Small spontaneous pneumothoraces do not always require treatment, as they are unlikely to proceed to respiratory failure or tension pneumothorax, and generally resolve spontaneously. This approach is most appropriate if the estimated size of the pneumothorax is small (defined as <50% of the volume of the hemithorax), there is no breathlessness, and there is no underlying lung disease. It may be appropriate to treat a larger PSP conservatively if the symptoms are limited. Admission to hospital is often not required, as long as clear instructions are given to return to hospital if there are worsening symptoms. Further investigations may be performed as an outpatient, at which time X-rays are repeated to confirm improvement, and advice given with regard to preventing recurrence (see below). Estimated rates of resorption are between 1.25% and 2.2% the volume of the cavity per day. This would mean that even a complete pneumothorax would spontaneously resolve over a period of about 6 weeks. There is, however, no high quality evidence comparing conservative to non conservative management.

Secondary pneumothoraces are only treated conservatively if the size is very small (1 cm or less air rim) and there are limited symptoms. Admission to the hospital is usually recommended. Oxygen given at a high flow rate may accelerate resorption as much as fourfold.

The treatment of pneumothorax depends on a number of factors, and may vary from discharge with early follow-up to immediate needle decompression or insertion of a chest tube. Treatment is determined by the severity of symptoms and indicators of acute illness, the presence of underlying lung disease, the estimated size of the pneumothorax on X-ray, and – in some instances – on the personal preference of the person involved.

In traumatic pneumothorax, chest tubes are usually inserted. If mechanical ventilation is required, the risk of tension pneumothorax is greatly increased and the insertion of a chest tube is mandatory. Any open chest wound should be covered with an airtight seal, as it carries a high risk of leading to tension pneumothorax. Ideally, a dressing called the "Asherman seal" should be utilized, as it appears to be more effective than a standard "three-sided" dressing. The Asherman seal is a specially designed device that adheres to the chest wall and, through a valve-like mechanism, allows air to escape but not to enter the chest.

Tension pneumothorax is usually treated with urgent needle decompression. This may be required before transport to the hospital, and can be performed by an emergency medical technician or other trained professional. The needle or cannula is left in place until a chest tube can be inserted. If tension pneumothorax leads to cardiac arrest, needle decompression is performed as part of resuscitation as it may restore cardiac output.

Hydropneumothorax is defined as the presence of both air and fluid within the pleural space. An upright chest x-ray will show air fluid levels. The horizontal fluid level is usually well defined and extends across the whole length of hemithorax.

This can be remembered by 4 'S'

- Straight line dullness

- Shifting dullness

- splash

- Sound of coin

- fullness of chest