Tag Archives: pneumothorax

How To Predict the Need for Chest Tube in Occult Pneumothorax

Occult pneumothorax occurs somewhere between 2% and 12% in all blunt trauma patients. Many of these pneumothoraces never progress and thus never need treatment. Is there a way that we can identify ones that are likely to get worse?

A retrospective study of 283 blunt trauma patients with occult pneumothorax was presented at the EAST Annual Scientific Assembly last January. A total of 98 of these patients underwent chest tube insertion within 7 days, and 185 patients were successfully observed.

The authors noted an inverse relationship between age and successful conservative management. Patients with more serious injuries failed expectant management more frequently. Finally, patients with more rib fractures also tended to fail.

The authors estimated the risk of failure of expectant management based on these critieria and found:

  • Age > 35 – 36%
  • ISS > 24 – 20%
  • Rib fractures >= 4 – 53%

The risk with having none of these was 10%, and the risk with all was 75%! 

The time interval for placement was also interesting. 80% of the failures requiring a chest tube occurred within 24 hours, with most occurring in the first 2 hours. The authors also found that 40% of patients who were placed on a ventilator failed.

Obviously, this is a small retrospective study and the exact criteria for placing a chest tube were not specified. Nevertheless, it provides a simple tool that allows us to keep an eye on a subset of patients who are likely to fail observation of occult pneumothorax.

Reference: Factors Predicting Failed Observation of Occult Pneumothoraces in Blunt Trauma. Selander, Med Univ of South Carolina. EAST 2010 Annual Scientific Assembly.

Extended FAST Exam in Trauma Patients

By now, every emergency medicine physician and surgeon knows what FAST is. This valuable technique allows us to quickly (get it?) determine whether a patient has blood in the abdomen or around the heart which might require operative management. Extended FAST (E-FAST) is an extension of the original technique that allows us to detect the presence of pneumothorax or hemothorax more quickly and accurately than with the conventional chest x-ray.

Both hemothorax and pneumothorax can be missed by x-ray. It takes at least 200cc of free fluid in the chest to show on the chest x-ray, assuming an ideal body habitus. As little as 20cc can be detected using the E-FAST. Studies have also shown that 30-50% of pneumothoraces are missed by x-ray. This diagnostic inaccuracy is due to the fact that hemothoraces settle out posteriorly and pneumothoraces anteriorly. Since the vast majority of chest x-rays in major trauma patients are taken with the patient supine to protect their spine, the bulk of the blood or air have layered out and cannot be seen well. A chest x-ray is still needed, however, to determine injury to the mediastinum and lung parenchyma.

E-FAST exam can be performed by using the standard curvilinear probe. It is usually placed longitudinally on the anterior chest to detect pneumothorax, using the space between two ribs as the “window” to the pleura. The depth setting should be adjusted so that only about 4cm is visible on the display. The junction of the visceral and parietal pleura should be visualized at the backside of the ribs. With a very steady hand, the junction between the two sets of pleura should be scrutinized closely.

If the two sets of pleura slide freely over each other, pneumothorax is unlikely. If not, it may be present. Pneumothorax is not a uniform phenomenon, except when it is of large size. It may be necessary to move the probe to a few other rib spaces to ensure that a smaller pneumothorax is not present.

FALSE POSITIVE ALERT! If the patient is not ventilating well, or if they have a right mainstem intubation, the affected lung(s) may not show the sliding sign, leading the examiner to think they have a problem when they may not.

To detect a hemothorax, the probe is directed upward somewhat when doing the right and left upper abdominal views. A dark triangle located above the diaphragm indicates fluid in the chest (blood). The dark crescent on the left in the image below is a large hemothorax.

E-FAST hemothorax

The bottom line: Extended FAST can be helpful in detecting a significant hemothorax or pneumothorax and can expedite the definitive management of those conditions. If you are already familiar with FAST, a little extra ultrasound training may be very helpful.

Management of Occult Pneumothorax

Occult pneumothorax is a pleural air collection that is seen only on CT. It is not detected by standard chest xray either because of small size, location of the air, or position of the patient during xray (usually supine).

Approximately 15% of major trauma patients undergoing CT are diagnosed with an occult pneumothorax. The tough question is, what to do about it. Larger pneumothoraces are frequently treated with thoracostomy, but this procedure has its own list of associated complications. Patients undergoing positive pressure ventilation with a visible pneumothorax have an increased risk for progression to tension pneumothorax.

At our trauma center, we manage occult pneumothorax expectantly. If a pneumothorax is seen on the chest portion of a CT scan but not on the initial supine chest xray, a repeat conventional chest xray is scheduled for 6 hours later. Ideally, this xray is taken using the best technique (upright, PA, xray source 6ft from patient). However, this is not always practical for severely injured patients.

If the pneumothorax remains occult on the followup xray, no further monitoring is performed. If the pneumothorax becomes visible, repeat chest xrays are obtained every 6 hours until it is stable or it becomes large enough to warrant insertion of a chest tube.

How large is large enough for a chest tube? That’s the subject for another day.

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.