High inspired CO₂ target accuracy in mechanical ventilation and spontaneous breathing using the Additional CO₂ method

Area of Science:

• Medical Imaging
• Physiology
• Respiratory Medicine

Background:

• Cerebrovascular reactivity imaging (CVR) assesses cerebral blood flow changes in response to stimuli.
• CO2 gas challenge is a common CVR method, but limited systems integrate with mechanical ventilation.
• This restricts CVR studies primarily to spontaneously breathing individuals.

Purpose of the Study:

• To develop and evaluate a novel method for CO2 gas challenge compatible with mechanical ventilation.
• To enable accurate control of inspired CO2 concentrations in ventilated patients for CVR assessment.
• To expand the application of CVR to critically ill patients requiring mechanical support.

Main Methods:

• Developed the 'Additional CO2' method, introducing concentrated CO2 into the ventilator circuit.
• Monitored respiratory gas flow to precisely adjust inspired CO2 levels.
• Validated the method using a test lung system and in spontaneously breathing subjects, including in an MRI environment.

Main Results:

• The Additional CO2 method demonstrated high accuracy in achieving target inspired CO2 levels.
• Consistent performance was observed in both mechanical ventilation and spontaneous breathing scenarios.
• The method proved effective within a magnetic resonance imaging environment.

Conclusions:

• The Additional CO2 method provides a reliable approach for CO2-induced CVR assessments during mechanical ventilation.
• This innovation facilitates broader implementation of CVR in mechanically ventilated patient populations.
• Enables crucial evaluation of cerebrovascular reserve in patients unable to breathe spontaneously.