Thoracic trauma: keys to success (Proceedings)
Traumatized small animal patients represent a population in which a standardized approach to diagnosis centered on thorough background knowledge of traumatic injuries coupled with a complete physical examination will allow for rapid therapeutic interventions and optimization of patient care. The following paragraphs will detail the pathophysiology, diagnostic methods, and emergency medical treatment for injuries sustained due to both blunt and penetrating thoracic trauma from an anatomically based approach.
Thoracic injury occurs most commonly as a result of blunt trauma. Common causes include being hit-by car, falling from a height (high-rise syndrome), big-dog-little-dog interactions, and human-animal interactions. Penetrating injury (projectile induced injury, big-dog-little-dog interactions, and impalement injuries) occurs with less frequency than blunt thoracic injuries, but it must be recognized that both can result in immediately life threatening problems.
Trauma Associated Pleural Space Disease:Pneumothorax, Hemothorax, and Diaphragmatic Hernia make up the three acute trauma associated pleural space diseases. Patients with clinically significant trauma associated pleural space diseases will likely display signs of tachypnea, dyspnea, and muffled heart and lung sounds on auscultation of the thorax.
Pneumothorax is the accumulation of air in the pleural space between the parietal and visceral pleura. Pneumothorax is classified as "open" when air enters the pleural space from an external wound, or "closed" when air enters the pleural space due to pulmonary or mediastinal injury. Tension pneumothorax occurs when air accumulates within the pleural space via a one-way-valve effect allowing air to enter, but not leave the pleural space. The resultant accumulation of air (and thus pressure) within the pleural space limits pulmonary expansion (ventilation) and venous return resulting in severe compromise to both the cardiovascular and respiratory systems. Pneumothorax is the most common of the trauma-associated pleural space diseases occurring in up to 47% of all dogs and cats with thoracic trauma. During our initial assessment of the traumatized patient, if we assume that a pneumothorax is present, we will make extra effort to both document and treat the condition.
Diagnosis of clinically significant pneumothorax is based on thorough auscultation of the chest and observation of the patient for signs of dyspnea. Positioned in sternal recumbency, patients with pneumothorax will tend to have decreased lung sounds dorsally to diffusely. Pneumothorax may be unilateral or bilateral. If pneumothorax is suspected based on auscultation and clinical signs, or if the clinician is unsure of the presence or absence of pneumothorax, thoracocentesis should be performed. Thoracocentesis is both diagnostic and therapeutic for pneumothorax. Radiographs of the thorax are not necessary for the acute diagnosis of a clinically significant pneumothorax and they may jeopardize the stability of the patient. When performed, radiographic evidence supportive of pneumothorax includes retraction of the lung from the chest wall (loss of vascular markings in this space), consolidation of lung lobes, and on lateral radiograph, the appearance of the heart "floating" on a cushion of air. The latter radiographic finding is due to the falling of the heart to the side of the atelectatic "down" lung.
Clinical evaluation of the patient's tolerance for its pneumothorax should guide treatment. Thoracocentesis may be performed with the patient in lateral or sternal recumbency. Most commonly, dyspneic patients will prefer to be sternal. Necessary equipment for thoracocentesis includes a 60cc syringe, three-way-stopcock, extension set and needle or catheter, or butterfly catheter.a-d In sternal recumbency, the needle or catheter is inserted through the skin off of the cranial edge of a rib (to avoid the neurovascular bundle) in the 8th – 11th interspaces. The needle or catheter is inserted perpendicular to the chest wall and advanced a few millimeters at a time with intermittent aspiration of the syringe until air is retrieved. If air is retrieved, the thoracic cavity should be completely evacuated until negative pressure is attained. When thoracocentesis is performed in lateral recumbency, the needle or catheter should be inserted at the highest point of the arch of the ribs. Most dyspneic animals will not tolerate being held in lateral recumbency. Numerous acceptable methods for thoracocentesis exist.
Once stabilized by restoring negative intrathoracic pressure and treating concurrent life threatening conditions, surgical exploration of the thorax is warranted in patients with open pneumothorax as damage to the internal structures, debris, and necrotic tissue are likely to be present. Closed traumatic pneumothoraces are often self-limiting with thoracocentesis or continuous pleural drainage (via thoracostomy tube) and rarely require surgical intervention.