- Describe the radiologic, gross, and microscopic appearances of the lungs
There is diffuse opacification from consolidation, along with the hyaline membrane formation and type II cell hyperplasia.
- What is the diagnosis? How does this process occur?
This is pulmonary diffuse alveolar damage (DAD) which clinically is often called adult respiratory distress syndrome (ARDS). There are many causes, including shock from trauma, infections, inhalation of chemical irritants or hot gases in a fire, drug therapy, and others. DAD is essentially the final common pathway for any severe lung injury. Oxygen toxicity also potentiates the lung injury leading to DAD. Unfortunately, oxygen therapy is needed to treat the lung injury. DAD starts with injury to the epithelial cells of alveoli and endothelial cells of capillaries, resulting in exudation of fluids and proteins that form the hyaline membranes.
- What is the natural history of this process?
The early acute, or exudative, phase of DAD, most prominent in the first week of injury, is characterized by interstitial and intra-alveolar edema, passive congestion, inflammation, and hyaline membranes. The hyaline membranes are composed of fibrin-rich edema fluid mixed with the cytoplasmic remnants of necrotic epithelial cells. The type II epithelial cells undergo proliferation in an attempt to regenerate to alveolar lining. Physiologic consequences include severe hypoxemia, reduced lung compliance (requiring higher ventilator end expiratory pressure), reduced functional residual capacity (FRC), and a large shunt effect.
As the process continues, the hyaline membranes diminish and the type II cells increase, while there is interstitial thickening and increasing numbers of mononuclear inflammatory cells. The next stage, the proliferative or organizing stage of DAD, occurs after 1 to 2 weeks. The exudates organize, and interstitial thickening becomes more prominent. Fibroblasts begin laying down more collagen. Near the end of a month, there is extensive fibrosis, with gross changes (seen in image 8.3) of "honeycomb" lung.
- In addition to this disease, what other conditions reduce movement of air into the lungs? Of those conditions, which increase airway resistance?
Restrictive lung diseases (interstitial lung dieases) in general diminish lung filling. Bronchitis will also do this. Asthma with bronchoconstriction reduces movement of air, though there is also trapping of air. Diseases of muscle, such as poliomyelitis, or dystrophic or neurogenic muscular diseases, diminish air movement.
Of those conditions, asthma and bronchitis will increase airway resistance. The others decrease lung volume.
- The patient has been intubated for a month, but has a steadily worsening respiratory status. Family members are arguing about what to do. What can you do?
The majority of ethics consults in the hospital occur in the ICU. But an ethics consult is a sign of waiting too long, and needing outside help. Once in the ICU most patients lack decision making capacity, and family decisions are always more complex: there are potential differences of opinion, and even a surrogate appointed by the patient can be unsure what to do.
Family meetings are common in ICU cases. It allows everyone to air their opinion, and allows the ICU team to let the entire family know the patient's condition and be made aware of who the designated decision maker will be and why.
