Tag Archives: occult

Is It Safe to Watch Occult Pneumothorax in Ventilated Patients?

An occult pneumothorax is one that is visible on chest CT but not conventional chest xray. The pneumo can be a single bubble, or it can be a larger one that layers out over the lung but cannot be seen on plain xray. This air is generally watched for a period of time, typically 6 hours, then a repeat plain radiograph is obtained to see if it has become visible. 

The pneumothorax literature cautions us about watching visible pneumothoraces in patients who are placed on positive pressure ventilation. The rationale is that this may force more air out of an acutely injured lung, resulting in an enlarging pneumothorax. Many have recommended that a chest tube be placed in any patient with a visible pneumothorax on positive pressure ventilation to avoid the possibility of developing a tension pneumothorax.

But what about the occult pneumothorax? Since they are generally very small, do they pose the same risk? A paper from 2008 retrospectively reviewed 79 patients with occult pneumothorax , 20 of whom were placed on ventilators. 51 of 59 of the non-ventilated patients had no change in their occult pneumo (86%), while 16 of 20 of the ventilated patients had no progression (80%).

The study numbers are small, but suggest that occult pneumothoraces can be safely watched. The real question is, how long do you have to watch it? Typically, ventilated patients get regular chest xrays, so monitoring for progression of the pneumo should be easy.

Reference: American Surgeon 74(10):958, 2008.

Factors Predicting Failure of Observation of Occult Pneumothorax

An occult pneumothorax is defined as one that is seen on CT scan, but not on plain chest x-ray. It is a common finding in blunt trauma that is evaluated using CT 2-12% of scans), but there is no consensus on management. It is recognized that some of these progress and require insertion of a chest tube, while many can be observed safely. The authors try to define what factors predict the need for chest tube management.

The authors reviewed their experience over a 3 year period, and identified 642 patients (10% of their registry entries) with a pneumothorax. 283 were occult, and 98 ultimately received a chest tube.

They found that age>35, ISS>24, more than 4 rib fractures, and need for positive pressure ventilation increased the risk for chest tube insertion. These seem to make sense, but there was one significant limitation in this study: there were no standard indications for a chest tube insertion among the surgeons involved with these patients. There was significant variability, so the actual need for tube insertion was probably less than reported.

An audience member related one anecdotal factor for chest tube as well: a heavy smoking history. This makes intuitive sense, but not everything that makes sense is borne out by research.

At Regions, we define an occult pneumothorax the same way these authors did. We routinely get a delayed chest xray 6 hours later. If there is still no visible pneumothorax, we stop looking. If it is visible, we will obtain periodic (q12-24 hrs) xrays until it stabilizes or grows to a size that demands tube or pigtail insertion.

Given the data conveyed in this paper, we will consider watching a bit longer than 6 hours in patients at higher risk.

Reference: Factors Predicting Failed Observation of Occult Pneumothorax in Blunt Trauma. Selander, Minshall, couillard, Leon. Medical University of South Carolina.

Presented at the 23rd Annual Scientific Assembly of the Eastern Association for the Surgery of Trauma