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very severe heart disease and clinical signs of CHF
do not have an audible murmur. Other auscultatory findings, such as a gallop sound or an arrhythmia are far more specific for significant heart disease. As such, the findings of a loud murmur, an arrhythmia or a gallop sound in an older cat with respiratory distress are highly supportive of a cardiogenic cause. Young cats are sadly not exempt from severe heart disease, and some cats seem to develop overt hypertrophic cardiomyopathy even in the first year of life.
Pulmonary auscultation and thoracic percussion are vital tools in identification of pleural space disease. In cats with a pleural effusion, the breath sounds are expected to be reduced and percussion should sound dull in
the sternal portion of the thorax. A fluid line may be identifiable by performing auscultation and percussion at different heights. In contrast, pneumothorax may be identified by an absence of breath sounds dorsally and hyper-resonant percussion in the same region.
Abnormal airway noises are useful in identifying
lower airway disease. Cats with chronic bronchitis or asthma may have loud, coarse pulmonary crackles accompanied by terminal inspiratory or expiratory wheezes. In CHF, pulmonary oedema is associated with soft, subtle crackles that may be focally distributed or even inaudible. Abnormal respiratory sounds in cats with upper-respiratory tract disease are, in contrast, less subtle. Inspiratory noise (stertor/stridor) may be audible without the use of a stethoscope, and laryngeal auscultation may detect loud or high-pitched inspiratory noise.
Thoracic ultrasonography
For cats with a restrictive, paradoxical or mixed respiratory pattern (or where the clinician is uncertain
as to the localisation of respiratory compromise), thoracic ultrasonography is an invaluable initial diagnostic test. Most practices have access to a basic ultrasound machine, and the identification of air or
fluid using ultrasound is a straightforward skill that is easy to learn (for a thorough review, see Lisciandro 2011). Although many clinicians are tempted to perform thoracic radiography, perhaps because of a low level
of confidence in their sonographic skills, the use of ultrasound has several advantages to the patient.
In contrast to relocating a patient and using manual restraint techniques for radiography, ultrasound can
be performed with minimal restraint, patient-side in a kennel or ward, whilst oxygen supplementation in sternal recumbency is ongoing. This constitutes the lowest-risk handling possible, whilst a lateral radiograph would be considered very high risk for a patient with respiratory compromise (Figure 1). In addition, ultrasound may be able to identify significant cardiac enlargement, a large mediastinal mass or a diaphragmatic rupture without the necessity for additional tests.
In the absence of obvious pleural fluid, identified as
an anechoic space between the thoracic wall and intrathoracic structures on ultrasound, lung ultrasound can assist in further narrowing the list of differential diagnoses. Normal lung ultrasound shows a bright pleural line in the near-field, which slides back and forth as the animal breathes (known as the “glide sign”). Deep to this line are parallel “A lines”, which represent the scatter of ultrasound in normal, aerated lung (Figure 2). In patients with pneumothorax, the glide sign is absent but A lines remain present, because the pleura are no longer adjacent to the thoracic wall and so cannot be visualised beyond the scatter caused by air in the pleural space. In contrast, the presence of B-lines excludes a pneumothorax (as does the normal glide). B-lines are vertical, hyperechoic artefact caused by an air-fluid interface within the pulmonary interstitium or alveoli (Figure 2). These are highly suggestive of pulmonary oedema and should raise the concern of CHF in a
cat presenting with respiratory distress. Recently, a prospective study determined that in cats with dyspnoea, thoracic ultrasound to look for B-lines had the same accuracy as thoracic radiography for both experienced and novice users (Ward et al, 2017).
Figure 1: Contrasting imaging techniques used to identify a pleural effusion: ultrasonography (left) is low-risk and may identify a mass or significant cardiac enlargement, whist radiography (right) is high-risk and further information regarding a mediastinal mass or cardiac remodelling is lost because of fluid effacement of soft tissue structures.
Figure 2: Schematic diagrams (inspired by Lisciandro 2011) of lung ultrasound in cats: the normal appearance of A lines (top left) and an abnormal appearance with
B lines (top right, and below on ultrasound images) which are highly suggestive of pulmonary oedema and exclude the presence of pneumothorax. B lines move back and forth during respiration and cause a “twinkling” appearance (also see Video 6). A pneumothorax is detected when the normal glide of the pleura, moving back and forth during respiration, is absent. A lines are present in both a pneumothorax and a normal lung, due to ultrasound scatter in air.
R, rib causing hypoacoustic shadow artefact
Thoracocentesis
Drainage of pleural fluid or air is indicated in cats with respiratory compromise caused by a pleural effusion or pneumothorax. It should be considered not only a diagnostic procedure but a therapeutic one. Diuretic therapy alone is not sufficient to reduce pleural fluid volume with the rapidity required to provide patient stability, and will certainly not work if the effusion is non-cardiogenic. Thoracocentesis, on the other hand, provides a rapid benefit to the patient and will be
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