Aspiration pneumonia in cats | VETgirl Veterinary Continuing Education Podcasts
We see cases of aspiration pneumonia quite often in the emergency hospital, but when is the last time you can remember seeing a cat with this diagnosis? Case reports of cats with aspiration pneumonia are quite few and far between. Since this underreported condition leaves us without much information in the way of feline studies for aspiration pneumonia, we are left with extrapolating our treatment recommendations and our medical expectations from cases of canine aspiration pneumonia. So, Levy et al wanted to evaluate this in a study entitled Clinical and radiographic findings in cats with aspiration pneumonia: retrospective evaluation of 28 cases. This was the first retrospective evaluation of cats diagnosed with aspiration pneumonia in the veterinary literature. In this study, medical records from cats at the Michigan State University were evaluated if the record contained a diagnosis of “aspiration pneumonia” or “bronchopneumonia.” Records were only included in this study if the patient’s radiographic findings were available and diagnosed as aspiration pneumonia by a boarded radiologist. Between 2001 and 2013, only 28 case records fit the criteria for this study. Although the ages of these cats ranged from 6 weeks to 16 years, the median age was on the younger side of life at 2.9 years. Median weight of cats was 3.8 kg. Males and females were evenly represented. Common presenting clinical signs in these cats included the typical complaints we would expect to find in dogs with aspiration pneumonia such as increased respiratory effort, anorexia, vomiting or regurgitation, and cough. Some less commonly thought of clinical signs were additionally observed such as drooling, oral bleeding, and diarrhea. Presenting temperatures were widely variable, ranging from 32.4C (90.3F) to 40.7C (105.2F) with a median temperature in the normal range at 38.7C (101.2F). Only 6 cats (21%) fell in the hyperthermic range (>39C; 102.2F) on presentation and only 3 cats (11%) were found to be in the hypothermic range, described as a rectal temperature <37.5C (99.5F). Median heart rate fell in the normal range at 200 beats per minute, but ranged anywhere from 120 to 250 bpm, so both bradycardia and tachycardia were observed with aspiration pneumonia. Oddly enough, most cats did not exhibit respiratory distress – only 11 cases (39%). Despite most cats exhibiting normal respiratory patterns, the median respiratory rates were outside normal reference ranges for a cat (20-30 bpm) at 41 breaths per minute. Presenting respiratory rates ranged from low at 16 bpm to severe tachypnea at 120 bpm. Sixty percent of cats exhibited “harsh lung sounds” or “increased bronchovesicular sounds” on presentation. Bloodwork abnormalities included an inflammatory leukogram without a degenerative left shift. About half of the cats (52%) were anemic (PCV < 35%) with normal total solids (median of 6.8g/dL). This type of anemia is relatively common in sick animals as an anemia of chronic disease or anemia from inflammatory conditions. Common radiographic abnormalities included an alveolar pattern found in 71% of cases, unstructured interstitial pattern present in 18% of cases, and mixed alveolar-interstitial pattern in 11% of cases. Similar to aspiration pneumonia in dogs, the most frequently affected lung lobe in cats was found to be the right middle lung lobe (64%). The next most commonly affected lung lobe was the left cranial lung lobe (57%). Remember that the left cranial lung lobe is divided into two subsegments, confusingly named the cranial and caudal subsegments of the left cranial lobe. In this retrospective evaluation, when the left cranial lung lobe was affected in feline aspiration pneumonia, both subsections were concurrently affected. Over half (57%) of cats exhibited multiple lung lobe involvement. The reason we see the right middle and left cranial lung lobes most commonly affected in aspiration pneumonia is due to the gravity dependent anatomy of the dog and cat in their natural four-legged stance. The bronchi branches leading to the right middle and left cranial lung lobes are the most proximal and gravity dependent of the big airways. In this study, the right caudal lung lobe appeared to be free of radiographic involvement in all cases. We can use this finding as a diagnostic tool – if right caudal lung lobe involvement is radiographically apparent in cats presenting in respiratory distress, the focus should be moved from aspiration pneumonia, to other pulmonary disease such as primary pulmonary neoplasia.
This retrospective evaluation found the following to be predisposing factors to the development of aspiration pneumonia in cats in descending order: vomiting, general anesthesia, upper respiratory disease, enteral nutrition, esophageal disease, chronic GI disease, neurologic disease, and laryngeal disease. Of the cats that developed aspiration pneumonia presumptive as a result of general anesthesia, clinical signs became apparent anywhere from 1 to 18 days with a median of 4 days after the anesthetic event. Anesthesia is a common predisposing factor for aspiration pneumonia in multiple species because the medications used to achieve anesthesia impair the body’s natural protective airway reflexes. Unfortunately, since the onset of clinical signs in the cats in this study that had undergone general anesthesia was so variable, there is a possibility that these numbers are not a true reflection of cats that developed aspiration pneumonia from anesthetic events since other factors may have popped up within that time frame. Of all cats affected by aspiration pneumonia, hospitalization ranged anywhere from 0 to 21 days with a median hospitalization of three days. More than half of the cats required oxygen supplementation via an oxygen cage. Duration of oxygen support varied from less than 24 hours up to 96 hours. All cats received antibiotics and a 14-day course was the most typical course assigned; no follow-up was included in this study to determine if the selected courses were effective in clearing the pneumonia. Only one cat received airway cultures, and they grew E.coli. Adjunctive therapies included intravenous fluids, anti-emetics, and gastroprotectants. 89% of cats lived to discharge with the other three cats dying of natural disease progression or being euthanized due to severity of respiratory distress. The overall survival rate of felines with aspiration pneumonia was found to be similar in dogs.
This retrospective study is limited by a small sample size, in part due to the lack of complete medical records and incomplete diagnostic workups. Some cats exhibited a mild cardiomegaly on radiographs that was interpreted as being clinically insignificant, but they lacked further investigation to ensure that cardiac disease was not a contributing factor to the cat’s respiratory distress and clinical signs. This study could have been more robust had all cats received airway cultures to first prove the diagnosis of a bacterial component to the airway disease and to provide useful information regarding typical bacterial colonies implicated in aspiration pneumonia and treatment options.
What can we take away from VETgirl podcast? Aspiration pneumonia is an uncommon condition identified in cats. Thoracic radiographs are a great diagnostic tool in cats with respiratory distress, but VETGirl urges you to strongly consider the risks when taking radiographs in cats presenting in significant respiratory distress as these sympathetically driven felines can easily die from the added stress of handling and positioning for radiographs. So use your judgement, use other tools such as a portable ultrasound if readily available, and use your patient history to help make a working diagnosis if radiographs cannot be taken. And if the right caudal lung lobe is radiographically affected, start focusing on causes of respiratory distress outside of aspiration pneumonia.
Levy N, Ballenger E, Koenigshof A. Clinical and radiographic findings in cats with aspiration pneumonia: retrospective evaluation of 28 cases. J Sm Anim Prac 2019;60(6):356-360.