Tag Archives: pneumothorax

What Percent Pneumothorax Is It?

What percent pneumothorax?

Frequently, radiologists and trauma professionals are coerced into describing the size of a pneumothorax seen on chest xray in percentage terms. They may say something like “the patient has a 30% pneumothorax.”

The truth is that one cannot estimate a 3D volume based on a 2D study like a conventional chest xray. Everyone has seen the patient who has no or a minimal pneumothorax on a supine chest xray, only to discover one of significant size with CT scan.

Very few centers have or use the software that can determine the percentage of chest volume taken up with air. There are only two percentages that can be determined by viewing a regular chest xray: 0% and 100%. Obviously, 0% means no visible pneumothorax, and 100% means complete collapse. Even 100% doesn’t really look like 100% because the completely collapsed lung takes up some space. See the xray at the top for a 100% pneumothorax.

If you line up 10 trauma professionals and show them a chest xray with a pneumothorax, you will get 10 different estimates of their size. And there aren’t any guidelines as to what size demands chest tube insertion and what size can be watched.

Bottom line: The solution is to be as quantitative as possible. Describe the pneumothorax in terms of the maximum distance the edge of the lung is from the inside of the chest wall, and which intercostal space the pneumothorax extends to. So instead of saying “the patient has a 25% pneumo,” say “the pneumothorax is 1 cm wide and extends from the apex to the fifth intercostal space on an upright film.”

Flying After Pneumothorax

Patients who have sustained a traumatic pneumothorax occasionally ask how soon they can fly in an airplane after they are discharged. What’s the right answer?

The basic problem has to do with Boyle’s Law (remember that from high school?). The volume of a gas varies inversely with the barometric pressure. So the lower the pressure, the larger a volume of gas becomes. Most of us hang out pretty close to sea level, so this is not an issue.

However, flying in a commercial airliner is different. Even though the aircraft may cruise at 30,000+ feet, the inside of the cabin remains considerably lower though not at sea level. Typically, the cabin altitude goes up to about 8,000 to 9,000 feet. Using Boyle’s law, any volume of gas (say, a pneumothorax in your chest), will increase by about a third on a commercial flight. 

The physiologic effect of this increase depends upon the patient. If they are young and fit, they may never know anything is happening. But if they are elderly and/or have a limited pulmonary reserve, it may compromise enough lung function to make them symptomatic.

Commercial guidelines for travel after pneumothorax range from 2-6 weeks. The Aerospace Medical Association published guidelines that state that 2-3 weeks is acceptable. The Orlando Regional Medical Center reviewed the literature and devised a practice guideline that has a single Level 2 recommendation that commercial air travel is safe 2 weeks after resolution of the pneumothorax, and that a chest xray should be obtained immediately prior to travel to confirm resolution.

Bottom line: Patients can safely travel on commercial aircraft 2 weeks after resolution of pneumothorax. Ideally, a chest xray should be obtained shortly before travel to confirm that it is gone. Helicopter travel is okay at any time, since they typically fly at 1,500 feet or less.

References:

  • Practice Guideline, Orlando Regional Medical Center. Air travel following traumatic pneumothorax. October 2009.
  • Medical Guidelines for Airline Travel, 2nd edition. Aerospace Medical Association. Aviation, Space, and Environmental Medicine 74(5) Section II Supplement, May 2003.

Don’t Get Lateral View Chest Xrays to Diagnose Pneumothorax

Pneumothorax is typically diagnosed radiographically. Significant pneumothoraces show up on chest xray, and even small ones can be demonstrated with CT.

Typically, a known pneumothorax is followed with serial chest xrays. If patient condition permits, these should be performed using the classic technique (upright, PA, tube 72" away). Unfortunately, physicians are used to ordering the chest xray as a bundle of both the PA and lateral views. 

The lateral chest xray adds absolutely no useful information. The shoulder structures are in the way, and they obstruct a clear view of the lung apices, which is where the money is for detecting a simple pneumothorax. The xray below is of a patient with a small apical pneumothorax. There is no evidence of it on this lateral view.

Bottom line: only order PA views (or AP views in patients who can’t stand up) to follow simple pneumothoraces. Don’t fall into the trap of automatically ordering the lateral view as well!

Lateral chest xray

Pneumothorax: How Big Is Too Big?

One of the big unanswered questions in the management of pneumothorax is, how big is too big? At what size is a chest tube of some type mandatory? 

The problem is that we just don’t have any good data. Seems like a simple problem, right? Unfortunately, it’s not. A pneumothorax is a three dimensional collection that surrounds the lung in very random ways. All we had to detect and “measure” them for decades was the lowly chest x-ray. Unfortunately, this is a 2D shadow picture that does not allow us to accurately estimate the size.

A few old papers exist that tried to quantify pneumothorax, but they are of no use now that we have chest CT. Unfortunately this new technology has drawbacks, as well. First, it’s just a stack of 2D images that our minds assemble into a 3D mental model, so it’s still difficult to quantify the air. And second, you shouldn’t be getting a chest CT just to diagnose pneumothorax. In blunt trauma, it’s really just for checking the thoracic aorta for injury.

So we’re left with the original question, and there are three answers. If there is any physiologic compromise (hypoxia, tachypnea, anxiety), then the chest should be drained. If the pneumothorax is enlarging over serial chest x-rays, then it should be drained before it causes physiologic change. And finally, if there is concern that it is so large that it will take too long to absorb, especially in older patients with comorbidities, a chest drain should be inserted. This is a somewhat soft indication, however.

Bottom line: The three reasons above are the usual answers to the question, “how big is too big?” For me, once the pneumothorax pushes the lung 1-2 cm away from the chest wall from apex to base, it’s time for a tube.

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