What should the RT recommend when a patient on mechanical ventilation suddenly shows cyanosis, trachea deviation, and absent breath sounds on the left?

When a patient on mechanical ventilation presents with cyanosis, tracheal deviation, and absent breath sounds on one side, this clinical picture is strongly suggestive of a tension pneumothorax. In this scenario, transillumination is a useful technique for confirming the presence of a pneumothorax. It involves shining a light on the chest wall; in the presence of a pneumothorax, the light will appear more diffuse on the affected side, supporting the diagnosis.

The other options may not effectively address the acute urgency of the situation. Increasing ventilator settings, for instance, would not resolve the underlying problem, which is the mechanical blockage of airflow due to the pneumothorax. Intubation, while it may seem necessary, is not the immediate solution to a tension pneumothorax and could potentially worsen the patient's condition if the problem is not addressed first. Switching to manual ventilation might temporarily assist in providing ventilation, but without addressing the pneumothorax, it would not be an effective long-term solution.

Overall, using transillumination to detect a pneumothorax is the most appropriate recommendation in this acute setting, providing vital information to guide further treatment, such as needle decompression or chest tube placement.