**Core Concept**
Positive pressure ventilation (PPV) is a life-supporting respiratory therapy that involves delivering air or oxygen at a pressure greater than atmospheric pressure into the lungs. This can cause overdistension of alveoli, leading to alveolar rupture and air leakage into the pleural space, known as pneumothorax.

**Why the Correct Answer is Right**
During PPV, the increased intrathoracic pressure can cause the alveoli to overinflate, leading to rupture of the alveolar walls and subsequent air leakage into the pleural space. This can result in a pneumothorax, which is a potentially life-threatening complication of PPV. The positive pressure can also cause the alveoli to become overdistended, leading to damage to the alveolar-capillary interface and subsequent pulmonary edema. The risk of pneumothorax is increased in patients with pre-existing lung disease, such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis.

**Why Each Wrong Option is Incorrect**
**Option B:** Bradycardia is not a direct complication of PPV. While bradycardia can occur in response to hypoxia or other complications of PPV, it is not a direct result of the positive pressure itself.

**Option C:** Decreased ventilation is not a complication of PPV. In fact, PPV is used to increase ventilation in patients who are unable to breathe on their own.

**Option D:** Arrhythmias can occur as a result of hypoxia or other complications of PPV, but they are not a direct complication of the positive pressure itself.

**Clinical Pearl / High-Yield Fact**
It is essential to carefully monitor patients on PPV for signs of complications, such as decreased oxygen saturation, increased respiratory rate, or decreased breath sounds on one side of the chest. Early recognition and management of these complications can help prevent serious morbidity and mortality.

**✓ Correct Answer: A. Pneumothorax**