Atelectasis

This code represents the partial or complete collapse of a lung or a lobe of a lung, resulting in reduced or absent gas exchange. It occurs when the alveoli within the lung become deflated or filled with fluid.

Use this code for acquired atelectasis in adults, often seen post-operatively, due to airway obstruction (e.g., mucus plug, foreign body), or external compression. Documentation should clearly state "atelectasis" and exclude congenital or newborn forms.

• Do not use for atelectasis documented as congenital or occurring in a newborn; refer to codes in Chapter 16 (P00-P96).
• Distinguish from tuberculous atelectasis, which is coded to A15 when active.
• Code any underlying cause of the atelectasis (e.g., pneumonia, tumor) as an additional diagnosis.