The incidence of NT among all severely injured trauma patients brought to a level 1 trauma centre was 1.5%. This fits within the published range4,5,17
and most closely approximates a prospective report5
of 1.7% among 6241 patients with major trauma. Among patients with blunt injuries in our cohort, the incidence of NT was 1.4%. This rate appears to be relatively consistent regardless of mechanism, as shown by Eckstein and Suyehara’s population, which was composed patients with a higher percentage of penetrating trauma (93%) and a lower mean ISS (22).5
The rationale for excluding all patients with a penetrating mechanism from our analysis was 2-fold. First, thoracic US and subsequent CT were used to identify NT success (i.e., placement into the pleural space). Patients with a penetrating injury were therefore excluded because they typically avoided both imaging procedures. More importantly, nearly all patients with penetrating trauma can be imaged with a standard upright anteroposterior chest radiograph. This avoids the limitations of the supine chest radiograph, which is the least sensitive of all plain radiographic techniques for detecting PTX.28–30
Most current literature also supports investigating a possible TPTX with imaging before performing definitive TT in a hemodynamically stable, nonhypoxic patient.3,5,17,20,31–34
As a result, the treatment algorithm for patients with gunshot and stab wounds is more straightforward. If a patient with penetrating trauma is stable and not intubated, confirmatory imaging can be completed before TT.
This sequence addresses the concerns about inappropriately low thresholds for NT,3,5,17,20,31–34
the frequent failure rate of NT insertion,13–24
and the 22% rate of major complications associated with TT.26
It also reflects the natural history of TPTXs, in that clinical decompensation typically requires a minimum of 30–60 minutes and often much longer.3,35–37
Furthermore, Clark and colleagues38
have also confirmed that virtually no patients with radiologic evidence of TPTX deteriorate while waiting for either imaging or subsequent TT.
It must be emphasized, however, that regardless of the mechanism, immediate NT and TT must be performed in any patient who presents with hemodynamic instability or hypoxia.12,35
It should also be noted that the NT placement decision analysis by a physician in a controlled trauma bay differs significantly from paramedics with field challenges that include suboptimal sedation, environment, vital sign monitoring and the potential pulmonary effects of altitude. As a result, paramedics appropriately place NTs with greater frequency than their hospital-based colleagues to prevent potentially catastrophic consequences in difficult scenarios. This likely results in NT placement for some patients who do not actually have a PTX or TPTX and could also reduce the observed effect difference.
Our primary goal was to identify the frequency of NT failure. Although subcutaneous emphysema or chest wall hematomas may inhibit decompression, the most common scenario is a catheter that is too short to reach the pleural space.3,13–24,31
This is the first clinical study to describe the effect of different catheter lengths on the ability to achieve adequate release of TPTX. All other publications have relied on the thickness of a patient’s chest wall as defined in cadavers studies or by US or CT.13–16,24
Although these indirect methods provide plausible explanations, they also have inherent limitations24
and therefore remain an extrapolation to clinical patient care.
Upon decompression of a TPTX, an audible rush of air preceding the resolution of respiratory and circulatory failure is evident.1–3
There should also be a return of apposition between the visceral and parietal pleural surfaces. This is confirmed by the reappearance of both lung sliding and comet tail artifacts on the EFAST examination.27
Among patients in the helicopter prehospital cohort (4.5-cm sheaths), unsuccessful attempts at decompression (i.e., positive thoracic US for a PTX) occurred in up to 6% of hemodynamically stable patients. This is compared with 77% of ground-transport patients with a 3.2-cm catheter. To confirm this disparity, all patients with negative EFAST findings (i.e., no PTX) who underwent subsequent CT imaging of the chest and/or abdomen. Of the 28 patients (55%) in the air ambulance group with a CT, only 1 had evidence of an OPTX. This single patient (4%) reflected either a false-negative EFAST result or continued leakage of air from a pulmonary injury in the interval between the US and CT. Whereas a direct comparison with the ground-transport group is difficult because of the small number of patients (5 patients with negative EFAST findings), 1 of 2 possible patients had an OPTX on a subsequent CT scan. Taken as a whole, it appears that up to 65% (17/26 total ground patients) of patients had a failed NT with a 3.2-cm sheath in comparison to 4% (3/75 total air patients) with a 4.5-cm cannula. This does not account for the 28% and 15% of helicopter and ground-transport patients, respectively, who presented with hemodynamic instability (NT in place) and underwent emergent TT before any imaging. On closer review, it appears that the vital signs of at least 2 patients in the ground-transport group normalized immediately after TT. We suspect that these were also decompression failures. Because it was unclear if the true cause of hemodynamic instability in patients undergoing immediate TT was failure to decompress a TPTX or hemorrhage, it is possible that the true overall rates of NT failure were actually higher than reported. More specifically, if all TT patients were also presumed to have a failed decompression, the rates would increase to 32% and 81% in the air- and ground-transport cohorts, respectively.
Previous studies describing chest wall thickness at the midclavicular line (second intercostal space) via CT (3.1 cm in 100 heterogeneous adults,16
3.41 cm in men,24
3.92 cm in women,24
4.24 cm in 111 resuscitated patients15
and 5.36 cm in military personnel13
) or US14
(57% thicker than 3 cm) support the observed 65% failure rate using a 3.2-cm sheath. These publications also describe patients with chest walls thicker than 4.5 cm that may not allow decompression with the larger catheters used by our air crews. This subgroup ranges from 4% among US-imaged patients,14
to 10% of men under 40 years of age, to 33% of women under 40 years.24
Given that our patients were mostly male (90%) with a mean age of 33 years, the NT failure rate of 6% in helicopter-transported patients with a 4.5-cm sheath is plausible.
Although some authors13,16
have called for 7- to 8-cm needles to ensure that all OPTXs are decompressed, it appears that even catheters as short as 4.5 cm can puncture the heart at standard insertion locations in 2.5% of trauma patients.24
Other complications include chest wall hematoma, hemothorax, empyema and dislodgement in up to 8% of patients.18,25
In an attempt to avoid these issues, as well as access the pleural space more reliably, support for axillary NT is increasing.3,18,22,25,39
This lateral location takes advantage of a thinner chest wall (mean 2.6 cm)16
and is the military’s first choice if under fire because it allows medics to keep a soldier’s body armor in place while achieving decompression.40
Although we observed no direct complications in our study, we support the use of a catheter at of least 4.5 cm in length.
This study has several limitations. First, it relied on both thoracic US and CT to identify NT failure. Whereas CT represents the gold standard for identifying PTX, the EFAST examination has a sensitivity of 92%–100% in acute settings.41–44
Although this is far superior to the supine chest radiograph, we cannot rule out the possibility that some patients who had a thoracic US that did not show a PTX (and who did not receive a subsequent CT scan) could have had an untreated PTX. This would have introduced conservative bias, however. It should also be noted that sonographic confirmation of TPTX resolution by the return of lung sliding is obvious and reliable.45
Second, the delay between an immediate thoracic US and the subsequent CT may also have introduced a conservative bias because 2 patients had an OPTX that was missed by the preceding EFAST examination. This represents either a false-negative EFAST finding or an interval accumulation of intrapleural air while waiting for a CT scan.
Third, no confirmatory imaging was available for the patients who presented with cardiorespiratory instability because TT was performed immediately. As a result, these patients may also have had NT failures.
Fourth, we could not definitively confirm the presence of a PTX. It can be argued that this actually strengthens our conclusions, however, because fewer patients with TPTX/PTX in the initial cohort would increase the proportion of NT failures.
Fifth, the patient groups (air v. ground transport) were not evenly matched for hemodynamic status, need for urgent intubation or mortality. Because the aim of this study was to define failure rates associated with different catheter lengths, not injury status, we believe that our conclusions remain intact. Finally, the skill level of individual paramedic crews was also not available to interpret the effect of experience on NT success.