Page 75 - JSOM Fall 2019

TABLE 1 Model Physical Characteristics FIGURE 5 Horizontal probe position. Tracheal cartilage (blue).
Model 1 Model 2
Height (m) 1.70 1.65
Weight (kg) 77.1 70.3
BMI (kg/m ) 26.6 25.8
2
Neck circumference (cm) 38 37.5
Height of CTM at midline (mm) 9.1 10.0
Depth of CTM from skin (mm) 4.6 3.6
Thyromental distance (cm) 9 8.5
Sternomental distance (cm) 9 12

in battle. Second, similar models served to reduce confounding the probe superiorly and inferiorly. After landmarks were re-
variables in the study. confirmed by US, the gel was wiped off and the landmark dots
were connected so that the superior and inferior borders and
Data collection midline resembled a sideways “H” on the models. A transpar-
Prior to participants entering the subject area, a dual emer- ent dressing was then placed over their necks (Areza Medical,
gency medicine (EM)/US fellowship-trained senior Army PA UPC 686751150661, ordered from www.amazon.com), as
(DSc, PA-C) served as the US subject matter expert (SME). was conducted in other CTM localization studies. 5,7,8,10 Both
He marked the upper and lower borders of the CTM, as models were positioned with their necks moderately extended
well as the midline, of both models after verifying landmarks by placing a rolled up T-shirt under their shoulder blades.
with a portable US (Sonosite iViz , primary DI number The purpose was to improve positioning for CTM identifica-
®
00841517103835). US was the standard for confirmation of tion, as performed in some CTM localization studies 7,8,11 but
anatomical location in all eight studies reviewed. 4–11 also simulate what could easily be accomplished in a tactical
environment.
The approach to marking the objective landmarks was similar
to previous studies. 4-6,8–10 A water-soluble conduction gel was Following the information brief, study participants were posi-
first applied to the models’ necks. A linear US probe (Sonos- tioned outside of the study area, so they were blinded to any
ite L38 10-5 MHz, primary DI number 00841517100469) aspects of the study before their turns. When called upon by
®
was then used, first in the vertical position, to visualize the the primary investigator and associate investigators (PI/AIs),
superior and inferior borders of the CTM (Figures 3 and 4). A two study participants entered the room at a time and were
large sewing needle was slid horizontally under the probe to assigned a randomized research identification number. Par-
cast a shadow of the superior border on the US monitor, and ticipants were given 6 minutes to familiarize themselves with
a pen was used to mark the skin on either side of the needle. the LHM by watching a video and reviewing an instructional
This pen and the ones used by participants are detectable only handout. Participants had 2 minutes to refresh themselves on
by UV light (SyPen Inc., ASIN B06WRR9QZN, ordered from the TM via an instructional handout.
www.amazon.com). The same technique was used to mark the
lower CTM border. After reviewing their first assigned method, participants were
asked to take a UV pen and position themselves on the side of
The probe was then turned horizontally to appreciate the mid- the model that was most comfortable to them for performing a
line of the CTM, which was aligned with the midline of the US SCRIC. The next timer, for identification and marking, began
screen (Figure 5). The UV pen was used to mark the midline of as soon as they touched the models. The study participants
were asked to mark the center of the CTM with crosshairs,
approximately 1 cm for each line; the instructional handouts
included an illustration of the requested size of the crosshairs.
The intersection of the two lines served as the point of mea-
surement to find the difference between the objective CTM, as
FIGURE 3 US identification of the CTM.
confirmed by US, and the subjective CTM.
During the identification and marking period, study partici-
pants were given a goal of 30 seconds to identify the CTM,
FIGURE 4 Vertical probe position. From cephalad to caudad: which is based on the UK DAS 2004 possible total time of
tracheal cartilage (blue), cricothyroid membrane (yellow), cricoid 30 seconds to perform a cricothyrotomy. Timing continued
13
cartilage (red). until the study participants completed their markings. Mark-
ings not completed by 2 minutes were to be deemed failures in
study results because long-term brain damage from hypoxia is
likely if a cricothyrotomy cannot be completed in 2 to 3 min-
utes. No participants exceeded the time requirement.
14
To prevent crossover of techniques, the informational sheet de-
scribing the traditional method emphasized that the nondomi-
nant hand can only be used to stabilize the larynx and cannot
be moved once on the patient. If participants performing either

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