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Basics ⬇

Basics

Definition

  • Air accumulation in the pleural space; categorized as traumatic or spontaneous.
  • Closed pneumothorax-no defects in the thoracic wall.
  • Open pneumothorax-defect in the thoracic wall resulting in communication of the pleural space with the atmosphere.
  • Tension pneumothorax-where pleural pressure in a closed pneumothorax exceeds atmospheric pressure; created by unidirectional transfer of air into the pleural space.

Pathophysiology

  • The pleural space is normally a potential space between visceral and parietal pleura containing a thin layer of fluid that contributes to “tethering” of the lungs to the thoracic wall. Air accumulation in the pleural space causes the lungs to collapse away from the thoracic wall.
  • Closed pneumothorax-air leakage from the pulmonary parenchyma, large airway, or esophagus.
  • Tension pneumothorax-typically due to a pleural or pulmonary flap-like defect that opens on inspiration to allow leakage of air into the pleural space and closes during expiration. Development of high intrathoracic pressure can reduce venous return to the heart.
  • Open pneumothorax-may or may not have associated pulmonary pathology; pleural pressure equals atmospheric pressure, leading to lung collapse.
  • Spontaneous pneumothorax associated with underlying pulmonary disease that ruptures, allowing air leakage.
  • Pneumothorax is usually bilateral disease due to mediastinal fenestrations.

Systems Affected

  • Respiratory
  • Cardiovascular

Incidence/Prevalence

Traumatic pneumothorax occurs in >40% of cases with chest trauma and 11–18% of dogs and cats presented for vehicular trauma. Pneumothorax has been reported in ∼ 25% of cases with intrathoracic grass awns and 70% of dogs with thoracic bite wounds.

Signalment

Species

Dog and cat

Breed Predilections

Spontaneous pneumothorax-more common in large, deep-chested dogs. Siberian huskies may be overrepresented.

Signs

Historical Findings

  • Traumatic-recent trauma, thoracocentesis, jugular venipuncture, lung aspirate, thoracotomy, mechanical ventilation, neck surgery. Recent anesthesia and intubation raises the possibility of tracheal trauma or pulmonary barotrauma.
  • Spontaneous-may or may not have previous history of pulmonary disease; usually acute, but can have a slowly progressive onset.

Physical Examination Findings

  • Respiratory distress (tachypnea, increased respiratory effort, +/- orthopnea).
  • Shallow, rapid abdominal breathing common.
  • Decreased to absent breath sounds dorsally (difficult to appreciate with severe distress).
  • Cyanosis.
  • Tachycardia.

Traumatic Pneumothorax

  • Signs of trauma (blunt or penetrating thoracic wall injury) or hypovolemic shock (pale mucous membranes, prolonged capillary refill time, altered mentation, poor pulse quality, tachycardia, decreased extremity compared to core temperature.
  • Subcutaneous emphysema in some cases with pneumomediastinum and/or tracheal trauma.

Causes

  • Traumatic: blunt trauma, penetrating thoracic or cervical injuries, post-thoracocentesis or thoracotomy, esophageal perforation, endotracheal tube-associated tracheal trauma, mechanical ventilation, pulmonary aspirate.
  • Spontaneous: bullous emphysema (most common in dogs), pulmonary bullae or bleb.
  • Migrating pulmonary foreign body, pulmonary neoplasia, pulmonary abscess, feline asthma, bronchopneumonia, mycotic pulmonary granuloma, parasitic pulmonary disease (Paragonimus, Dirofilaria immitis-pulmonary bullae rupture), congenital pulmonary cyst, congenital lobar emphysema, secondary to lung lobe torsion.
  • Extension of pneumomediastinum.

Risk Factors

  • Trauma
  • Thoracocentesis
  • Thoracotomy
  • Overinflation of endotracheal cuff
  • Excessive airway pressure during ventilation
  • Pulmonary disease/pathology
  • Migrating grass awns

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Pleural effusion
  • Diaphragmatic hernia
  • Pulmonary parenchymal disease (i.e., pulmonary contusions, pneumonia)

CBC/Biochemistry/Urinalysis

Neutrophilia with a left-shift if pulmonary infection or inflammation.

Other Laboratory Tests

  • Arterial blood gases-hypoxemia; hypocapnia or hypercapnia can occur.
  • Fecal sedimentation or zinc sulfate centrifugation-flotation for Paragonimus.

Imaging

Thoracic Radiography

  • Delay until patient is stable; may not be able to get more than one view.
  • Air in pleural space, pulmonary vascular pattern does not extend to the chest wall, cardiac silhouette elevated off the sternum.
  • Pulmonary pathology can be obscured by lung lobe collapse; often need to repeat radiographs following thoracocentesis.
  • Traumatic pneumothorax-evaluate for other traumatic injury such as contusions, rib fractures, diaphragmatic hernia, hemothorax, foreign bodies.
  • Spontaneous pneumothorax-evaluate for any sign of parenchymal pathology.
  • Right lateral horizontal beam results in the highest rate of detection and severity gradation while VD/DV views have the lowest rate.

Thoracic Ultrasound

  • Pneumothorax evidenced by loss of the “glide sign.”
  • Sensitivity of 78% and specificity of 93% compared to thoracic radiographs in identification of traumatic pneumothorax in dogs.

Thoracic Computed Tomography

  • Used preoperatively to improve localization of pulmonary pathology in cases with spontaneous pneumothorax.
  • CT can fail to detect pulmonary bullae prior to surgical exploration; larger pulmonary bullae more readily identified than smaller bullae.

Diagnostic Procedures

  • Thoracocentesis-confirms diagnosis; remove maximal amount of air from pleural space.
  • Bronchoscopy-consider if evidence of tracheal or large airway trauma.

Pathologic Findings

  • Will vary depending on underlying disease.
  • Gross evaluation-may be able to visualize pulmonary blebs, pulmonary or airway tears, pulmonary parenchymal disease or masses.
  • Histopathology-blebs are most commonly found at the apex and are contained entirely within the pleura; bullae are lined by pleura, fibrous pulmonary tissue, and emphysematous lung.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Inpatient care until air accumulation has stopped or has stabilized.
  • Animals in respiratory distress must have thoracocentesis and a maximal amount of air removed. Thoracocentesis can be performed with an intravenous catheter attached to an extension set and stopcock or via a butterfly needle.
  • ALWAYS provide oxygen therapy until patient is stabilized.
  • If large open chest wound-cover as cleanly as possible with airtight bandage (use of sterile lubricant/ointment around periphery of wound). Must be accompanied by chest tube placement; will require surgical closure once animal is stable.
  • Tube thoracostomy-use if unable to stabilize with thoracocentesis or repeated thoracocentesis required for continued pneumothorax; chest tube placement (under local or general anesthesia)-skin entrance site aseptically prepared in dorsal caudal quadrant of lateral thorax; skin incision similar in size to the tube is made over rib space 11–12 or 12–13; skin is then pulled cranially by an assistant so that the incision now lies over rib spaces 7–8 or 8–9. Chest tube is passed into pleural space, aiming cranioventrally; skin can then be released and a subcutaneous tunnel is formed. Purse string suture around insertion site and secure tube with finger trap suture pattern; thoracic radiographs should be performed after chest tube placement to ensure proper positioning.
  • If pneumothorax is rapidly accumulating-use continuous chest tube suction via one-, two- or three-bottle drainage system with an underwater seal. If pneumothorax is not severe or is resolving-use intermittent tube aspiration.
  • In emergency situation of life-threatening tension pneumothorax-consider emergency thoracotomy to convert problem to an open pneumothorax; animal can then be intubated and ventilated with positive pressure until stabilized.
  • Open traumatic pneumothorax-surgery as soon as patient is stable.
  • Closed traumatic pneumothorax-rarely requires surgical intervention.
  • Spontaneous pneumothorax-early surgical intervention recommended in dogs; exploratory thoracotomy often performed via median sternotomy if location of lesion is unknown. Pleural access port placed for medical management.

Nursing Care

  • Intravenous fluids required in most cases of trauma.
  • Appropriate pain control.
  • Chest tube maintenance-ensure all connections are airtight (cable ties are excellent for securing connections); ensure that tube is attached to animal at two points to reduce chance of inadvertent tube removal. Clean tube site and change dressing once daily. Do not allow animal to chew at chest tube.

Activity

Strict rest for at least a week following resolution of pneumothorax in an effort to minimize the chance of recurrence.

Client Education

  • Traumatic pneumothorax-discuss possibility of a chest tube and need for hospitalization; some animals require surgery.
  • Spontaneous pneumothorax-recommend early surgical intervention in most canine cases. Discuss possibility of underlying pulmonary disease that can make resolution challenging and recurrence possible. Warn owner that even with thoracotomy, the source of the pneumothorax may not be found and recurrent disease is possible.

Surgical Considerations

  • Do not use positive-pressure ventilation for closed pneumothorax. Place chest tube prior to ventilation or await thoracotomy prior to ventilation.
  • Thoracoscopy-may allow visualization of local lesion; allows instillation of substances for pleurodesis.
  • Thoracotomy-if lesion is not evident, can fill thorax with saline and look for bubbles as sign of a leak. Greater than one lesion is not uncommon. Partial or full lung lobectomy for localized lesions. Traumatic lacerations can be sutured. In some cases the location of the leak may not be evident at surgery. Thoracostomy tube should be placed at time of surgery in all patients.
  • Pleurodesis with mechanical abrasion of the pleura or instillation of an inflammatory substance, such as talc, into the pleural space (success rate is believed to be poor).
  • Autologous blood-patch treatment for persistent pneumothorax is a simple and relatively safe procedure that can be considered in patients that have failed conservative or surgical management.

Medications ⬆ ⬇

Medications

Drug(s)

Judicious use of pain control.

Precautions

Beware excess respiratory depression with opiates.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Respiratory rate-increased rate suggests recurrence of pneumothorax.
  • Serial thoracic radiographs to quantitate accumulation of air.
  • Pulse oximetry if breathing room air can help determine oxygenation status. Arterial blood gases give the best evaluation of oxygenation status if lung disease is present.
  • Central venous (jugular) blood gases can be used to evaluate ventilation status via PvCO2.
  • Rate of air production from chest tube-on continuous drainage with a three-bottle suction system need to count bubbles/minute produced in middle chamber; if intermittent aspiration, can quantitate with syringe.

Prevention/Avoidance

Keep pets confined-less likely to be injured.

Possible Complications

  • Death from hypoxemia and cardiovascular compromise.
  • Incorrect placement of chest tube or trauma associated with thoracocentesis-lung lobe laceration, cardiac puncture, diaphragmatic laceration, liver trauma.
  • Pleural infection from thoracocentesis or chest drain.

Expected Course and Prognosis

  • Traumatic pneumothorax-if thoracic trauma is not severe, the prognosis is good with thoracocentesis ± chest drain placement. With severe thoracic trauma, patient can deteriorate despite all efforts to stabilize it-usually because of severe pulmonary contusions.
  • Spontaneous pneumothorax-prognosis depends on underlying cause. If a single, focal lesion can be surgically resected, prognosis is good. If unable to locate lesion or diffuse or neoplastic pulmonary disease is present-prognosis is poor.

Miscellaneous ⬆

Miscellaneous

Synonyms

Punctured lung

Authors Laura Cagle and Kate Hopper

Consulting Editor Lynelle R. Johnson

Client Education Handout Available Online

Suggested Reading

Lisciandro GR, Lagutchik MS, Mann KA, et al. Evaluation of a thoracic focused assessment with sonography for trauma (TFAST) protocol to detect pneumothorax and concurrent thoracic injury in 145 traumatized dogs. J Vet Emerg Crit Care 2008, 18:258–269.

Oppenheimer N, Klainbart S, Merbl Y, Bruchim Y, Milgram J, Kelmer E. Retrospective evaluation of the use of autologous blood-patch treatment for persistent pneumothorax in 8 dogs (2009–2012). J Vet Emerg Crit Care 2014, 24:215–220.

Puerto DA, Brockman DJ, et al. Surgical and nonsurgical management of and selected risk factors for spontaneous pneumothorax in dogs: 64 cases (1986–1999). J Am Vet Med Assoc 2002, 220:1670–1674.

Reetz JA, Caceres AV, Suran JN, et al. Sensitivity, positive predictive value, and interobserver variability of computed tomography in the diagnosis of bullae associated with spontaneous pneumothorax in dogs: 19 cases (2003–2012). J Am Vet Med Assoc 2013, 243:244–251.

Scheepens ET, Peeters ME, L'eplattenier HF, Kirpensteijn J. Thoracic bite trauma in dogs: A comparison of clinical and radiological parameters with surgical results. J Small Anim Pract 2006, 47:721–726.