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How Does the Veterinarian Diagnose Fluid in a Cat’s Chest?

November 16, 2011
Black Mowgie with round orange eyes lays in sink at animal hospital

Castiel After Treatment

Castiel’s Future Depended on a Fast, Accurate Diagnosis

Castiel, the one-year-old domestic short-haired black cat came to Doc Truli in a state of severe respiratory distress.  He was panting and his elbows stuck out to his sides in order to spread his chest wider to get air in.  He did not have long to live and needed risky chest x-rays to guide his treatment plan. Unfortunately, a stethoscope cannot distinguish the causes of the panting, and thus the cure for the problem.  Castiel needed stat radiographs of his chest (X-Rays).

Oxygen So Castiel Could Survive X-Rays

The nurses placed an oxygen mask over his little nose so he could breathe pure 100% oxygen, instead of 70% oxygen which is normal in room air at sea level.  The mask is technically tricky in a dyspneic cat. (pronounced disp-knee-ick, admittedly, a terrible combination of consonants, hard to get out, just like it’s hard to breath if you are dyspneic.)  If Castiel panicked because of the mask over his face, and if he thought the mask was making it harder for him to take in oxygen, he would increase his oxygen needs just through sheer nervousness.  It takes a clam, professional nurse to apply an oxygen mask effectively.

An alternative to the emergency oxygen mask is to place the patient in an “oxygen cage” which is a tank or cage designed for oxygen, temperature, and humidity control.  The patient may not panic as much because he or she is not being held and controlled, but the oxygen tank can rarely sustain 100% oxygen levels, so there is a compromise in oxygen levels.

These decisions about oxygen delivery methods must be made- and the results lived-with by the veterinarian- in a matter of moments.

 Radiographs Essential for Most Breathing Problem Diagnosis

Castiel was so sick, he accepted his face mask and his breathing calmed a little bit.  We carried him to the X-Ray room still wearing his oxygen mask.  Radiology is another choke point – literally – in the diagnosis and treatment of a cat with a breathing problem.  If a veterinary team can pre-oxygenate the patient, and provide oxygen during any handling, then the cat can handle the metabolic stress of the slightly increased heart rate and breathing rate that goose with necessary medical care.  If oxygen is not available, then there is a significant risk of pulmonary and cardiac failure on the radiology table.

Cas withstood his X-Rays well.  He accepted his oxygen and the nurses gently allowed him to stay on his chest and keep his elbows out so he could breathe easier on the table.  Ideally, chest x-rays emphasize features of the heart when the patient is laying on his chest ad they show more details of the lungs when the cat is placed on his spine with his chest facing up to the X-Ray tube.  In Cas’s case, rolling him over onto his back would likely kill him just from the change in the chest position.  He was breathing so poorly that his whole survival strategy was adapted to the position of laying on his chest, as he had been doing at home for hours.

In order to see what is really going on in the lungs, a second angle is needed for the X-Rays.  Cas was doing well, so the nurses quickly and gently rolled him ever-so-slightly onto his side and watched to see if his breathing worsened.  He stayed steady so they snapped “a lateral.”  A lateral is the term for an x-ray taken when the cat is placed on his or her right or left side and the x-rays penetrate side-to-aide instead of back to front.  Usually, in veterinary medicine, we place the patient in right lateral recumbency (laying with the right side down.)

 Castiel’s X-Rays Reveal Pleural Effusion

 What Does a Normal Cat Chest Look Like?

The heart can be seen clearly in the middle of the chest and the whole chest under the ribs is filled with lungs which look black like air on an X-Ray

Normal Cat Lungs X-Ray

Mediastinum – Heart, Windpipe, Esophagus, and What-Not

In a normal cat (or dog, or human), the heart lives in the center of the chest.  The heart suspends within a virtual space called the mediastinum (pronounced mee-dee-ah-sti-num).  The reason the mediastinum is a virtual space is because normally it contains only a few drops of fluid that helps everything stay lubricated so it doesn’t rub together, but also creates a surface tension. Surface tension on a glass of water that lets the water round up higher than the top of the glass, and also lets a drop of water hold together into a round drop and not just a thin sheet of water. The mediastinal space can fill up with blood or pus or cancer cells, or what-not, but normally it only contains a few drops of physiologic liquid and is thought of as a virtual space.

 The mediastinum contains the thymus, lymph nodes, the windpipe, the esophagus, and the heart.  It lies in the center of the chest and is defined by a see-through thin layer of connective tissue called the pleural lining (pronounced ploor-ull).  That pleural lining wraps the mediastinum and the heart like biological wrapping paper and continues in one continuous sheet around the inner surface of the ribcage and actually also around all the lung lobes, too.

The Lungs

There are 7 lung lobes (warning:this links to cadaver pictures, informative, but disgusting!) in the cat.  Normally, they fill up the whole of the chest.  The pleural lining actually adheres through the surface tension of a tiny amount of fluid that floats in another virtual space called the pleural space.  So a normal chest x-ray would show the heart and windpipe, maybe the esophagus is it is filled with air or fluid (otherwise it’s just a meaty muscle tube), and the black of air because the lungs are mostly made up of alveoli, little microscopic air sacs (pronounced al-vee-oh-lie).

What Is Pleural Effusion?

Pleural effusion means the virtual pleural space around the lungs, and between the lungs, mediastinum (containing the heart), and the muscles around the ribcage, is full of fluid.  Lots and lots of fluid.  Like potentially, Liters of fund, not just a normal teaspoon or so.

Side X-Ray of Cat's chest shows all white fluid in the chest except for a little triangle of normal lungs in the back and top of the chest. That's all he had left for breathing!

Before the Chest Tap, The black triangle is all the lung space Castiel had to work with!

The lungs are literally floating in fluid.  They are suspended in a pool of fluid.  Plus, to make matters even more complicated, the fluid can be compartmentalized into pockets of fluid, not just one big connected pool.  There are thin, normally clear connective tissue sheets branching from the lung lobes to the walls of the chest and each other.  They  are slightly different in every individual.

Cats Often Have Separate Right and Left Pleural Cavities

(Cavity=Space, Like a Cave)

Cats, especially, tend to have a full sheet in between the right and left side of the chest separating the fluid into compartments.  Dogs often do not have this separation, and a veterinarian can remove the fluid all form one side or the other.

Cats often need multiple puncture holes through the side of the chest wall to access enough of the fluid pockets to drain the pleural effusion from the pleural space.

 What Is the Liquid in the Chest?

After the x-rays Doc Truli still did not know what the fluid was, and therefore what the cause was, and therefore, what the odds of a cure were.  Cas’s mom had to make the decision, very quickly, whether or not to proceed with a painful and expensive procedure called a pleural tap, otherwise known as a thoracocentesis (like amniocentesis, except the needle goes into the thorax (aka chest) instead of the amniotic sac of a fetus).  Cas’s mom had to make the decision without knowing if it would permanently help Cas.  Unfortunately, this decision always plays out this way in a dyspneic cat with evidence of pleural effusion on the radiographs.  The doctor needs a sample of the fluid to tell what the fluid actually is.

To be continued…

Read VirtuaVet’s Next Post: Castiel’s Chest Tap Proves Invaluable


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