Respiratory Work-Up in Horses

Performing a thorough physical examination, including (1) rebreathing auscultation of the trachea and left and right hemithoraces and (2) percussion of the sinuses is essential in the sick horse. Endoscopic examination of the upper and lower respiratory system is also critical for definitively diagnosing certain conditions. The veterinarian also is assisted in diagnosing respiratory disease in the horse by ultrasonographic evaluation, tracheal lavage (TL) techniques and broncho-alveolar lavage (BAL) and more rarely radiographs (more in foals). Thoracocentesis and thoracic drainage may be used diagnostically and therapeutically. Lung biopsy is used rarely but can be a useful tool.

EVALUATION OF THE PATIENT FROM A DISTANCE

-The first thing to notice is the condition score of the horse, as this may help determine whether there is underlying chronicity to the disease state.
-Then note the respiratory effort that the horse is making by watching the movement of the nares and the abdomen. Flaring nares are indicators of either upper or lower respiratory distress, as is abdominal effort in breathing. It is very important to attempt to discern whether or not the horse is in predominantly expiratory or inspiratory distress

-In general, horses with upper respiratory (i.e. extrathoracic) compromise/partial obstruction have greater difficulty during inspiration, whereas horses with intrathoracic non-fixed obstruction usually demonstrate greater effort during expiration. However, if horses have fixed intra- or extra-thoracic obstructions, then dyspnoea may occur during both inspiration and expiration.

WHY do we care ?

-Assessment of the external abdominal oblique musculature is important. If it is hypertrophied (“heave line”), then the effort of breathing presumably has been greater than normal (hyperpnoea). This is often particularly noticeable in cases of Recurrent Airway Obstruction [RAO, Inflammatory airway disease (IAD), Chronic obstructive Airway Disease, COPD].
-Horses with pleural pain or effusion often have shallow breathing and abducted elbows. Sometimes there may be a plaque of sternal oedema (the badge of pleuropneumonia” !). You have to try to discern this from ventral oedema due to hypoalbuminaemia (eg. colotyphlitis (diarrhoea loss!) etc.) and rarely local trauma.
-If the horse has either puncture wounds, lacerations (especially of the thorax, axillary (elbow), pectoral or cervical regions), then these should be observed, but also warrant closer inspection, palpation and ultrasonographic and/or radiological evaluation. Smaller puncture wounds penetrating air-filled thoracic or tracheal structures may only show up as emphysema (crackly feeling in skin).

PHYSICAL EXAMINATION OF THE HORSE

A thorough physical examination is essential. Horses with apparent respiratory distress may suffer from respiratory disease, however, in a large number of cases tachypnoea may occur secondary to involvement of other systems and manifest because of pain or acid-base complications. Common causes for tachypnoea of non- pulmonary origin in equine neonates are fever, septicaemia, shock and neurological abnormalities.

-the resting respiratory rate in horses with a history or obvious clinical signs of respiratory distress should be performed before exciting the horse in any way. To best perform this measurement on foals, the foal should not be restrained in any manner, as this can substantially change the resting values for the respiratory and heart rates.
-The normal respiratory rate:
1) adult horses = (8)12 to 24 breaths per minute (bpm) – usually < 16 bpm
2) foals during the first weeks of life the respiratory rate = 20 to 40 BPM.
3) foals (new born - first few hours after parturition), the respiratory rate is
often elevated to approximately 60 to 80 bpm.

-Respiratory depth and effort should also be ascertained.
-In horses with thoracic pain of pleural origin (pleurodynia) their breathing pattern is often shallow, so that expansion and tension of inflamed tissues is not exacerbated (i.e. minimise the pain !). Palpation of the pectoral, axillary and thoracic regions is important in cases of trauma, as emphysema [feels crackly (crepitus) and sometimes looks bumpy and “blown up” may be better recognized via palpation rather than visually]. [...]