a. All Open and/or Sucking chest wounds should be treated by immediately applying gloved hand over the wound/defect, followed by placement of a vented or non-vented occlusive seal to cover the defect.

- If hair clippers are not available, consider placing petroleum impregnated gauze on the underside of the chest seal to facilitate forming an occlusive seal between the skin and the chest seal.
- Secure in-place on all four-sides with adhesive tape or with a snug, not overly tight, circumferential chest wrap.

b. Monitor /assess the MWD for development of tension pneumothorax and treat as necessary (see section d below).

c. Suspect a tension pneumothorax in the setting of known or suspected torso trauma or primary blast injury and one or more of the following:

- Severe or progressive respiratory distress
- Severe or progressive tachypnea
- Rapid, shallow, restrictive and open-mouth breathing
- Absent or markedly decreased sounds on one or both sides of chest
- Circulatory shock [weak to absent femoral pulses, pale mucous membranes, prolonged capillary refill time (> 3 – 4 seconds), decreased mental status, cold extremities, tachycardia to bradycardia).
- Traumatic cardiac arrest without obviously fatal wounds.
- Hemoglobin oxygen saturation < 90% on pulse oximetry.

Notes:

- Signs of respiratory distress in MWDs may include:
  - o Acting agitated, unable to get comfortable, or reluctance to lie down,
  - o Head and neck extended with elbows held out away from body (e.g. tripod position),
  - o Dyssynchronous breathing pattern (g. abdomen and chest move in opposite directions during inspiration),
  - o Minimal chest excursion with increased abdominal breathing,
  - o Lack of drive and response to even basic commands, unwillingness to move,
  - o Cyanotic (blue) gums (late finding).
- If not treated promptly, tension pneumothorax may progress from respiratory distress to circulatory shock and traumatic cardiac arrest.

d. Initial treatment of suspected tension pneumothorax consider:

- “Burping” or removing the occlusive chest seal (if present); if this doesn’t relieve the MWDs clinical signs, prepare to perform a chest needle decompression.
- Perform a chest needle decompression (NDC)
  - Allow a conscious MWD to assume the ‘position of comfort’ (often the canine will elect to sit or stand). If unconscious, place in the recovery (sternal) position or lateral recumbency, placing the injured/affected side facing up.
  - Use a 10 to 14-gauge, 2 to 3.25 inch (5 – 8 cm) over-the-needle/catheter unit.
  - Insert in the 7th to 9th intercostal space midway up the lateral thoracic wall or at the junctions of the upper 1/3rd and lower 2/3rd of the thoracic wall.
    - Drawing a line from the point of the shoulder (greater tubercle of the proximal humerus) to the distal tip of the last rib, defines the appropriate landmark for a chest- NDC in a MWD.
      - o NOTE: Canines have 13 ribs, the first 12 ribs are attached to the sternum via cartilaginous extensions and the 13th rib “floats” free of sternal attachment; in comparison, humans have 12 ribs.
    - Ensure that the needle enters cranial (towards the head) of the rib.
    - Insert the needle/catheter unit perpendicular to the chest wall.
    - Insert the needle/catheter unit together until the needle can be felt entering the pleural space. Two distinct “pops” will be felt through the needle – the first will be felt as the needle/catheter unit passes through the skin and the second will be felt when the needle penetrates the pleural cavity (this occurs when the catheter is inserted to ½-¾ of its length). As the needle enters the pleural space, direct the needle/catheter unit ventral (towards the sternum) to allow the needle/catheter unit to lie parallel along the long axis of the internal thoracic wall as it is inserted to the hub; this mitigates any risk of inducing lung or cardiovascular trauma when inserting the needle/catheter unit to the hub.
    - Note: Because of conformational differences, MWDs will have a shorter distance between their skin and the lateral thoracic wall (similar to the anterior axillary chest NDC site in humans); therefore, “hubbing” a 3.25 inch or longer catheter is typically not necessary in an MWD and may cause damage to intrathoracic structures if performed incorrectly.
    - Ensure the bevel of the needle faces away from the inner thoracic wall and towards to the lungs.
    - Hold the needle/catheter unit in placed for at least 5 – 10 seconds to allow full decompression to occur.
    - Once air is evacuated, remove the needle stylet. Consider leaving the catheter in place to alert subsequent care providers that the MWD has received treatment for a suspected tension pneumothorax.
      - DO NOT assume that the catheter will reliably continue to decompress the pleural space; it may become occluded with clotted blood, or quickly kink or migrate out of the pleural space due to the highly extensible nature of the canine skin.
    - Consider decompressing Both Sides (Left & Right) of the chest, particularly, if decompression of the initial side, fails to fully relieve signs consistent with a tension pneumothorax or in the presence of a traumatic cardiac arrest an concurrent torso trauma or primary blast injury;
      - Canines often have a fenestrated /communicating mediastinum that allows air to migrate to both sides of the thoracic cavity.
    - Consider the NDC successful if a combination of any of the following is identified:
      - Respiratory distress improves, or
      - An obvious hissing sound is heard as air escapes from the chest (most likely difficult to hear in high-noise environments), or
      - Hemoglobin oxygen saturation increases to 90% or greater (may take several minutes to reflect change and may not happen at altitude), or
      - A MWD with no vital signs has return of consciousness and/or femoral pulse.

- If initial NDC fails to improve MWDs clinical signs from the suspected tension pneumothorax:
  - Reposition MWD, if needed, and perform a second NDC on the opposite chest wall using a new needle/catheter unit.
  - If the MWD was initially in sternal recumbency, you may consider re-attempting the NDC on the same side by repositioning the MWD into lateral recumbency with the desired side to decompress (injured side) facing up. Perform a second NDC on the same side using a new needle/catheter unit.

Note: Re-positioning the canine into lateral may allow air to redistribute, rise and accumulate to the highest point on the affected side.

- If initial NDC is successful, but clinical signs re-develop:
  - Perform a another NDC on the same side; use a new needle/catheter unit:
- Continually reassess – reassess!.
- If the second needle decompression is also unsuccessful:
  - Continue on to the Circulation section of the Canine- TCCC guidelines.

e. When available, initiate pulse oximetry and monitor pulse oximetry in all MWDs suffering moderate to severe TBI. The presence of circulatory shock or marked hypothermia (< 95°F / 35°C) may adversely influence readings.

f. Consider administering oxygen supplementation when SpO2 < 94% on room/atmospheric and when available.

Notes:

- Due to the extensible nature of the canine’s skin and their vast subcutaneous space (SC), placing a chest seal that occludes only the external skin wound, and not the defect in the chest wall, may allow air from chest cavity to leak and become trapped into the SC space, resulting in significant amount of subcutaneous emphysema. With that in mind, if a tension pneumothorax develops after placement of an occlusive chest seal, burping or removing the chest seal may not completely resolve a tension pneumothorax in canines, particularly, if the occlusion is occurring at the level of the defect in the chest wall (due pieces of tissue, bone, etc.).
- Always consider decompressing both sides of the chest when treating a tension pneumothorax in a MWD, even with trauma isolated to one side of the MWDs thorax. Since, the canine mediastinum is fenestrated (like a cheesecloth) in a large proportion canines it is common for air to migrate to both sides of the thoracic cavity.
- The intercostal artery, vein, and nerve run on the caudal aspect (behind or towards the tail) of each rib; therefore, similar to the technique in human casualties, the best approach for inserting chest-NDC device is in the center of the intercostal space or at the cranial aspect (towards the head) of the rib to avoid damaging the nerve and vascular structures.
- Pulse oximetry probes used for people (typically finger probes) are best placed on the tongue for optimal reliability in unconscious, sedated or anesthetized dogs. In conscious dogs, use the ear pinna, lip fold, or inguinal skin fold; while not optimal for oximetry, these alternate sites generally yield reliable results in most instances. Alternatively a neonatal pulse oximetry adhesive sensor attached to the base of a canine’s tail may be used as alternative site in MWDs.