Final answer:
The immediate action should be to assess the regularity and quality of the man's breathing. Following the assessment, the need for oxygen or airway management should be determined. It is important to refrain from initial interventions that can be invasive until the assessment is done.
Step-by-step explanation:
If a 40-year-old man is conscious but has an increased rate of breathing, the best immediate course of action is to assess the regularity and quality of breathing (C). Determining the pattern and effectiveness of the man's respirations will allow you to decide what subsequent steps are necessary, such as providing supplemental oxygen or using more advanced airway management techniques.
Applying 100% oxygen via a nonrebreathing mask (A) could be appropriate if the man has hypoxia, but it is essential to evaluate his breathing first. Immediately inserting a nasopharyngeal airway (B) or using a bag-mask device for ventilation (D) is not indicated unless the man is unable to maintain his airway or his breathing is inadequate. These interventions could potentially be harmful if not used correctly or if used prematurely before a proper assessment.
It's also vital to consider the context in which the individual is experiencing increased breathing. It could be due to a variety of causes, including anxiety, heart conditions, or other respiratory issues. You might need to consider measures like monitoring oxygen saturation, looking for signs of cyanosis, or checking for other symptoms that require immediate intervention.