The most important step in the initial evaluation is deciding whether an airway needs to be established. Pulse oximetry should be monitored in patients with upper airway obstruction, but it must be emphasized that blood oxygenation can remain normal right up to the time of respiratory arrest. A normal pulse oximetry should not be interpreted as a sign that obstruction is not significant. The clinician must assess the patient's work at breathing and his or her overall status. One should look for signs of retractions in the neck or abdomen during inspiration.
Retractions are a warning sign that accessory muscles are necessary to maximize airflow.
Any patient using this degree of effort to breathe may collapse at any time and must be considered for respiratory support. Certain features in the patient history can be very useful in the differential diagnosis. A history of heavy alcohol or tobacco consumption is suspicious for squamous cell carcinoma. Use of ACE inhibitors or a family history of airway problems suggest angioedema. In these cases, the patient should be asked if any minor episodes of swelling preceded the presenting complaint.