Inner wall of the body cavities lined by single layer of mesothelial cells. Pleura covering the surface of the lung is the visceral (pulmonary) pleura.
What is the mediastinum?
Left and right pleural sac around the lungs. Mediastinum is the space between them. More or less in the midline of the thorax. Mediastinum is continuous in most species. Thin in dogs and cats. Contains important structures: blood vessels, nerves, oesophagus, heart and trachea.
What is pleural disease?
Accumulation of:
Fluid - pleural effusion
Air - pneumothorax
Soft tissue mass - abdominal organs.
Severity of disease depends on the quantity of fluid or air, or size of the mass.
In addition to direct compression of lungs can also lead to a loss of negative pressure causing the lungs to collapse.
Orthopnoea - elbow abduction, sternal recumbency, using theit bodies to open their lungs as much as possible, this is only normal in tortoises as they do not have diaphragms.
Cyanosis.
Pleural effusion
Accumulation of fluid. On auscultation can hear muffling of lung and heart sounds especially ventrally when standing. On percussion there is increased dullness. A number of different fluid types can be present.
What are the causes of pleural effusion?
Leaky capillaries, increased intravascular pressure, increase in interstitial lung fluid, decrease in pleural pressure, increase in pleural fluid protein (increases oncotic pressure), disruption of the thoracic duct or blood vessels.
What is hypoalbuminaemia?
Less albumin in the blood than there should be, transudate will pool when you have less albumin. Occurs when have a condition causing you to loose protein from the gut, e.g. proteinlosing enteropathy.
Modified transudate in pleural effusion causes?
Most common cause is due to increased hydrostatic pressure secondary to right sided heart failure (e.g. pericardial disease, cardiomyopathy, pulmonary hypertension, pulmonary stenosis). Caused by diaphragmatic hernia or lung lobe torsion or neoplasia.
There is pleural effusion in the X-ray because the lung has been pushed away by the pleural fluid.
Thoracocentesis
Local anaesthetic rarely needed unless large bore catheter.
Clip area - if possible use quiet clippers (minimise stress).
Quickly surgically prepare the site.
Butterfly needle or catheter at intercostal space 6-8.
Ideally localise large pocket of fluid with the ultrasound first.
Aseptic technique.
Thoracostomy (chest drains)
Use in animals that will require multiple thoracocentesis over a short period of time, if there are large volumes of effusion, pneumothorax, chest wall injuries (flail chest/ flail segment), bite wounds, most Pyothorax cases or following chest surgery.
Management of effusion
Heart failure - treatment of HF
Pericardial effusion - treat effusion with drainage
Pyothorax - antibiotics, systemic and local (broad spectrum and treat anaerobes), be aware that cultures will often come back as negative, Lavage, long course of treatment with guarded prognosis.
Percussion - increased resonance (sounds like a drum).
Diagnosing pneumothorax
Physical examination. Assesment of respiratory status. Thoracic radiographs, if the animal is stable enough. Routine heamotology/ biochemistry. Blood gases and pulse oximetry - helps to asses severity.
Pathophysiology of pneumothorax
Loss of negative pressure in pleural space means that lungs are not effectively ’coupled’ to rib cage. As rib cage is raised lungs do not inflate. Lungs collapse and tidal volume is very low. Severity depends on degree of the pneumothorax and underlying disease.
Treatment of traumatic pneumothorax
Oxygen treatment, drain pneumothorax as necessary (avoid over drainage). Approximately 90% recovery with strict cage rest up to 2 weeks. Some will require chest drains and Heimlich valve. If no improvement then surgical exploration and correction will be required. If open wounds the sterile dressings and surgery as soon as patient is stable.
Spontaneous pneumothorax
History; dyspnoea, anorexia, vomiting, may present with rapid progression of respiratory distress.
Most common cause is ruptures pulmonary bulla or sub-pleural bleb.
Can occur with chronic asthma in cats.
management of spontaneous pneumothorax
Medical management to stabilise until diagnostic tests decide whether surgical intervention is required. Lobectomy as necessary. Prognosis is dependant on the underlying cause.
Mediastinal lymphoma
Most common in young cats, also seen in cats with multi centric or stage 3-5 lymphoma if so is considered a negative prognostic indicator. Tachypnoea, inspiratory hyper-Noel, dull heart sounds, pleural effusion. Non-compressible anterior mediastinum
Check FeLV/FIV status (~50% positive for FeLV).
treat with chemo +/- radiotherapy.
Thymoma
Rare, commonest in older dogs. From thymi’s epithelium, often infiltrated with lymphocytes. Benign or malignant, mets rare from both. 60% feline version cystic. Present with respiratory distress +/- cranial caval syndrome +/- myaesthenia gravis. Megaoesophagus also common if focal MG or disrupted due to presence of mass.
Cranial caval syndrome
Mass pressing on the cranial vena cava and causing problems where the restart of the blood is building up in the body and the only way it can go is leak out the valve and you get this effusion around the face.
Pleural tumour
Mesothelioma - RARE
From epithelial lining cells - pleural, abdominal, pericardial. Major links with asbestos inhalation, complex mechanism. Causes large volume effusions and pain. Multifocal small masses, hard to image, ultrasound and CT most useful.