To eliminate beam hardening artifact from degrading the
images of the chest on CT, standard protocol is to position
patients in the CT scanner with their arms elevated (up)
\whenever possible. However, in certain circumstances, such
as trauma, this is not always possible. We note in this study
that the CWT increased for men and women when their arms
were left ‘down’. For female patients in the supine position
with their arms positioned ‘up’, breast tissue tends to fall
outwards and to the side, resulting in a thinner CWT. In
female patients whose arms are left ‘down’ during the CT
scan, breast tissue may not be as spread out and this may
result in a significantly higher number of female patients with
aCWT⬎4.5 cm. This is a very important practical consid-
eration because while most female patients are scanned in the
arms ‘up’ position, most emergent NTs are performed with
the patient’s arms in what would be the arms ‘down’ position.
This study suggests that a 5-cm needle with a 4.5-cm
sheath may fail to decompress a pneumothorax in around
10% of the male patients under 40 years of age and around
19% of the male patients over 40 years of age. For female
patients, this risk is even higher with approximately one-third
of the women under 40 and one-fourth of the women over 40
years of age having a CWT exceeding 4.5 cm. It also shows
that men increase their CWT over the years; for women, the
effects of age on body habitus may actually reduce CWT at
the second ICS. The number of patients whose pneumotho-
races might not be decompressed by a 4.5-cm needle is
potentially even higher given the effect of arm elevation on
decreasing CWT during imaging.
Givens et al.,
in a similar study in 2004 in Texas,
reported a convenience sample of 111 patients. Twenty-two
percent of all patients had a CWT over 5 cm. The authors did
not differentiate in this percentage between male patients and
female patients. We found in this considerably larger study, a
lower percentage of male patients having a CWT over 4.5 cm
and a higher percentage of female patients having a CWT
over 4.5 cm, even with this lower cut-off point. The IV-
catheter from BD Insyte was used as a reference. The sheath
of the needle measures 2.1 ⫻ 45 mm, the needle itself 50 mm.
An assumption was made that a CWT of exactly 4.50 cm
would not be decompressed by a 4.5-cm catheter in case of
The CWT has been measured in a trauma population to
resemble the population in which a TPT is most likely to
occur. Givens et al.
excluded a woman with a CWT over 10
cm because of subcutaneous air; in this study all people with
subcutaneous emphysema, anterior hematomas, or other chest
wall abnormalities are included. The patients requiring an NT
are more likely to be found in this group.
This study demonstrated that in 2.5% of all trauma pa-
tients, a 4.5-cm needle used for NT could puncture the heart
at the second ICS MCL. This is a potential concern on the left
side; interestingly, in one patient it was the case on the right
side because of a mediastinal shift.
Although CT may be the most suitable, accurate, and
reproducible tool to measure the CWT, there are some limi-
tations with this method, especially in a retrospective review.
The accuracy of where to take the measurement of CWT is
critical, as a small error 1 cm to either side of the MCL could
make a significant difference in the measured CWT because
of the acute degree of slope high in the chest cavity at the
second ICS in some patients. In addition, when patients in a
cervical spine collar are positioned in the CT scanner with
their arms ‘up’, their subcutaneous soft tissues can be distorted
and compressed against the collar. This creates abnormal
skin folds that can spuriously increase the measured CWT.
These anatomic and practical limitations could challenge
the reproducibility of this studies findings. However, we
think that the large sample size makes up for these limita-
tions. Since only one investigator measured all the CT scans
with the cut-off point in mind, this could have lead to a bias.
Practical application of NT would undoubtedly encompass
some variability in site of decompression.
The lack of cadaver verification is a limitation of this
study. CT correlation with cadavers has been limited by
freezing and preservation that changes soft tissue dimensions.
Use of recent CT technology and comparison to fresh cadaver
studies demonstrates very high correlation.
CT imaging is
currently being used for preoperative sizing of implantable
medical devices with very good fit at time of surgery or
The study has been performed retrospectively in only
one health center in Canada. This population may not be
anatomically representative of other trauma systems with
variation in height, build, and body mass index.
The catheter used in needle decompression of a TPT may
not reach the pleural space in 10% to 19% of men and a
fourth to a third of women, depending on age. However,
do not advise a longer catheter because
of the possibility of subclavian or pulmonary artery injury
and cardiac tamponade. One author actually did recommend
a longer needle if the 14-gauge needle fails.
In cases of subcutaneous air or chest wall hematoma,
pressure on the catheter may collapse the lumen. To prevent
this, the needle can be left in place
with use of a stabili-
which also creates more length and prevents
kinking. But leaving the needle in place can be a danger,
potentially leading to damage to lung tissue or vital struc-
tures. Another suggestion is to use the lateral midanterior axillary
line (used for chest tubes) for needle decompression,
since there is less fat and muscle tissue and less chance of
damage to vessels and heart. However, pleural adhesions are
more likely to be encountered and may increase the risk of
lung injury when a large pneumothorax is not present.
Considering the tools available now and their advantages and
NT in the Treatment of a TPT in Trauma Patients
Volume 64 • Number 1 113