How accurate is chest ultrasonography compared to supine chest radiography for diagnosis of traumatic pneumothorax in the emergency department?

Why is improving the diagnosis of traumatic pneumothorax important?

Air that collects between the lung and the chest wall is described as a pneumothorax. Pneumothorax 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 cause life-threatening shock. Physicians may perform tube thoracostomy — a procedure with risk of complications such as haemorrhage, organ injury, and infection — to evacuate the air trapped. Not recognizing a pneumothorax (false negative (FN)) can lead to heart and lung failure and death. An incorrect diagnosis of a pneumothorax (false positive (FP)) may lead to inappropriate tube thoracostomy.

What is the aim of this review?

To determine how accurate chest ultrasonography (CUS) is compared to chest X-ray (CXR) in diagnosing pneumothorax in trauma patients in the emergency department (ED). Researchers included 13 studies to answer this question.

What was studied in the review?

We compared the diagnostic accuracy of two tests, CUS and CXR. We then compared these two tests to computed tomography (CT) or, if clinically necessary, tube thoracostomy as the reference standard.

What are the main results of the review?

The analysis included results from 1271 trauma patients, where 410 had traumatic pneumothorax.

The results of these studies indicate that, in theory, if CUS was used on a group of 100 patients where 30 (30%) have traumatic pneumothorax, then an estimated 28 would have a CUS result positive for pneumothorax (TP) and of these one (3.6%) would be incorrectly classified as having the pneumothorax (FP); of the 72 patients with a result negative for pneumothorax, three (4.2%) would actually have a pneumothorax (FN).

In theory, if CXR was used on a group of 100 patients where 30 (30%) have traumatic pneumothorax, then an estimated 14 would have a CXR result positive for pneumothorax (TP) and of these none (0%) would be incorrectly classified as having the pneumothorax (FP); of the 86 patients with a result negative for pneumothorax, 16 (18.6%) would actually have a pneumothorax (FN).

How reliable are the results of the studies in this review?

The numbers shown in the results are averages across all studies in the review. While CUS results were fairly consistent, CXR results were quite varied; thus, we cannot be sure that CXR will always produce the same results. In the included studies, the diagnosis of traumatic pneumothorax was confirmed by CT or tube thoracostomy. Although there were some problems with how some of the studies were conducted, their results did not differ from the more reliable studies.

Who do the results of this review apply to?

The results may not be representative of patients in different settings or with pneumothorax of different aetiologies. Studies included in the review were focused on diagnosing traumatic pneumothorax in the ED, conducted in three continents. The average prevalence of traumatic pneumothorax was 30% and ranged from 21% to 52%.

What are the implications of this review?

The studies in this review show that CUS is more accurate than CXR in diagnosing pneumothorax in ED trauma patients, which may lead to more timely treatment with tube thoracostomy, reducing pneumothorax-related complications, and improving outcomes. The risk of missing the diagnosis with CUS is low (4.2% of those whose CUS suggests they do not have a pneumothorax) suggesting that only a few patients may not immediately receive tube thoracostomy. The risk of incorrectly diagnosing traumatic pneumothorax using CUS is low (3.6% of those whose CUS suggests they have a pneumothorax) and may result in receiving unnecessary tube thoracostomy.

In comparison, the risk of missing a traumatic pneumothorax with CXR is high (18.6% of those whose CXR suggests they do not have a pneumothorax) suggesting that a large number of patients may not immediately receive tube thoracostomy. The risk of wrongly diagnosing traumatic pneumothorax using CXR is low (0% of those whose CUS suggests they have a pneumothorax).

How up to date is this review?

The review authors searched for and included publications from 1900 to 10 April 2020.

Authors' conclusions: 

The diagnostic accuracy of CUS performed by frontline non-radiologist physicians for the diagnosis of pneumothorax in ED trauma patients is superior to supine CXR, independent of the type of trauma, type of CUS operator, or type of CUS probe used. These findings suggest that CUS for the diagnosis of traumatic pneumothorax could be incorporated into trauma protocols and algorithms in future medical training programmes. In addition, CUS may beneficially change routine management of trauma

Read the full abstract...
Background: 

Chest X-ray (CXR) is a longstanding method for the diagnosis of pneumothorax but chest ultrasonography (CUS) may be a safer, more rapid, and more accurate modality in trauma patients at the bedside that does not expose the patient to ionizing radiation. This may lead to improved and expedited management of traumatic pneumothorax and improved patient safety and clinical outcomes.

Objectives: 

To compare the diagnostic accuracy of chest ultrasonography (CUS) by frontline non-radiologist physicians versus chest X-ray (CXR) for diagnosis of pneumothorax in trauma patients in the emergency department (ED).

To investigate the effects of potential sources of heterogeneity such as type of CUS operator (frontline non-radiologist physicians), type of trauma (blunt vs penetrating), and type of US probe on test accuracy.

Search strategy: 

We conducted a comprehensive search of the following electronic databases from database inception to 10 April 2020: Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MEDLINE, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL) Plus, Database of Abstracts of Reviews of Effects, Web of Science Core Collection and Clinicaltrials.gov. We handsearched reference lists of included articles and reviews retrieved via electronic searching; and we carried out forward citation searching of relevant articles in Google Scholar and looked at the "Related articles" on PubMed.

Selection criteria: 

We included prospective, paired comparative accuracy studies comparing CUS performed by frontline non-radiologist physicians to supine CXR in trauma patients in the emergency department (ED) suspected of having pneumothorax, and with computed tomography (CT) of the chest or tube thoracostomy as the reference standard.

Data collection and analysis: 

Two review authors independently extracted data from each included study using a data extraction form. We included studies using patients as the unit of analysis in the main analysis and we included those using lung fields in the secondary analysis. We performed meta-analyses by using a bivariate model to estimate and compare summary sensitivities and specificities.

Main results: 

We included 13 studies of which nine (410 traumatic pneumothorax patients out of 1271 patients) used patients as the unit of analysis; we thus included them in the primary analysis. The remaining four studies used lung field as the unit of analysis and we included them in the secondary analysis. We judged all studies to be at high or unclear risk of bias in one or more domains, with most studies (11/13, 85%) being judged at high or unclear risk of bias in the patient selection domain. There was substantial heterogeneity in the sensitivity of supine CXR amongst the included studies.

In the primary analysis, the summary sensitivity and specificity of CUS were 0.91 (95% confidence interval (CI) 0.85 to 0.94) and 0.99 (95% CI 0.97 to 1.00); and the summary sensitivity and specificity of supine CXR were 0.47 (95% CI 0.31 to 0.63) and 1.00 (95% CI 0.97 to 1.00). There was a significant difference in the sensitivity of CUS compared to CXR with an absolute difference in sensitivity of 0.44 (95% CI 0.27 to 0.61; P < 0.001). In contrast, CUS and CXR had similar specificities: comparing CUS to CXR, the absolute difference in specificity was −0.007 (95% CI −0.018 to 0.005, P = 0.35). The findings imply that in a hypothetical cohort of 100 patients if 30 patients have traumatic pneumothorax (i.e. prevalence of 30%), CUS would miss 3 (95% CI 2 to 4) cases (false negatives) and overdiagnose 1 (95% CI 0 to 2) of those without pneumothorax (false positives); while CXR would miss 16 (95% CI 11 to 21) cases with 0 (95% CI 0 to 2) overdiagnosis of those who do not have pneumothorax.

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