Treatment of a pneumothorax often requires insertion of an intercostal chest drain. Usually the tube is connected to an underwater seal which acts as a one way valve, allowing air to escape from the pleural space and thereby preventing the development of a tension pneumothorax. We wish to highlight the case of a patient who developed a potentially life threatening problem resulting from the partial occlusion of a chest drain bottle air outlet port by a plastic cap supplied with the equipment.

A 60 year old man with COPD developed a large right pneumothorax. Aspiration was unsuccessful so a chest drain was inserted. This was connected to an underwater seal using a chest drain bottle supplied by Rocket Medical plc (Watford, UK). The patient's symptoms initially improved and a chest radiograph showed the chest drain to be in a good position. The fluid in the chest tube varied with the respiratory cycle. Approximately 6 hours after insertion of the tube the patient developed dyspnoea and widespread surgical emphysema. It was also noted that the fluid in the chest drain was no longer moving with respiratory manoeuvres. A further chest radiograph showed that the position of the chest drain was unchanged. It was then noticed that a plastic cap was occluding the air outlet port of the chest drain bottle. Once the cap was removed there was an immediate release of air through the chest drain and symptomatically the patient became less breathless.

The plastic disposable bottle described in this case is in widespread use in the UK and is supplied in a sealed plastic wrapping. It has two ports in the lid—one for the distal end of a chest drain tubing set (covered by a red cap) and the second is an air outlet (covered with a green cap). The cap is shaped so as not to form a complete seal over the air outlet port and we understand its main purpose is to prevent spillage on disposal. No instructions are supplied to indicate that the cap should be removed after connection to a chest drain to allow escape of air. It would therefore be easy to overlook removal of the cap or even for a member of medical or nursing staff not familiar with the management of chest drains to replace it. In vitro studies in our laboratory have demonstrated a significant rise in pressure inside the chest drain bottle under circumstances of high flow, particularly when the cap had been pushed in (details available on request). In theory this rise in pressure in the bottle could impair drainage and lead to a tension pneumothorax. The fact that the cap does not form a complete seal means that this complication may not develop for a period of time after the chest drain has been inserted.

Since we considered the design of this bottle was unsafe we reported the events to the manufacturers. In turn, the manufacturer modified the design of the occluding cap to increase the amount of flow through it. We would be interested to hear of similar problems that have been encountered with this device or other chest drain systems in which there is an occluding cap.