Elsevier

Injury

Volume 40, Issue 1, January 2009, Pages 44-47
Injury

Clinical predictors of occult pneumothoraces in severely injured blunt polytrauma patients: A prospective observational study

https://doi.org/10.1016/j.injury.2008.07.015Get rights and content

Abstract

Introduction

The supine antero-posterior (AP) chest radiograph (CXR) is an insensitive test for detecting post-traumatic pneumothoraces (PTXs). Computed tomography (CT) often identifies occult pneumothoraces (OPTXs) that were not diagnosed on CXR. The purpose of this study was to prospectively determine the incidence, and validate previously identified clinical predictors, of OPTXs after blunt trauma.

Methods

All severe blunt injured patients (injury severity score (ISS)  12) presenting to a level 1 trauma centre over a 17-month period were prospectively evaluated. Thoracoabdominal CT scans and corresponding CXRs were reviewed at the time of admission. Patients with OPTXs were compared to those with overt PTXs regarding incidence and previously identified predictive risk factors (subcutaneous emphysema, rib fractures, female sex and pulmonary contusion).

Results

CT imaging was performed concurrent to CXR in 405 blunt trauma patients (ISS  12) during the study period. PTXs were identified in 107 (26%) of the 405 patients. Eighty-one (76%) of these were occult when CXRs were interpreted by the trauma team. Concurrent chest trauma predictive of OPTXs was limited to subcutaneous emphysema (p = 0.003). Rib fractures, pulmonary contusions and female sex were not predictive.

Conclusions

OPTXs were missed in up to 76% of all seriously injured patients when CXRs were interpreted by the trauma team. This is higher than previously reported in retrospective studies and is likely based on the difficult conditions in which the trauma team functions. Subcutaneous emphysema remains a strong clinical predictor for concurrent OPTXs.

Introduction

The occult pneumothorax (OPTX) is a pneumothorax diagnosed on computed tomographic (CT) scanning that was not previously identified on a supine, anteroposterior (AP) chest radiograph (CXR) (Fig. 1A and B).2, 8, 20, 21, 30, 35, 39 Upon consideration of the accelerating use of both CT and thoracic ultrasound (US) in patients with blunt thoraco-abdominal trauma, as well as the reality that pneumothoraces (PTX) are the most common manifestation of intra-thoracic blunt chest injury,7, 29, 34 the detection of OPTXs is increasing.2, 8, 20, 21, 30, 35, 39 The incidence of OPTXs reflects the inception cohorts involved.4, 8, 12, 15, 17, 23, 25, 26, 28, 39, 41 It varies from 3.7% in injured children presenting to an emergency department,18 to 64% in intubated, multi-trauma patients with an average injury severity score (ISS) of 30.16 Because of the importance of spine immobilisation in the acutely injured patient, it is also evident that the technological limitations of a supine AP CXR performed in the trauma bay will not be overcome in the near future. This is compounded by the fact that the supine CXR is known to be the least sensitive of all the plain radiographic techniques for demonstrating a PTX.36, 37, 40 These factors make the accurate, rapid and reliable diagnosis of PTXs a significant challenge.

In spite of the frequency of OPTXs, data outlining predictive risk factors is extremely limited. Ideally, a clinician could use a series of clinical predictors, available in the trauma bay, to assess the likelihood of the injured patient having an OPTX. This could also be extended to identifying those patients who require therapeutic chest thoracostomy. At the present time, only subcutaneous emphysema, pulmonary contusions, rib fractures and female sex have been offered as predictive factors in diagnosing an OPTX.4 The true need for chest tube insertion is also unclear. Although it has been suggested that a scoring system, using the largest diameter of an OPTX in conjunction with its proximity to the pulmonary hilum, may predict the need for subsequent chest tube insertion, this formula has yet to be prospectively validated.12

Thoracic injury accounts for 25% of all trauma mortality,24, 31 and PTXs are a notable cause of preventable death, for which relatively simple interventions may be life saving.7, 29, 34 OPTXs are especially concerning in trauma patients with diminished cardiopulmonary reserve or who require positive pressure mechanical ventilation.1, 10, 25, 27 Our primary goal was therefore to prospectively validate, previously identified clinical predictors of OPTXs (subcutaneous emphysema, pulmonary contusions, rib fractures and female sex) that are available early during the resuscitation phase. Furthermore, we insisted on using the trauma team's real-time interpretation of plain CXRs to determine the presence or absence of an OPTX, rather than a delayed radiologist dictation. Our secondary goal was to prospectively identify the incidence of OPTXs in a busy trauma centre. Institutional review board approval was completed.

Section snippets

Materials and methods

Institutional review board ethics approval was obtained prior to commencement. The initial study population consisted of all trauma patients who presented to our level 1 trauma centre (Foothills Medical Centre, Calgary, Alberta) between 1 May, 2005 and 5 August, 2006, with an ISS  12, who had either a complete (chest, abdomen and pelvis) or limited (abdomen and pelvis with standard lower thoracic images) CT scan. All patients had corresponding computed radiographs of supine AP CXRs. Imaging was

Results

Records for 1156 blunt injured patients were available for the 17-month study period. Five hundred and eighty-five incomplete data forms were excluded. Four hundred and five of the remaining 571 (71%) trauma patients had both a CT scan and plain CXR, and comprised our study population. One hundred and fifty eight patients (39%) underwent CT imaging limited to the abdomen and pelvis. The remainder (247 patients) had a complete chest, abdomen and pelvis CT scan. All patients had a supine AP CXR.

Discussion

The aim of this study was to prospectively validate previously identified, clinical predictors of OPTXs.4 These markers were intended to be readily available to the treating clinician early in the resuscitation phase of a severely injured patient. Our goal was to use them to compensate for the poor diagnostic sensitivity and effectiveness of the supine AP CXR. While 4 distinct factors (subcutaneous emphysema, pulmonary contusion, rib fracture(s) and gender) were found to be independently

Conclusions

In summary, subcutaneous emphysema is an independent factor strongly predictive for a concurrent occult pneumothorax. If this finding is identified in the resuscitation phase of an injured patient, the impetus is on the clinician to rule out an OPTX with CT imaging or upright CXR. The presence of pulmonary contusions, rib fracture(s) and female sex are not predictive of OPTXs on a prospective basis. Up to 76% of all PTXs in seriously injured patients will be missed by a standard supine AP CXR

Conflict of interest

None.

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