This study is designed to compare three ultrasound-based aeration scores that were previously validated in specific populations, and to assess their correlation with computed tomographic measurement of pulmonary aeration in a population with different pathologies.

Hypothesis: The "Loss of Aeration Score" will be more accurate than a simplified version and another widely used score, the "Lung Ultrasound Score".

Assessment of lung aeration may have a great impact in the management of mechanical ventilation and follow-up of diverse lung pathologies. Computed tomographic scan is the gold standard method of lung aeration measurement but is rarely used because it requires transport of critically ill patients end exposes them to radiations. For these reasons, lung ultrasound would be an attractive alternative. Variants of different ultrasound-based aeration scores have been validated in different specific populations, but there is no comparison study that defines the more accurate score that should be used in a population with different pathologies.

Methods: Patients undergoing a computed tomographic scan for dyspnea or hypoxemia will have a standardized lung ultrasound examination on Day 1. For mechanically ventilated patients only, a lung ultrasound examination will be repeated on Day 2 to 4. End expiratory lung volume will also be measured in mechanically ventilated patients on Day 1 and Day 2 to 4. Lung ultrasound images will be interpreted blindly. Correlation of ultrasound-based aeration scores will be done with lung aeration measured by computed tomographic images.

Inclusion Criteria:

• Hospitalized or visiting the emergency room
• Will undergo a computed tomographic scan for dyspnea or hypoxemia

Exclusion Criteria:

• Poor echogenicity (morbid obesity, multiple thoracic dressings)
• Contraindications to superior limbs or torso mobilization