The aim of this study is to evaluate/validate a new non-invasive method to continuously monitor effective lung volume in critically ill patients.

The capnodinamyc method is a new monitoring method that provides continuous (breath by breath) measurements of effective pulmonary blood flow (EPBF) and effective end-expiratory l lung volume (EELVCO2). The former refers to the non-shunted fraction of cardiac output and the latter to the functional end-expiratory lung volume (EELV) that contains CO2.

The capnodynamic method is based on the advanced analysis of CO2 kinetics and the law of Conservation of mass. It states that lungs have to eliminate a similar amounts of CO2 as produced by aerobic metabolism and reaches the lung via pulmonary perfusion. For its calculation, two different measurements are needed:

1. Exhaled CO2 measured by infrared optic sensor technology placed in a mainstream configuration between the endotracheal tube and the "Y" piece of the ventilator respiratory circuit.
2. Flow, airway pressure and ventilatory volumes measured by the mechanical ventilator spirometer.

The method requires the generation of cyclic small changes in the alveolar concentration of CO2 which is achieved by introducing a slightly modified breathing pattern. It consists of adding a short expiratory hold in each 3 out of 9 consecutive breaths and requires the patient to be in passive breathing conditions under mechanical ventilation.

EPBF and EELVCO2 have been validated in experimental conditions and the first validations in patients in the setting of general anesthesia are under way.

Methods:

This study on EELVCO2 in critically ill patients involves 2 types of evaluations:

The validation of absolute values of EELV by comparing it with CTsan. The trending ability of EELVCO2 in critically ill patients by comparing it with EIT.

A calculated sample size of 30 patients is required for each objective.

Inclusion Criteria:

• All patients on mechanical ventilation in passive breathing conditions in which a thoracic CTscan has been indicated for medical reasons and those with an EIT and a continuous cardiac monitoring
• Informed consent

Exclusion Criteria:

• Hemodynamic instability
• Presence of barotrauma/ pneumothorax
• Presence of bronchopleural fistulas
• Thorax alterations that preclude the positioning of the EIT electrode belt (usually at the IV intercostal space).

Critically ill patients undergoing mechanical ventilation