Dyspnea Due to Acute Asthma

Lower respiratory tract disease produces typical clinical signs in cats, including chronic cough and wheeze as well as dyspnea that may have a sudden onset. Owners may report an increase in respiratory rate (> 30–40 breaths per minute), increased expiratory effort and lethargy. Clinical signs may be mild to severe and may be chronic or intermittent.

Since feline asthma is characterized by airway inflammation and bronchoconstriction, therapy is aimed at reversing these changes. There are many treatments for feline asthma, including some experimental modalities borrowed from human medicine. Many of these treatments have not been well evaluated in the cat. See Table 1 for a list of commonly used drugs.

Treatment of Lower Airway Disease Patients with Acute Clinical Signs

Patients in acute respiratory distress may be unstable and should be examined and treated with great care. Cats only breathe through the mouth when they have severe respiratory compromise. Nonspecific treatment may be required to stabilize the patient to make further handling for diagnostic procedures (e.g., radiographs, blood collection) safe. Be aware that some drugs may cause a temporary increase in heart and respiratory rate. When using combination drug therapy, be aware of the risk of arrhythmia in stressed, hypoxic cats. Some very anxious and stressed dyspneic cats may benefit from mild sedation with a low dose of acepromazine (0.05 mg/kg, IM, SQ). An intravenous catheter should be placed as soon as safely possible for vascular access.

First Line Therapy

 Supplemental oxygen: Preferably using an oxygen cage

 Bronchodilators: Best via nebulizer or metered dose inhaler as the effects are seen within 5 min (versus 15–30 min by injection); give 2–4 puffs of inhaled drugs such as albuterol every 20 min; repeat injectable drugs in 15 min if required. Parenteral bronchodilators may be contraindicated in some cats with cardiac disease.

 Short-acting corticosteroid: Intravenous dexamethasone or prednisolone sodium succinate; may take 3–6 hours for maximum effect; useful in cats on chronic oral bronchodilator therapy to reverse down-regulation of airway β-adrenergic receptors causing drug tolerance

Second Line Therapy

 Anticholinergics: Atropine, glycopyrrolate; block vagal input causing bronchoconstriction and decrease bronchial secretions; not useful for long-term therapy as these drugs will cause increased viscosity of airway mucus

Third Line Therapy

 Epinephrine: α- and β-agonist, can reverse bronchoconstriction; may cause arrhythmia

Table 1. Drugs commonly used in the treatment of acute feline asthma

Urethral Obstruction

Cats with urethral obstruction should be treated as emergencies when presented. A thorough assessment of the cat's condition should be made before attempting to relieve the obstruction. Placement of an IV catheter should be the first procedure in order to administer fluids and medication. Analgesia should be provided at the earliest opportunity. Blood samples are collected for a complete blood cell count and serum chemistries/electrolytes. Treatment of the patient can begin before all the results are received. Obstructed cats may have moderate to severe dehydration. Any isotonic crystalloid is adequate for rehydration and stabilization at 4–6 ml/kg/h. Avoiding fluids containing potassium is no longer considered necessary. In severely dehydrated, moribund, or hypotensive cats, 20 ml/kg may be administered as an initial intravenous bolus.

Common Metabolic Abnormalities

Common abnormalities in cats with urethral obstruction that may require correction include azotemia, hyperkalemia, metabolic acidosis and hypocalcemia. With severely ill patients, part of the assessment plan should include an ECG (lead II). In most cases, azotemia, acidosis and hyperkalemia resolve with administration of fluids and relief of the obstruction. Sodium bicarbonate may be required to resolve severe metabolic acidosis (pH < 7.1). If blood gases are not available and metabolic acidosis is suspected, administer 1–2 mEq/kg of sodium bicarbonate slowly. It will take 30 min or more to see effects. It is important to monitor serum calcium as sodium bicarbonate lowers the ionized portion of plasma calcium and some patients are already hypocalcemic at presentation.

The effect of hyperkalemia in cats with severe ECG disturbances can be countered with calcium gluconate, which directly antagonizes the high potassium at the cell membrane level and is therefore cardioprotective. Administer 50–100 mg/kg IV (about 3 ml of 10% calcium gluconate) over 5 min while monitoring the ECG. The effects are almost immediate and will last about 30 min. Plasma potassium can be further decreased if necessary by driving it intracellularly, using regular insulin (1 unit, IV). The insulin should be followed with an IV bolus of 50% dextrose (0.5 g/kg, diluted) to prevent hypoglycemia. Serum potassium will decrease within 30–60 min and the effect lasts 1–2 hours. Blood glucose should be monitored for several hours after administration of insulin, and fluids can be supplemented with 2–5% dextrose to maintain normoglycemia.

Cats with severe hypocalcemia (< 1.6 mEq/L) may have impaired cardiac electrical and mechanical dysfunction, requiring administration of IV calcium (as detailed above).

Relieving Urethral Obstruction

Cystocentesis can be useful to decompress the bladder before attempting to catheterize the urethra. This helps relieve pain and distension as well as re-establish renal function, and makes subsequent attempts to flush the urethra easier. It is critically important to minimize bladder trauma with good technique. Save samples for urinalysis and urine culture.

Radiographs of the complete urinary tract including the urethra should always be taken to evaluate for uroliths and other abnormalities. Establishing urethral patency is begun after the patient's cardiovascular system is stable. The choice of sedation versus anesthesia, and the drug protocols employed will vary depending on the condition of the patient and the experience of the clinician.

A sacrococcygeal epidural provides regional anesthesia to the perineum, penis, urethra, colon and anus by blocking the pudendal, pelvic and caudal nerves while preserving motor function to the hindlimbs. Urinary catheters should be of soft, nontraumatic materials and gentle technique should be used for placement to avoid urethral trauma. An indwelling urinary catheter is not required for all obstructed patients. Factors such as ease of establishing urethral patency, quality of urine stream, size of bladder at presentation, marked hematuria at presentation, and the presence of systemic illness must all be considered.

Indwelling catheters are generally left in place from 1–3 days. Indications for catheter removal include resolution of clinical signs such as lethargy, weakness, anorexia and vomiting, diminishing hematuria, and resolution of metabolic derangements and postobstructive diuresis. A recovered bladder will feel small and firmly contracted around the tip of the catheter on palpation. It is not recommended to begin antibiotic therapy while an indwelling catheter is in place. While antibiotics may reduce the risk of postcatheter bacterial infection, infections that do occur may be highly resistant. Antibiotic use with an indwelling catheter is reserved for cats with evidence of urinary tract or systemic infection at the time of diagnosis. Antibiotics may or may not be required once the catheter is removed.

Ongoing Monitoring

After stabilization, ongoing monitoring should include assessment of hydration, temperature, mentation and urine output. Any abnormalities on initial assessment should be re-evaluated as needed (electrolytes, ionized calcium, blood glucose, BUN, creatinine, acid/base status, etc.). Cats that were obstructed for over 48 hours or that are severely azotemic may experience significant postobstructive diuresis (urine output > 2 ml/kg/h) for a period of 2 to 5 days. Urine output should be monitored and fluid therapy carefully titrated to avoid dehydration. Monitor carefully for hypokalemia. After azotemia resolves, fluid therapy may be tapered gradually.

Ongoing analgesia can be provided with buprenorphine (either SC or transmucosal). Urethral spasms are a common cause for re-obstruction once a urethral plug or urolith has been removed, so pre-emptive therapy with an antispasmodic is warranted in many cats. Acepromazine may be useful for its antispasmodic effects on urethral smooth muscle in stabilized patients. Alternative drugs to decrease urethral smooth muscle tone are the α-1 antagonists such as phenoxybenzamine and prazosin. Phenoxybenzamine appears to take 2–3 days to maximal effect, so the drug should be started before the urinary catheter is removed. Diazepam may be used to relax the striated muscle component of the urethra, although its clinical efficacy is unclear.

Table 2. Drugs used in the management of cats with urethral obstruction

References

1.  Gunn-Moore D. How to choose a cat urinary catheter. Companion. 2008;13.

2.  O'Hearn AK, Wright BD. Coccygeal epidural with local anesthetic for catheterization and pain management in the treatment of feline urethral obstruction. J Vet Emerg Crit Care. 2011;21:50–52.

3.  Rieser TM. Urinary tract emergencies. Vet Clin North Am Small Anim Pract. 2005;35:359–373, vi.

4.  Sabino C, Boudreau A, Mathews K. Emergency management of urethral obstruction in male cats. Clin Brief. 2010;57–61.

5.  Thomovsky EJ. Managing the common comorbidities of feline urethral obstruction. Vet Med. 2011;106:352–357.

6.  Walker D. How to manage feline urethral obstruction. Companion. 2010:12–16.