Final answer:
Postoperative atelectasis primarily results from impaired respiratory mechanics due to the relaxing effects of anesthesia and lack of mobility post-surgery, with reduced lung compliance and increased airway resistance as contributing factors.
Step-by-step explanation:
The major contributing factor in the development of postoperative atelectasis is the impairment of normal respiratory mechanics due to factors such as anesthesia and immobility. During general anesthesia, for example, the muscles necessary for breathing and moving the tongue can relax excessively, sometimes partially or fully blocking the airway and inhibiting normal lung function. To avoid such complications during surgery, the safest procedure is endotracheal intubation, which maintains an open airway to the lungs. However, post-surgery, there may still be a period where the muscles of respiration have not regained full control, leading to a risk of atelectasis. Additionally, reduced lung compliance and increased airway resistance can lead to a V/Q mismatch, further contributing to the development of postoperative atelectasis.