Pneumothorax in Horses (Equis) | Vetlexicon
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Pneumothorax

ISSN 2398-2977


Introduction

  • Pneumothorax is air in the pleural cavity via lung, mediastinal or thoracic wall disease or injury.
  • Can be divided into open, closed or tension pneumothorax.
  • Signs: unilateral condition is quite well tolerated; respiratory distress, change in breathing patterns and arterial oxygen concentrations accompany severe or bilateral disease.
  • Diagnosis: chest auscultation and percussion, thoracic radiography, ultrasonography and thoracocentesis are helpful.
  • Treatment: includes aspiration of air and oxygen insufflation as well as treatment of any underlying cause.
  • Prognosis: guarded, varying with initiating cause.

Presenting signs

  • Signs of respiratory distress, tachypnea, nostril flaring with hypoxemia and cyanosis in severe cases.
  • Trauma or injury to chest wall.
  • Severe lung disease.
  • Thoracocentesis or other intervention.
  • Minimal clinical signs in mild unilateral cases.
  • Prolonged choke or tracheal foreign body.
  • Post partum in neonate due to rib fractures lacerating lungs.

Age predisposition

  • Adults.
  • Neonates.

Cost considerations

  • Treatment.
  • Loss of animal.

Pathogenesis

Etiology

  • Trauma:
    • Penetrating wounds to thorax .
    • Puncture or rupture of trachea (intrathoracic)   Trachea: foreign body  .
    • Rupture of esophagus   Esophagus: trauma  , eg following choke, FB.
    • Parturitional trauma in neonates - fractured ribs.
  • Secondary to:
  • Iatrogenic:
    • Thoracotomy - especially standing   Thorax: thoracotomy  .
    • Subsequent to repair of diaphragmatic hernia   Diaphragm: hernia  .
    • Thoracocentesis or thoracic drainage   Thorax: thoracentesis  .
    • Excessive positive pressure ventilation, especially in the neonate   →   ruptured alveoli, bullae and pleural blebs.

Pathophysiology

  • Uncommon.
  • Air escapes into the pleural cavity via the lung, mediastinal space or thoracic wall.
  • May be uni- or bi-lateral.
  • Open, closed or tension pneumothorax.
  • Leads to pulmonary collapse and prevents inspiratory lung expansion.
  • A potentially life-threatening condition.
  • Air can gain access to the pleural space by traversing the lung, mediastinal space and thoracic wall.
  • Open pneumothoraxoccurs when a wound allows air to enter and leave the pleural cavity.
  • Closed pneumothoraxinvolves trapping air within the chest.
  • Tension pneumothoraxoccurs when a flap of tissue acts as a one way valve allowing air to enter but not leave the thorax.
  • Unilateral pneumothorax may be tolerated quite well in the horse but if the thin, fenestrated caudal mediastinum breaks down, bilateral pneumothorax will ensue   →   severe impairment of lung function   →   death.

Diagnosis

Presenting problems

  • Chest trauma.
  • Pleuropneumonia.
  • Respiratory distress/dyspnea.

Client history

  • Trauma or wounds to chest.
  • Severe lung disease.
  • Previous surgery or drainage of the thoracic cavity.
  • Tracheal foreign body.
  • Choke.
  • Difficult foaling in neonate.

Clinical signs

  • Tachypnea.
  • Dyspnea.
  • Changes in breathing pattern - shallow and rapid, becoming irregular or deep and slow.
  • Evidence of other problems:
  • Depends on the amount of air and whether uni- or bi-lateral:
    • Small amounts on one side - no clinical signs.
    • Larger amounts, especially if bilateral   →   respiratory distress
  • Cyanosis if arterial oxygenation impaired.
  • Sudden change in breathing pattern and oxygenation levels subsequent to procedure such as thoracocentesis or positive pressure ventilation.
  • In new born foals there may be chest wall bruising, palpable rib fractures or no external evidence of trauma, eg the foal may stand and nurse without difficulty.

Diagnostic investigation

Other
  • Chest auscultationboth sides of chest   Thorax: auscultation  :
    • Absence of normal lung sounds dorsally.
    • Abnormal sounds ventrally related to lung pathology.
    • However, in normal adult horses, lung sounds may not be audible over the entire thorax.
    • Bubbling sounds may be audible if air is escaping ventral to a fluid line.
  • Thoracocentesis  Thorax: thoracentesis  :
    • Aspiration of air from pleural space.
  • Chest percussion  Thorax: percussion  :
    • Increased resonance dorsally.
Ultrasonography
  • Thoracic ultrasonography  Ultrasonography: thorax  :
    • Failure to detect lung tissue against, and no structures beyond, the thoracic wall (reflected sound waves).
    • Sudden change as pass transducer from free air dorsally to aerated lung ventrally. Aerated lung will move with respiratory cycle.
    • Use may be limited by thoracic wall damage and subcutaneous emphysema.

Radiography

  • Thoracic radiography  Thorax: radiography  - particularly useful in the foal:
    • Collapsed lung (radiologically dense) with retraction of lungs away from the vertebral column and diaphragm.
    • Evidence of trauma, eg rib fracture, foreign bodies.
    • Ruptured diaphragm.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History and clinical signs.

Definitive diagnostic features

  • Ancillary diagnostic aids.

Differential diagnosis

Treatment

Initial symptomatic treatment

  • Treatment is necessary if the animal exhibits respiratory distress.
  • Pneumothorax without respiratory distress can be monitored carefully and the air allowed to gradually reabsorb.
  • Tension pneumothorax is an emergency.
  • Treat underlying cause, eg seal wounds by suturing or packing with sterile bandages.

Standard treatment

  • Remove air from pleural space:
    • Needle, stopcock and syringe.
    • Or trocar catheter connected to suction device.
    • May require repeating every 12-24 hours. Introduce dorsally under strict asepsis and local anesthesia just in front of ribs 12-15.
    • Thoracic drainage tube with unidirectional airflow devices such as Heimlich valve, which allows air to escape, during exhalation but not to re-enter during inspiration, can be used if persistent aspiration is required.
  • Nasal insufflation of oxygen (15 l/min) if respiratory distress, labored breathing and hypoxemia.
  • Covering broad spectrum antibiotics especially if indwelling tubes are in place.

Subsequent management

Monitoring

  • Clinical signs including auscultation.
  • Ultrasonography.
  • Thoracocentesis.

Prevention

Outcomes

Prognosis

  • Depends on original inciting cause.
  • Good in uncomplicated cases.
  • Rapid pulmonary re-expansion or large prolonged pneumothorax may predispose to pulmonary edema and death.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Joswig A & Hardy J (2013) Axillary wounds in horses and the development of subcutaneous emphysema, pneumomediastinum and pneumothorax. Equine Vet Educ 25 (3), 139-143 VetMedResource.
  • Epstein K L (2009) Pneumothorax and pneumomediastinum: Causes, diagnosis and treatment. Equine Vet Educ 21 (12), 642-647 Wiley Online Library.
  • Cornelisse C J et al (1999) What is your diagnosis? Bilateral pneumothorax. JAVMA 214 (9), 1323-1324 PubMed.
  • Jorgensen J S (1997) What is your diagnosis? Unilateral pneumothorax with collapse of the left caudal lung lobe. JAVMA 210 (8), 1109-1110 PubMed.
  • Hance S R et al (1992) Subcutaneous emphysema from an axillary wound that resulted in pneumomediastinum and bilateral pneumothorax in a horse. JAVMA 200 (8), 1107-1110 PubMed.
  • Spurlock S L et al (1988) Consolidating pneumonia and pneumothorax in a horse. JAVMA 192 (8), 1081-1082 PubMed.
  • Rantanen N W (1986) Disease of the thorax. Vet Clin North Am Equine Pract (1), 49-66 PubMed.
  • Thomson J U (1977) Emergency field treatment of pneumothorax in the horse. Vet Med Small Anim Clin 72 (2), 250 PubMed.
  • Lowe J E (1967) Pneumothorax in a horse from a puncture wound - A case report. Cornell Vet 57 (2), 200-204 PubMed.