Thoracic sonography for pneumothorax: The clinical evaluation of an operational space medicine spin-off
Introduction
The distinct challenges of space medicine have led to unique medical solutions not only for space medicine, but also for terrestrial healthcare at large [1]. Ultrasound (US) technology for the diagnosis of pneumothorax is another such example. Pneumothoraces are a notable cause of preventable death, for which relatively simple interventions may be life-saving [2]. Serious thoracic injury causes one-quarter of all trauma deaths, with pneumothoraces being the most common serious intra-thoracic injury following blunt trauma [2], [3]. There is a high frequency of pneumothoraces, reported up to one in five in major blunt trauma victims found alive [4]. Pneumothoraces also cause disproportionately severe derangements of the cardiopulmonary status compared to other chest injuries of comparable anatomic severity [4]. Large or symptomatic pneumothoraces should be diagnosed clinically, but they are all too often missed even when radiography is available. Simple classic supine antero-posterior thoracic radiography (CXR) has shown a sensitivity of only 50–70% in the demonstration of pneumothorax when compared to computed tomography [5], [6]. Thus, there is merit in exploring other diagnostic modalities.
Recent North American interest in the use of ultrasonography to detect post-traumatic pneumothoraces during the resuscitation of the acutely injured patient was actually driven by an operational space medicine concern. Traumatic injury has been ranked at the highest level of concern on a graph of the “probable incidence versus impact on mission and health” [7]. Astronauts aboard the International Space Station (ISS) are at risk for pneumothoraces from both trauma and hypobaric exposures during space walks [8]. The National Aeronautics and Space Administration mandates the ability to stabilize injured or ill astronauts and effect their timely evacuation [9]. A timely intervention, or even an evacuation, would rely on prompt identification of a pneumothorax. This would be extremely difficult currently, as there is no radiography or computed tomographic (CT) scanning aboard the ISS, and noise levels preclude auscultation in many parts of the station [10], [11]. The Human Research Facility (HRF) of the ISS does though, contain an US capacity, a modified ATL/Philips HDI-5000 (Advanced Technology Laboratories, Bothell, WA) US system that could be used in a clinical setting [12]. Although investigations carried out on behalf of NASA demonstrated the utility of US in weightlessness during parabolic flight in abdominal and interventional roles [13], [14], [15], as well as for detecting hemo/pneumothoraces [8], a further dimension of the entire project is the translation of these findings back to the terrestrial trauma patient. Prior to these investigations, the US detection of pneumothoraces was extremely novel. Pioneering investigators had explored the potential of US to infer the presence of pneumothoraces in veterinary settings [16], after lung biopsies [17], [18], [19], in the medical intensive care unit [20], [21], [22], and in a mixed group that included three stable trauma patients [23]; but US had never been used during the early resuscitation of trauma victims. This manuscript thus reviews the physiologic rationale, recent clinical, and potential future application of focused thoracic sonography in acute trauma care as an example of an operational space medicine spin-off.
Section snippets
Physiologic rationale
At first it might seem an apparent paradox to detect pneumothoraces, collections of air, with US. The direct depiction of a pneumothorax by US is physically impossible. Air normally almost completely reflects sound waves at commonly used frequencies, and thus only artifacts are normally seen deep to the visceral–parietal pleural interface (VPPI) [18]. Thoracic trauma with resultant subcutaneous emphysema is actually the most common cause for abdominal trauma sonography to be indeterminate [24].
Terrestrial clinical research corroborated with chest radiography
The Space Medicine Organization at the NASA Johnson Space Center, besides operational medical support to astronauts, makes a sustained effort to identify, ameliorate, and validate medical techniques and technologies to improve medical care in space. Discussions between experts in radiology, space medicine, and trauma care originally identified both the necessity and the theoretical potential to use US to diagnose pneumothoraces [personal communications, Hamilton DR, Sargsyan AE, Dulchavsky SA,
Airway management
Protection of the airway is of paramount importance in managing any medical emergency, especially multi-system trauma. In critically injured patients, definitive airway control often involves placement of an endotracheal tube [3]. If these tubes are misplaced though, they can obstruct rather than protect the airway leading to further injury or death. Unfortunately, the greater the medical urgency, the higher the rate of tube misplacement—up to a quarter of all intubations in some observations
Conclusions
Portable thoracic sonography is an important aspect of the physical examination that may be utilized frequently whenever appropriately trained clinicians resuscitate the critically ill and injured. It can quickly infer the presence of pneumothoraces with greater accuracy than the supine radiograph. This same examination can confirm ventilation of the left lung excluding major tube malpositions in the paralyzed patient. A wider recognition of US as a reliable modality, coupled with the
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2011, Critical Care MedicineCitation Excerpt :In very unstable patients with right chamber dilation, thrombolysis should be started, especially if compression sonography is positive. Although air-containing lung and air within the pleural space may exhibit the same ultrasound pattern (A-lines), certain signs (Table 2) allow the diagnosis and/or exclusion of a PTX by TS (5–8, 13, 15, 23–29). If PTX is suspected by clinical exploration, patients should be in a reclined position during investigation, because air collects within the anterior nondependent portions of the pleural space.