Sometimes, a subtle sign can be an indication of a potentially serious problem. A cough here, nasal discharge and flared nostrils there. A rapid heart rate. These manifestations of respiratory distress can be the early indicators of respiratory disease, a major cause of morbidity (illness) and mortality in horses.
At the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida, Rodney Belgrave, DVM, MS, Dipl. ACVIM, of Mid-Atlantic Equine Medical Center, in Ringoes, New Jersey, described how to diagnose and treat respiratory emergencies in horses.
First, he listed signs of respiratory distress, which “may or may not be obvious depending on the rate of onset of the condition and its severity.” These include nostril flare, tachypnea (increased respiratory rate), short shallow breaths, cough, nasal discharge, varying degrees of exercise intolerance, and reluctance to walk due to pleural (lung) pain.
Then Belgrave described four respiratory emergencies a veterinarian might encounter and how to manage each.
This severe form of pneumonia is characterized by inflammation of the pleural membranes that line the chest cavity and cover the surface of the lungs, with subsequent fluid accumulation in the chest cavity. Other causes of fluid accumulation include fungal pneumonia, upper respiratory viral infections such as equine herpesvirus-5, hemothorax (blood pooling in the chest cavity), and neoplasia (tumors).
Racehorses seem to be most at risk, said Belgrave, due to their communal lifestyles, long-distance transportation to events, dirt/mud contamination of their lower respiratory tracts when racing, and incidence of exercise-induced pulmonary hemorrhage.
Clinical signs vary and include fever, anorexia, lethargy, coughing, increased expiratory effort, exercise intolerance, and pleural pain leading to a reluctance to move.
Belgrave said he diagnoses bacterial pleuropneumonia by looking at the horse’s history, listening to his lungs during a rebreathing exam, taking bloodwork to look for elevated serum amyloid A (SAA) and/or low white blood cell counts, performing an endoscopic exam looking for upper airway tract abnormalities, taking thoracic radiographs and ultrasound, and collecting transtracheal wash samples (material flushed from the trachea and bronchi). With the exception of thoracic radiographs, the veterinarian can perform these procedures in the field.
“Thoracic ultrasound is the most valuable diagnostic procedure in the diagnosis and management of this condition,” said Belgrave, as it allows the veterinarian to closely assess the pleural space and lung tissues.
“Trigger points for a more in-depth workup while in the field are a fever after 72 to 96 hours of antibiotic therapy, an SAA spike, a sharp drop in white blood cells, or a progressively more compromised respiratory effort,” he said.
Once a diagnosis has been made, Belgrave says he treats the horse with antibiotics in conjunction with nebulized antibiotic therapy, assessing the horse’s response via serial ultrasounds. If enough fluid has accumulated in the lungs, he will drain it to allow the lungs to re-expand.
He said he might also perform bronchial lavage to remove exudate (pus) from the lower respiratory tract and small airways.
Chronically affected horses might require a thoracotomy (an incision into the pleural space to remove fluid) and rib resection, which Belgrave says has an 88% survival rate and 45% return to activity.
“Depending on early, aggressive intervention, many of these horses go on to their previous level of activity,” he said.
Pneumothorax and Hemothorax
These two respiratory conditions are characterized by air and blood, respectively, in the pleural space. Clinical signs for both include tachypnea, dyspnea (labored breathing), coughing, and tachycardia (rapid heart rate). Tachycardia and pale mucous membranes are particularly indicative of hemothorax.
“Either condition should be strongly suspected with a history of thoracic trauma,” said Belgrave.
Thoracic ultrasound is very important for diagnosing both conditions, while radiographs are warranted for pneumothorax.
Once a diagnosis is made, however, Belgrave suggests referring the horse to an equine hospital right away, as these conditions are difficult to manage in the field. Treatment of both conditions involves closing any wounds involved and performing a thoracocentesis to drain the fluid or air from the lungs.
Rib Fractures in Foals
Rib fractures are relatively common in newborn foals, Belgrave said, occurring with a frequency rate of 20-65%, based on previous studies. Fillies are more frequently affected than males, and left ribs seem more susceptible than the right.
“In most instances, the rib fractures are of little clinical significance,” said Belgrave. “However, depending upon their location and degree and manner of displacement, they have the ability to inflict severe damage to organs within the thoracic cavity with sometimes fatal consequences.”
Clinical signs of fractures include tachypnea, nostril flare, thoracic wall swelling, ventral edema (fluid swelling), and an unwillingness to move or lie down. Belgrave said he palpates the ribcage with the foal standing as well as recumbent and listens to the foal’s breathing. If he suspects a rib fracture, he then takes ultrasound images, which are four times more sensitive than radiographs at identifying these injuries.
Most rib fractures heal normally on their own. If a foal has a displaced fracture of left ribs three through six, he might require surgery due to the insult’s proximity to the heart. Complete fracture of two or more ribs also warrants surgical correction.
Acute Respiratory Distress Syndrome (ARDS) in Foals
Foals can develop this life-threatening condition due to widespread inflammation of the lungs, which can occur secondary to pneumonia, aspiration, or sepsis, said Belgrave. Common clinical signs include fever, tachypnea, and tachycardia.
Belgrave said he makes a diagnosis based on a history of respiratory distress, elevated SAA levels, radiographic and ultrasound imaging, and transtracheal wash results. He treats these cases using oxygen therapy, antibiotics, and corticosteroids, the latter of which he said is a critical component, particularly in the early stages of treatment.
“Prognosis for survival in foal afflicted with ARDS is considered poor,” said Belgrave. “However, treatment with a combination of systemic corticosteroids, broad-spectrum antimicrobials, and inhalational oxygen may positively affect the outcome of these cases.”
If your horse’s breathing is labored or you suspect one of these respiratory emergencies, contact your veterinarian right away. Early therapeutic intervention is key to a successful outcome. Some conditions practitioners can treat on the farm, while more serious ones required referral to a clinic.