from mechanical ventilation defined as the development of at least one of the following:
1. Respiratory acidosis with pH <7.32 and arterial CO2 pressure (PaCO2) >45 mmHg
2. Arterial oxygen saturation <90% with FiO2 >0.5
3. RR>35/min
4. Clinical signs of respiratory fatigue

Secondary outcome measures


Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Aged 18 years or older
2. Under mechanical ventilation for at least 48 hours
3. Satisfied the weaning criteria. The readiness to wean criteria were:
3.1 The resolution or improvement of the underlying cause of respiratory failure for which the patient was intubated
3.2 Hemodynamic stability, defined as heart rate (HR) < 140/min and systolic blood pressure between 90 and 160 mmHg with no or minimal doses of vasopressors
3.3 Stable respiratory status, defined as oxygen saturation >90% with fraction of inspired oxygen (FiO2) ≤0.4 and positive end expiratory-pressure (PEEP) ≤8 cmH2O, respiratory rate (RR) ≤35/min, spontaneous tidal volume (Vt) >5 mL/kg, ratio of RR/Vt <105/min per liter, and no significant respiratory acidosis
3.4 Adequate mental status (Glasgow Coma Scale score >13)
3.5 Adequate cough.
4. Patients also had to have an arterial catheter and a central line with the tip confirmed by x-ray to be in the superior vena cava near at the entrance or in the right atrium.

Participant type


Age group




Target number of participants

85 patients

Participant exclusion criteria

1. Tracheotomized patients
2. Do-not-reintubate orders
3. Pregnancy
4. No informed consent
5. Poor cardiac echogenicity

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Centre Hospitalier de Lens
99 Route de la bassee

Trial participating centre

Centre Hospitalier d'Arras
Boulevard Georges Besnier

Trial participating centre

Centre Hospitalier de Cambrai
Avenue de Paris

Sponsor information


Centre Hospitalier de Lens

Sponsor details

99 Route de la bassee

Sponsor type

Hospital/treatment centre



Funder type


Funder name

Investigator initiated and funded

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Planned publication in a high-impact peer-reviewed journal

IPD sharing statement:
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request

Intention to publish date


Participant level data

Available on request

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

10/09/2019: Internal review. 06/09/2019: Trial’s existence confirmed by Comité d’éthique, Centre Hospitalier de Lens