Which of the following conditions could worsen a patient's respiratory status?

Endotracheal tube obstruction directly impacts a patient's ability to receive adequate airflow, which is critical for maintaining oxygenation and ventilation. When the endotracheal tube is obstructed, whether due to mucus plugging, kinking, or any other cause, it restricts airflow into and out of the lungs. This can lead to reduced tidal volumes and inadequate ventilation, causing rising levels of carbon dioxide (hypercapnia) and declining levels of oxygen (hypoxemia), ultimately worsening the patient's respiratory status.

In contrast, low tidal volume ventilation can be a deliberate strategy in certain scenarios, such as lung-protective ventilation in ARDS, and while high PEEP levels can complicate the patient's hemodynamics or create alveolar overdistension, they do not create an immediate obstruction to airflow like endotracheal tube obstruction. Increased respiratory rate can also be a compensatory mechanism for hypoventilation or hypoxemia, but it doesn't directly cause obstruction and may be beneficial in some cases. Thus, among the options provided, endotracheal tube obstruction is the most critical factor that can acutely worsen a patient’s respiratory status.