Which of the following is a common sign of respiratory distress?

Nasal flaring is a common sign of respiratory distress, particularly in children and infants, but it can also be observed in adults. This physical response occurs when an individual is struggling to breathe and indicates that their body is trying to increase air intake. When nasal flaring is present, it often signals that the lungs are not providing adequate oxygenation, resulting in increased effort to breathe. This phenomenon reflects the engagement of accessory muscles in breathing and the body's attempt to compensate for inadequate respiratory function.

In contrast, the other options are not indicative of respiratory distress. For instance, weight gain can be linked to various factors unrelated to respiratory status, drowsiness might be a symptom of hypoxia, but it is less specific than nasal flaring, and improved oxygen saturation actually suggests that respiratory function is adequate or improving, which is contrary to the idea of respiratory distress. Thus, nasal flaring serves as a clear and observable physical sign that a patient may be in respiratory distress, highlighting the need for further evaluation and possible intervention.