CONDITION
Pulmonary Thromboembolism
Pulmonary thromboembolism describes a situation in which a clot forms in a blood vessel and travels to the lungs, where it blocks one or more of the arteries that carry blood through lung tissue. When this happens, parts of the lung may not receive the blood flow they need to function, and the heart may need to work harder to push blood through the remaining open vessels. Owners often arrive at this page because their dog or cat has developed sudden difficulty breathing, seems unable to settle, or is breathing rapidly even at rest. In some cases, the animal may have a known condition elsewhere in the body—such as a heart problem, a hormonal disorder, or an immune condition—that has been mentioned as carrying this risk. The signs can appear without warning and may vary depending on how much of the lung's blood supply has been affected. This page explores what patterns tend to raise concern, what may be happening in the circulation and lung tissue, how the picture is investigated when this process is suspected, and what approaches exist once the condition is identified.
Why this matters now
Pulmonary thromboembolism can occur at any age, though it tends to appear in animals who already carry another condition that affects how blood clots or how it flows through the body. Dogs with immune-mediated diseases, certain heart conditions, or hormonal disorders such as hyperadrenocorticism are more often affected. Cats may develop clots in the context of heart muscle disease or conditions that cause protein to be lost through the kidneys or gut. The event itself often arises without obvious warning, though the underlying risk may have been building quietly for weeks or months.
The course varies considerably depending on how much of the lung's circulation has been blocked and how quickly the body can begin to dissolve or work around the obstruction. In some animals the signs remain stable after the initial event, whilst in others breathing may become progressively more laboured over hours or days. Some clots begin to break down within the first week, allowing gradual improvement, though this process is unpredictable and in other cases the obstruction persists or new clots form. Recovery, when it occurs, may take weeks, and the risk of recurrence often depends on whether the underlying condition can be managed.
Signals & patterns
Early signals
Sudden rapid breathing at rest
The animal may begin breathing noticeably faster than usual even when lying quietly, often with a shallow, effortful quality. This reflects the fact that parts of the lung are not exchanging oxygen efficiently, so the body attempts to compensate by increasing the rate of breathing.
Restlessness or inability to settle
Many animals seem unable to find a comfortable position and may move from place to place, shift posture frequently, or appear anxious. This behaviour can reflect the discomfort of working harder to breathe or the body's response to lower oxygen levels.
Pale or grey gum colour
The mucous membranes inside the mouth may lose their usual pink tone and appear paler or take on a greyish tint. This change can indicate that less oxygen is reaching the tissues, though gum colour alone does not confirm the cause.
Coughing
Some animals develop a cough, which may be dry or occasionally produce small amounts of blood-tinged fluid. This can occur when inflammation develops in the affected parts of the lung or when fluid leaks into the airways.
Later signals
Bluish tinge to gums or tongue
In more advanced cases, the mucous membranes may take on a blue or purple hue, a sign that the blood is carrying significantly less oxygen than normal. This pattern tends to emerge when a large portion of the lung's circulation is obstructed.
Collapse or profound weakness
The animal may suddenly lie down and be unable to rise, or may show extreme lethargy and disinterest in surroundings. This can reflect severe oxygen deprivation or the strain placed on the heart as it attempts to push blood through narrowed or blocked vessels.
Open-mouth breathing in cats
Cats in particular may begin breathing with their mouth open, a behaviour that is uncommon in this species and typically signals significant respiratory distress. It suggests the animal is working very hard to move air and is no longer able to breathe comfortably through the nose alone.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
Last reviewed: Invalid Date ·