The objective of this study is to compare the accuracy and correlation of the capnodynamic method for measuring mixed venous oxygen saturation (SvO2) with the standard reference method (pulmonary artery catheter), with the potential for the capnodynamic method to replace the traditional method in selected cases.

The main objective is to evaluate the accuracy and correlation of mixed venous oxygen saturation (SvO2) measured using the capnodynamic method in comparison with the invasive standard method using co-oximetry with a pulmonary artery catheter (PAC) Swan-Ganz, with the potential to replace it in selected cases, in patients who would benefit from hemodynamic monitoring with PAC for their clinical management and decision-making.

The investigator will also study the following secondary objectives:

• To assess whether the capnodynamic method (Capno-SvO2) detects changes over time in the studied variable (SvO2), showing good concordance and magnitude compared to the reference method.
• To evaluate the progression and trend of the Capno-SvO2 method in different clinical situations, such as in adult respiratory distress syndrome and patients with other respiratory pathologies, as well as patients with cardiac conditions.
• To assess the ability of the Capno-SvO2 method to detect changes in mixed venous oxygen saturation in response to therapeutic interventions (e.g., adjustments in mechanical ventilation, use of inotropes, vasopressors, or fluid therapy) or moderate hemodynamic changes.
• To evaluate the correlation between mixed venous oxygen saturation measured using the Capno-SvO2 method and other hemodynamic parameters, such as cardiac output, central venous pressure, and cardiac index.

Inclusion Criteria:

• Age > 18 years
• Not participating in any other interventional study at the time of the study.
• Patients under controlled mechanical ventilation in passive conditions.
• Situations where the responsible physician deems that, for the benefit of clinical management and therapeutic decision-making, the patient would benefit from the placement of a pulmonary artery catheter (Swan-Ganz) and/or monitoring of central or mixed venous saturation.
• Obtaining informed consent.

Exclusion Criteria:

• Failure to obtain informed consent.
• No need for invasive mechanical ventilation.

The study will be conducted in the ICU of the Hospital Universitario de la Princesa.

The study population will include all patients with medical conditions (respiratory or cardiac) who could benefit from the placement of a PAC and/or the monitoring of mixed venous saturation for clinical management and decision-making, or monitoring of central venous saturation if a pulmonary artery catheter is not required.