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Standards of Care July 2009 (Vol 11, No 6)

Tension Pneumothorax

by Michelle E. Goodnight, DVM, MA, Amy L. Butler, DVM, MS, DACVECC

    CETEST This course is approved for 1.0 CE credits

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    Introduction

    Tension pneumothorax is a life-threatening situation that most commonly occurs after a significant traumatic event involving penetrating thoracic injury or blunt force trauma. Iatrogenic tension pneumothorax can result from positive-pressure ventilation, inadvertent tracheal laceration during intubation, thoracic surgery, thoracocentesis, or fine-needle lung aspiration. Tension pneumothorax is reported less frequently in cats than in dogs.

    Tension pneumothorax develops when a flap of tissue forms secondary to thoracic injury. In open pneumothorax secondary to a penetrating injury, the flap can be skin or muscle. In closed pneumothorax resulting from blunt trauma, the flap is usually pulmonary parenchyma. This flap effectively creates a one-way valve, allowing air into the pleural space during inhalation but preventing its escape during exhalation. This prevents the development of negative intrathoracic pressure and increases intrapleural pressure, which prevents pulmonary expansion, leading to respiratory distress, severe hypoxemia, decreased venous return to the heart, hemodynamic instability, and death. Tension pneumothorax is a clinical diagnosis, and treatment should never be delayed to obtain laboratory or radiography results. Immediate thoracocentesis and/or chest tube placement is required to save the patient's life.

    Diagnostic Criteria

    Historical Information

    • Known history of blunt force or penetrating thoracic trauma or a procedure with the potential to cause pneumothorax.

    Gender/Age/Breed Predisposition

    • None.

    Owner Observations

    • Respiratory distress.
      — Severe, often with open-mouthed breathing.
      — Rapidly progressive.
    • Collapse.
    • Restlessness.
    • Barrel-chested appearance.
    • Pale mucous membranes.
    • Cyanosis.
    • Recent traumatic event.

    Other Historical Considerations/Predispositions

    • Spontaneous tension pneumothorax is relatively rare.

    Physical Examination Findings

    • Severe respiratory distress.
      — Restrictive pattern.
      — Abdominal effort.
      — Nasal flaring.
    • Minimal chest excursion despite significant respiratory effort.
    • Decreased to absent lung sounds.
    • Tachypnea.
    • Cyanosis.
    • Hyperresonance on thoracic percussion.
    • Barrel or "sprung" chest appearance.
    • Tachycardia.
      — Heart sounds can be muffled.
    • Hypertension or hypotension depending on patient's cardiovascular status.
    • Marked deviation of cervical trachea to the unaffected side.
    Key To Costs

    Laboratory Findings

    This is a clinical diagnosis! Do not wait for laboratory results. Perform a needle thoracocentesis immediately, then conduct diagnostic testing when the patient is stable.

    Arterial Blood Gas $

    • Evidence of alterations in ventilation.
      — Hypoxemia (decreased PaO2; reference range [RR]: 80-100 mm Hg on room air).
      — Hypoventilation (increased PaCO2) secondary to inability to expand lungs or decreased thoracic excursions (RR [mm Hg on room air]: dogs, 30.8-42.8; cats, 25.2-36.8).
      — Hyperventilation (decreased PaCO2) secondary to anxiety and dyspnea (RR [mm Hg on room air]: dogs, 30.8-42.8; cats, 25.2-36.8).
      — Respiratory acidosis or alkalosis possible (RR: pH 7.4).

    Complete Blood Count $

    • Usually normal. Changes in packed cell volume/hematocrit and total solids may be the result of unrelated disorders, such as hypovolemia or dehydration.
      — RR for dogs: packed cell volume, 37%-55%; total solids, 5.8-7.2 g/dL.
      — RR for cats: packed cell volume, 24%-45%; total solids, 5.7-7.5 g/dL.

    Chemistry Panel $

    • May be normal or exhibit findings consistent with trauma.
      — Increased creatine kinase (RR: dogs, 36-155 IU/L; cats, 21-275 IU/L).
      — Increased ALT due to hepatocellular damage (RR: dogs, 4-91 IU/L; cats, 13-75 IU/L).

    Urinalysis $

    • May be normal or exhibit findings consistent with dehydration or trauma.
      — Increased urine specific gravity (RR: dogs, >1.030; cats, >1.035).
      — Hematuria.
      — Myoglobinuria.
    About VECCS

    Other Diagnostic Findings

    Again, this is a clinical diagnosis. Do not delay treatment to obtain thoracic radiographs. Perform a needle thoracocentesis immediately, then conduct thoracic radiography when the patient is stable.

    Thoracic Radiography $

    • Mediastinal shift to the contralateral side.
    • Air opacity and consolidated lung consistent with pneumothorax on the affected side.
    • Depression of the ipsilateral hemidiaphragm.
    • Elevation of cardiac silhouette away from the sternum.
    • Retraction of lung lobes away from the thoracic wall.

    Summary of Diagnostic Criteria

    • Severe respiratory distress.
    • Absent lung sounds.
    • Pneumothorax.
    • History of trauma.

    Diagnostic Differentials

    • Intrathoracic mass.
      — Identified on thoracic radiographs or ultrasonography.
      — Negative needle thoracocentesis.
    • Bilateral pleural effusion.
      — Identified on thoracic radiographs and thoracocentesis.
    • Pneumomediastinum.
      — Identified on thoracic radiographs.
    • Diaphragmatic hernia.
      — Identified on thoracic radiographs or ultrasonography.

    Treatment Recommendations

    Initial Treatment

    • Thoracocentesis. $
      — This is a lifesaving procedure that must be performed quickly if tension pneumothorax is suspected.
      — Needle thoracocentesis should be performed in the seventh, eighth, or ninth intercostal space. Use an appropriately sized needle (22 to 25 gauge for small patients, 20 gauge for larger patients). Place the needle in the mid to upper thorax and connect it to a three-way stopcock and appropriately sized syringe via an extension set. (Other techniques may be described in the literature. Use a technique with which you and your staff are familiar and comfortable.) Attempts should be made to evacuate all free air from the thorax until negative pressure is obtained. It is important to record the amount of air and/or fluid removed from the thorax so that trends can be identified if the pneumothorax persists. Always maintain sterile technique to reduce the risk of infection.
    • Oxygen supplementation. $
      — Provide supplementary oxygen via an oxygen cage, mask (during initial stabilization), nasal cannula, or prongs or via an endotracheal tube, depending on the severity of respiratory distress and status of the patient.
    • Analgesia and sedation. $
      — Required to reduce patient anxiety and improve ventilation.
      — Avoid medications that may worsen cardiovascular compromise, such as dexmedetomidine and acepromazine.
      — If the patient requires sedation for thoracocentesis, use a benzodiazepine in addition to a low-dose opioid. For example:
      • Diazepam: 0.1-0.5 mg/kg IV (dogs and cats)
        or
      • Midazolam: 0.1-0.5 mg/kg IV (dogs and cats)
        and
      • Hydromorphone: Dogs, 0.05-0.2 mg/kg IV, SC, or IM; cats, 0.1-0.2 mg/kg IV or SC. Useful as a constant-rate infusion (CRI) at a rate of 0.01-0.03 mg/kg/hr for dogs and cats. May induce vomiting, especially if administered IV.
        or
      • Fentanyl: 2 µg/kg bolus IV followed by a CRI of 2-5 µg/kg/hr IV (dogs and cats). Fentanyl is effective for only approximately 15-20 minutes, so it must be administered as a CRI.
        or
      • Oxymorphone: Dogs, 0.05-0.2 mg/kg IV, IM, or SC; cats, 0.1-0.2 mg/kg IV, IM, or SC. May induce vomiting, especially if administered IV. Animals may become hypersensitive to noise.
    • Thoracostomy tube placement. $
      — Required in severe cases, but not necessary in all patients.
      — Indications for placement:
      • Unable to obtain negative pressure with needle thoracocentesis.
      • More than two thoracocenteses required within a 1-hour period.
      • More than three thoracocenteses required within a 24-hour period.
      — Always indicated if the patient has tension pneumothorax and requires positive-pressure ventilation. The positive intrapulmonary pressures necessary for ventilation frequently result in recurrence of the pneumothorax.
      — Multiple techniques for thoracostomy tube placement have been described in the literature. Use a technique with which you and your staff are familiar and comfortable. The authors prefer the following technique:
      • Use strict aseptic technique to prevent bacterial contamination of the pleural cavity. Clip and aseptically prepare the skin over the seventh, eighth, and ninth intercostal spaces on the affected side.
      • Insert the tube in the seventh, eighth, or ninth intercostal space. Create a subcutaneous tunnel to help prevent air leakage into the thorax. Have an assistant gently pull the skin cranially. Keep the skin in this position until the procedure is complete.
      • Place the thoracostomy tube at the junction of the upper third and lower two-thirds of the thorax.
      • Carefully measure the tube to determine how far to insert it into the thoracic cavity. To estimate the proper length, measure from the desired rib space cranially to the second rib. Note the distance or mark the appropriate spot on the tube with a sterile marker.
      • Perform a local lidocaine block at the desired location. Infuse lidocaine into the subcutaneous tissue and intercostal musculature down to the level of the pleural surface.
      • Make a stab incision through the skin and subcutaneous tissue overlying the selected location. The incision should only be the size of the thoracostomy tube or slightly larger. This will help prevent air leakage around the tube. Occlude the free end of the tube throughout the placement procedure until a drainage system is connected.
      • Use the tip of the trocar to bluntly tunnel through the intercostal muscles. To minimize the risk of damaging vasculature and nerves, keep the trocar in contact with the cranial aspect of the rib behind the insertion point.
      • Briefly halt mechanical ventilation when advancing the trocar through the pleural layer and into the pleural space. This minimizes the risk for iatrogenic trauma to the pulmonary parenchyma.
      • Slowly advance the thoracostomy tube to the predetermined position. Carefully remove the trocar, leaving the tube in place.
      • Gently move the skin back into its normal anatomic position. This creates a short subcutaneous tunnel around the thoracostomy tube.
      • Suture the thoracostomy tube in place, using a finger-trap suture to secure the tube and prevent unintentional advancement or removal. Mark where the tube enters the skin so that proper positioning can be verified throughout patient hospitalization. Connect a drainage system and verify the tube is functioning properly.
      • Use a syringe to evacuate the pleural space until negative pressure is obtained. This can be accomplished through a system similar to that described for needle thoracocentesis. Once negative pressure is obtained, the thoracostomy tube can be sealed with a cap or attached to a continuous suction device.
      • Keep the thoracostomy tube insertion site clean by covering with a bandage. Evaluate the site daily to monitor for complications such as infection or subcutaneous emphysema.
      — Anesthetic considerations:
      • Always provide oxygen supplementation during placement of a thoracostomy tube.
      • If the animal is obtunded or comatose, no general anesthesia is required. Use of local anesthetics as described is typically adequate for placement.
      • If the patient is compromised but still responsive, intubation and airway control are necessary. Use an opioid and benzodiazepine combination for induction. Inhalant anesthesia is used to maintain general anesthesia. This allows thoracostomy tube placement without further compromising cardiovascular status.
      • If the pneumothorax involves damaged pulmonary parenchyma with a penetrating thoracic wound, significant leakage of inhalant anesthetic into the room is possible.
    • Surgical intervention. $$-$$$
      — Very rarely required in traumatic tension pneumothorax, but lung lobectomy is sometimes necessary in cases that do not respond to conservative treatment.
      — Consider thoracic exploration if pneumothorax does not resolve within 5 to 7 days with appropriate treatment.
      — May be indicated in cases of penetrating thoracic injury if the patient fails to respond to conservative treatment or when a large airway laceration is suspected.

    Alternative/Optional Treatments/Therapy

    • None. Failure to resolve the tension pneumothorax quickly results in the death of the patient.

    Supportive Treatment

    • Appropriate analgesia and sedation. $
      — Essential to achieve a quick recovery.
      — Improves ventilation by increasing patient comfort and the quality of chest excursions.
      — Consider an opioid for adjunctive sedative effects. See Initial Treatment section for recommended doses.
      — Consider buprenorphine (dogs: 5-30 µg/kg IV, IM, or SC; cats: 5-10 µg/kg IV, IM, SC, or PO), as it is well absorbed by the oral mucosa in cats. This may not be adequate pain control in patients with significant musculoskeletal injury.
    • Thoracostomy tube. $
      — Required if unable to correct the initiating factor. Placement may not be necessary if the primary injury is corrected and pneumothorax does not recur.
    • Intravenous fluid therapy. $
      — Indicated for treatment of traumatized patients suffering from hypovolemic shock.
      — Hypovolemic/hypotensive resuscitation to maintain a low-normal systolic blood pressure may be indicated in patients with concurrent bleeding.
      — Maintenance of appropriate fluid balance while hospitalized.
    • Antibiotics. $
      — Unnecessary unless pneumothorax is secondary to a nonsterile penetrating injury (e.g., bite wound) or if bacterial infection is documented.
    • Mechanical ventilation. $$$
      — Indications for positive-pressure ventilation are patient dependent. General guidelines include an arterial Pco2 consistently greater than 50 mm Hg, a Pao2 less than 50 mm Hg with oxygen supplementation, or muscle fatigue secondary to extended dyspnea and increased respiratory effort.
      — Risks of mechanical ventilation include barotrauma to the pulmonary parenchyma, anesthetic death, and asphyxiation if the ventilator malfunctions.
      — Complications associated with performing mechanical ventilation include pneumothorax, bacterial and aspiration pneumonia, oral ulceration, peripheral edema formation, corneal ulceration secondary to extended sedation, tracheal tube occlusion, aspiration of tracheal tube if sedation is insufficient, and gastric distention.

    Patient Monitoring

    • Respiratory status.
      — Hourly monitoring of respiratory rate and effort, including auscultation of the thorax to verify presence of lung sounds in all fields.
      — Monitor for trends in the volume of air being removed via the thoracostomy tube or repeated thoracocenteses.
      — Reevaluate thoracic integrity if the volume of evacuated air increases or remains the same 12 to 24 hours after initiating appropriate treatment.
      — Perform serial arterial blood gas analysis or pulse oximetry measurements to monitor status of the lung parenchyma.
    • Hemodynamic status.
      — Monitor blood pressure, capillary refill time, and pulse rate and quality.
    • Adequate analgesia and sedation.
      — Monitor respiratory rate, heart rate, and mobility.
    • Thoracic radiography.
      — May help identify cause in some cases of tension pneumothorax (e.g., fractured ribs in cases with closed, unobserved trauma).
      — Required if thoracocentesis is unsuccessful or respiratory distress persists after obtaining negative pressure with thoracocentesis/thoracostomy tube drainage.
    • All cases of tension pneumothorax should receive 24-hour monitoring in an appropriate intensive care facility after initial stabilization is complete.

    Complications

    • Infection resulting from the primary injury or repeated thoracocenteses.
    • Iatrogenic pneumothorax.
    • Intrathoracic organ damage secondary to repeated thoracocenteses or thoracostomy tube placement.
      — Severe hemorrhage.
      — Cardiac tamponade secondary to myocardial laceration.

    Home Management

    • Restricted exercise and cage rest for 1 to 3 weeks after release.
    • Monitor for evidence of respiratory distress, including decreased activity levels, anorexia, orthopnea, and collapse.
    • Instruct owner to keep the pet indoors, in a fenced area, or on a leash.

    Milestones/Recovery Time Frames

    • Thoracostomy tube removal.
      — Less than 2 mL/kg of air and/or fluid obtained for the previous 24 hours.
      — Fluid production of less than 2 mL/kg/24 hr is often secondary to irritation from the tube rubbing against the pleural surfaces.
      — Verify resolution of pneumothorax through physical examination or radiography before removal.
    • In most cases, air leakage will resolve within 3 to 5 days with appropriate supportive care. Animals that do not recover as expected should undergo additional diagnostics, such as thoracic computed tomography, magnetic resonance imaging, or exploratory surgery.

    Treatment Contraindications

    • Tension pneumothorax must be immediately treated or it will quickly lead to the death of the animal. The only contraindication during treatment is administration of medications causing cardiovascular compromise.

    Prognosis

    The prognosis for recovery is good, provided the underlying cause is survivable and treated appropriately.

    Favorable Criteria

    • Rapid response to treatment.
    • Resolution of pneumothorax without repeated thoracocenteses.
    • Limited to no cardiovascular compromise.
    • Absence of respiratory distress.
    • Normal body temperature on presentation (cats).

    Unfavorable Criteria

    • Persistent pneumothorax despite appropriate treatment of the underlying cause, thoracostomy tube placement, and pain management.
    • Severe thoracic ribcage trauma.
    • Cardiovascular compromise.
    • Complications secondary to the trauma or underlying cause of the pneumothorax.
    • Development of reexpansion pulmonary edema.

    Hassel DM. Thoracic trauma in horses. Vet Clin North Am Equine Pract 2007;23(1):67-80.

    Hawkins EC. Pneumothorax. In: Nelson RW, Couto CG, eds. Small Animal Internal Medicine. 2nd ed. St. Louis: Mosby; 1998:317.

    Mertens MM, Fossum TW. Pneumothorax. In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine. 6th ed. Philadelphia: WB Saunders; 2005:1282-1283.

    Miller LA. Chest wall, lung and pleural space trauma. Radiol Clin North Am 2006;44(2):213-224.

    Plunkett SJ. Emergency Procedures for the Small Animal Veterinarian. 2nd ed. Philadelphia: WB Saunders; 2008:57-59.

    Sauvé V. Pneumothorax. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. Philadelphia: WB Saunders; 2009:129.

    Sigrist NE. Thoracocentesis and thoracostomy tube placement and drainage. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. Philadelphia: WB Saunders; 2009:131-137.

    Ullman EA, Donley LP, Brady WJ. Pulmonary trauma: emergency department evaluation and management. Emerg Med Clin North Am 2003;21(2):291-313.

    Click here to download this article as a PDF.

    CETEST This course is approved for 1.0 CE credits

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