In most cases of flail chest, each affected rib is fractured at multiple sites; however, a flail segment can be present in animals with single fractures on affected ribs or with dislocations or flexible costal cartilage (Figure 1). This may result in respiratory compromise caused by pain, trauma to the lungs, or decreased ventilation. Flail chest is a potential consequence of a traumatic event involving extreme external forces (eg, dog attack, automotive trauma).¹

During normal respiration, changes in pressure gradients cause air to move in and out of the lungs. During inspiration, the diaphragm and intercostal muscles contract, causing loss of concavity of the diaphragm and abduction of the ribs, respectively. Lung pressure then falls below atmospheric levels and creates a negative gradient that pulls air into the alveoli.

As air fills the lungs, the pressure reaches atmospheric levels and air flow stops. The lungs then exhibit elastic recoil, which creates positive pressure in the alveoli that causes air to move out of the lungs during expiration.²

In flail chest cases, the negative pressure gradient that normally pulls air into the lungs also exerts this force on the freely movable flail segment, causing inward displacement of the segment. This results in pain and decreased intrapleural space, which limits lung expansion. Similarly, the positive pressure generated during expiration pushes the segment outward. This abnormal movement produces the paradoxical motion—or flailing—that is typical of the condition.³

In dogs, experimentally induced flail chest not associated with pleural damage can result in respiratory abnormalities consequential to pain and decreased lung expansion. These abnormalities can include tachypnea, decreased minute volume, and decreased tidal volume. Such cases do not, however, cause hypoxemia or hypercapnia.⁴ This suggests that mortality in patients with flail chest is likely a result of concurrent injuries.

Diagnosis is typically based on visualization of paradoxical movement of the fractured rib segment(s). Thoracic radiography can be used to definitively identify affected ribs and any additional injuries. Concurrent pneumothorax and pulmonary contusions are identified on radiographs in >50% of dogs with flail chest resulting from thoracic bite wounds.¹

CT scans can provide more specific information about the extent of the injuries (Figure 2); however, CT requires deep sedation or general anesthesia, which limits its use in patients with marked respiratory distress.⁶

Because flail chest is created by acute trauma, patients are often presented in shock. Patient stabilization is priority; standard triage procedures should be used to assess airway, breathing, and circulation. Supplementary oxygen should be provided and an IV catheter placed for fluid and analgesic administration.

Patients may require fluid resuscitation with crystalloids with or without colloids. In dyspneic patients, oxygenation and tissue perfusion can be assessed via pulse oximetry, measurement of blood gases, and serial blood lactate concentrations. In intubated patients, end-tidal CO₂ measurements can be used. Some patients may have concurrent pulmonary contusions and pneumothorax,³ so a thoracic-focused assessment with sonography for trauma can be performed to provide diagnostic information and facilitate thoracocentesis when indicated. Markedly dyspneic patients can be imaged in sternal recumbency.

When ultrasonography is not available, a diagnostic bilateral thoracocentesis may be pursued to diagnose and treat pneumothorax.^7,8 In patients with tension pneumothorax (ie, buildup of air in the pleural space that results in positive intrapleural pressure) or in those that require 2 or more therapeutic thoracocenteses, thoracostomy tubes should be placed.⁸

After thoracocentesis, a chest wrap can be placed over the flail segment and around the thorax (see Step-by-Step: Bandaging for Flail Chest) if a chest tube or open wound is present. Potential benefits of thoracic stabilization include decreased motion of the flail segment, reduced pain, and decreased risk for lung and intercostal vessel laceration.⁵

Patients with flail chest require aggressive pain management. Many benefit from a pure -agonist (eg, fentanyl, hydromorphone), but analgesia should be selected on a case-by-case basis. Fast- acting, multimodal combinations (eg, fentanyllidocaine, morphinelidocaineketamine) delivered as a constant-rate infusion and titrated to effect are useful.^8,9 Intercostal or epidural nerve blocks may also be beneficial.¹⁰

Open wounds should be clipped, cleaned, and covered with sterile dressings, and affected patients should be started on broad-spectrum antibiotics (eg, amoxicillinclavulanic acid, ampicillinsulbactam).¹¹

Treatment options include conservative therapy or surgical stabilization of the flail segment. Conservative management can be successful in many patients. Surgical stabilization should be considered if clinical signs do not resolve or if the patient is undergoing a thoracotomy for other conditions (eg, lung lobe laceration).

• Bandaging to cover any wounds and provide structural support to the chest

• Closed external stabilization of the flail segment with a splint by using towel clamps or circumcostal sutures passed percutaneously
• Open stabilization of rib fractures with Kirschner wires, small intramedullary pins, screws, intersegmental wire placement, or absorbable polylactic acid plate and screws¹²
• Removal of rib fragments (to prevent migration into viscera) and stabilization of the local soft tissue with suture, muscle flaps, and/or implants (eg, mesh)

In one retrospective study, the overall mortality rate for dogs and cats was 17%³; the exact cause of death was unknown in many of the animals and may have been related to concurrent conditions (eg, disseminated intravascular coagulation, infection).

One study involving 24 dogs and cats undergoing treatment for flail chest showed mortality rates for conservative management and surgical treatment with internal or external stabilization of 6.3% and 33%, respectively.³

• Wound-care materials (eg, clippers, gloves, chlorhexidine scrub and solution, sterile gauze, topical dressings)
• Packing material (eg, gauze sponges, roll gauze, laparotomy pad)
• Adhesive drape or skin tape to hold packing in place
• Cast padding
• Roll gauze (optional)
• Nonadhesive wrap for a tertiary layer

After the patient is stabilized, clip and clean any external wounds. Cover the wounds with an appropriate topical antimicrobial and sterile dressing.

Place wound dressings over any open wounds. Secure them in place with skin tape.

Place a small amount of padding over the flail segment to keep the area level with the surrounding thoracic wall and reduce paradoxical motion. Secure the padding with skin tape.

If wounds are present, place an adhesive drape over the area. This will keep the padding in place and allow wound dressings to be evaluated for strike-through. If strike-through occurs, remove the drape over the wound dressing; change the dressing and replace that portion of the adhesive drape.

As an alternative, apply cast padding around the chest and between the forelimbs; cover with a self-adhesive tertiary wrap. The wrap should be snug but should not limit respiration. To prevent excessive compression, unroll and reroll bandage material before use.