Pulmonary contusions and other thoracic trauma (Proceedings)

Traumatic thoracic injuries are prevalent in small animals, particularly in dogs. The most common causes of thoracic trauma are motor vehicular accidents and bite wounds. Other possible, although less common mechanisms include gunshot, knife wounds or being kicked by a larger animal (horse/cow). Injuries may range from mild to life threatening.

The initial evaluation of the patient with thoracic trauma should concentrate on the major body systems (heart, lungs, brain). A patient with significant thoracic trauma frequently has other injuries as well. The patient should be immediately taken to a treatment room for further therapy. An IV catheter should be rapidly placed and samples collected for determination of a packed cell volume, total solids, glucose and BUN. Supplemental oxygen should be administered if any signs of respiratory distress are present. Intravenous fluids should be given if shock is present. After the patient's condition has stabilized, further testing (such as radiographs) may be performed.

Pneumothorax refers to the development of free air within the pleural space. The air gets to the pleural space either from the outside or via air leakage from the pulmonary parenchyma. Radiography, thoracocentesis or auscultation may identify pneumothorax. Auscultation of dogs with pneumothorax may be misleading if respiratory sounds are louder than average. In many emergency practices, dogs showing respiratory distress may undergo thoracocentesis based upon trauma history and increased respiratory effort. Approximately 25-30 ml/kg of air generally needs to be removed to provide significant improvement to respiratory status. Occasionally, a thoracostomy tube is required to prevent either continuous or intermittent chest drainage. Generally, a dog is considered a candidate for a chest tube if it requires greater than three needle thoracocentesis in less than 12- 18 hours or if no end-point is reached during thoracocentesis. Animals will breathe with a restrictive pattern (short shallow breaths).

Pulmonary contusion is another common traumatic thoracic injury. Pulmonary contusion occurs when blunt trauma to the chest causes alveoli to fill with blood and fluid (inflammation). Pulmonary contusion occurs in a large percentage of animals with thoracic trauma. Contusion may be identified radiographically as interstitial to alveolar infiltrates or clinically by tachypnea/increased respiratory effort in dogs following trauma. Therapy for pulmonary contusion is supportive and includes oxygen and fluid therapy as needed to maintain adequate circulating volume. Some clinicians vividly recall dogs with pulmonary contusion that appeared to rapidly deteriorate following a large volume of intravenous crystalloids. Most dogs with pulmonary contusion improve significantly in 2-3 days and recover completely in less than one week.

Hemothorax is another common sequalae of thoracic trauma. The impact of hemothorax is more likely from hypovolemia from the blood loss, than from the pleural effusion. Hemothorax is usually a presumptive diagnosis after identification of pleural effusion on chest radiographs from a trauma patient. Treatment is supportive. Thoracocentesis is avoided unless otherwise indicated. Surgical exploration is a last resort.

Rib fractures are also common in the patient with thoracic trauma. Rib fractures appear to be painful, particularly on inspiration. Individual fractured ribs do not themselves typically affect lung function, but reflect a severe injury to the chest. Therapy for rib fractures typically is conservative and includes pain management (opoids and local blocks). Some clinicians advocate loosely applied support bandages. If multiple ribs are fractured at several sites, an unstable piece or flail segment may be formed. This "flail" segment moves paradoxically with respiration. Various methods of stabilization have been described; however, frequently the underlying contusions may actually be more detrimental to lung function.

Diaphragmatic hernias may also occur in animals with significant chest injuries. The muscular portion of the diaphragm is the area most frequently torn. In general, animals with traumatic diaphragmatic hernias have other significant intrathoracic injuries try to better clarify the margins of the diaphragm.The timing of surgery may be equally important in successful patient outcome. Surgery should be undertaken when the patient is cardiovascularly stable. This should be within 12-24 hours of the injury. However, if the stomach is in the chest cavity, this is a surgical emergency because the stomach may distend with air and severely compromise ventilation. In general, in the patient with an acute diaphragmatic hernia, associated injuries may also play a significant role in deciding the time of surgery. Remember that surgery and anesthesia (and the recovery period) may be stressful to the critically injured dog. Safe anesthesia requires a rapid intubation and positive pressure ventilation from the time of entry into the abdominal cavity until the integrity of the diaphragm is restored. All efforts should be made to limit anesthesia and surgery time.

Post-operative care usually involves standard attention to adequate intravascular volume, oxygen supplementation and pain relief (local and opoids). Most dogs with acute traumatic diaphragmatic hernias recover well from surgery, but the adequate monitoring and support in the post-operative period is critical.

Cardiac arrhythmias are common following trauma in dogs and are generally self-limiting. However, severe tachycardias may occasionally require therapy (such as lidocaine). Animals having sustained severe trauma should be monitored for cardiac complicatons as well.

Most dogs with traumatic thoracic injuries recover uneventfully from their injuries with no lasting complications. The standard course is for the patient to look the worse for the first 24 hours after presentation and then to make relatively rapid recovery. Successful management includes appropriate identification of injuries and well-timed interventions.

Fluid therapy with lung disease

Fluid therapy in patients with either respiratory distress or radiographic pulmonary infiltrates may be very challenging. Excessive fluids may worsen respiratory distress while inadequate fluids may result in poor perfusion and ultimately shock. Fluids therapy after trauma can be particularly challenging. Fluid movement within the body is governed by a Starling's forces, which reflect oncotic and hydrostatic forces. The pulmonary parenchyma is inherently resistant to the development of edema. However, should vascular injury or an inflammatory process develop, extra lung water (edema) may develop. Edema interferes with gas exchange by alveolar flooding, loss of functional residual capacity and decreasing pulmonary compliance.

A multitude of fluids are available for clinical use in animals. These include crystalloids, colloids (artificial and natural) and packed red blood cells (pRBCs) and whole blood. Hemoglobin-based oxygen carriers (HBOC) such as Oxyglobin® are no longer widely available although this may change in the future. Crystalloids are fluids containing water and electrolytes. The fluid can easily diffuse across blood vessels and in fact, only ~ 15% of any infused fluid is still present within the intravascular space one hour later. Crystalloids may be hypertonic solutions, such as 7.5 % saline (hypertonic saline), replacement fluids which contain sodium in concentrations equal to the extravascular space (eg. 130-155 meq/L) or maintenance fluids which are low sodium. (50-70 meq/L). Commonly used replacement crystalloids include lactated Ringer's solution, 0.9% saline, Plasmalyte and Normsol- R. Maintenance fluids are uncommonly used in veterinary medicine. Colloidsare fluids containing water and poorly diffusible solutes. When administered intravenously, colloids act to hold water within the intravascular space. If colloids are administered or accumulate extravascularly, then will pull water with them and may magnify edema. Blood products (whole blood and pRBCs) will also primarily stay within the intravascular space. In general, crystalloids are considered the "safest" fluid in lung disease as any extravasations are relatively easier to "fix" than colloidal leaks.

Fluids are indicated for two separate although occasionally overlapping reasons; namely hypovolemia and dehydration. Dehydration represents a loss of fluid from the interstitial space and reflects a failure to drink enough water. Common causes for dehydration include vomiting and diarrhea, renal failure and diabetes. Clinical signs of dehydration include lethargy, dry mucous membranes and poor skin turgor. Fluids administered for dehydration should be administered with the goal of correcting dehydration in 12-24 hours. If the underlying cause is not remedied or if the cause is very severe, dehydration can progress to hypovolemia. Hypovolemia represents the lack of intravascular volume. Intravascular volume should be replaced rapidly in order to limit perfusion deficits and on-going shock. In all cases, when fluid therapy is chosen, it is important to distinguish why fluid are indicated as this will be essential in determining the type and rate.

Specific examples

Cardiac disease

The patient with on-going congestive heart failure does not require any fluids, even in the face of apparent dehydration. Following treatment for a bout of congestive heart failure, a patient become dehydrated. If pulmonary signs (tachypnea, crackles, radiographic infiltrates) have resolved, the first approach to dehydration should be to decrease or stop the diuretics. If this is not adequate, then judicious fluid therapy with crystalloids (LRS or Plasmalyte) at 10-15 ml/lb/day may be initiated. Colloids should be avoided at all costs, as the volume expansion that accompanies them may be dramatic.

For the patient with heart disease that is now sick with something else, fluid therapy should be titrated on an individual basis, encompassing the pet's underlying heart disease and the specific condition that is triggering the urge to give fluid therapy. Dogs with mitral regurgitation and cats with hypertrophic cardiomyopathy often tolerate fluids quite well in the face of dehydration while animals with dilated cardiomyopathy are often poorly tolerant of fluids. A central line (for measurement of CVP) may be useful in adjusting fluids although in a dehydrated pet with heart disease it may be remarkably challenging to place a central line. It is also essential to recall that it is IMPOSSIBLE to determine intrinsic renal function in a pet receiving diuretics. It is inappropriate to give diuretics with fluids. In vomiting or anorexic pets receiving digoxin therapy, the digoxin should be stopped and a digoxin level submitted.

Pneumonia

Pneumonia represents infection and inflammation in the lungs. Inflammatory infiltrates (white blood cells, proteins) will flood alveolar spaces and interfere with gas exchange. There may be permeability alterations in the alveoli-capillary membrane. Patients with pneumonia require adequate intravenous fluids to maintain hydration and to promote adequate airway hydration to help clear dried or adherent secretions. Additionally, in the presence of fever, intravenous fluids are useful to help cool a patient. Fluid therapy for a patient with pneumonia who only mildly dehydrated is usually set at a rate of ~ 45 ml/lb/day. Overhydration should be avoided. Therapy with colloids is rarely needed. Recall that cats are very unlikely to get pneumonia and most cats initially suspected of having pneumonia if fact have congestive heart failure.

Pulmonary Contusion

Pulmonary contusions represent a particular challenge in fluid therapy. Contusions represent bruising and hemorrhage into the lung parenchyma. The alveolar-capillary membrane is disrupted and the blood in the alveolar space is inflammatory. However, due to the extent of the trauma, hypovolemia may also be present. Excessive fluids are inappropriate as are colloids and potentially hypertonic saline. Dogs with pulmonary trauma should be closely assessed on a frequent basis. "Hypotensive" resuscitation has been described in people with penetrating trauma and is occasionally used in dogs. Specifically, hypotensive resuscitation refers to limiting the volume of fluid infused in order to decrease the potential for on-going active hemorrhage. Hypotensive resuscitation has not been specifically evaluated in patients with pulmonary contusions.

Due to the loss of integrity of the capillary-alveolar membrane, infused fluids may easily cross the capillary-alveolar interface and worsen alveolar infiltrates and gas-exchange. Conversely, occasionally clinicians are tempted to give diuretics to dogs with pulmonary contusions, with the thought potentially encouraging them to "clear" faster. This is a poor idea. The rationale for diuretics removing pulmonary infiltrates is through their impact on hydrostatic pressure. The mechanism of pulmonary infiltrates in pulmonary contusion is not hydrostatic but due to disruptions in the capillary-alveolar membrane. Thus fluid therapy for contusions is extremely challenging. As guidelines, infused fluids should be kept to a minimum, but adequate to maintain perfusion. Colloids and hypertonic saline should not be used unless overwhelming evidence of hypoperfusion exists. Diuretics should never be administered to the trauma patient.

Non-cardiogenic pulmonary edema

Non-cardiogenic edema (NCPE) is any form of pulmonary edema that is not due to heart failure. Commonly in veterinary medicine, non-cardiogenic pulmonary edema refers to pulmonary edema that develops in response to acute insults like choking or electrocution (biting an electric cord). However, NCPE really should be thought of in the broader sense as referring to any pulmonary edema that develops due to permeability alterations in the lungs, and thus would include acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Fluid therapy in these patents should be on an individual basis but excessive fluids should be avoided. Colloids and hypertonic saline are contraindicated. Colloids may leak across damaged capillaries and hypertonic saline may result in marked increases in hydrostatic pressure which may magnify the edema. Unless there is a clear-cut indication, fluids should be avoided and if required given at a low "keep 'em dry" rate to prevent worsening edema.

Pleural effusion

Fluid therapy in pleural effusion is contingent upon identifying the cause of the effusion. Animals with right-sided congestive heart failure (including pericardial effusion) do not require any intravenous fluids, while animals with infection (pyothorax) may well require fluids to help provide intravascular support during recovery from sepsis.

Fluid therapy in pulmonary disease requires that the clinician is diligent in identifying the underlying reason for the lung disease in addition to recognizing the mechanisms that are responsible for the development and perpetration of pulmonary edema. As a guideline:

      1. limit fluid in non-septic pulmonary disease

      2. avoid diuretic in trauma patient or in conjunction with IV fluids

      3. Avoid colloids with any form of pulmonary edema