Causes

Causes of pleural effusion in cats include:

In the author’s experience, neoplasia and congestive heart failure (see Ch. 31) are the two most common causes identified in cats (see Figures 32.1–32.4).

Figure 32.1 Right lateral thoracic radiograph of a cat with pleural effusion secondary to a cranial mediastinal mass.

Figure 32.2 Right lateral thoracic radiograph of a cat with severe pleural effusion (diagnosis not made).

Figure 32.3 Right lateral thoracic radiograph of a cat with pleural effusion secondary to feline infectious peritonitis (FIP).

Figure 32.4 Right lateral and dorsoventral thoracic radiographs of a cat with idiopathic chylothorax (a, b) before and (c, d) after thoracocentesis. The post-drainage films were taken the day after under general anaesthesia; an oesophageal stethoscope is visible.

Observation

The cat was initially briefly observed in his carrier. He appeared alert and pupils were not mydriatic. Respiratory rate was increased with a moderate mixed increase in respiratory effort (including increased abdominal effort). The cat was not obviously cyanotic and was sitting in sternal recumbency with no obvious evidence of trauma.

Brief examination

It was possible to remove the top of the cat’s carrier and as he appeared relatively calm, a brief examination was performed while he remained sitting in the same position. Flow-by oxygen supplementation had been started already. Sternal cardiac auscultation revealed a subjectively normal heart rate and neither a gallop sound nor a cardiac murmur could be heard. However, the heart sounds appeared muffled. Lung sounds were very dull ventrally and this appeared bilaterally symmetrical. Femoral pulses were normal.

Oxygenation and client discussion

Following the brief examination, the cat was placed in an oxygen cage, still in his carrier with the top off, and kept under close observation. As the cat was readily compliant, morphine (0.1 mg/kg i.m.) was administered at this point in anticipation of thoracocentesis. The owner was advised that it was suspected that the cat had a pleural effusion for which the two most common causes in cats are neoplasia, especially lymphoma, and congestive heart failure; other possibilities in this case included pyothorax and an idiopathic effusion. The owner was keen to persevere with trying to stabilize the cat with a view to achieving a definitive diagnosis.

Further case management

The cat’s respiration had improved to some extent following initial oxygen therapy but there was still a marked increase in respiratory effort. Given the suspicion of pleural effusion, it was decided to perform thoracocentesis for diagnostic and potentially therapeutic purposes (see p. 291). The procedure was only performed on the right side as a large volume of pleural fluid was removed (250 ml, approximately 50 ml/kg) and the cat’s breathing improved significantly almost immediately. The cat was returned to the oxygen cage following thoracocentesis after clipping the fur over both cephalic veins and applying topical local anaesthesia (EMLA^® cream 5%, AstraZeneca – see Ch. 5) to both sites. The pleural effusion was grossly milky in appearance. In-house cytology revealed that more than half of the cells present were small lymphocytes, and no bacteria were seen. It was therefore presumptively classified as a chylous effusion but samples had also been collected into additional sterile containers for submission to an external laboratory.

The cat remained comfortable in the oxygen cage and a cephalic intravenous catheter was placed later using minimal restraint and gentle handling. Blood was obtained via the catheter for an emergency database to be performed that was essentially unremarkable. As congestive heart failure remained a possibility, the cat was not started on intravenous fluid therapy at this time and the catheter was kept patent by regular flushing. Morphine (0.1 mg/kg slow i.v. q 6 hr) was continued but no other medications were indicated at this stage.

The cat remained stable overnight and it was possible to wean him off oxygen therapy. He was referred the next morning for further investigations which revealed a cranial mediastinal mass that was confirmed to be due to lymphoma. The cat was started on chemotherapy and was doing well at his most recent follow-up examination.