All about pleural space and mediastinal diseases
In today’s post we’re continuing our respiratory series, talking all about disorders of the pleural space and mediastinum. Pleural space disease cases are great fun to nurse (who doesn’t love a chest drain?!), and we also have the potential to make a huge difference to our mediastinal disease patients, especially those with neoplasia, who need to come in regularly for chemotherapy.
But before we can start talking about nursing these patients, we need to have a thorough understanding of what each disease does, how it affects our patients, and the signs we see. Once we’ve got that down, we can start planning our nursing care.
Mediastinal Disease
The mediastinum is the central compartment of the thoracic cavity (the area between the lungs), made up of a number of structures and surrounded by connective tissue. These structures include the heart, oesophagus, trachea, thymus, thoracic duct, phrenic and cardiac nerves, and the central thoracic lymph nodes. Diseases of the mediastinum include mediastinitis and mediastinal neoplasia.
Mediastinitis
This is inflammation of the mediastinum. Patients with mediastinitis often present with gagging, hypersalivation, dysphagia, vomiting, lethargy, weight loss, pyrexia, and/or respiratory distress.
Pathophysiology
The condition can result from thoracic trauma, or secondary to a foreign body causing partial obstruction and then penetration of the oesophagus, causing an abscess.
Diagnostics
A range of diagnostic tests are often performed, to exclude other conditions. These include biochemistry/haematology, abdominal ultrasound, thoracic and/or abdominal radiographs, barium swallow studies and endoscopy.
Treatment
Treatment depends on the type, cause and severity of infection. Supportive treatment with intravenous fluid therapy, placement of thoracostomy tubes and administration of antibiotics is the typical treatment (treatment can range from 2 weeks to 6 months, depending on the type of infection). In cases of abscessation, surgical debridement and flushing is indicated.
Mediastinal Neoplasia
The most common mediastinal diseases seen are due to neoplasia. Typical neoplasia’s for this area include lymphoma, thymoma, carcinoma and chemodectoma. Non-neoplastic masses are also reported, these may be abscesses, granulomas, haematomas or cysts.
Clinical Signs
These usually cause respiratory distress, as lung tissue is displaced by the mass, and functional lung volume decreases. Secondary pleural effusion may also be seen.
Other clinical signs include coughing, regurgitation, pleural effusion, respiratory distress and facial oedema.
Diagnostics
Diagnostic tests include thoracic radiography, thoracocentesis (if pleural effusion is present), fine needle aspirates and cytology of the fluid or aspirates obtained, thoracic ultrasound, and CT.
Treatment
Treatment depends on the underlying cause (i.e. Neoplastic or non-neoplastic); surgical removal is indicated in cases of non-neoplastic disease; neoplastic disease may be treated using one, or a combination of surgery, chemotherapy and radiotherapy.
Nursing Care
Mediastinal neoplasia patients present regularly for chemotherapy (depending on the tumour type). Care considerations for these patients include keeping each visit as stress-free and positive as possible - because we want these patients coming in each week happily for their chemo! We also need to be careful with vein preservation and rotation, check a haematology at each visit, and monitor the patient closely for any signs of pleural effusion or any changes at home. Getting an updated history is key at each visit, as is client education - and these are both areas where us nurses can really come into our own.
Pleural Space Disease
The pleura are serous membranes that coat the lungs and line the thoracic cavity; they aid movement of the lungs against the heart and thoracic wall without friction. The pleural space is a potential space between the thoracic wall, and the lungs; this normally contains a very small amount of pleural fluid which lubricates the pleural surface.
Pathophysiology
In pleural space disease, an accumulation of air, fluid or tissue occurs within the space, reducing the available space within the thorax and reducing functional lung volume. This results in hypoventilation and reduced gaseous exchange.
The pleural space may be filled with either air (pneumothorax), pleural effusion, blood (haemothorax), chyle (chylothorax) or septic fluid (pyothorax). The presence of tissue in the pleural space is usually seen in cases of diaphragmatic hernia/rupture, or thoracic wall neoplasia.
Clinical Signs
Clinical signs of pleural space disease include tachypnoea, shallow breathing, dyspnoea, orthopnoea and cyanotic mucous membranes. These patients usually present with a restrictive airway pattern (rapid, shallow breathing). The heart may be muffled on auscultation, especially ventrally (as pleural fluid settles in this region), and lung sounds may also be muffled in this region. Pyrexia, anorexia and weight loss may also be seen.
Initial Stabilisation
Stabilisation with oxygen therapy and a ‘hands-off’ approach should be used in all respiratory patients, especially those with pleural space disease or pulmonary disease. Diagnostic tests should be delayed until the patient’s condition has stabilised, with the exception of a point-of-care thoracic ultrasound, which can be performed non-invasively without causing additional stress in most cases. Thoracocentesis (at least partially if full drainage is not tolerated initially) should be performed as soon as the patient will tolerate it, to restore adequate ventilation.
Diagnostics
Diagnostic tests typically performed in cases of pleural space disease include haematology and biochemistry. Leukocytosis may be seen in cases of pyothorax, lymphopenia may be seen in cases of chylothorax, anaemia or thrombocytopenia in cases of haemothorax, and hypoalbuminaemia in cases of pleural effusion.
Arterial blood gases may show hypoxaemia and possibly hypercapnia associated with hypoventilation.
Performing cytology and bacterial culture on the fluid collected is vital for diagnosis; this should include visual examination (milky/clear/purulent/haemorrhagic appearance) and measurement of total protein (using a refractometer) to classify the fluid.
In cases of suspected chylothorax, triglyceride levels should also be measured on the fluid.
Thoracic radiographs are useful to confirm the presence of pleural disease and can highlight any underlying causes such as diaphragmatic hernia or neoplasia. These should only be performed after stabilisation – and should include a lateral and dorsoventral view if possible.
Treatment
Treatment of pleural space disease involves the immediate removal of pleural fluid/air and provision of oxygen therapy, and then treatment of the underlying cause:
Pleural effusion: diuretics, colloidal support in patients with reduced oncotic pressure due to hypoalbuminemia
Haemothorax: blood transfusion may be required in cases of severe or ongoing haemorrhage causing anaemia. However, care should be taken when performing thoracocentesis to avoid removing too much blood, as this will in time be reabsorbed. Only enough to improve ventilation should be removed.
Pneumothorax: Cage rest and monitoring may be sufficient in subclinical to mild cases as pleural air will be reabsorbed over days to weeks. In cases demonstrating clinical signs, thoracostomy tube placement may be required and potentially, continuous drainage using a ThoraSeal device may be indicated. In cases of pneumothorax not resolving, surgical management (i.e. resection of the damaged lung lobe) may be indicated.
Chylothorax: thoracocentesis to aid ventilation; care with removing large volumes of chyle as the fluid contains proteins, fats, electrolytes and lymphocytes, and circulating levels can be quickly depleted. Feeding a low-fat diet is recommended to reduce the lipid content of the fluid; this can help the fluid reabsorb across the pleural membranes. Chylothorax is often managed with thoracostomy tubes and supportive treatment, but improvement can take weeks to months. In cases not improving on medical management, surgical ligation of the thoracic duct or pericardiectomy may be considered.
Nursing Considerations
These patients will often have a thoracostomy tube placed; these may be unilateral or bilateral.
These should be drained at appropriate intervals based on the patient’s clinical condition and the veterinary surgeon’s assessment.
Volumes of fluid and air retrieved from each drain should be recorded and a drain output in ml/kg/hour calculated.
Patients losing large volumes of fluid through the drain should receive appropriate fluid therapy to match ins and outs, where required.
Thoracostomy tubes are painful and so appropriate analgesia should be provided based on pain assessments (ideally using a pain scoring system validated for the species you are assessing). We can also use the drain itself to administer local anaesthetic agents, to provide further analgesia.
When handling the drain, strict aseptic technique should be followed, with gloves worn; the drain sites should be checked, cleaned (if appropriate) and re-dressed at least once daily. Using a ‘string vest’ or medical protection shirt can help secure the drains to the body and avoid them being pulled or caught, as well as prevent patient interference. Preventing interference is vital in these patients, as any damage to or self-removal of the chest tube can cause a huge influx of air into the pleural space - a massive pneumothorax. In most patients, keeping the drains covered and secured close to the body is enough, but in our recovering pleural space disease patients, you may need to reach for a buster collar, too!
When draining, avoid placing excessive negative pressure on the drain, as this can cause pleural trauma, and ensure gate clamps are closed unless a syringe is attached, to prevent iatrogenic pneumothorax. The use of one-way valves (Centesis valves) can also be considered to allow drainage without disconnecting syringes or using three-way taps.
So that’s an overview of the common pleural space and mediastinal diseases we see in practice, and their treatment and nursing considerations! Do you look after many chest drains in practice? Let me know below! And don’t forget to check back for our next post where we’re concluding the respiratory series with an in-depth look at nursing respiratory patients!
References
Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.
Kirby, R. and Linklater, A. 2016. Monitoring and intervention for the critically ill small animal: the rule of 20. Wiley-Blackwell.
