Page 76 - Journal of Special Operations Medicine - Fall 2015

pleural space. A 2004 study measured CWT on 111 absolute worst-case scenario, with incorrect, maximally
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trauma CT scans of men and women presenting to a inferior needle placement, three of our patients could
military Level 1 trauma center in San Antonio, Texas, have suffered a small diaphragm laceration, despite rec-
and found that a catheter length of 50mm would only ommending this conservative 60mm limit.
reliably have penetrated 75% of patients, indicating a
longer catheter should be considered. Ball et al. at- Study Limitations
9
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tempted to the identify the failure rate of NCD asso- Our retrospective survey is limited in its design to a UK
ciated with varying catheter length in their descriptive male military population; however, 99% of UK military
Atlanta study, suggesting that a conservative 45mm war casualties are men. Direct extrapolation of our re-
catheter (50mm needle) had a failure rate of 4%, es- sults to UK civilian trauma patients must be done with
pecially when placed laterally. These findings are sup- caution, which gives a good basis for a follow-on study.
ported by Britten et al, who used ultrasound to measure We did not have access to weight or height measure-
8
CWT at the 2ICS MCL in UK civilian patients aged 18– ments for our survey sample, which could affect survey
55 years, recommending a minimum 45mm catheter to results. Although an accepted method by other studies,
achieve penetration into the pleura in 96% of cases. The CWT as measured on CT is only a surrogate marker for
overall average CWT at all sites in our study was 36mm, the distance needed to penetrate the pleural cavity on a
where a 45mm catheter would have a 15% overall fail- static image where no accounting could be made for the
ure rate. The predicted failure rates for various lengths viscoelastic properties of tissues and the dynamic nature
of device are shown in Table 1. of needle entry (e.g., momentum of the hand, arm, and
body weight of the inserter; external chest wall compres-
The observed difference in our results between mean sion; and internal chest wall displacement of the subject).
values for the 2ICS versus the 5ICS, when compared
by hemithorax, for patients with CWT less than 42mm Radiographic CWT was affected by a number of fac-
could be attributed to a physiologically larger pectoralis tors. It is our protocol that trauma scans are taken with
major to serratus anterior muscle. Those with an overall the arms by the patient’s side; however, in the case of
greater CWT showed no significant difference between those with upper limb pneumatic tourniquets in place,
anterior and lateral CWT, perhaps as a result of bal- the anatomy at the fifth intercostal space could theoreti-
anced hypertrophy of muscles through physical training. cally have been compressed. Pleural debris and consoli-
However, device design must be based on the maximum dation made it difficult in two cases to estimate the level
CWT and, therefore, this difference does not alter our of the pleural cavity and, therefore, those measurements
recommendations. We found no specific entry point may be difficult to reproduce, leading to potential over-
to be more advantageous in a UK military population. or underestimation of CWT. Equally it could be argued
Consequently, as permitted within Advanced Trauma that in the clinical setting, the intrathoracic pressure of
Life Support and CGO guidelines, both the 2ICS MCL a patient with TP would create a larger safety distance
4,5
and the 5ICS MAL are valid options for NCD using the to critical structures prior to decompression. All mea-
same device. surements were made using axial sections. We were re-
assured, however, after receiving statistical advice, that
All emergent life-saving procedures carry some risk, but the cohort of 63 patients measured had a satisfactory
such risk must be balanced against likely adverse out- statistical distribution.
comes of not performing the procedure. Recent stud-
ies have recommended larger 80mm needles to ensure It would not be possible to replicate this survey with a
100% chance of decompression 7,13 ; however, there have representative number of female patients, given the war
been several case reports of life-threatening iatrogenic casualty population (one female cross-sectional imagery
injury following laceration of critical structures, lead- of the thorax since 2008 was available), but future stud-
ing to possible subclavian or pulmonary artery injury ies, perhaps involving real-time USS of fit Servicemem-
and cardiac tamponade. In the military prehospital en- bers of both sexes should be considered.
vironment, most stressed medics will insert any needle
or catheter to its maximum depth as a reflex action. For Conclusion
this reason, some authors have advised against these
longer catheters. 18,19 Zengerink et al. reported a 2.5% This is the first study to review the optimal length of
10
risk of pericardial penetration when using a 45mm nee- device and site needed for needle decompression of a
dle at the 2ICS MCL in Canadian civilians. We demon- tension pneumothorax in a UK military population. No
strate that there is a maximum safe distance (Figure 2) significant difference between sites for NCD was dem-
and suggest that any UK device should not be longer onstrated. This study does not recommend use of devices
than 60mm to avoid potential injury to the heart, aorta, longer than 60mm for UK service personnel. Any device
or central/segmental pulmonary arterial vessels. In the that leaves a 55mm catheter in place will decompress

64 Journal of Special Operations Medicine Volume 15, Edition 3/Fall 2015