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Standards of Care September 2009 (Vol 11, No 7)

Flail Chest

by Elizabeth Abato, DVM, Christopher G. Byers, DVM, DACVECC, DACVIM (SAIM)

    CETEST This course is approved for 1.0 CE credits

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    Flail chest results from the segmental fracture and/or dislocation of two or more adjacent ribs. This type of injury is uncommon in dogs and cats because of the compliance and anatomic shape of the thoracic cage. A common clinical sign of flail chest is the paradoxical movement of the unstable ribs or flail segment during respiration (Figure 1). Blunt trauma and dog bite injuries are the most common causes of flail chest in dogs and cats. Concurrent pulmonary damage is a major contributor to morbidity associated with this condition.

    Several techniques for stabilization of flail chest have been introduced. Recently, increased knowledge of the pathophysiology of flail chest has focused attention on the underlying pulmonary injuries as the primary causes of respiratory dysfunction. As a result, stabilization of flail chest is less commonly performed. However, stabilization is still recommended if thoracotomy is needed to address any associated injuries, rib fractures may cause further injury, or conservative medical management is ineffective.

    Mechanical ventilation had been the standard practice in humans with flail chest and secondary pulmonary injuries. Recent literature recommends a more selective application of ventilatory support because of the possible complications associated with mechanical ventilation. In veterinary medicine, mechanical ventilation is recommended for patients with flail chest and evidence of hypoxemia while receiving supplemental oxygen, hypoventilation, or failure to respond to conservative medical management.

    Common injuries associated with flail chest include pulmonary contusions (most common), subcutaneous emphysema, and pneumothorax. Pulmonary contusions lead to decreased pulmonary compliance, decreased ventilation, and shunting, all of which cause hypoxemia. Splinting due to pain during respiration leads to a decreased cough reflex, inadequate ventilation, hypoxemia, and atelectasis. Therefore, the treatment plan for a patient with flail chest must focus on the underlying intrathoracic injuries, pain management, and oxygen support.

    Diagnostic Criteria

    Historical Information

    Gender Predisposition

    • More common in intact animals.
    • More common in males.

    Age Predisposition

    • May occur at any age, but more common in younger animals.

    Breed Predisposition

    • None.

    Owner Observations

    • History of trauma.
    • Paradoxical movement of the unstable flail segment.
    • External skin wounds.
    • Lethargy.
    • Vocalization due to pain.
    • Dyspnea and/or tachypnea.

    Other Historical Considerations/Predispositions

    • Unsupervised activity (roaming, proximity to roads).
    • Most common causes are dog bite trauma, motor vehicle accidents, and other forms of blunt trauma.

    Physical Examination Findings

    • Paradoxical movement of the unstable flail segment.
    • Dyspnea and/or tachypnea.
    • Increased bronchovesicular sounds if pulmonary contusions are present.
    • Decreased lung sounds if pneumothorax is present.
    • Splinting of the abdominal and thoracic musculature.
    • Cyanosis.
    • Crepitus or subcutaneous emphysema near the flail segment.
    • Skin lacerations.
    • Other fractures.
    • Cardiac arrhythmias or pulse deficits.

    About VECCS

    Key To Costs

    Laboratory Findings

    • Complete blood count: Unremarkable; however, inflammatory changes can be present, including a left shift. Signs of blood loss if polytrauma has resulted in significant bleeding. $
    • Chemistry: Unremarkable, unless organ dysfunction is present due to trauma or preexisting disease. $
    • Arterial blood gas: $
      — Hypoxemia.
      — Respiratory alkalosis.
      — Respiratory acidosis.
      — Metabolic acidosis (lactic acidosis).
      — Elevated alveolar-arterial gradient.
      — Low oxygenation index (Pao2:Fio2 ratio): acute lung injury if <300; acute respiratory distress syndrome if <200.

    Other Diagnostic Findings

    • Thoracic radiography: Two or more consecutive segmental rib fractures +/- pulmonary contusions, pneumothorax, subcutaneous emphysema, pneumomediastinum, pleural effusion, and diaphragmatic hernia. $
    • Computed tomography: Provides greater accuracy for identifying rib fractures and chest wall, pulmonary, and intraabdominal injuries. $$$$
    • Pulse oximetry: <92% Spo2 at a Fio2 of 21% indicates the need for supplemental oxygen. $
    • TFAST (thoracic focused assessment with sonography for trauma): Used to assess for thoracic wall defects ("step signs"); may detect other injuries such as pneumothorax and pleural or pericardial effusion. $
    • Electrocardiography (ECG) should be used to identify cardiac dysrhythmias; may not be present for 12 to 48 hours after injury. $
    • Echocardiography to identify and localize possible structural and functional abnormalities associated with injured myocardium.$$

    Summary of Diagnostic Criteria

    • History of trauma.
    • Paradoxical movement of the flail segment during respiration.
    • Radiographic evidence of two or more consecutive segmental rib fractures.
    • Clinical signs such as dyspnea, tachypnea, and abdominal splinting.
    • Subcutaneous emphysema.

    Diagnostic Differentials

    • Pathologic rib fractures.
    • Paradoxical movement of the skin caused by torn intercostal muscles along with a pneumothorax.

    Treatment Recommendations

    Initial Treatment

    • Assess for any life-threatening conditions and appropriately stabilize. Establishment of a patent airway, adequate ventilation, and oxygenation are needed immediately. Pain management should also be initiated at this time, taking into account the cardiovascular status of the patient. $-$$$$
    • After or during initial stabilization, the patient should be placed in lateral recumbency with the flail segment down to minimize the paradoxical movement of the flail segment.
    • The type and volume of fluid required for stabilization will depend on the cardiovascular status of the patient. Avoid overhydration, which may increase capillary permeability, thereby worsening pulmonary injuries. $-$$
    • Cardiac dysrhythmias due to posttraumatic myocardial contusions or myocardial ischemia may be noted on ECG and should be treated accordingly. $-$$
    • If the patient is cyanotic, has an Spo2 <92%, or has clinical evidence of respiratory compromise, provide supplemental oxygen and be prepared to rapidly induce anesthesia to perform orotracheal intubation. $-$$
    • Pain management $-$$
      Peripheral nerve blockade: Using a 22- to 25-gauge needle, inject 0.25 to 1 mL of one of the following analgesics at each fracture site and at the caudal border of the rib near the level of the intercostal foramen to block each intercostal nerve. Block at least one to two intercostal spaces cranial and caudal to the flail segment. Good local analgesia and improved ventilation are preferred because systemic opioids may cause respiratory depression, hypoventilation, and suppression of the cough reflex.
      • Bupivacaine (0.25%-0.5%): Total dose of 1-2 mg/kg for dogs and cats q6h or until other analgesic treatments are initiated. Do not exceed 2.2 mg/kg. Toxic side effects seen at >4 mg/kg.
      • Lidocaine (1%-2%): 1-4 mg/kg for dogs q6-8h as needed for pain. Caution must be used in cats as they are more sensitive to lidocaine and at greater risk for developing central nervous system toxicosis. Do not exceed 4 mg/kg q6h. Lidocaine is preferred by the authors.
      • Alternative protocol: 0.5% bupivacaine (2 mg/kg) with 2% lidocaine (2 mg/kg). Inject 0.5-1 mL per site as directed above q6-8h or as needed for pain. Do not exceed levels indicated above.

    Intrapleural block: May be performed using a butterfly catheter (22 gauge), through-the-needle catheter (20 gauge), or preplaced chest tube. Place the patient in lateral recumbency with the affected side down for 20 minutes after administration of the interpleural block. $-$$
    Intravenous analgesia: Care must be taken to minimize respiratory depression.

    • Hydromorphone: Dogs: 0.05-0.2 mg/kg IM, IV, or SC q2-4h; Cats: 0.02-0.05 mg/kg IM, IV, or SC q2-4h.
    • Buprenorphine: Dogs and cats: 0.005-0.03 mg/kg IM, IV, or SC q6-8h; Cats only: 0.01-0.02 mg/kg sublingual q6-8h.
    • Fentanyl: Dogs: loading dose of 2-10 µg/kg IV, followed by 2-10 µg/kg/hr IV; Cats: loading dose of 1-5 µg/kg IV, followed by 1-5 µg/kg/hr IV.
    • CRI combination therapy: Two or all three agents (morphine or fentanyl and ketamine, +/- lidocaine) can be added to a bag of 0.9% NaCl or administered separately via an infusion pump. Specifics for calculation of CRI infusions are dependent on clinician comfort and standard hospital procedures.
      Morphine—Dogs: loading dose of 0.15-0.5 mg/kg IV, followed by 0.1-1 mg/kg/hr IV. Cats: loading dose of 0.05-0.1 mg/kg IV, followed by 0.025-0.2 mg/kg/hr IV; Lidocaine—Dogs: loading dose of 1-2 mg/kg IV, followed by 15-50 µg/kg/min IV. Cats: loading dose of 0.25-0.5 mg/kg IV, followed by 10-25 µg/kg/min IV. Maximum lidocaine CRI use in cats is 6-8 hours. Extreme caution must be used in cats due to their increased sensitivity and potential for seizures and cardiopulmonary depression. Ketamine—Dogs and cats: loading dose of 0.5 mg/kg IV, followed by 2-5 µg/kg/min IV. Ketamine should be used with caution or avoided in patients with possible head trauma or cardiac, renal, or hepatic disease. Fentanyl—see above.

    Epidural (lumbosacral) analgesia: Usually administered once with the patient under heavy sedation or general anesthesia. A preservative-free solution should be used. Maximum dose of 6 mL; 1 mL per 3-5 kg may be needed to reach the thoracic spine but must be injected slowly. Monitor for respiratory depression with opioids. $-$$

      • Lidocaine (2%): 1 mL/3.5 kg in dogs only. Onset of action: 5 minutes. Duration of action: 45-90 minutes.
      • Bupivacaine: Dogs: 0.6-2 mg/kg; Cats: 1 mg/kg. Onset of action: up to 60 minutes. Duration of action: 4-6 hours.
      • Morphine: 0.1-0.4 mg/kg in dogs; 0.16 mg/kg in cats. Onset of action: up to 20 to 60 minutes. Duration of action: 6-24 hours.
    • Surgical stabilization of the flail segment is addressed after initial stabilization of life-threatening emergencies is achieved. Surgical stabilization is recommended if thoracotomy is needed, rib fractures may cause further injury, paradoxical movement causes severe pain or dyspnea, or conservative medical management is ineffective and mechanical ventilation is required.

    Checkpoints: Flail Chest

    Alternative/Optional Treatments/Therapy

    • Positive-pressure mechanical ventilation (continuous or intermittent): Case dependent. Intubate if arterial Pao2 is <60 mm Hg with oxygen supplementation, if Paco2 is >60 mm Hg at a Fio2 of 21%, or if severe dyspnea is present and medical management does not result in clinical improvement. If ventilation is required, surgical stabilization is recommended to decrease the duration of intubation. $$$$
    • Surgical stabilization: External stabilization is recommended due to ease of fixation and the lack of need for general anesthesia. $$-$$$$
      External stabilization:
      • Using monofilament nonabsorbable suture (2-0 to 2) with a large curved needle, secure the affected ribs to a sheet of plastic splinting material that is molded to conform to the thoracic wall. Aseptically pass the suture material percutaneously around the affected ribs, keeping the sutures as close as possible to each rib to avoid inadvertently trapping the intercostal vessels and nerves or the underlying pulmonary tissue. Several techniques have been described for the precise placement of the sutures. The circumcostal sutures can be passed in at least two sites, one ventrally and one dorsally, to avoid pivoting of the flail segment. The clinician may also place one suture centrally around each rib, but it is recommended that these sutures be staggered to avoid pivoting. Predrill holes within the malleable external splint at locations that correspond to each sutured rib, and securely tie the sutures to the splint. Padding should then be applied between the thoracic wall and the external splinting material (Figure 2).
      • Aluminum rods may be used instead of malleable plastic splinting material and should conform to the patient's body. The external splint should be designed to fit the patient over the nonaffected ribs to help stabilize the flail segment. Circumcostal sutures should be placed as described above and can be secured to the external frame for stabilization of the flail segment (Figure 3).
      • An alternative method involves the placement of a single percutaneous suture at the midpoint of each affected rib. Each suture should be tied to a stiff device (e.g., tongue depressor) and these devices aligned along the dorsoventral axis of the ribs. Place additional splints on the unaffected part of the chest wall beneath and perpendicular to the dorsal and ventral ends of the sutured, vertically positioned splints. The flail segment is then drawn outward by placing cotton padding between the horizontal counterbraces and the ends of the sutured vertical splints.
      Internal stabilization (less common): May be required in patients with large thoracic wall defects, multiple unstable rib fractures, or open pneumothorax. A thoracotomy tube should be placed if internal stabilization is performed. 

    Supportive Treatment

    • For all patients with flail chest, supportive care includes adequateoxygen supplementation, rest, hydration, and nutrition. All coexisting conditions should be addressed accordingly. $-$$$
    • Oral pain management may be provided after several days of parenteral pain management or for at-home pain management. $-$$
    • The use of NSAIDs as adjunctive therapy is contraindicated in patients with renal or liver insufficiency or bleeding disorders.
    • Prophylactic antibiotic therapy specifically for the treatment of pulmonary contusions is not indicated unless clinical and radiographic changes consistent with bronchopneumonia are present. If indicated, once the patient is stable, a transtracheal or endotracheal wash should be performed to obtain cytology and culture samples to identify any specific bacterial growth and antibiotic sensitivity. Antibiotic therapy, however, is often indicated due to concurrent injuries such as skin lacerations and bite wounds. $
    • If the patient is recumbent, turn q4-6h to diminish the development of atelectasis. $
    • If a thoracostomy tube is placed, the patient may be placed on continuous suction, or aspiration of the chest tube may be performed q1-4h. $-$$

    Patient Monitoring

    • Close monitoring of respiratory rate, effort, and Spo2 q2-4h initially.
    • Close monitoring for signs of pain q2-4h.
    • Arterial blood gas q12-24h.
    • Venous blood gas q12-24h.
    • Central venous pressure, arterial blood pressure, urinary output, and thoracic auscultation q2-4h.
    • Continuous ECG monitoring.
    • Postoperative surgical stabilization:
      — Recommend serial bandage changes to assess thoracic auscultation, motion of splint, loosening of sutures, and possible development of sores.
      • Splint may be removed within 2-4 weeks after callus begins to bridge ribs, flail segment is stabilized, and no pain or crepitus is noted.
      • Reevaluate radiographs 2-3 weeks after discharge to assess callus formation and healing of fractures. Pulmonary contusions may require more than 10 days to resolve radiographically.

    Home Management

    • Cage rest for several weeks.
    • Closely monitor patient for signs of increased respiratory rate/effort and signs associated with pain.
    • Pain management.
    • Monitor for signs of secondary pneumonia such as coughing, mucopurulent nasal discharge, lethargy, and inappetence.
    • If surgical repair of the flail chest is performed, the owner should be instructed to monitor the surgical site for signs of increased redness, swelling, and discharge.

    Milestones/Recovery Time Frames

    • External splints may be removed in 2-4 weeks. Thoracic radiographs should be assessed to evaluate fracture healing before removal of any stabilizing material.
    • For patients receiving mechanical ventilation, improvement of pulmonary function is noted when the Pao2:Fio2 ratio is >150-200 with Fio2 <0.5 or positive end-expiratory pressure is ≤5 cm H2O.

    Treatment Contraindications

    • Chest wrap or external bandaging is unlikely to provide sufficient support, may compromise ventilation, and may cause the ribs to heal in an abnormal position, further compromising ventilation.
    • Diuretics are not recommended for treating pulmonary contusions unless fluid overload and pulmonary edema are present.
    • Corticosteroids should not be used. Several studies have shown reduced bacterial clearance and predisposition of pneumonia associated with pulmonary contusions and the use of corticosteroids.
    • Epidural analgesia is contraindicated in unstable patients or in patients with increased intracranial pressure, pelvic fractures, or superficial pyoderma or wounds near the area of administration.


    Favorable Criterias

    • Minimal concurrent injuries or disease.
    • If mechanical ventilation is required, prognosis is better in larger dogs.

    Unfavorable Criteria

    • Need for mechanical ventilation.
    • Extremely large flail chest defects.
    • Concurrent injuries.
    • Cardiac dysrhythmias.

    Anderson M, Payne JT, Mann FA, et al. Flail chest: pathophysiology, treatment, and prognosis. Compend Contin Educ Pract Vet 1993;15(1):65-75.

    Bastos R, Calhoon JH, Baisden CE, et al. Flail chest and pulmonary contusion. Semim Thorac Cardiovasc Surg 2008;20:39-45.

    Bjorling DE. Surgical management of flail chest. In: Bojrab MJ, Ellison GW, Slocum B, eds. Current Techniques in Small Animal Surgery. Baltimore: William and Wilkins; 1998:421-423.

    Olsen D. Thoracic wall disease, neoplasia and flail chest (V278): Proc WVC 2008.

    Olsen D, Renber W, Perret J, et al. Clinical management of flail chest in dogs and cats: a retrospective study of 24 cases (1989-1999). JAAHA 2002;38:315-320.

    Orton EC. Thoracic wall. In: Slatter D, ed. Textbook of Small Animal Surgery. 3rd ed. Philadelphia: Saunders-Elsevier; 1993:376-378.

    Smith MM. Flail chest. In: King LG, ed. Textbook of Respiratory Disease in Dogs and Cats. St. Louis: Saunders-Elsevier; 2004:647-651.

    Click here to download this article as a PDF.

    Dr. Abato discloses that she has received financial support from Royal Canin.

    Dr. Byers discloses that he has received financial support from Dechra Pharmaceuticals, Waltham, and Animal Clinical Investigation LLC.

    CETEST This course is approved for 1.0 CE credits

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