Stertor and Stridor in Dogs
Dogs experiencing noisy breathing often exhibit either stertor or stridor, indicating air passage through narrowed pathways, encountering resistance due to partial blockage. These obstructions can occur in various areas such as the nasopharynx, pharynx, larynx, or trachea, leading to audible breathing issues even without a stethoscope.
Stertor, characterized by loud breathing during inhalation, manifests as a low-pitched, snoring-like sound caused by fluid vibration or relaxed tissue vibration in the throat’s airway blockage. Stridor, on the other hand, presents as high-pitched, noisy breathing due to rigid tissue vibration during airflow passage. It often results from nasal or laryngeal blockage or cervical tracheal collapse.
Noisy breathing is prevalent among brachycephalic breeds with short noses and flat faces. In certain breeds like Bouviers des Flandres, Siberian Huskies, Bulldogs, and Dalmatians, inherited laryngeal paralysis may cause these issues. Acquired laryngeal paralysis, more common in giant breeds like St. Bernards and Newfoundlands, as well as large breeds such as Irish Setters, Labrador Retrievers, and Golden Retrievers, typically affects older dogs. Inherited paralysis tends to be observed in dogs younger than one year, with a male-to-female ratio of 3:1.
Symptoms and Types
- Change or loss of voice, leading to an inability to bark.
- Partial blockage of the upper airways initially results in increased airway sounds before a noticeable change in breathing patterns.
- Unusually loud breathing sounds may persist for several years.
- Breathing sounds can be discerned from a distance without the need for a stethoscope.
- The nature of the sounds varies from abnormally loud to evident fluttering to high-pitched squeaking, depending on the extent of airway narrowing.
- Increased breathing effort may be observed, often accompanied by noticeable body changes such as extended head and neck posture and open-mouth breathing.
Causes
- Brachycephalic airway syndrome, a condition found in short-nosed, flat-faced animals, characterized by a combination of narrowed nostrils (stenotic nares), overly long soft palate, everted laryngeal saccules, laryngeal collapse, and edema of the voice box or larynx.
- Narrowing of the nasopharynx.
- Laryngeal paralysis, which can be inherited or acquired.
- Benign or malignant tumors of the voice box or larynx.
- Granulomatous laryngitis, causing nodular, inflammatory lesions.
- Tracheal collapse or tracheal stenosis, resulting in reduced diameter of the windpipe.
- Tumors or foreign bodies in the windpipe or other airway parts.
- Nasopharyngeal polyps originating from the middle ear or eustachian tube.
- Acromegaly, leading to excessive growth hormone levels.
- Nervous system or muscular dysfunction.
- Anesthesia or sedation, especially if anatomical abnormalities like a long soft palate exist.
- Abnormalities or tumors of the soft palate.
- Redundant pharyngeal mucosal fold causing excessive tissue lining the throat.
- Pharyngeal or laryngeal tumors.
- Edema or inflammation of the palate, pharynx, and larynx secondary to various factors such as coughing, vomiting, turbulent airflow, upper respiratory infection, or bleeding.
Risk Factors
- High environmental temperature.
- Fever.
- Elevated metabolic rate due to conditions like hyperthyroidism or sepsis.
- Exercise.
- Anxiety or excitement.
- Any respiratory or cardiac condition increasing lung ventilation.
- Turbulence caused by increased airflow leading to swelling and exacerbating airway obstruction.
- Eating or drinking.
Diagnosis
To diagnose your pet’s condition, your veterinarian will first gather a detailed history of your pet’s health leading up to the onset of symptoms. Using a stethoscope, they will listen carefully from the pharynx to the trachea. If the abnormal sound persists when your pet opens its mouth, a nasal cause can be mostly ruled out. If the sound occurs only during expiration, it likely indicates airway narrowing. Conversely, if the abnormal sounds are loudest during inspiration, the issue may lie elsewhere in the chest. Any change in your dog’s voice may suggest abnormality in the larynx.
Your veterinarian will systematically listen over the nose, pharynx, larynx, and trachea to pinpoint the location and phase of respiration when the abnormal sound is most prominent. Identifying the source and any aggravating factors is crucial.
Internal imaging techniques such as radiography and fluoroscopy play a vital role in assessing the cardiorespiratory system and ruling out additional causes of respiratory difficulty. Conditions beyond upper airway obstruction may contribute, worsening a subclinical condition. X-rays of the head and neck can reveal abnormal soft tissues, while a computed tomography (CT) scan offers detailed anatomical information. In cases where physiological inheritance, such as brachycephalic traits, influences diagnosis, veterinarians consider the most affected location and plan accordingly.
Treatment
Maintain your dog in a cool, quiet, and calm environment. Anxiety, exertion, and pain can exacerbate airflow, potentially worsening the condition. Prolonged, severe blockage to airflow can result in low oxygen levels in the blood and tissues, and decreased air movement in and out of the lungs. While supplemental oxygen isn’t always necessary for managing partial airway collapse, it’s essential to closely monitor sedatives, as they can relax upper airway muscles and worsen airflow blockage. Be prepared for emergency intervention if complete obstruction occurs.
In cases of extreme airway blockage, emergency measures may be necessary, such as intubation—a procedure involving the passage of an endotracheal tube through the mouth and into the windpipe (trachea) to facilitate oxygen delivery to the lungs. If obstruction prevents intubation, emergency tracheotomy—a surgical opening into the windpipe—or the passage of a tracheal catheter to administer oxygen may be the only options to sustain life temporarily. However, a tracheal catheter can only provide brief oxygenation while a more permanent solution is sought. Surgery might be required if biopsy results indicate a mass in the airways.
Living and Management
Close monitoring of your dog’s breathing rate and effort is essential. There’s a risk of complete blockage or obstruction even after a seemingly stable patient is taken home, especially if continuous observation isn’t possible. Following surgery, some degree of obstruction may persist for 7 to 10 days due to postoperative swelling. During this period, it’s crucial to protect your dog from complications arising from labored breathing.
After surgery, your dog may experience soreness and will require adequate rest in a calm environment away from other pets and active children. Consider cage rest for a brief period until your dog can safely resume activity without strain. Your veterinarian will prescribe a short course of pain relievers and mild antibiotics to prevent opportunistic bacterial infections. It’s important to administer medications precisely as directed, at the correct dosage and frequency. Be mindful that overdosing on pain medications is a preventable cause of death in household animals.
Prevention
To prevent respiratory issues, it’s important to steer clear of strenuous exercise, high ambient temperatures, and excessive excitement. Your veterinarian will provide guidance on the appropriate level of exercise suitable for your dog’s condition.