Which feature of a patient's breathing could indicate severe respiratory distress?

The use of accessory muscles during breathing is a significant indicator of severe respiratory distress. In healthy individuals, breathing is primarily a passive process that uses the diaphragm and intercostal muscles. However, when someone is experiencing severe respiratory distress, the body attempts to enhance ventilation by recruiting additional muscles, such as those in the neck (sternocleidomastoid) and abdomen. This engagement of accessory muscles demonstrates that the body is struggling to meet its oxygen demands.

In contrast, shallow breathing might suggest a number of different issues, including pain or fatigue, but it does not specifically indicate the level of respiratory distress as clearly as the use of accessory muscles. Quiet breathing generally suggests a stable respiratory pattern and can often indicate that the person is not in distress. Periodic breathing, which involves alternating patterns of fast and slow breathing, can occur for a variety of reasons and does not solely signify severe distress, as it may be seen in some stages of sleep or other non-emergency conditions. Thus, the use of accessory muscles is the most definitive sign of severe respiratory distress.