Thoracic surgery is generally considered to be a complex and high-risk type of surgery due to various factors. Here are a few reasons:

1. Proximity to vital organs: The thoracic region of the body contains critical organs such as the heart, lungs, and major blood vessels. Any surgical intervention in this area requires extreme care as even minor mistakes could have severe consequences.

2. Complexity of procedures: Thoracic surgeries often involve intricate procedures like lung resections, heart surgeries, and major blood vessel repairs. These procedures require a high level of surgical skill and expertise, and any errors could result in substantial complications or even death.

3. Physiological challenges: Unlike some other surgeries, thoracic surgeries can pose unique challenges due to the physiological changes that occur during the procedure. Manipulating the lungs can lead to difficulties in maintaining ventilation and oxygenation, potentially causing respiratory problems.

4. Post-operative complications: Thoracic surgeries may carry a higher risk of post-operative complications compared to other types of surgeries. These complications include pneumonia, infection, bleeding, blood clots, air leaks, and problems with wound healing, among others.

5. Limited surgical access: The thoracic cavity is surrounded by the rib cage, which limits access for the surgeon. This restricted access can increase the complexity of the surgery and potentially lead to more complications.

It is important to note that advancements in surgical techniques, technology, and anesthesiology have significantly reduced the risks associated with thoracic surgery. However, due to the intricate nature of the procedures and the importance of the organs involved, thoracic surgery is still generally considered to be a high-risk surgical field.