Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Alongside the many thousands of Cochrane Reviews of the effects of interventions, our reviews of diagnostic test accuracy, or DTA, provide evidence to help clinicians choose between different techniques for diagnosing a health problem. In July 2020, we published the new DTA review on ultrasound versus x-ray for diagnosing pneumothorax in trauma patients. Here's lead author, Kenneth Chan from the Department of Emergency Medicine in the University of Calgary in Canada, to tell us what they found.

Ken: Traumatic pneumothorax is a common complication when someone suffers a chest injury. It occurs when air collects between the lung and the chest wall and can cause collapse of the lung, change the position of the heart and other structures in the chest, reduce the blood flow back to the heart, and lead to life‐threatening shock. A tube thoracostomy is often used to release the trapped air, but this invasive procedure carries a risk of complications such as bleeding, organ injury, and infection. It's important, therefore, to be able to diagnosis if someone has a pneumothorax when they arrive in the emergency department, because missing one can lead to heart and lung failure and death; while a “false positive”, of diagnosing that a patient has one when they don't may lead to inappropriate tube thoracostomy. Therefore, to help with this, we have compared the accuracy of two common diagnostic techniques: x-ray and ultrasound.
Supine chest x-ray has been the traditional diagnostic method for traumatic pneumothorax, but it takes time, resources, and equipment that may delay the acute resuscitation of the trauma patient. On the other hand, a chest ultrasound can be done at the bedside in a much quicker manner, doesn't require additional equipment or human resources, and doesn't expose the patient and care providers to ionizing radiation. It also means that the patient doesn't have to be moved out of the trauma resuscitation area in the emergency department.
We identified nine prospective comparative diagnostic accuracy studies with nearly 1300 patients that directly compared chest ultrasound to supine chest x-ray against a reference standard of either chest computed tomography - a CT scan - or positive findings by tube thoracostomy. 
Starting with the statistics, we found that ultrasound had a summary sensitivity of 91% and specificity of 99%; whereas x-rays had a summary sensitivity of only 47% and specificity of 100%. These findings suggest that if a group of 100 patients contained 30 people with a traumatic pneumothorax, chest ultrasound would miss 3 cases (ie. false negatives) and over-diagnose 1 (false positive); but although chest x-ray would have no false positives it would miss 16 of the 30 cases.
In summary, the diagnostic accuracy of chest ultrasound performed by frontline non-radiologist physicians for the diagnosis of traumatic pneumothorax in the emergency department is superior to supine chest x-ray. It may lead to more timely diagnosis and treatment with tube thoracostomy, reducing pneumothorax-related complications and improving outcomes for patients. Our findings suggest that chest ultrasound should be incorporated into trauma protocols and algorithms in future medical training programmes and that it may change routine management of trauma for the better.

Monaz: If you would like to look in more detail at this evidence, the review is easy to find online. Just visit Cochrane Library dot com and search 'diagnosis of pneumothorax'.