Page 16 - JSOM Summer 2023

Goal of this Study The AIS and the composite injury severity scale (ISS) are based
We sought to describe the incidence and variables associ- on estimated mortality from the totality of injuries to each
ated with the development of combat-associated aspiration of six body regions (head/neck, face, thorax, abdomen, ex-
pneumonia. 12–16 tremities, skin/superficial). 23–25 The scale ranges from 0 (minor
injuries, 0% estimated risk of death) to 6 (maximal injuries,
non-survivable injury). An example of an AIS of 0 would be a
Methods
superficial abrasion or minor laceration or less. An example of
Data Acquisition an AIS of 6 would be a complete transection of the aorta. The
This is a secondary analysis of previously described data from composite score—the ISS—represents the three most severely
the Department of Defense Trauma Registry (DoDTR) built injury body regions, squaring each score, and then summing
26
2
2
on a search request for casualties that had at least one pre- the three squared numbers (ISS = A + B + C ). An ISS of
2
hospital assessment or intervention recorded from 1 January >15 is considered major polytrauma. Given the right-skewing
2007 to 17 March 2020. The US Army Institute of Surgical of AIS scores and to give the reader a better sense of those se-
17
Research (USAISR) regulatory office reviewed protocol H-20- riously injured (estimated mortality >10% from injuries to the
015nh and determined it was exempt from Institutional Re- body region) versus those not seriously injured, we converted
view Board oversight. We obtained only de-identified data. the AIS metrics into a binary variable of serious (≥3) versus not
serious (<3). This has been done in previous studies. 21,22,27 The
Department of Defense Trauma Registry Description scoring of the AIS is performed by trained personnel within the
The DoDTR, formerly known as the Joint Theater Trauma Joint Trauma System.
Registry (JTTR), is the data repository for DoD trauma-
related injuries. 18,19 The DoDTR includes documentation re- We present continuous variables as means with 95% confi-
garding demographics, injury-producing incidents, diagnoses, dence intervals; non-parametric continuous variables and ordi-
treatments, and outcomes of injuries sustained by US/non- nal variables as medians with interquartile ranges; and nominal
US military and US/non-US civilian personnel in wartime and variables as percentages and numbers. Inferential comparisons
peacetime (including humanitarian) from the point of injury were performed using 95% confidence intervals, student’s
to final disposition. Short-term outcome data are available for t-test, Wilcoxon Rank Sum, chi-square, and Fisher’s exact test
non-US casualties. The DoDTR comprises all patients admit- as appropriate. We analyzed the data under the assumption of
ted to a Role 3 (fixed-facility) or forward resuscitative sur- accurate documentation of all care rendered. Given low inci-
gical detachment (FRSD) with an injury diagnosis using the dence of disease within our population, we used a binominal
International Classification of Disease 9th Edition (ICD-9) generalized linear regression model with Firth bias-adjusted es-
between 800 and 959.9, near-drowning/drowning with associ- timates to search for associations in a multivariable model. 28,29
ated injury (ICD-9 994.1) or inhalational injury (ICD-9 987.9) Firth models are used to weight low incidence variables within
and trauma occurring within 72 hours from presentation. We the model. Models with low incidence events—such as serious
defined the prehospital setting as any location prior to reach- facial injuries in our model—enable analysis without the model
ing a FRSD, field hospital (FH), or a combat support hospital dissociation seen with standard multivariable logistic regres-
(CSH). This includes Role 1 (point of injury, casualty collec- sion models. The probability that any differences between mea-
tion point, battalion aid station) and Role 2 without surgical sured parameters existed merely by chance were expressed as
capabilities (temporary limited-capability forward-positioned exact p values. We present p- values so the reader can assess
hospital inside a combat zone, including brigade support med- the strength of the inferences. Analysis was performed using
ical companies). Excel version 10 (Microsoft, https://www.microsoft.com/en-us/
microsoft-365/excel) and SAS (JMP Statistical Discovery,
Analysis https://www.jmp.com/en_us/home.html).
The dataset was searched for all casualties that underwent
a prehospital advanced airway procedure such as intubation Results
or supraglottic airway device and with documentation of
subsequent aspiration, aspiration pneumonia, or pneumonia Within the DoDTR from 1 January 2007 to 17 March 2020,
within three days of the initial prehospital intervention. 5,20 there were 28,950 encounters with documentation of prehos-
We included all casualties that were entered into the regis- pital assessment or intervention, of whom 25,897 (89.5%)
try, which thus means they survived long enough to reach a were adults. There were a total of 1,509 casualties who under-
military treatment facility with surgical capabilities. Survival went airway device placement prehospital. Of these, 41 (2.7%)
was based on survival to hospital discharge during their initial met inclusion criteria for aspiration pneumonia (Figure 1). The
hospitalization. We dichotomized the abbreviated injury scale median age was slightly lower for the non-aspiration cohort
values as “serious” for an abbreviated injury scale (AIS) ≥3 (25 versus 27, p = 0.025), but mechanisms of injury and pa-
and “not serious” as AIS <3, as previously established with tient categories were generally similar (p = 0.215, p = 0.147,
registry analyses. 21,22 We excluded non-specific interventions respectively). The non-aspiration cohort had a lower median
documented, such as “rapid sequence intubation (RSI) drugs” injury severity (19 versus 25, p = 0.075). The non-aspiration
or “paralytic” from the regression analyses, but the intubation cohort had fewer median ventilator (2 versus 6, p < 0.001),
was included in the overall analysis. The variables we selected intensive care unit (2 versus 7, p < 0.001), and hospital (3 ver-
to test were informed by our prior work and included the type sus 8, p < 0.001) days. The median ISS in the non-aspiration
of advanced airway intervention and the pharmacologic agent cohort was lower than the aspiration cohort (19 versus 25,
associated with RSI. 9–14 Given the relatively low incidence of p = 0.075). Survival was lower in the non-aspiration cohort
aspiration pneumonia and the infrequent use of supraglottic/ (74.2% versus 90.2%, p = 0.017, Table 1). On comparison
cricothyrotomy procedures, we aggregated all airway inter- of interventions, the administration of succinylcholine was
ventions into one category to maximize statistical power. 14 higher in the non-aspiration cohort (28.0% versus 12.2%,

14 | JSOM Volume 23, Edition 2 / Summer 2023