A. Bersenas
Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
Cats presenting with respiratory distress have minimal reserve and frequently present as emergencies.1 The initial assessment must be stress free, brief, and must not exacerbate the patient’s condition.
Regardless of etiology, immediate oxygen supplementation is appropriate. Sedation is also paramount, and butorphanol is preferred; if pain is suspected, then a more potent mu opioid agonist is selected. Benzodiazepines can be added with minimal cardiovascular depression.
Emergency intubation should always be prepared for when dealing with patients with respiratory distress. Intubation allows the provision of 100% oxygen and positive pressure ventilation. Further stabilization and diagnostics (e.g., thoracocentesis/radiography) can be performed under controlled conditions.
Sedation/Induction Agents with Minimal Cardiovascular Suppression
- Butorphanol (0.2–0.4 mg/kg IM/IV)
- ± Midazolam (0.2 mg/kg IM/IV) or diazepam (0.2 mg/kg IV)
- ± Alfaxolone (1–2 mg/kg IM; 0.5 mg/kg IV) or propofol (0.5–1 mg/kg IV)
- Alternatively, +/ketamine:valium (1:2 ratio), 0.1 ml/kg IV
A cursory physical examination is performed on arrival, or following sedation, with minimal handling, and while receiving supplemental oxygen. Assessments include respiratory rate and character, and thoracic auscultation noting pulmonary crackles, wheezes, dullness, and cardiac abnormalities such as murmurs or a gallop rhythm.2 Perfusion parameters including mucous membrane colour, capillary refill time (CRT), temperature of the extremities, and pulse assessment are noted. A rectal temperature is strongly advised, as is evaluation of the robustness of the jugular veins. Blood pressure is recorded. In the respiratory distressed patient, a full physical examination is postponed until the cat is more stable.
An intravenous catheter should be placed as soon as the cat is able to tolerate such handling. An IV catheter will allow for IV drug administration which optimizes the drugs’ onset of action. An IV catheter also allows for quick induction should emergency intubation be required.
Thoracic point-of-care ultrasound (POCUS) is exceedingly helpful to quickly establish the presence of pleural effusion. Emergency room echocardiography is also helpful in the diagnosis of feline CHF. Cardiac assessment is based on images acquired from the right thorax. A short axis view at the base of the heart allows assessment of the left atrial-to-aorta size ratio (LA:Ao).3 An LA:Ao ratio >1.5 is considered abnormal (normal LA:Ao ratio ∼1:1).4
Thoracocentesis should be performed immediately in a dyspneic cat if pleural effusion is noted on POCUS or is suspected based on physical examination prior to radiographic assessment or further manipulation of the patient.5 Fluid administration is contraindicated for patients with respiratory distress associated with heart failure. Conversely feline trauma patients may demonstrate increased respiratory effort secondary to hypovolemic shock; if lung sounds are audible, ± POCUS examination reveals no pleural effusion, fluid resuscitation using 10–15 ml/kg fluid boluses are advised for trauma patients. For all other patients with respiratory signs, fluid administration is conservative with fluid deficits (dehydration) corrected over a full 24 hours.
Radiography must be postponed in a patient with significant respiratory distress, until stabilized. Thoracic radiographs clarify the degree of lower airway disease, pulmonary parenchymal disease, and pleural space disease.
Cardiac Disease
On physical examination patients with CHF are often hypothermic (rectal temperature 36.5–37.5°C), and tachycardic (HR>200 beats/min) although bradycardia (HR 130–140 beats/min) has also been reported.5 Cold extremities, a prominent jugular vein, and prolonged CRT are noted. Thoracic auscultation will sometimes reveal a heart murmur, gallop or an arrhythmia (up to 40% of cases).4,6 Pulmonary crackles may be auscultable.
Thoracic Radiographs
Heart size is invariably difficult to assess. Assessment of the major pulmonary vessels is preferred. Pulmonary venous congestion (pulmonary vein larger than the artery), and/or hazy bordered vessels suggests pulmonary congestion. In cats with CHF, the distribution of pulmonary edema is highly variable diffuse, focal, multi-focal, caudal, ventral, or perihilar.7 Pleural effusion is also frequently noted with cardiac disease.
Point of Care Ultrasound
An LA:Ao ratio ≥2 is very suggestive of CHF.3 Left atrial enlargement is consistent with a cardiac cause of pulmonary infiltrates and respiratory distress (cardiogenic pulmonary edema).4,5 Even a trace amount of pericardial effusion is also highly suggestive of CHF.4
Biomarker Testing
Markedly elevated serum NT-proBNP and cardiac troponin (cTnI) concentrations are suggestive of cardiac disease as a cause of respiratory distress.3,4,8,9 However, further diagnostic testing is advised to differentiate cardiac from non-cardiac disease.4,8,9 These tests are best used to rule out cardiac causes of respiratory distress in the emergency patient.
Treatment
Diuretics
Furosemide 1–2 mg/kg IV (IM if IV access not obtained) every 1–2 hours until the respiratory effort has improved. Rarely do cats require more than a total of 4–6 mg/kg of furosemide in the initial hours of presentation. Thereafter, furosemide can be reduced to 2 mg/kg IV q 4 hours for the remaining 24 hours, before further tailoring of daily furosemide. Cats are more sensitive to furosemide than dogs, readily developing severe hypokalemia, metabolic alkalosis and renal compromise. Vasodilators are indicated for patients with CHF however, oral medications (e.g., benazepril, pimobendane) are not initiated during the initial stabilization of the cat in heart failure. Volume of IV medications/flushes should be minimized. Free access to water should be provided.
Feline Asthma
On history cats with asthma often have a history of a cough.
On Physical Examination
Cats are normothermic (generally ∼38.5C), and tachycardia is not a prominent clinical feature. The dyspnea is characterized by an expiratory pattern where an exaggerated expiratory effort is noted.5 Thoracic auscultation often reveals pulmonary crackles or wheezes. Mucous membranes are usually pink, and CRT <2 seconds. Pulses are strong and the extremities are usually warm. The jugular vein is not prominent.
Thoracic Radiographs
An over-expanded, hyperinflated lung field with a flattened diaphragm is noted. On close inspection, a bronchial pattern is usually evident. In chronic asthma the right middle lung lobe may be collapsed.
Treatment
Oxygen supplementation is indicated as are corticosteroids (dexamethasone 0.25 mg/kg IV q 12 to 24 hours). In severe cases, bronchodilation is recommended. Selective beta-2-agonists are preferred for severe bronchoconstriction. Bronchodilation can be provided by Salbutamol puffer (Ventolin™), in combination with the Aerokat™ chamber, which delivers 100 mcg/metered dose. For respiratory distress, 2 puffs of Ventolin™ are recommended.
This can be repeated every hour for 2–4 hours as needed in crisis and subsequently delivered BID. Cats should breathe the drug through the mask and spacer for 7–10 seconds. Positive clinical effect should be seen within 5–10 minutes. In addition, beta-2 agonists can also be administered intravenously, intramuscularly or subcutaneously. Terbutaline is dosed at 0.01–0.02 mg/kg IV, IM, or SQ. Salbutamol injectable is dosed at 4 µg/kg IV diluted and repeated in 15 minutes if required. Side effects of the beta-2-agonists include tachycardia, hypotension and muscle tremors. Alternatively, aminophylline can be used at 10 mg/kg IV, given slowly, (or 5 mg/kg orally).
Pleural Effusion
Patients presented secondary to trauma are more likely to have pleural space disease. On physical examination the respiratory pattern is characterized by short, shallow breaths on both inspiration and expiration. Severe pleural effusion may cause inspiratory distress and abdominal breathing.
Auscultation reveals quiet lung sounds ventrally. Cats with pleural effusion secondary to heart failure will present with similar signs to those outlined under the heart failure section. Other etiologies for pleural effusion include venous occlusion due to mediastinal or thoracic masses, neoplastic effusions, idiopathic (e.g., chylothorax), pyothorax, and less frequently hemothorax.2
Thoracic radiographs or POCUS are diagnostic for pleural effusion. Neither the presence, volume, nor distribution of pleural effusion is useful in discriminating between CHF and non-cardiac disease.4
Treatment
Cats with pleural effusion require thoracocentesis, alleviation of clinical signs is dramatic post-thoracocentesis. Cytology and further fluid analysis may provide a diagnosis. Multiple thoracocentesis (>2x/24-hour period, or repeat thoracocentesis over multiple days) should prompt chest tube placement.
References
1. Swift S, Dukes-McEwan J, Fonfara S, et al. Aetiology and outcome in 90 cats presenting with dyspnoea in a referral population. J Small Anim Pract. 2009;50:466–473.
2. Sharp CR, Rozanski EA. Physical examination of the respiratory system. Top Companion Anim Med. 2013;28:79–85.
3. DeFrancesco TC. Management of cardiac emergencies in small animals. Vet Clin North Am Small Anim Pract. 2013;43:817–842.
4. Ward JL, Lisciandro GR, Ware WA, et al. Evaluation of point-of-care thoracic ultrasound and NT-proBNP for the diagnosis of congestive heart failure in cats with respiratory distress. J Vet Intern Med. 2018;32(5):1530–1540.
5. Sumner C, Rozanski E. Management of respiratory emergencies in small animals. Vet Clin North Am Small Anim Pract. 2013; 43:799–815.
6. Smith S, Dukes-McEwan J. Clinical signs and left atrial size in cats with cardiovascular disease in general practice. J Small Anim Pract. 2012;53:27–33.
7. Benigni L, Morgan N, Lamb CR. Radiographic appearance of cardiogenic pulmonary oedema in 23 cats. J Small Anim Pract. 2009;50:9–14.
8. Hezzell MJ, Rush JE, Humm K, et al. Differentiation of cardiac from noncardiac pleural effusions in cats using second-generation quantitative and point-of-care NT-proBNP measurements. J Vet Intern Med. 2016;30:536–542.
9. Hori Y, Iguchi M, Heishima Y, et al. Diagnostic utility of cardiac troponin I in cats with hypertrophic cardiomyopathy. J Vet Intern Med 2018;32(3):922–929.