Occult Pneumothorax in Patients With Blunt or Penetrating Trauma

Thoracic injuries are the third most common cause of trauma-related morbidity/mortality and hospitalization after heart disease and malignancies. At least 25% of blunt traumatic deaths are a direct consequence of chest trauma. Additionally, rib fracture and pneumothorax are the first two most frequent blunt thoracic traumas, respectively.

Pneumothorax (PTX) is a common life-threatening complication and frequently seen in patients who have been admitted to the Emergency Department (ED) and Intense Care Units (ICU). Some traumatic PTXs are clinically and radiologically silent, not identified during the initial assessment and cannot be visible on supine chest x-ray (CXR), but later diagnosed by computed tomography (CT). This type of PTX is called occult pneumothorax (OPTX) and has been found in 30-55% of chest trauma cases. The clinical diagnosis of PTX is incorrect in approximately 30% of all traumatic cases. Besides, it has been stated that PTX has the potential to elevate the mortality rate in patients with trauma if it is not quickly managed.

On the other hand, small or medium undetected PTX usually is not life-threatening. However, delays in the diagnosis and management may result in a rapid progression of OPTX to tension PTX and lead to severe dyspnea and even death. Therefore, early detection is crucial and may influence the evaluation and management of PTX and probably be a lifesaving action.

The initial diagnostic screening test of PTX is usually CXR. However, studies reported that CXR is an insensitive and unreliable test. When the chest x-ray of the patient is acquired in a supine position, even if all of the symptoms related to pneumothorax are present (since the air is not located at the apical pulmonary region), there may not be an image consistent with PTX. For this reason, although CXR is usually used for many thoracic injuries as a screening test, it may miss the diagnosis of some thoracic injuries, including rib fractures, pulmonary contusions, and OPTX.

On the other hand, the role of CT in the assessment of chest injuries has expanded considerably in the management of both blunt and penetrating traumas. The increasing use of CT in the evaluation and management of patients with chest trauma has led to correct and sensitive identification of undetected injuries, including OPTX.

There are limited, but conflicting data about the ideal management type of OPTX in blunt trauma. Some physicians prefer the insertion of a tube thoracostomy (TT) for all OPTX patients, while others favor close observation without chest drainage. Physicians who prefer to insert a TT claim that an untreated OPTX can rapidly evolve into a tension PTX with catastrophic consequences. However, those who favor close observation without TT claim that patients should not be subjected to unnecessary invasive processes.

This study aimed to identify the incidence of OPTX in patients with blunt or penetrating trauma.

This study is a single-center (Emergency Department of Ankara Training and Research Hospital) retrospective analysis of trauma registry data. All consecutive participants over the age of 16 who were admitted to the ED between the 1st of January 2008 and 31st of December 2010 due to multi-trauma, consulted by a thoracic surgeon and underwent both CXR and CT were included in the study. Files of 615 patients who were admitted to ED with a thoracic trauma were reviewed (2008; n=187, 2009; n=168, and 2010; n=260). Patients who had no simultaneous CXR+CT or no pathology in their CT were excluded (n=458). Also, patients not referred to a chest surgeon, and those referred to some other hospital were excluded (n=52). Data for the remaining 105 patients were analyzed. The CT interpretation was considered as the gold standard for the PTX diagnosis. Electronic medical records were then searched for patient characteristics (age and gender), trauma types (blunt or penetrating), accompanied traumas (intra-cerebral and intra-abdominal systems), etiology of the chest trauma (traffic accidents, falls, other), and CXR and CT results. Additionally, the intervention types (thoracostomy tube insertion, thoracentesis, no intervention) during the early phase of the management were recorded. All chest x-rays were performed on the supine position based on the trauma protocol of the hospital. Cases missed by the CXR but identified in the CT were defined as OPTX. Using the web-based Java applet developed by Russ Lenth (https://homepage.divms.uiowa.edu/~rlenth/Power/), a post hoc sample size calculation was performed based on a 7% expected prevalence of OPTX. Given an infinite population and a margin of error of 5%, a sample size of 100 cases is required to estimate OPTX in the study population with a confidence interval of 95%. Statistical analysis was performed with the Statistical Package for the Social Sciences version 22 (SPSS, IBM, Armonk, NY, USA). The 'number (n),' 'percentage (%),' 'mean,' and 'standard deviation (SD)' was given for the descriptive statistics. Pearson Chi-Square or Fisher's exact tests used to compare categorical data. Age between groups was analyzed using the Mann-Whitney U test. Logistic regression analysis was applied to check for independent factors affecting the presence of OPTX. The results were evaluated with a confidence interval of 95%, and the level of significance, p, was set at <0.05.