Clinical Management of Flail Chest

in Dogs and Cats: A Retrospective

Study of 24 Cases (1989-1999)

Cases of flail chest injury for 24 client-owned companion animals following various traumas were
evaluated. Concurrently sustained injuries, initial emergency treatments, and definitive treatment
and outcome for regimens that utilize stabilization of the flail segment were compared with cases
treated with no stabilization.
Flail chest was confirmed in 24 animals: 21 dogs and three cats. There was an even division
(12 each) of right and left flail segments. The median number of ribs involved was three (range,
two to seven). Flail segment stabilization was performed in nine, and 15 were treated with no sta-
bilization. Statistical analysis using multiple data permutations evaluating all combinations failed
to reveal a significant difference in outcome between stabilized and unstabilized cases.
J Am Anim Hosp Assoc 2002;38:315–320.

Dennis Olsen, DVM, MS, Introduction

Diplomate ACVS Flail chest exists when the intrinsic costal arch support of a section of
Walter Renberg, DVM, MS, the thoracic wall has been lost due to multiple (a minimum of two) frac-
Diplomate ACVS tures of at least two adjacent ribs. The section is said to “flail” asynchro-
nously with the normal motion of the thorax during respiration. This
Jamis Perrett, MS “flailing” motion is paradoxic with normal thoracic wall movement and
is characterized by inward displacement during inspiration and outward
Joe G. Hauptman, DVM, MS,
displacement during expiration. The clinical signs of difficult and exag-
Diplomate ACVS
gerated breathing that often accompany flail chest were thought for
Don R. Waldron, DVM, MS, many years to be due, in large part, to the paradoxic movement of the
Diplomate ACVS flail segment.1-7 The basis for this assumption was that pendulous air-
flow between lungs was thought to result from the loss of thoracic wall
Eric Monnet, DVM, PhD, integrity (Pendelluft theory).1,2,5,6 The theory states that air in the lungs
Diplomate ACVS beneath the flail segment would flow across to the lung in the opposite
hemithorax during inspiration and then back again during expiration.
The abnormal airflow was said to contribute to an increase in the physio-
logical “dead space.” When this is combined with decreased vital and
RS functional residual capacities, decreased pulmonary compliance, and
increased airway resistance resulting from the flail segment, severe res-
piratory distress may result. This thinking led to the widespread recom-
mendation that the flail segment be stabilized as soon as possible, and in
many instances this perspective still prevails.3,4,8,9 Consequently, there
have been many techniques described for stabilization—from proce-
dures that place and maintain traction on the unstable ribs to internal fix-
ation of the ribs in an effort to restore synchronous thoracic
motion.1,3,6-9
From the Department of Clinical Sciences, Increased understanding of the pathophysiology of flail chest has
College of Veterinary Medicine,
redirected focus from the unstable flail segment to underlying pul-
1800 Denison Avenue,
Kansas State University, monary damage (e.g., contusion) as the primary cause of respiratory
Manhattan, Kansas 66506-5606. dysfunction.1,2,5-7,10,11 Pulmonary contusions are commonly seen in
JOURNAL of the American Animal Hospital Association 315
316 JOURNAL of the American Animal Hospital Association July/August 2002, Vol. 38

cases of thoracic trauma.12-17 When trauma is sufficient to differences in the treatment regimens, duration of hospital-
result in solitary rib fractures or create a flail chest, pul- ization, complications, and outcome were evaluated. Statis-
monary contusions are almost inevitable.1-3,5-11,18 How- tical analysis was performed using Pearson’s chi-square test
ever, the dramatic appearance of a “flailing” chest wall may and Fisher’s exact test with multiple permutations of the
cause the less readily apparent pulmonary contusion to be data. Significance levels were established at P≤0.05.
overlooked. Pain is another component of the pathophysiol-
ogy of respiratory distress that accompanies flail Results
chest.1,5,7,8,18 Pain impairs ventilation because of the reluc- Flail chest was confirmed in 24 patients: 21 dogs and three
tance to fully expand the thoracic wall. This results in cats. Canine males (n=15) were more common than females
hypoventilation, which can contribute to hypoxemia and (n=6), and intact dogs were more common than neutered,
pulmonary atelectasis, and also in a diminished cough with 12 intact males and four intact females. Of felines, two
reflex that leads to the accumulation of pulmonary secre- were female (one intact; one neutered) and one was male
tions.1,5,19,20 Medical treatment for flail chest often (neutered). Median age among canines was 5 years (range,
includes specific therapy directed at the pulmonary pathol- 8 months to 13 years), and median age for felines was 1
ogy that leads to inappropriate oxygen (O2) exchange. This year (range, 1 to 11 years). There was an even division (12
generally includes O2 supplementation and drug therapy, each) of right and left flail segments. The median number
but in very severe cases may also require positive-pressure of ribs involved was three (range, two to seven). Dog-bite
ventilation with ventilator management and precautions trauma was the most common cause, with nearly twice as
taken to prevent iatrogenic barotrauma.1,5,6,17 Pain manage- many cases (n=13) as the next most-common cause, auto-
ment is another facet of flail chest treatment where medical mobile trauma (n=7). Other causes included kicked by a
therapy is focused. horse, gored by a bull, a fight with a bear, and unknown
The purposes of this retrospective study were to investi- trauma with one case each. Stabilization of the flail seg-
gate flail chest trauma and concurrently sustained injuries; ment was performed in nine cases, and 15 were treated con-
to evaluate initial emergency treatments used; to compare servatively with no stabilization. Methods of stabilization
definitive treatment and outcome for regimens that utilize were divided into two general categories. The first category
stabilization of the flail segment with those that direct ther- included all techniques involving percutaneous placement
apy at accompanying pathology and do not stabilize; and to of sutures that encircled ribs within the flail segment, then
use the information obtained in an attempt to determine a securing the sutures to some form of external brace that
preferred course of therapy. used the adjacent intact thoracic wall to provide counter-
traction for stabilization. Five of the nine stabilized cases
Materials and Methods utilized this method of fixation. The four remaining cases
Medical records from five separate veterinary medical facil- were viewed in a second category that included all methods
ities (i.e., Kansas State University, Virginia Tech, University of internal surgical fixation of the ribs. A summary of flail
of Georgia, Colorado State University, and Michigan State segment stabilization techniques is provided in Table 1.
University) were searched over a 10-year period (1989- Median total days of hospitalization were 6 (range, 1 to 16
1999) to locate cases of flail chest. Flail chest was ascer- days) for stabilized cases and 5 (range, 1 to 14 days) for
tained by radiographic confirmation of rib fractures that nonstabilized cases. Median days in ICU were 5 (range, 1
resulted in a clinically apparent loss of thoracic wall conti- to 9 days) for stabilized cases and 3 (range, 1 to 14 days)
nuity. At least two adjacent ribs with fractures at different for nonstabilized cases. Pulmonary contusion, subcutaneous
levels (i.e., dorsal and ventral) were noted by evaluation of emphysema, and pneumothorax were the most prevalent
thoracic radiographs. Information derived from the search additional radiographic abnormalities noted, regardless of
included signalment of the animal, cause of trauma, loca- the group. A greater percentage of the cases in the nonstabi-
tion and number of ribs involved in the flail segment, con- lized group exhibited the additional radiographic abnormal-
current radiographic findings, and the emergency therapy ities. A summary of all additional radiographic findings
utilized. Additional information included whether or not the with a group breakdown is given in Table 2.
flail segment was stabilized and, if so, what method was Emergency therapy at presentation, regardless of flail
used. If there was no stabilization of the flail segment, the segment stabilization status, consisted of intravenous (IV)
methods utilized for patient care were recorded. The dura- fluid administration at or near accepted rates for shock
tion of time in an intensive care unit (ICU) and total hospi- (16/24), supplemental O2 (13/24), thoracocentesis for pneu-
talization were noted. Complications encountered and the mothorax (12/24), analgesic drug administration (9/24), and
final outcomes were also determined. a chest bandage (7/24). Assisted ventilation was provided
The primary criterion used to divide the cases into two only in cases undergoing surgical stabilization (and then
groups was whether or not the flail segment was stabilized. only during the procedure and not as an initial emergency
Both groups were then evaluated and compared to deter- therapy).
mine if differences existed between the apparent extent of Following initial emergency treatment and patient stabi-
the injuries (such as number of ribs fractured, location, and lization, the most common therapies utilized for cases man-
other significant injuries) and clinical presentation. Also, aged without flail segment stabilization included IV fluids
July/August 2002, Vol. 38 Flail Chest in Dogs and Cats 317

and final outcome between stabilized and nonstabilized flail

Table 1 chest (P=0.1304).

Methods of Flail Segment Stabilization Discussion

Treatment of flail chest in veterinary medicine is largely
Stabilization extrapolated from therapeutic recommendations in the
Methods No. of Cases human field. A plausible explanation for the dependence on
the human field is the paucity of cases in veterinary medi-
External thoracic brace 5 cine. Other reports concerning thoracic trauma have found
that flail chest is an uncommon condition in veterinary
Internal fixation:
Intramedullary pins 1 patients.1,4,6 This retrospective study concurs. Despite
Interfragmentary wire 2 searching medical records of five university teaching hospi-
Suture approximation 1 tals for a 10-year period, only 24 cases were found. Perhaps
these selected teaching hospitals had low numbers of flail
chest simply by chance, and other institutions may have had
(10/15), pain management (10/15), antimicrobial drugs higher numbers of cases. Various authors have proposed
(9/15), and supplemental O2 (6/15). Common therapies for possible explanations for the low number of veterinary
flail segment stabilized cases after initial emergency treat- cases. The anatomical configuration and potentially
ment included supplemental O2 (7/9), IV fluids (6/9), and increased pliant nature of the small animal thoracic cage are
chest tube placement (6/9). speculated to be reasons that flail chest is uncommon.1,13,15
Short-term complications, identified after initial patient Another potential explanation is that the degree of trauma
care, were limited to ventricular premature contractions in necessary to create a flail chest may also be rapidly fatal;
two of the unstabilized cases and one stabilized case, and therefore, the diagnosis is never made.3,15
atelectic lung fields with one case from each group. Long- The number of dogs diagnosed with flail chest was con-
term complications noted were limited to the nonstabilized siderably greater than cats. When the most common etiolo-
group and consisted of a persistent, slight chest wall defor- gies of flail chest (namely, dog-bite trauma and automobile
mity in two cases and slight paradoxic movement in one impact) are considered, some possible explanations become
case. These long-term complications were not deemed to be apparent. Dogs have a tendency to be very interactive when
clinically significant. another dog is encountered, and this increases the potential
Six (66.7%) of the surgically stabilized cases survived, for adverse contacts. When one dog is considerably larger,
whereas 14 (93.3%) of the conservatively managed cases sur- severe trauma such as bite wounds to the chest and vicious
vived. Overall success was 20/24 (83.3%), and mortality was shaking can occur. Cats, as opposed to dogs, do not have
4/24 (16.7%). Statistical analysis using multiple data permu- the innate tendency to interact with dogs; this likely
tations was performed looking at all combinations. Regard- decreases the potential for adverse contacts, although every
less of the permutation, statistical analysis failed to case of feline flail chest in this study was caused by a dog
demonstrate significant differences in the extent or number of attack. Impact to the thoracic area by an automobile is more
injuries sustained, hospitalization duration, complications, likely to occur in the dog simply because of the size of

Table 2

Additional Radiographic Abnormalities Identified in Patients With

Flail Chest and Number of Cases Affected in Each Group

Abnormality Nonstabilized* Stabilized† Total

Pulmonary contusion 14 4 18
Subcutaneous emphysema 12 4 16
Pneumothorax 12 2 14
Pneumomediastinum 3 1 4
Pleural effusion 3 1 4
Pulmonary collapse 2 0 2

* Nonstabilized cases: n=15

† Stabilized cases: n=9
318 JOURNAL of the American Animal Hospital Association July/August 2002, Vol. 38

some breeds. Larger dogs may also be propelled away from Pneumothorax and subcutaneous emphysema were diag-
the car following impact, as opposed to being run over, nosed 58% and 67% of the time, respectively. Pneumothorax
which may influence survival and subsequent presentation is commonly diagnosed when thoracic trauma is significant
for medical therapy. Seven of the canine cases in this study enough to cause pulmonary contusion, and the occurrence
were hit by cars, and of those seven, all but one was ≥27.3 in this study is somewhat higher than that found in other
kg. The smallest of the seven was a 7.3-kg, mixed-breed investigations.13,15-17,24 A possible explanation for the
dog. As mentioned previously, it is reasonable to speculate higher rate is that the trauma resulting in flail chest is
that the trauma likely to cause flail chest has a high possi- greater than the trauma resulting in contusions without rib
bility of being fatal for smaller dogs and cats.15 fractures. Closed pneumothorax can be caused when a
The distribution of affected dogs according to gender is fractured rib fragment lacerates the pulmonary parenchyma
similar to another study of trauma.15 Twice as many sexu- or an airway and air escapes from the laceration. Rupture
ally intact than neutered animals were included in the popu- or tearing of the lung can also occur because of a rapid
lation. Intact male dogs comprised 57% of the population, increase in airway pressure secondary to blunt impact. The
while intact females comprised 19%. Roaming behavior of pressure change may be so rapid and of such a magnitude
intact animals, specifically males, is thought to contribute that local tissue failure occurs.3,25 Another potential cause
to the increased potential of traumatic incidents.15 is shear forces within the lung tissue that result when there
Previous reports have indicated that flail chest may occur is an abrupt change in velocity, such as might be expected
more commonly in older animals because of the increased in severe trauma. Tissue of different densities would have
brittleness of the bones.6,21 The results obtained from this differing rates of acceleration and deceleration, and shear
retrospective study do not support this point. Seventeen of forces between them would result in tears and escaping
the 24 animals were ≤5 years of age, and 10 were <3 years air.3 Laceration of pulmonary parenchyma can also result
of age. One credible explanation for young animals having when there is penetration of the thoracic wall by the teeth
an increased incidence in this study is that younger animals of an attacking animal, creating an open pneumothorax.
are involved in trauma incidents more frequently than older When considering open pneumothorax caused by bite
animals.15,22 Possible reasons for the increased incidence wounds and the stabilization of the thoracic wall, it is
are offered; namely, younger animals may not be as familiar interesting to note that seven of the nine stabilized cases
with surroundings and vehicular traffic, and they may have were from bite trauma while only six of 15 nonstabilized
an increased inclination to roam.15 The tendency for roam- cases were from bite trauma. It is reasonable to suggest
ing may also be tied to the reproductive status of the animal, that the increased rate of stabilization in cases caused by
as previously suggested. Therefore, the type of trauma that bite trauma may be due to the higher probability of having
leads to flail chest may have more to do with occurrence an open pneumothorax that required closure, and that dur-
than with the physical characteristics of the bones. However, ing wound debridement and thoracic wall closure the flail
it is also possible that older animals may not have survived segment was also stabilized. This course of action would
the severe trauma because of concurrent age-related health be prudent as an attempt to restore normal thoracic wall
problems and are therefore under-represented in the study. form and function.
Intrathoracic injuries concurrent with flail chest that were The occurrence of subcutaneous emphysema was con-
noted are very consistent with other studies of thoracic siderably higher in this study than in other studies of tho-
trauma. Pulmonary contusions were diagnosed in 75% of racic trauma where it is mentioned only briefly, if at all.16
the cases and likely would have approached 100% if addi- The most common cause of flail chest in this study was
tional thoracic radiographic studies had been per- dog-bite wounds. The tissue disruption from the bite could
formed.13,17 It has been shown in both veterinary and allow air accumulation from the external environment as
human investigations that diagnosis of thoracic injuries can well as from perforation of the thorax and lung and allow
be complicated, because many patients are able to compen- air to escape from the pulmonary tissue and pleural space
sate for severe injury due to a significant pulmonary into the disrupted tissues. There are other plausible explana-
reserve, thereby diminishing the severity of clinical tions for such a high incidence. Air that escapes from the
signs.13,15 Additionally, the small tidal volumes of many lungs because of tears or rupture of the parenchyma or air-
small animal patients can complicate diagnosis of pul- ways could pass from the pleural space in cases of pneu-
monary injury via auscultation.13,15 The possibility that mothorax and infiltrate disrupted tissue planes that result
clinical signs may be minimal offers an explanation for the when multiple ribs are fractured in multiple locations.
diagnosis of contusion to be <100%. One of the best meth- When the pleura has not been torn, escaping air can migrate
ods for diagnosing pulmonary contusions is radiography, through the pulmonary interstitium along the bronchi to the
but it is well known that radiographically visible evidence mediastinum and eventually reach the subcutaneous tissues
of contusions may not be seen for 4 to 6 hours.15,17,23 and cause emphysema.
Therefore, radiographic findings early in the course of eval- Other conditions that accompanied the flail chest were
uation may be regarded as negative for pulmonary contu- pneumomediastinum, pleural effusion (both approximately
sions. Had additional radiographs been taken after 24 hours, 17%), and pulmonary atelectasis (approximately 8%). Pneu-
the rate of diagnosis would likely have been increased. momediastinum and pleural effusions have been mentioned
July/August 2002, Vol. 38 Flail Chest in Dogs and Cats 319

in previous studies regarding thoracic trauma, but at similar were obtained, a significant difference might be found; but
or lower rates of occurrence.13,15,24 Possible explanations it is also feasible that there may indeed be no difference in
for the increased incidence are similar to those for pneu- hospitalization times and survival rates. Another potential
mothorax. Despite radiographic diagnosis of these accom- reason for the apparent difference in hospitalization and
panying complications, there were no immediate attempts survival is that those stabilized were clinically in more criti-
made in those cases to treat the condition. This would infer cal condition. This possibility exposes an inherent weak-
that the problems were not considered sufficient to con- ness in a retrospective study where clinical status cannot be
tribute to the clinical condition. Lung-lobe atelectasis was accurately ascertained or comparisons between different
the least common of the intrathoracic injuries, and this is cases be made. Even though additional abnormalities, such
similar to the findings of other investigators.15 as pulmonary contusions and pneumothorax, were found to
Therapeutic recommendations in veterinary medicine for be more common in the nonstabilized cases, the severity of
many years have largely involved surgical stabilization of the injury cannot be determined. However, as indicated by
the flail segment. As a result, there are many different meth- this finding, cases afflicted with multiple problems may be
ods described for stabilization.1,3,4,6-9 An interesting find- treated without thoracic wall stabilization. This, however,
ing in this retrospective study is that despite the many does not suggest that aggressive therapy utilizing analgesic
recommendations for immediate stabilization of a flail seg- drugs, O2 therapy, and even ventilatory support should be
ment, the majority of cases (15/24) were treated without withheld if they are clinically indicated. Appropriate fluid
any form of stabilization. This suggests that some clini- therapy with isotonic or hypertonic crystalloids or colloids
cians, based on extrapolated evidence and experience, may should also be utilized when indicated, and great care
have realized that stabilization is not always necessary should be taken to avoid fluid overload that would aggra-
when the underlying pulmonary damage is treated appropri- vate respiratory compromise.
ately. One interesting finding in this series is the relatively The overall mortality in this retrospective study was
low use of analgesics for pain management. Only two- 16.7%, which compares favorably to the highly variable
thirds (16/24) of all the cases received drugs for pain man- rates of up to 40% published in some of the human litera-
agement at some point during treatment. This was evident ture.5,26 While this number is somewhat encouraging, it is
during the initial emergency stabilization period, where difficult to determine from this study whether any specific
only nine out of all cases were treated with analgesic drugs. emergency or definitive therapy has contributed to the rela-
After the cases were separated into the two categories, only tively good success rate. Conversely, since the exact cause
three of the nine stabilized cases and 10 of 15 nonstabilized of mortality (e.g., respiratory or cardiovascular arrest) was
cases received drugs for pain control. The reasons for the not recorded in the four cases, it is difficult to say if the
apparent lack of use of analgesic drugs are difficult to eluci- degree of trauma was of sufficient magnitude to lead to
date from this study. One possible explanation is failure to death or if excessive therapy may have contributed to death.
properly record all medications used during hospitalization. When initial emergency and definitive therapies for all
Emergency situations may contribute to this failure because cases are scrutinized, it becomes apparent that there is no
of increased levels of stress and activity. Should this be the standard protocol that is routinely followed for every case.
case, it emphasizes the need for a conscious effort to assure
Conclusion
the accuracy of the recorded therapies. Another possible
reason is the changing perception of the need for pain con- This retrospective study indicates that flail chest is an
trol during the time period of the study. Approximately 87% uncommon condition. Therapy must be directed at all facets
of the cases treated with analgesic drugs were presented of this complex condition. The results of this study also
from 1993 to 1999, whereas 55.5% of the cases presented indicate that there was no demonstrable difference in the
from 1989 to 1992 apparently had no analgesic medications outcome of stabilized versus nonstabilized cases. The
provided. The higher percentage of pain management dur- results of this study clearly indicate that a specific treatment
applicable to every case of flail chest does not exist. The
ing the later years of the study may be a reflection of this
clinician must be prepared to evaluate each aspect of the
altered perception.
flail chest syndrome for each case individually and then use
Initial evaluation of stabilized and nonstabilized flail
the clinical findings to determine the optimal course of
chest data seems to suggest important differences in the
therapy. Failure to recognize this point and simply applying
method of therapy. There was a slight difference between
the same therapy to every case would result in inadequate
the groups as far as time spent in the ICU and hospital.
treatment for some and excessive treatment for others,
Nonstabilized cases had a trend for less time spent in the which in either case could lead to a poorer outcome as a
ICU and overall hospitalization. Also, approximately 67% direct consequence of the therapy.
of those stabilized survived, whereas 93% of the conserva-
tively managed cases survived. Nevertheless, statistical References
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because of the low population number. If additional cases (Continued on next page)
320 JOURNAL of the American Animal Hospital Association July/August 2002, Vol. 38

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