Abstract
Background: Although adult respiratory distress syndrome is an
important early complication of blunt trauma, the epidemiology and risk
factors for its development remain poorly defined. The aims of this study were
to determine the prevalence and demographics of this complication in a
prospective cohort series of patients admitted to the hospital following
injury. We also assessed the contribution of the severity and pattern of the
injury to the risk of this complication developing. By identifying factors
associated with the highest risk of the development of adult respiratory
distress syndrome, we aimed to produce guidelines to facilitate earlier
detection.
Methods: We prospectively studied 7192 patients admitted to a single
university hospital, over an eight-year period, for treatment of a traumatic
injury. With the exception of patients who had sustained a hip fracture or who
had been discharged within seventy-two hours after admission, all patients who
required hospital admission following trauma, were older than thirteen years
of age, and were a resident within the catchment area were included in the
analysis. The prevalence and demographics of posttraumatic adult respiratory
distress syndrome were identified for patients who had sustained
musculoskeletal, thoracic, abdominal, and head injuries, either in isolation
or in combination. The relative risks of this condition developing were
calculated according to the injury pattern. Multiple logistic regression
analysis was performed to identify the most highly significant predictors of
the development of adult respiratory distress syndrome.
Results: Adult respiratory distress syndrome developed in thirty-six
(0.5%) of the patients. The prevalence was significantly higher among younger
patients (p = 0.002), and 83% of the cases followed high-energy trauma. The
prevalence of adult respiratory distress syndrome after isolated thoracic,
head, abdominal, or extremity injury was <1%. Patients with injuries to two
anatomical regions had a higher prevalence (up to 2.9%), and those with
injuries to three anatomical regions had an even higher prevalence (up to
10.2%). Multiple logistic regression analysis showed the Injury Severity
Score, the presence of a femoral fracture, the combination of abdominal and
extremity injuries, and observations of compromised physiological function on
admission each to be an independent predictor of the later development of
adult respiratory distress syndrome.
Conclusions: The prevalence of adult respiratory distress syndrome
increases with injury severity and combinations of injuries to more than one
anatomical region. We have been able to quantify the importance and relative
risks associated with these injuries. The implications of our findings with
regard to facilitating early detection of this complication are discussed.
Level of Evidence: Prognostic study, Level I-1
(prospective study). See Instructions to Authors for a complete description of
levels of evidence.
Adult respiratory distress syndrome is a rare but serious complication of
trauma, associated with a mortality rate of approximately 50% and with
considerable morbidity among
survivors1. The
etiology and pathophysiology of the condition are poorly
understood2 and the
early clinical signs are subtle and easily
missed3, which often
results in delays in diagnosis. An understanding of the epidemiology of adult
respiratory distress syndrome is therefore important for identifying patients
who are potentially at risk.
A number of risk factors for the development of adult respiratory distress
syndrome following trauma have been proposed, including long-bone fracture,
pelvic fracture, head injury, direct chest injury, tissue hypoxia, and massive
blood
transfusion4-6.
The relative importance of each of these insults, either in isolation or in
combination, has not been previously characterized in a prospective cohort
study, to our knowledge.
The principal aims of this prospective study were to determine the
prevalence and demographics of adult respiratory distress syndrome in a large
cohort of patients who had been admitted to the hospital following trauma as
well as to describe the relative importance of injuries to the extremities,
thorax, head, and abdomen to the risk of development of this condition with
use of validated generic and injury-specific scoring systems. On the basis of
these findings, we tried to identify a series of criteria that would allow
identification of patients who were at risk for this complication and thus who
might benefit from early vigilant monitoring and therapy.
Study Design
Between January 1993 and December 2000, a prospective cohort study of all
patients, thirteen years of age or older, who were admitted to our institution
following trauma, was conducted by the Scottish Trauma Audit Group. Patients
over sixty-five years of age who had sustained a fracture of the femoral neck
or pelvic ramus, those discharged within seventy-two hours after admission,
and those who died before admission to the hospital were excluded in order to
conform with the Major Trauma Outcome
Study7. Such
patients were considered to be at low risk for the development of adult
respiratory distress syndrome, and that hypothesis was verified by a
subsequent review in which no patient in the excluded group was found to have
been readmitted to the hospital with respiratory complications after initial
discharge from the emergency department. Patients who died within two days
after admission were also excluded from our analysis because they were likely
to have died from their injuries before adult respiratory distress syndrome
could develop.
The demographic details, medical history, mechanism of injury, anatomical
location, severity of injury, and physiological observations were recorded at
the time of admission by specially trained research workers who were not
involved in any subsequent data analysis. In addition, validated scoring
systems, including the Abbreviated Injury
Score8, the Revised
Trauma Score (Table
I)9, the
Injury Severity
Score10, and the
Glasgow Coma
Scale11 were used
to grade the severity of injury. All patients' cases were reviewed daily by
research workers until death or discharge, and the development of any
respiratory complications was noted.
Patient Management
Our institution is a major university teaching hospital providing all
trauma services to a stable population of 600,000. The majority of serious
injuries result from road traffic accidents and falls, and there are
relatively few penetrating or gunshot injuries. There is a helicopter service
for some tertiary referrals but not for routine transportation of trauma
victims. A pre-hospital-care land-ambulance staffed by senior accident and
emergency physicians is used to provide on-site resuscitation when prolonged
extrication of trauma patients is anticipated; it is available over a radius
of 50 mi (80.5 km), and it attends an average of seventy-five trauma calls per
annum. The accident and emergency department physicians carry out initial
resuscitation and physiological stabilization. Definitive management is
multidisciplinary and is conducted according to trauma protocols.
Hemodynamically unstable patients with unstable pelvic fracture initially
undergo pelvic external fixation in the operating theater immediately prior to
laparotomy or thoracotomy by general abdominal surgeons and cardiothoracic
surgeons when this is required. Interventional radiology facilities for iliac
arterial embolization are available on site for pelvic fractures remaining
hemodynamically unstable. There are facilities for immediate computerized
tomographic scanning, and invasive intracranial pressure monitoring on a
dedicated neurological intensive-care unit is available. Unstable patients are
managed in the intensive-care unit, and additional definitive surgery is
generally avoided during the "flow" phase of the stress response,
between two and five days after the injury.
Our policy for the management of patients who have sustained trauma is to
stabilize all fractures, with use of internal or external fixation when
possible, as soon as the patient's physiological condition permits. In
physiologically stable patients, isolated injuries are stabilized on their
merits within twenty-four hours. All long-bone diaphyseal fractures in the
lower limbs of adults are treated with reamed, locked intramedullary
nailing.
Patient Demographics
The study included 7192 consecutive trauma admissions. The median age of
the patients was forty-nine years (interquartile range, thirty to sixty-eight
years), and 3968 (55%) of the patients were male. Blunt trauma was responsible
for the injury in 6987 patients (97%).
Characteristics of the Extremity, Thoracic, Abdominal, and
Head-Injury Groups
The median age of the patients with an extremity injury was fifty-one years
(interquartile range, thirty to sixty-nine years), which was higher than that
of the patients with an abdominal injury (median age, thirty-one years;
interquartile range, 23.5 to forty-three years), a thoracic injury (median
age, forty-three years; interquartile range, twenty-eight to sixty-one years),
or a head injury (median age, forty-two years; interquartile range, twenty-six
to sixty-three years). The sex distribution was equal in the extremity-injury
group (3116 [51%] of the 6067 patients were male), but it was markedly skewed
in the abdominal-injury group (275 [80%] of the 345 patients were male), the
thoracic-injury group (612 [70%] of the 878 patients were male), and the
head-injury group (859 [72%] of the 1190 patients were male).
The most common mechanism of injuries to the extremities was a fall from a
height of <2 m (3236 patients, 53%). The most common mechanism in the
remaining three groups was a road traffic accident (429 [49%] of the patients
with a thoracic injury, 164 [48%] of those with an abdominal injury, and 488
[41%] of those with a head injury).
Outcome Measures
The primary outcome measure was the development of adult respiratory
distress syndrome, as defined by the American-European Consensus Conference
(Table
II)12,
during the index admission. The original medical notes on the patients in whom
respiratory insufficiency had been suspected were examined in order to ensure
that the diagnosis complied with the consensus diagnostic criteria.
Statistical Methods
The relationship between the prevalence of adult respiratory distress
syndrome in the cohort and each potential explanatory variable was first
described and examined with use of Mann-Whitney U tests (continuous
variables), Fisher exact tests (two-category variables), and chi-square tests
(variables with three or more categories). Complete data were available for
all patients, except in the socioeconomic status category (data in this
category were available for 3317 patients seen between 1996 and 2000) and
pre-existing medical conditions category (data on cardiovascular, respiratory,
central nervous system, renal, and diabetic conditions were available for 3963
patients seen from 1996 to 2000 and data on known malignant tumors,
alcoholism, psychiatric problems, and substance abuse were available for 2147
patients seen from 1998 to 2000). We then conducted a multiple logistic
regression analysis to identify variables that were independently predictive
of the subsequent development of adult respiratory distress syndrome. All data
analysis was conducted with use of SPSS software (version 10; SPSS, Chicago,
Illinois).
Demographic and Admission Data
Prevalence and Demographics of Adult Respiratory Distress
Syndrome
Adult respiratory distress syndrome developed in thirty-six (0.5%) of the
7192 trauma patients, an annual incidence of 0.8 per 100,000 population per
year. The prevalence was highest among younger patients (less than forty years
of age; Table III), and the
median age of the patients in whom adult respiratory distress syndrome
developed was twenty-nine years, which was significantly younger than the
median age (fifty years) of those in whom the syndrome did not develop (p =
0.001). There was no significant difference in sex distribution (twenty male
patients and sixteen female patients) or between different socioeconomic
groups (based on postal code of residence). The presence of comorbidities
(including respiratory disease, cardiovascular disease, diabetes mellitus,
renal disease, known malignant tumors, alcohol abuse, drug abuse, and
psychiatric illness) was not found to be significantly associated with the
prevalence of adult respiratory distress syndrome among those for whom such
data were available (Table
III).
Mechanism of Injury
Thirty (83%) of the cases of adult respiratory distress syndrome developed
following high-energy injuries (a road traffic accident or a fall from a
height of >2 m) (Table III),
and all cases occurred following blunt trauma. In one case, the mechanism of
injury was unknown, as the patient had been found unconscious, with a head
injury, in the street. The risk of adult respiratory distress syndrome
developing was significantly higher after high-energy injury than it was after
low-energy injury (the remaining mechanisms of injury) (p < 0.001), with a
relative risk of 5.1 (95% confidence interval, 4.8 to 27.8). The median age of
the patients who sustained high-energy injuries was thirty-five years, which
was significantly younger than the median age (fifty-six years) of those who
sustained low-energy injuries (p < 0.001).
Observations on Admission and Initial Management
The prevalence of adult respiratory distress syndrome was significantly
higher among the patients with a score on the Glasgow Coma Scale of <8 (p
< 0.001; relative risk, 5.8 compared with the remainder; 95% confidence
interval, 4.0 to 8.3), the patients with a systolic blood pressure of <90
mm Hg on admission (p < 0.001; relative risk, 5.4; 95% confidence interval,
2.7 to 10.6), and the patients with either a respiratory rate of less than ten
or more than thirty breaths per minute (p < 0.001; relative risk, 6.0; 95%
confidence interval, 2.4 to 15.3) (Table
IV). Patients in whom a laparotomy was the initial surgical
intervention had a significantly higher prevalence of adult respiratory
distress syndrome than did those requiring an initial orthopaedic procedure
(relative risk, 5.3; 95% confidence interval, 1.8 to 15.4) or not requiring
any surgical intervention (relative risk, 3.9; 95% confidence interval, 1.3 to
12.0). Adult respiratory distress syndrome developed in none of the
twenty-eight patients requiring an initial thoracotomy and in only one (0.6%)
of the 159 patients requiring initial neurosurgical intervention.
Severity and Anatomical Location of Injury
Injury Scores
The prevalence of adult respiratory distress syndrome increased
significantly with an increasing Injury Severity Score (p < 0.001;
Table IV). The condition did
not develop in any patient with a score of <9, whereas the prevalence was
3.7% among those with a score of =25. Observations of compromised
physiological function on admission (Table
I) were also associated with a significantly increased prevalence
of adult respiratory distress syndrome (p < 0.001;
Table IV).
Anatomical Location of the Injury
The prevalence of adult respiratory distress syndrome increased
significantly with increases in the maximum injury severity in the patients
with head, chest, and extremity injuries (p = 0.02 to p = 0.001;
Table V).
The prevalence of adult respiratory distress syndrome associated with
specific injuries in each region is shown in
Table VI. The prevalence was
>2% (i.e., more than four times more frequent than in the study population
as a whole) among patients with a pneumothorax or hemothorax, more than three
fractured ribs, a femoral fracture, or an unstable pelvic ring fracture.
Injury Combinations
The prevalence of adult respiratory distress syndrome after an isolated
injury to any body region was <1% (Table
VII). Most combinations of two injuries were associated with a
similarly low prevalence; however, the combination of abdominal and extremity
injuries resulted in a prevalence of 2.9%. Injuries to three anatomical sites
resulted in an increased prevalence of between 2.5% and 10.2%, with the
highest prevalence observed when injuries to the extremities, thorax, and
abdomen had been sustained in combination. Injuries to all four regions
resulted in a prevalence of 6.4%, which was not significantly higher than that
associated with a combination of three injuries.
Fractures of the tibial or femoral diaphysis and unstable fractures of the
pelvic ring were associated with a higher prevalence of adult respiratory
distress syndrome when they were accompanied by a concomitant head, thoracic,
or abdominal injury (Tables
VIII,
IX, and
X).
Multivariate Analysis of Occurrence of Adult Respiratory Distress
Syndrome
On univariate testing, some variables or variable combinations were found
to be associated with a high prevalence of adult respiratory distress
syndrome. For example, a Glasgow Coma Scale score of 3 to 8 was associated
with a 5% prevalance; chest injuries with an Abbreviated Injury Score of
=4, with a 4.9% prevalence; and a tibial, femoral, or pelvic fracture
combined with an abdominal injury, with a 10% to 15% prevalence. However,
these variables were identified in only three to thirteen of the thirty-six
patients affected by adult respiratory distress syndrome. Other variables
identified more affected patients but referred to higher numbers of patients
at risk. For example, adult respiratory distress syndrome developed in
twenty-five (1.6%) of the 1560 individuals involved in a road traffic
accident, twenty-one (3.3%) of the 636 patients with compromised physiological
function on presentation, and twenty-six (3.2%) of the 814 patients with an
Injury Severity Score of 16 to 75. Given that so many variables were
associated with the occurrence of this condition and yet were related to other
variables (for example, the mechanism of injury was associated with the Injury
Severity Score, and the Abbreviated Injury Score was associated with the total
Injury Severity Score), we tested their combined effects with logistic
regression analysis (Table
XI).
The Injury Severity Score was the first variable to be entered into the
forward stepwise logistic regression model; it explained 18.5% of the
variation in the prevalence of adult respiratory distress syndrome. A femoral
fracture explained an additional 3.8% of the variation in the prevalence, and
the addition of a combined extremity and abdominal injury in the same patient
and the Revised Trauma Score explained a total of 27.3% of the variance.
Proactive monitoring of the 814 patients with an Injury Severity Score of
16 to 75 would have identified twenty-six of the thirty-six patients with
adult respiratory distress syndrome. Monitoring of the 525 patients with a
femoral fracture would have identified twelve affected patients, monitoring of
the 197 with combined extremity and abdominal injuries would have identified
thirteen, and monitoring of the 636 with compromised physiological function on
presentation would have identified twenty-one. Many patients fell into more
than one of these categories, and we therefore developed criteria for
monitoring that would have allowed identification of the maximum number of
patients in whom adult respiratory distress syndrome later developed.
Altogether, thirty-five (97%) of the thirty-six cases of adult respiratory
distress syndrome would have been identified by active monitoring of all
patients with an Injury Severity Score of =16, a femoral fracture, a
combination of extremity and abdominal injuries, and/or observations of
compromised physiological function on admission. Given that no cases of adult
respiratory distress syndrome were recorded in the 1993 patients with minor
injuries (Injury Severity Score between 1 and 8), this high rate of
identification of patients in whom adult respiratory distress syndrome would
develop could have been achieved by monitoring 1516 (21%) of the study
population of 7192 patients. If resources for monitoring were an issue, the
low Revised Trauma Score could be removed as a criterion with the result of
missing only one of the thirty-five patients. If that had been done,
thirty-four (94%) of the thirty-six patients with adult respiratory distress
syndrome would have been detected by monitoring 1324 (18%) of the 7192
patients in the study population. The one patient with adult respiratory
distress syndrome who was not identified by any of these criteria was a
twenty-five-year-old patient who had sustained isolated comminuted fractures
of the shafts of the right tibia and fibula in a sports injury.
Previous investigators have examined the incidence of adult respiratory
distress syndrome. The first estimate of the "all-causes"
incidence was reported by the National Institutes of Health, in 1972, to be 75
per 100,000 general population per
year13. Although
widely quoted, this figure is an order of magnitude greater than the
incidences reported in most recent intensive-care-based epidemiological
studies, which have ranged between 1.5 and 13.5 per 100,000 per
year4,5,13-15.
Although the incidence of adult respiratory distress syndrome following trauma
admissions has not previously been reported, to our knowledge, the population
incidence due to trauma alone can be estimated from the incidences presented
in four previous
studies4-6,14
(see Appendix). These incidences ranged between 0.4 and 2.0 per 100,000
population per year, which is similar to our finding of 0.8 per 100,000 per
year.
Direct comparison of the results of our work with those of previous studies
is not possible because of variations in the definitions of adult respiratory
distress syndrome and differing case-mix. The nomenclature for pulmonary
injury has been inconsistent in previous studies, with variable use of terms
such as shock-lung, fat embolus syndrome, and neurogenic
pulmonary edema. More than half of the published reports did not provide
a definition of the
condition1. More
recently, the diagnostic criteria proposed by the American-European Consensus
Conference in
199412 have allowed
comparisons between studies, despite some criticism of the measurements
used16. However,
previous studies either have been based entirely on intensive-care data, with
the features of a different patient population and a wide variety of
precipitating etiologies, or have investigated a highly selected subgroup of
patients with
polytrauma17-19.
To our knowledge, no previous report has described the incidence of adult
respiratory distress syndrome, as described with use of modern criteria, among
general trauma admissions or has addressed the importance of the injury
pattern and the combination of injuries with regard to contributing to the
risk of the development of the syndrome.
We have shown that adult respiratory distress syndrome is rare after blunt
trauma: the overall prevalence was 0.5% in our cohort. High-energy injury,
young age, compromised physiological function on admission, specific injuries
such as skull fracture or pleural injury, and long-bone and pelvic fractures
were all associated with an increased prevalence. An increased prevalence was
also seen among patients who were given high scores with each of the generic
and injury-specific assessment systems used in the study.
Patients with an injury in only one anatomical region had a low prevalence
of adult respiratory distress syndrome (<1%). Although the complication
developed in only a small number of patients, the prevalence increased in
patients who had injuries to more than one anatomical region. Patients with
two injuries had a prevalence as high as 2.9%, whereas those with three
injuries had a prevalence as high as 10.2%. In addition, patients with a
lower-extremity injury had a significantly greater prevalence when they also
had a concomitant injury to the head, thorax, or abdomen.
Multivariate regression analysis was performed in order to stratify these
individually significant factors, many of which were linked with each other.
The best combination of variables for predicting the risk of adult respiratory
distress syndrome was the Injury Severity Score, the presence of a femoral
fracture, the combination of an extremity and an abdominal injury, and
observations of compromised physiological function at presentation.
The Injury Severity Score, which provides a crude estimate of the
"dose of injury," was the most important factor, explaining 18.5%
of the variation in the prevalence of adult respiratory distress syndrome. The
complication did not develop in any patient with an Injury Severity Score of
<9, suggesting that there may be a threshold level for the
"dose" of trauma required for its development.
The presence of a femoral fracture was the second independent variable
entered into the model (Table
XI). The importance of this injury as a cause of respiratory
insufficiency has long been
recognized2. The
term fat embolus syndrome has been used in this context, as the
pathophysiology has been assumed to center on the release and intravasation of
medullary fat after the fracture and its embolization to the cerebral and
cutaneous circulations as well as the pulmonary vascular
bed20. Although,
historically, affected patients were considered to be too sick to be operated
on, the advantages of early skeletal stabilization of such fractures have been
established in a number of studies and
meta-analyses21-25.
The influential randomized controlled trial reported by Bone et al., for
example, demonstrated that multiply injured patients had a higher prevalence
of respiratory insufficiency and a longer stay in the intensive-care unit when
femoral stabilization had been
delayed26. As our
policy is to stabilize all long-bone fractures definitively as early as the
patient's condition allows, we have not been able to study the effect of the
timing of surgery.
Combined injuries to the extremities and abdomen was the next variable
entered into the model. Abdominal injury represents a heterogeneous group,
potentially combining a number of pathological entities that contribute to the
development of respiratory complications. Visceral injury results in
hemorrhage, hypovolemic shock, and tissue hypoperfusion, leading to the
release of cytokines and activation of the coagulation and inflammatory
cascades. Abdominal pain and swelling result in diaphragmatic splinting,
hypoventilation, and
atelectasis2, which
may exacerbate hypoxemia. Patients with combined injuries to the abdomen and
extremities may require a prolonged period of recumbency, which may also
increase the risk of pulmonary complications.
Combined Injuries to the Femur and Thorax, and Damage-Control
Orthopaedics
Although intramedullary stabilization of long-bone fractures reduces
morbidity and mortality after injury, a paradox is evident in that the process
of reaming and nailing causes increased fat
embolism27 and
possibly an incremental activation of the stress
response28. A
number of animal studies in which surrogate outcome measures were used have
suggested modifications to surgical technique that might reduce fat embolism,
including the use of intramedullary nails without
reaming29,30,
alterations in the design of
reamers31, faster
reamer revolutions with slower introduction of the
reamer32, and
venting of the distal
fragment33, but the
advantages of these strategies have not been substantiated by clinical
studies. In a subgroup of severely injured patients who are physiologically
unstable, with hypovolemic shock, hypothermia, or coagulopathy, immediate
definitive fracture stabilization by nailing may be detrimental and a rapid,
minimally invasive procedure (such as the application of an external fixator)
to provide skeletal stability followed by a period of physiological
stabilization in the intensive-care unit is beneficial. This concept has
recently been formalized as damage-control orthopaedic
surgery34,35.
The patient with combined thoracic and long-bone injuries has been
particularly implicated as being at increased risk and suitable for the
"damage-control" approach. Because only a small number of patients
are affected by this combination of injuries, and adult respiratory distress
syndrome develops in only a small proportion of them, it would be difficult to
prove the efficacy of a change in the timing and type of orthopaedic
intervention in this group of patients in a randomized trial. On the basis of
our findings in this cohort, a power calculation suggests that in order to
have an 80% chance of detecting a 50% reduction in the prevalence of adult
respiratory distress syndrome as a result of a modified surgical strategy, a
study recruiting 1154 patients with combined femoral and thoracic injuries
would be required. A study of 8600 such patients would be required to show a
20% reduction in prevalence.
Although, in the present study, the additional presence of a thoracic
injury increased the prevalence of adult respiratory distress syndrome after
femoral fracture from 1.7% to 7.7%, this combination was not independently
predictive of adult respiratory distress syndrome and did not enter the final
regression model. This finding is in agreement with that of a recent review of
the available literature, in which the authors concluded that, in patients
with both thoracic and long-bone injuries, it is the thoracic injury that
determines the likelihood of adult respiratory distress syndrome and the
additional presence of a long-bone injury (however treated) does not influence
that likelihood2.
Our data suggest that it is likely that the total "dose" of
injury, as measured by the Injury Severity Score, is more important in the
development of adult respiratory distress syndrome than is this particular
combination of injuries per se.
Limitations of This Study
Not all cases of adult respiratory distress syndrome in our study were
explained by the presence of severe trauma or other such risk factors; a
proportion remain apparently sporadic or idiosyncratic. This is illustrated by
the otherwise unaccountable development of adult respiratory distress syndrome
in an individual in our series who sustained an isolated tibial fracture in a
sports injury. Phenotypic variations in the expression of components of both
the inflammatory and the coagulation system have been identified in
association with other hyper-stimulatory conditions and may be important in
individuals in whom adult respiratory distress syndrome develops
unexpectedly36-39.
Such genetic predisposition clearly cannot be predicted by this type of
epidemiological study.
There are numerous other insults that have a possible association with the
stress response and respiratory dysfunction and that may have had an
additional influence on the development of adult respiratory distress
syndrome. These include transient hypotension or hypoxemia, capillary bed
hypoperfusion, hypothermia, gastric aspiration, sepsis, and massive blood
transfusion2. We
were unable to identify with confidence the number of patients affected by
those putative insults and were unable to analyze their contribution.
Some patients with more subtle respiratory compromise may not have been
included in our analysis. Subclinical forms of hypoxemia are known to occur
after trauma in up to one-third of patients and to resolve completely with
supportive
treatment3. These
were not detected by the methods employed in this study.
Although we have presented the prevalence of adult respiratory distress
syndrome following trauma, the inclusion criteria used for our study
population were inevitably subjective. We did not include the entire
population of patients presenting to the accident and emergency department
following trauma or those who were discharged within forty-eight hours, as we
believed them to be at low risk for the development of respiratory
complications. This assumption was confirmed, as no patient was readmitted
with respiratory compromise after early discharge during the period of the
study. Our data are based on a population who sustained mainly blunt trauma
and presented to a single European center, and caution is required when
extrapolating our results to other populations such as North American urban
populations, in whom the proportion of penetrating injuries is
higher40,41.
The demographic distribution of the patients with extremity injuries was
different from that of the patients with head, abdominal, and thoracic
injuries. Extremity injuries affected a higher proportion of older women, and
more of them were low-energy injuries. The contemporary pattern of trauma is
changing, and our results reflect the increasingly common problem of
low-energy osteopenic fractures in the
elderly42. These
patients are at lower risk for adult respiratory distress syndrome, and this
fact may have skewed the results in the extremity-injury group when compared
with the groups with injuries in other anatomical regions.
Recommendations
We identified and stratified a number of demographic, physiological, and
injury-related risk factors for the development of adult respiratory distress
syndrome. The mortality associated with this condition remains high, partly as
a consequence of our incomplete understanding of its pathogenesis, the lack of
specific therapeutic treatments, and the failure to recognize the subtle early
signs of impending respiratory compromise. Prompt identification of patients
who are at increased risk is therefore important for improving management.
We suggest that, while clinical suspicion and observation remain central to
the diagnosis of adult respiratory distress syndrome, patients with an Injury
Severity Score of =16, those with a femoral fracture, those with combined
injuries to the extremities and abdomen, and those with observations of
compromised physiological function on admission would benefit from close
physiological monitoring in a high-dependency setting, in order to facilitate
early detection and allow appropriate intervention to be instituted for
patients in whom adult respiratory distress syndrome develops.
A table summarizing previous studies on adult respiratory distress syndrome
is available with the electronic versions of this article, on our web site at
(go to
the article citation and click on "Supplementary Material") and on
our quarterly CD-ROM (call our subscription department, at 781-449-9780, to
order the CD-ROM). ?
Note: The authors acknowledge the help and practical support of
the Scottish Trauma Audit Group during this project.
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