Cats presenting with a respiratory emergency are particularly difficult to manage. The adrenaline surge associated with travel to the clinic may cause the cat to initially appear stable, but they decompensate quickly with excessive handling. Cats with signs of respiratory compromise need to therefore be handled with minimal stress in order to prevent any worsening of their condition. In this second lecture on the cryptic cat, we shall discuss the approach to the dyspnoeic cat, focusing on tips and tricks for handling and ways to differentiate between congestive heart failure and non-cardiac causes of dyspnoea.

The stress of travel to the clinic followed by prolonged handling for physical examination may precipitate a deterioration in the cat’s condition. As such, the initial assessment of a dyspnoeic cat should focus on the major body systems: neurological, cardiovascular, and respiratory systems. The neurological assessment can be brief, focusing on key clinical questions such as: Is the cat alert and responsive, is it able to ambulate? The cardiovascular system assessment should focus on heart rate, rhythm, presence of a gallop or murmur, pulse quality, mucous membranes, and capillary refill time. An assessment of the respiratory system involves an assessment of breathing rate, effort, and thoracic auscultation. The initial respiratory rate should be interpreted with caution; respiratory rates in excess of 100 breaths/minute have been reported in healthy cats on initial examination, and respiratory rate alone does not reliably identify respiratory disease (Dijkstra et al. 2018; Sigrist et al. 2011).

The respiratory rate and effort of a cat are best performed at a distance when the cat is settled. It is recommended after the initial “hands on” major body system assessment that the cat is placed in a quiet kennel with a noninvasive source of oxygen supplementation. Should the cat be particularly stressed on initial examination, an intramuscular dose of 0.2 mg/kg butorphanol can be administered to alleviate stress. However, in a cat with a known or suspected history of trauma, analgesia should be administered instead.

Distant examination of the breathing rate and effort may help with respiratory disease localisation. Inspiratory noise is associated with upper respiratory disease, of which nasal and laryngeal diseases are commonly seen in older cats. Expiratory effort with associated wheeze in a cat with a history of coughing should raise the index of suspicion for feline asthma. An asynchronous breathing pattern (outward movement of the chest and inward movement of the abdomen during inspiration) alongside reduced lung sounds on auscultation is highly sensitive for diagnosis of pleural space disease; however, this pattern of breathing can also be seen with other respiratory disorders (Sigrist et al. 2011). Therefore, in any cat with an asynchronous breathing pattern, early assessment with point-of-care ultrasound is recommended to assess for pleural space disease. Although the original TFAST lung ultrasound protocol was performed in lateral recumbency (Lisciandro et al. 2008), restraint in this position should be avoided in dyspnoeic cats; adaptation of the technique should be performed so the patient is scanned in a position that minimises stress (usually standing or sternal). In the emergency setting, the primary focus should be on relieving dyspnoea by performing emergency therapeutic thoracocentesis as required.

Causes of pleural space disease include pleural fluid, pneumothorax, intrathoracic mass, and diaphragmatic rupture. Point-of-care ultrasound may also be beneficial alongside physical examination findings in identifying these abnormalities. However, abnormalities may be missed on point-of-care ultrasound, and therefore, follow-up imaging is recommended once the cat is more stable (Walters et al. 2018; Cole et al. 2021).

Pleural effusion is a common cause of dyspnoea in the cat and has various causes, of which congestive heart failure and neoplasia are most commonly reported (Ruiz et al. 2018; König et al. 2019). Differentiating congestive heart failure (CHF) from other causes of pleural space disease as well as primary lung disease can be difficult in the unstable cat. Certain historical and physical examination findings may help increase the index of suspicion for CHF. Cats presenting with CHF are more likely to be hypothermic compared to non-cardiac causes of dyspnoea (Dickson et al. 2018; König et al. 2019). Although both a murmur and gallop rhythm occur frequently in cats with CHF, cats with CHF are less likely to have a murmur than asymptomatic cats with hypertrophic cardiomyopathy and the presence of a murmur cannot be used in isolation to reliably differentiate between cardiac and non-cardiac causes of dyspnoea (Payne et al. 2010; Dickson et al. 2018). An algorithm (RAPID CAT) comprised of the presence of a gallop rhythm, heart rate >200 bpm, respiratory rate >80 bpm, temperature <37.5°C is a potentially useful tool for differentiating cardiac from non-cardiac causes of dyspnoea (Dickson et al. 2018).

Point-of-care-ultrasound and measurement of cardiac biomarkers may further support a diagnosis of CHF. Identification of a subjectively enlarged left atrium to aorta ratio on point-of-care ultrasound is highly accurate predictor of CHF as the cause of dyspnoea but this skill requires practice (Ward et al. 2018; Janson et al. 2020). However, with practice the technique is very useful in helping diagnose CHF. Additional point-of-care ultrasound findings supportive of a diagnosis of CHF include the presence of a pericardial effusion and the presence of >3 B-lines (lung rockets) per site on lung ultrasound. Combining lung ultrasound with measurement of the cardiac biomarker NT-ProBNP increases the accuracy of the diagnosis of CHF (Ward et al. 2018). Restraining a cat in respiratory distress for blood sampling is not recommended; however, blood can be retrieved directly from the intravenous catheter at the time of placement. NT-ProBNP can also be measured directly from the pleural fluid. Measurement of NT-ProBNP on a point-of-care test can reliably rule out cardiac disease as a cause of dyspnoea but can also be elevated in non-cardiac causes of dyspnoea (Hezzell et al. 2016; Janson et al. 20220). Therefore, this biomarker should be used alongside other historical, physical examination and point-of-care ultrasound findings where possible to support a diagnosis of CHF. In certain individuals, cardiac and non-cardiac diseases cannot be easily differentiated, and in these cases, a trial dose of diuretic (for example, 2 mg/kg furosemide) can be considered and the cat monitored closely for any response to therapy. In a cat with a history of coughing, expiratory wheeze, normal heart rhythm, and minimal–no B lines with a normal left atrium:aorta ratio on point-of-care ultrasound, feline asthma should be considered as the most likely differential, and early administration of a bronchodilator (terbutaline 0.02 mg/kg SC) is recommended. Again, it is important to re-assess the cat after empirical therapy.

The dyspnoeic cat can be a challenging case to manage. Examination and assessment should be performed to minimise stress to the cat. Physical examination findings including auscultation and observation of respiratory pattern can help direct emergency procedures and investigations. Point-of-care ultrasound can further support a diagnosis and management but requires practice. In some cases, differentiating the cause of dyspnoea may be extremely challenging, and in such cases, empirical treatment can be considered as long as the cat is closely monitored to document any response to therapy.

References

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