This is a prospective clinical trial with each patient serving as his/her own control. Patients will be recruited in three different Hong Kong hospital. All patients at the recruitment centers with ongoing air leak after ≥ 3 days from the initial diagnosis of SSP will be approached by site investigators. Patient consented to enter the study will have their rate of air leak measured on day 3 (or after if enrolled later than day 3) byreplacing the conventional chest drain system with the digital chest drainage device (Thopaz).

Autologous blood patch will be instilled if the patient still has persistent air leak on day 5 of chest drain insertion ( or 48 hours of electronic chest drain measurement of airleak).

The patient must have a chest tube in place and checked to be patent. Approximately 1.5ml/kg of venous blood will be withdrawn from the patient and immediately instilled it into the pleural cavity with aseptic technique via the chest tube already in situ. (There is no standard amount of blood used for ABPT. A small randomized study advocated that the use of 1.5ml/kg as it provided the optimal benefits.) The drain is then flushed with 20ml normal saline to avoid clotting. The tube of the drain is immediately elevated to 60cm above the insertion point of the chest tube at the patient's chest wall for 2 hours. This method allows ongoing evacuation of any air leak while the instilled blood can stay within the pleural cavity. The tube is never clamped at any stage to avoid any risk of tension pneumothorax. The patient was asked to change his position in bed every 10 minutes (supine, right lateral, prone, left lateral, head down and sit upright) during the two-hour period to aid distribution of blood over the visceral pleura. The tube is returned to normal position after two hours and the patient is free to ambulate. Analgesia is freely available for the patient should the need arise, but will not be prescribed routinely as existing data suggest it is uncommon.

Patients will remain under close observation after the instillation for the next 6 hours by experienced respiratory doctors and nurses, in particular for any suggestion of tube blockage or worsening pneumothorax. The tube will be flushed with saline (of an amount similar to the dead space of the tube) if that occurs. In the very unlikely event that the blockage is not correctable, a new chest tube may be placed if deemed clinically necessary. Prophylactic antibiotics will be given at the discretion of the attending clinician. The amount of air leak is measured continuously before and after ABPT using Thopaz system. Patients are free to receive any other therapy (except pleurodesis) during the treatment period.

Inclusion Criteria:

• aged 18 years or older;
• radiographically proven pneumothorax and underlying lung disease (either pre-existing or shown in diagnostic imaging at presentation);
• chest tube inserted which still shows an air leak at day 5 (or later) after the first radiographic evidence of a pneumothorax.

Exclusion Criteria:

• inability to provide informed consent;
• a chest tube smaller than 12 F (because of the risk of blockage by blood)
• bilateral pneumothorax
• uncorrectable coagulopathy
• active or recent (within 6 weeks) pleural infection
• use of long term steroid or immunosuppressant
• septicaemia or active extrapleural infection (eg pneumonia)