What is advisable when dealing with a patient who is experiencing a severe allergic reaction?

When a patient is experiencing a severe allergic reaction, particularly one that could lead to anaphylaxis, preparing for potential intubation is critical. This is due to the risk of airway compromise caused by swelling in the throat and difficulty breathing, which may develop rapidly. In cases of anaphylaxis, the body's reaction can lead to severe bronchospasm and airway edema, potentially obstructing airflow.

By preparing for intubation, medical personnel can ensure they are ready to secure the airway if the patient's condition deteriorates. This proactive approach can be life-saving, as it allows for timely intervention should the patient experience complete airway obstruction or respiratory failure.

The other options either lack urgency or are inappropriate for managing a severe allergic reaction. Encouraging the patient to relax does not directly address the immediate challenges posed by the reaction. Starting oxygen therapy without addressing the airway could miss critical steps needed to stabilize the patient. Providing a glass of water is contraindicated as it could increase the risk of aspiration if the patient has compromised airway protection. Therefore, preparing for intubation is a crucial step in the management of severe allergic reactions.