Treatment of traumatic pneumothorax (Figure 1) will depend upon the volume of air present, rate of ongoing leakage and the status of the animal.

Hypoventilation caused by significant collapse of the lungs due to significant pneumothorax can reduce the expired CO₂ and oxygen saturation of the blood (spO₂). Oxygen saturation below 85–90% on 21% or more inspired O₂ can be considered an indication for therapeutic thoracocentesis as can respiratory acidosis if blood gas analysis results are available (usually not necessary). Evidence of the animal's fatigue due to the effort required to maintain ventilation is also an indication for treatment.

Traumatic pneumothorax usually seals spontaneously soon after the injury with the result that low volume leakage that is not causing significant hypoventilation can be treated conservatively. Small volumes of air can be absorbed from the pleural cavity without the need for thoracocentesis.

Figure 1. Lateral radiograph of a dog suffering from traumatic pneumothorax.

Therapeutic Thoracocentesis

The ideal position in which to place the animal for the procedure can vary. Conscious, dyspnoeic patients often prefer sitting, sternal recumbency or standing during the procedure. Lateral recumbency can be used providing it does not cause distress or further respiratory embarrassment.

1.  Mid-way up the thoracic wall at the seventh or eighth intercostal space (caudal to the sixth rib to avoid the heart) is usually suitable for drainage of pneumothorax.

2.  The site is clipped and aseptically prepared. Sterile gloves should be worn.

3.  The butterfly needle or over-the-needle cannula is inserted perpendicular to the chest wall, along the cranial aspect of the rib at the chosen intercostal space to avoid iatrogenic damage to the neurovascular bundle. Once in the pleural space, the needle is repositioned so that it lies more parallel with the chest wall to prevent lung laceration (Figure 2).

4.  Pleural membrane puncture can be painful but is usually well tolerated by dyspnoeic patients treated with relatively small diameter needles or cannulae. Local anaesthetic is usually not necessary unless placing an indwelling thoracostomy tube.

Figure 2. Diagram showing a butterfly catheter with extension tubing being inserted off the cranial edge of a rib with the bevel facing dorsally (A), before being angled slightly ventrally (B), prior The extension tubing is connected to a syringe via a three-way tap to facilitate effective drainage.

Effective thoracocentesis in an animal experiencing significant hypoventilation as a result of pneumothorax will usually result in almost immediate improvement in respiratory character and oxygen saturation.

The mediastinum is often incomplete in small animals with the result that it is usually possible to drain both sides of the chest via unilateral thoracocentesis. Thoracic auscultation and, where necessary, dorsoventral radiography following unilateral thoracocentesis are useful steps to evaluate whether bilateral thoracocentesis is necessary. It is not uncommon for a small volume pneumothorax to remain following successful thoracocentesis.

Post-drainage radiographs (dorsoventral, left and right lateral projections if possible) are important both to assess efficacy of drainage and to act as a reference point against which future images can be compared to determine the rate or presence of ongoing leakage. Assessment of pulmonary pathology is also carried out from these images, and it should be remembered that pulmonary contusions are not uncommon following blunt thoracic trauma. Contusions can result in significant hypoventilation that does not require or respond to additional thoracocentesis. Radiographic evidence of pulmonary contusions can lag 24 hours or more behind the trauma episode and onset of compromise of gas exchange.

Once the animal is stable and post-drainage radiographs have been obtained, close monitoring is indicated to monitor for signs of further leakage. Many traumatic air leaks seal quickly and do not therefore require more than one or two drainage procedures.

In the event of continued leakage, intermittent needle thoracocentesis or placement of thoracostomy tubes may be necessary. Which of these is most appropriate will depend on variables of the case itself.

Thoracostomy Tube Placement

General anaesthesia is usually indicated for placement, but larger amenable dogs may be suitable for placement under sedation and with manual restraint. Lateral recumbency is usually preferable but often not possible due to the respiratory status of the animal. As much preparation as possible is carried out before anaesthesia.

1.  The entire hemithorax is clipped and aseptically prepared.

2.  An intercostal nerve block and/or local infiltration is used in conscious patients or administered before the end of anaesthesia to aid in achieving smooth recovery.

3.  The drain is typically placed at the seventh to eighth intercostal space and half way up the thoracic wall.

4.  A small skin incision is made several centimetres behind the chosen intercostal space (usually over the tenth or eleventh space).

5.  Most clinicians prefer a drain designed to be inserted over a sharp trochar for closed tube placements such as is described here. The potential for iatrogenic lung damage requires that the drains only be placed when there is significant pneumothorax present and the lungs are therefore separated from the thoracic wall.

6.  The drain is pushed through the incision in a cranial direction subcutaneously to create a tunnel and then elevated perpendicular to the thoracic wall.

7.  The intercostal neurovascular bundle caudal to each rib is avoided by inserting the tube at the cranial edge of the appropriate rib.

8.  The tube and trochar are pushed into the pleural space with a controlled but forceful movement perpendicular to the thoracic wall.

9.  The tube itself is then advanced the desired distance into the thoracic cavity in a cranial direction whilst the trochar is held in place (the trochar itself is not advanced much beyond the pleural membrane). The aim is usually to place the tip of the drain at the level of the first or second intercostal space.

10.  Once the trochar is removed, the drain should be closed with an atraumatic tubing clamp (often supplied with the kit) and a connector attached.

11.  The drain is usually then suctioned to ensure correct placement and stabilise the animal before it is secured to the skin with a Roman sandal suture.

12.  All connections are secured (for example with superglue) and the tube(s) covered with a chest bandage (e.g., stockinete).

13.  An Elizabethan collar is essential whilst the drain(s) are in place, and the animal should be closely supervised due to the potential for disconnection or displacement of the tubes.

Following thoracic drain placement, radiography is indicated to document tube position in addition to the reasons outlined for radiographs following needle thoracocentesis. Indications for bilateral versus unilateral drain placement are the same as those outlined above for needle thoracocentesis.

The frequency of thoracocentesis should be guided by the clinical circumstances and the rate of ongoing leakage. There is no proven benefit from leaving lungs partially deflated in terms of sealing of leaks. Most leaks will seal within hours or a few days. On the rare occasion that leakage is high volume and almost constant, continuous drainage using an underwater seal may be required (Figure 3).

Unlike tube placement to treat pleural fluid, recovery of air should cease almost entirely before the tube(s) are removed. It should be remembered that the presence of the tube is likely to result in a low volume (e.g., 1–2 ml/kg/ day) of pleural effusion and this should therefore not preclude removal. If the tube has been in place for several days, culture of the tip can be considered in order to check for potential contaminants, although this is rare.

The majority of traumatic pneumothorax cases are managed by one or two therapeutic thoracocentesis procedures, and those that require intermittent or constant drainage usually self-seal within 3–5 days. Exploratory thoracotomy may be required in cases with significant leakage beyond this period. This procedure requires considerable expertise and can still carry a guarded prognosis.

Figure 3. Photograph of a three-chambered water seal device used to provide a constant safe level of negative suction pressure and allow collection of fluid (Thora-seal IIITM; Argyl Medical).

Tension Pneumothorax

Damage to the lung parenchyma, bronchial tree or thoracic wall that results in a one-way valve for air to accumulate in the pleural cavity causes a tension pneumothorax. This differs from a conventional pneumothorax in that positive pressure develops in the pleural space and causes complete collapse of the lungs and great veins resulting in rapidly life-threatening hypoventilation and fall in cardiac output. Tension pneumothorax requires rapid treatment with frequent or constant thoracocentesis until the lesion seals or the cause can be treated.