Spontaneous pneumothorax: marker gas technique for predicting outcome of manual aspiration [published erratum appears in BMJ 1991 Mar 23;302(6778):697] OBJECTIVE--To determine whether in a patient with spontaneous pneumothorax the presence or absence of a pleural leak can be shown at the time of manual aspiration by use of a marker gas. Also, to find out if the technique can predict whether manual aspiration will be successful, hence avoiding the need for intercostal tube drainage. DESIGN--Prospective study of 25 episodes of pneumothorax during which patients breathed air from a Douglas bag that contained chlorofluorocarbon gases from a metered dose inhaler while the pneumothorax was aspirated. SETTING--Medical unit of a district general hospital. PATIENTS--22 patients who presented over nine months with acute pneumothorax. MAIN OUTCOME MEASURES--Presence or absence of chlorofluorocarbon marker gases in the aspirate. Presence or absence of sustained re-expansion of the affected lung in the chest radiograph. RESULTS--Marker gas was detected in the aspirate from 16 out of 25 pneumothoraces. Of these, 13 required intercostal tube drainage because of failure of the lung to re-expand. Marker gas was not detected in nine cases, and in all of these cases manual aspiration resulted in sustained re-expansion of the lung. CONCLUSIONS--The presence or absence of a pleural leak during manual aspiration of spontaneous pneumothorax can be shown by using this technique. The absence of marker gas in the aspirate implies that manual aspiration will be successful, whereas its presence predicts, in most cases, either failure of manual aspiration to expand the lung or early re-collapse of the lung. 