When blood accumulates inside the chest, which is also called the pleural cavity, the condition is referred to as Hemothorax. The usual reasons are bleeding from tumors inside the chest or abnormalities in blood clotting. A trauma inflicted on the chest can also cause hemothorax.
Impediments to the flow of blood or lymph can result in fluid accumulating in the chest, to form Hydrothorax. When a lymph vessel ruptures inside the chest, lymphatic fluid high in triglycerides may flood the chest; a condition known as Chylothorax. This rarely occurs in dogs.
When there is an accumulation of blood or other fluids in the chest, it results in respiratory distress. Rapid breathing, which is shallow and labored, is the usual symptom. The dog becomes listless and weak too. The veterinarian may drain the fluid and investigate the reason for the flooding, but the prognosis is usually poor.
Pneumothorax results from the accumulation of air in the chest cavity, probably due to trauma. It can occur without any apparent reason too. The lungs may collapse from the increased pressure in the chest. The dog breathes laboriously, taking in quick but shallow breaths. When these symptoms appear suddenly, the dog should be taken to the veterinarian immediately for emergency treatment.