Final answer:
A neonate becoming cyanotic and bradycardic during invasive positive pressure ventilation, with hyperlucency on the left chest, likely has a pneumothorax, which requires immediate treatment to re-expand the lung.
Step-by-step explanation:
If a neonate is receiving invasive, positive pressure ventilation and suddenly becomes cyanotic and bradycardic, with transillumination revealing hyperlucency of the left chest, the most likely cause of the patient's unstable presentation is a pneumothorax. The hyperlucency on transillumination suggests the presence of air in the pleural space, which is characteristic of a pneumothorax. This condition leads to the collapse of the lung on the affected side, causing acute respiratory distress and decreased oxygenation, evidenced by cyanosis. Bradycardia can occur as a reflex to the hypoxia. Immediate intervention, which may include needle decompression and chest tube placement, is critical to re-expand the lung and stabilize the patient.