Patients presenting to the emergency department with acute dyspnea undergo arterial blood gas measurement and monitoring of transcutaneous capnography using the TCM5 monitor. The aim of this study is to determine whether GapCO2, the difference between transcutaneous and arterial pCO2 (PaCO2 - PtcCO2), is correlated with the congestive or non-congestive origin of dyspnea.

Upon arrival at the emergency department, patients are placed in the vital emergency reception area for monitoring. An emergency physician will review the selection criteria and offer the patient participation. The information sheet will be provided to the patient along with a copy of the non-opposition form in case of patient agreement.

Before the introduction of any treatment, a TC 92 sensor is placed on the earlobe (or on the forehead if the earlobe is inaccessible), connected to a Radiometer TCM5 monitor, measuring SpO2 (Massimo technology), perfusion index, and transcutaneous capnography (PtcCO2).

After a 5-minute equilibration period, measurements were taken throughout the duration of patient management. Standard diagnostic and therapeutic management will be provided according to the attending physician's prescription. The attending physician won't consider PtcCO2 (nor GapCO2) measurements in patient management.

At the time of data analysis, an adjudication committee comprising 2 emergency physicians from the inclusion service but not involved in patient care will review the complete medical records of patients to determine whether dyspnea was of congestive or non-congestive origin.

Inclusion Criteria:

• Age ≥ 18 years
• Patient presenting with acute dyspnea defined by a sensation of respiratory discomfort with at least one of the following criteria: RR ≥ 22 and/or SpO2 < 95%
• Arterial blood gas sampling performed as part of care
• Inclusion less than 1 hour after arrival time to the emergency department
• Non-opposition to participation in the study

Exclusion Criteria:

• Temperature greater than or equal to 37.5°C
• Patient who has already received a diuretic or vasodilator treatment in the emergency department or by a prehospital medical team
• Systolic blood pressure less than or equal to 100 mmHg and/or signs of peripheral hypoperfusion
• Inability to express refusal to participate in the study

Patient presenting to the emergency department of the inclusion center for acute dyspea