Issues

Pneumothorax

 

Air accumulation in the pleural space; is categorized as traumatic or spontaneous.

Closed pneumothorax—no defects in the thoracic wall.

Open pneumothorax—defect in the thoracic wall resulting in the communication of the pleural space with the atmosphere.

Tension pneumothorax— where pleural pressure in a closed pneumothorax exceeds atmospheric pressure; created by the 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 the “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. The 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 is associated with the underlying pulmonary disease that ruptures, allowing air leakage.
• Pneumothorax is usually a 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 raise the possibility of tracheal trauma or pulmonary barotrauma.
• Spontaneous—may or may not have a 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 is 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

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 the patient is stable; may not be able to get more than one view.

Air in pleural space, the 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 another 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 the 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 are more readily identified than smaller bullae.

 

DIAGNOSTIC PROCEDURES

Thoracocentesis—confirms the diagnosis; remove the maximal amount of air from pleural space.

Bronchoscopy—consider if evidence of tracheal or large airway trauma.

 

PATHOLOGIC FINDINGS

Will vary depending on the 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

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 the patient is stabilized.
• If large open chest wound—cover as cleanly as possible with an airtight bandage (use of sterile lubricant/ointment around the periphery of the wound). Must be accompanied by chest tube placement; will require surgical closure once the animal is stable.
• Tube thoracostomy—use if unable to stabilize with a 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. A 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 the pneumothorax is rapidly accumulating—use continuous chest tube suction via one-, two- or three-bottle drainage system with an underwater seal. If the pneumothorax is not severe or is resolving—use intermittent tube aspiration.
• In the emergency situation of life-threatening tension pneumothorax—consider emergency thoracotomy to convert the problem to an open pneumothorax; the animal can then be intubated and ventilated with positive pressure until stabilized.
• Open traumatic pneumothorax—surgery as soon as the 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 the location of the lesion is unknown. Pleural access port is placed for medical management.

 

NURSING CARE

• Intravenous fluids are 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 the chance of inadvertent tube removal. Clean tube site and change dressing once daily. Do not allow animals to chew at chest tubes.

ACTIVITY

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

 

CLIENT EDUCATION

• Traumatic pneumothorax—discuss the possibility of a chest tube and need for hospitalization; some animals require surgery.
• Spontaneous pneumothorax—recommend early surgical intervention in most canine cases. Discuss the 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 the local lesion; allows instillation of substances for pleurodesis.

Thoracotomy—if the lesion is not evident, can fill thorax with saline and look for bubbles as a 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 the surgery. A Thoracostomy tube should be placed at the 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

DRUG(S)

Judicious use of pain control.

 

PRECAUTIONS

Beware excess respiratory depression with opiates.

 

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 the middle chamber; if intermittent aspiration can quantitate with a 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, the patient can deteriorate despite all efforts to stabilize it—usually because of severe pulmonary contusions.
• Spontaneous pneumothorax—prognosis depends on the underlying cause. If a single, focal lesion can be surgically resected, the prognosis is good. If unable to locate lesion or diffuse or neoplastic pulmonary disease is present—prognosis is poor.

 

MISCELLANEOUS

SYNONYMS

Punctured lung

 

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