Pyothorax in dogs – symptoms, chest drainage and treatment

Overview

Pus accumulates around the lungs

In pyothorax, inflammatory fluid lies in the pleural cavity. Fluid accumulating around the lungs can cause breathing difficulty. Inflammation of the pleura and lung tissue can occur in the same dog.

Pyothorax is usually caused by bacterial infection. Several bacterial types can occur together. Finding fluid alone does not establish its cause. Blood or lymphatic fluid can also accumulate in the pleural cavity.

Treatment often involves hospital care combining pus drainage, antimicrobials and supportive care. Some cases need surgery. Treatment choice also depends on whether a removable foreign body or another structural problem is found.

Causes

A foreign body, injury or another infection source

In dogs, pyothorax can result from a plant foreign body migrating through tissues. Chest injury is another possible starting point. A bite can also introduce bacteria into the chest cavity. Infection can spread from a lung abscess into the pleural space.

Oesophageal perforations and surgical site infections have also been found with the disease. Some dogs have had concurrent cancer. The precise source cannot always be established. In one study of 43 dogs, the cause remained unidentified in 23/43 cases, or 53%.

Many bacterial types can be involved

Anaerobes are bacteria that grow in low-oxygen conditions. Canine pyothorax can involve bacteria such as Bacteroides and Fusobacterium. E. coli and Klebsiella pneumoniae are also common findings. Actinomyces and, less often, Nocardia can be causes. Identifying the organism helps target treatment.

Risk factors

Predisposing situations involve bacteria entering the chest. Migrating plant material and penetrating injuries are key possible underlying factors in dogs. Bite wounds are considered too. A lung abscess or pneumonia can be the infection source.

Pyothorax is not confined to one age or size group. One study of 43 dogs included small, medium-sized and large dogs. There were 20 males and 23 females. In this study, age, size and sex did not distinguish survivors from non-survivors. This is not a risk comparison across the whole dog population.

Previous chest procedures and associated infection are also considered in the history.

Typical symptoms

A change in breathing may be the most visible sign. Possible observations include:

• Faster breathing.
• Shallow breathing.
• Coughing.
• Chest pain.
• Eating less than usual.
• Tiredness or reduced exercise tolerance.
• Possible fever.
• Possible weight loss.

A healthy dog's usual breathing rate is around 12–30 breaths per minute. At rest, breathing is generally slower and deeper than during exercise. Assessment of pyothorax considers breathing effort and general condition as well as rate.

Pleural disease can cause asynchronous breathing. The chest then expands during inhalation while the abdominal wall moves inwards. Investigation of a severely ill dog is not delayed simply because they are not coughing.

In the canine study's histories, reduced appetite was reported in 26 dogs, or 60%. Tiredness, weakness or reduced exercise tolerance was described in 19, or 44%. Coughing was reported in 12, or 28%.

Complications and consequences

Breathing and circulatory problems can progress quickly

With respiratory distress, the body does not receive enough oxygen for its needs. Severe infection can lead to sepsis, an abnormal host response causing organ dysfunction. Recognising sepsis requires assessment of organ dysfunction alongside infection.

The highest mortality in pyothorax patients has been described during the first 48 hours in hospital. In one study, 11/16 dogs that died or were euthanased, or 68.8%, did so within this period. These figures include euthanasia, so they do not describe only death despite treatment.

Disease can persist or recur after medication ends. The fluid is then reassessed and new cultures taken.

Diagnosis at the vet

Breathing is stabilised before stressful tests

Your vet assesses the breathing pattern and listens to the chest. Breath sounds over fluid may be quiet. X-rays can stress a dog struggling to breathe and cause rapid deterioration. Imaging is performed only once your dog can tolerate it.

Ultrasound can reveal pleural fluid. Some patients tolerate it better than X-rays. Removing fluid that impairs breathing serves both treatment and diagnosis. After drainage, X-rays also assess areas of lung consolidation.

Pus-filled fluid undergoes cell and bacterial tests

Pleural fluid is examined by cytology. The same fluid undergoes aerobic bacterial culture and susceptibility testing. Anaerobic culture is also included. Gram staining can complement bacterial identification.

In one study, bacteria were seen microscopically in fluid from 29/41 tested dogs, or 71%. Among microscopy-negative samples, aerobic culture was positive in 5/9 cases, or 56%. Culture is therefore needed even when bacteria are not visible in the sample.

Fluid protein concentration and cell count can also be measured. Of microscopy-positive samples, 25, or 86%, showed a combination of several bacterial types. Filamentous bacteria were seen in 10 samples, or 34%. Both intracellular and extracellular bacteria were found in 27 samples, or 93%.

Special staining for acid-fast bacteria can provide further information about the organism.

The laboratory is told if Actinomyces or Nocardia is suspected. Special growth conditions and prolonged incubation may be needed.

With strong suspicion of sepsis, blood culture may be needed if other samples do not identify the organism. A negative blood culture does not exclude bacteria in the bloodstream. CT can complement localisation of lung and pleural changes.

Circulation and the inflammatory response are monitored

Blood tests assess values including white blood cells, glucose and lactate. Blood lactate can help assess disease severity. In one study, median admission lactate was 3.4 millimoles per litre in non-survivors and 2.0 millimoles per litre in survivors. The same study found no significant association between glucose and survival. An individual measurement is interpreted alongside the dog's overall situation.

Treatment

Removing pus is central to treatment

Medication is combined with drainage of pus from the chest cavity. Drainage can begin with a chest tap. If repeated drainage is needed over a short period, a chest drain may be placed. This allows continuous or intermittent suction.

The pleural cavity can also be flushed. Placing antibiotics directly into it is not recommended because evidence is insufficient. Fluids support circulation where needed. Oxygen can be used to treat breathing difficulty.

In the group treated without surgery, 13 dogs received chest drains. Of these, 8 had a drain on one side and 5 had drains on both sides. Treatment without surgery therefore does not mean medication alone.

If respiratory exhaustion threatens, intubation, placing a breathing tube into the trachea, and mechanical ventilation may be needed to secure oxygen supply.

Antimicrobials depend on the organisms and response

Initial medication can be given by injection. Your vet selects antibiotics according to culture, susceptibility and your dog's condition. Treatment must also cover anaerobic bacteria. Anaerobes can be involved even if culture fails to grow them.

Alongside resistance found on culture, whether your dog improves is considered. Treatment may need changing if bacteria are resistant and the response is insufficient. Specialist consultation is recommended for multidrug-resistant findings.

Culture from the infection site helps plan further care. Sampling must not delay starting treatment in a severely ill patient with sepsis. Fluid balance and tissue circulation are also monitored in hospital.

Surgery can remove the infection source

Surgery is considered for structural disease or failure of other treatment. Surgical debridement can remove infected tissue. Procedures used in studies also include lung lobe removal. Some patients need a procedure to repair oesophageal injury.

Hospital stay and recovery

In one study of 43 dogs, 27 survived to discharge. Survivors stayed in hospital for a mean of 7.1 days, ranging from 3–13 days. Of surgically treated dogs, 17/21, or 81%, survived to discharge. Of dogs treated without surgery, 10/22, or 45.5%, survived to discharge. Treatment groups were not randomised, so these figures cannot establish a suitable treatment choice for every dog.

Surgical survivors stayed in hospital for a mean of 7.8 days, ranging from 5–13 days. Non-surgical survivors stayed for a mean of 5.8 days, ranging from 3–12 days.

The first follow-up X-rays are recommended around 10–14 days after treatment starts. Imaging is repeated when treatment ends too.

Prevention

Not all sources can be identified: one study left the cause unclear in 53% of dogs. Prevention therefore focuses on identifiable exposure situations. Penetrating chest injuries and bites can carry bacteria into the pleural space. Having such injuries examined is reasonable even when the visible skin opening is small.

A possible plant foreign body is considered according to your dog's environment and history. Identifying infection arising from a lung abscess is another way to address an underlying source. If signs recur, a new sample and culture help plan treatment again.

Important for dog owners

Calm transport in a cool vehicle

If possible, phone the emergency vet before arrival. Keep the car cool, as heat can increase panting and worsen breathing. Speak calmly and avoid unnecessary exertion. If your dog cannot stand, they can be supported lying on their chest with the chin on padding and neck extended.

Report previous bites, injuries, chest procedures and possible plant foreign bodies. These may relate to the infection's origin. Keep previous culture results and names of medicines used.

After discharge, record resting breathing rate, breathing effort, appetite and activity. Before discharge, agree how follow-up will work and whom to contact if your dog worsens. New difficulty breathing needs urgent assessment.

Frequently asked questions

Is pyothorax the same as pneumonia?

In pyothorax, pus-filled fluid is in the pleural cavity. However, infection from pneumonia can spread into the pleural space. The same dog can therefore have both diseases. X-rays after chest fluid drainage help your vet also examine consolidation within lung tissue itself.

Can an antibiotic alone be enough?

Draining pus is central to treatment alongside antibiotics. Some dogs also need surgery. Surgery may be chosen because of a structural cause or ineffective other treatment. An appropriate combination of care is selected in hospital according to your dog's situation.

Does a microscopic sample without bacteria exclude infection?

Not necessarily. In one study, 5/9 microscopy-negative samples were positive on aerobic culture. Both cytology and bacterial cultures are therefore recommended for pleural fluid. These tests provide different, complementary information about the fluid and its organisms.

Why is the laboratory told about suspected Actinomyces?

These organisms can need unusual growth conditions and longer incubation. Actinomyces and Nocardia are possible causes of canine pyothorax. Your vet telling the laboratory about the suspicion helps it choose the necessary tests and growth conditions.

How long is hospital care needed for pyothorax?

In one canine study, survivors stayed in hospital for a mean of 7.1 days, ranging from 3–13 days. Surgical survivors stayed for a mean of 7.8 days. This describes patients in a particular study; your dog's discharge depends on their own condition.