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PULMONARY OEDEMA

First broadcast on www.provet.co.uk  


This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Veterinarians often use the terms "pulmonary oedema" or "water on the lungs" - but what is it ?

Pulmonary oedema is water collection in the lungs. 

To understand pulmonary oedema it is important to understand a bit about lung anatomy. Basically the lung consists of:

  • Tubes that carry air into the lung tissue - called bronchi
  • Alveoli - pockets of air which are surrounded by 
  • Thin walls of supporting tissue and 
  • Small blood vessels (mainly capillaries)

The lungs are well supplied with blood because their main function is gas exchange between the air and the blood. Oxygen enters the blood from air breathed into the alveoli and it is carried around the body to the tissues as oxyhemaglobin in the red blood cells. Waste gases such as carbon dioxide pass  from the blood into the alveolar spaces and then they are expelled out of the lungs when the animal breathes out..

The complex forces involved in water movement into and out of the lung tissue normally leaves the lungs "dry", but when something goes wrong with the circulation, or if water moves into the area for other reasons, fluid can accumulate and fill the both the lung tissue, and the spaces in the alveoli which air usually occupies. This is called oedema and when this happens normal gas exchange can not take place. The animal becomes deprived of oxygen - which all tissues need - and toxic waste gases build up in the bloodstream....a very serious state of affairs.

There are several causes of pulmonary oedema including :

  • Heart failure
  • Changes in the concentration of substances in the blood -  eg if the amount of protein (albumin) in the blood falls too low (called hypoalbuminemia)  water moves out of the blood.
  • Damage to the pulmonary blood vessels causing them to leak, for example :
    • Inflammation - eg smoke inhalation
    • Electrocution
    • Allergic reactions
    • Reaction to a toxin eg paraquat
    • Septicemia
  • Obstruction to air movement - eg upper airway obstruction in short-nosed breeds of dogs eg Bull Terriers.
  • Following seizures (fits) or head injuries

The signs of pulmonary oedema can come on gradually or appear suddenly and they include  :

  • Difficulty breathing
  • Increased breathing rate
  • Slow laboured breathing
  • Coughing - especially when rising from lying or during mild exercise
  • Inability to exercise
  • Visible membranes eg lips, tongue may appear blue (called cyanosis)
  • Dogs may extend their neck and gasp to breath
  • Cats will breath through their open mouths rather than through their noses
  • Both dogs and cats may panic if they are handled or forced to move
  • Clear or blood-tinged frothy fluid may appear down the nostrils or, occasionally, in the mouth
  • When listened to with a stethoscope there are loud "bubbling" noises and crackles over the lung area.

Diagnosis of pulmonary oedema is made from the presenting signs and on XRays .

Pulmonary oedema can be treated by;

  • giving drugs to increase water removal from the body - diuretics. 
  • drugs can be given to help with circulation of blood to and from the lungs
  • animals with acute and severe pulmonary oedema are usually given oxygen.

Underlying problems also need to be treated specifically, for example :

  • Protein and fluid replacement
  • Corticosteroids in cases of  "shock"
  • Antibiotics to treat/prevent infection

Acute severe pulmonary oedema - especially following electrocution, an allergic reaction or poisoning (eg paraquat) can be life-threatening and the prognosis is often poor.  Pulmonary oedema associated with heart failure, on the other hand, is usually controllable with diuretics and other treatment.

 

Updated October 2013