Acute Respiratory Distress Syndrome (ARDS) is a severe lung condition characterized by poor oxygenation and stiff lungs. It begins within seven days of an inciting event and involves fluid accumulation in the air sacs, leading to difficulty breathing. Computed tomography (CT) scans are a detailed imaging tool used to assess lung changes associated with ARDS.
Why a CT Scan is Used for ARDS
A CT scan is used for patients with ARDS due to its ability to provide detailed information about the lung’s condition. While a standard chest X-ray shows bilateral lung infiltrates, a CT scan offers greater detail for diagnosis and ongoing assessment. It helps confirm ARDS by showing specific patterns of lung injury.
CT images allow medical professionals to assess the severity and extent of lung damage, which is often heterogeneous. CT can distinguish ARDS from other conditions with similar symptoms, such as heart-related pulmonary edema, by showing features like a normal-sized heart. Beyond initial diagnosis, CT scans can also detect complications like pneumothorax, which are difficult to identify with X-rays alone.
Key Features of ARDS on a CT Scan
CT scans reveal characteristic patterns in the lungs of individuals with ARDS. One common finding is ground-glass opacities, which appear as hazy areas. These opacities represent a partial filling of the air spaces with fluid and inflammation, allowing some air to still pass through.
Another observation is consolidation, which shows as denser, whiter areas. Consolidation indicates a more severe filling of the air sacs with fluid and inflammatory cells, leading to a complete loss of air in those regions. These opacities often appear in the dependent, or lower, lung zones due to gravity.
Atelectasis, or collapsed lung tissue, is also a common feature, particularly in the most dependent lung regions where gas volume can be significantly reduced. Pleural effusions, which are fluid collections around the lungs, can also be seen. Air bronchograms, where air-filled bronchi are visible within consolidated lung tissue, and bronchial dilation are common findings.
How CT Guides ARDS Treatment
Information from CT scans influences ARDS management and treatment. These images help medical teams optimize ventilator settings. CT findings can inform decisions about positive end-expiratory pressure (PEEP) levels, which help keep the air sacs open, and the benefit of prone positioning.
CT scans demonstrate that placing a patient in the prone position (lying on their stomach) can redistribute lung densities, moving them from dorsal to ventral areas, which improves oxygenation. This change in position can lead to more homogeneous aeration of the lung by reducing pleural pressure gradients and improving the distribution of ventilation. Prone positioning can significantly improve oxygenation in ARDS patients.
Beyond guiding ventilation, CT scans are also useful for identifying complications that require specific interventions. They can detect issues such as pneumothorax (collapsed lung from an air leak), pleural effusions, or the development of superinfections like lung abscesses or blebs. Identifying these complications promptly allows for targeted treatment, such as guided drainage of effusions or pneumothorax under CT guidance. Serial CT scans can also monitor the progression of the lung condition over time, helping clinicians track improvement or worsening and adjust treatment plans.